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The invention relates to antenna-feeder devices, namely to ultrashort radio wave antennas and microwave antennas for emitting horizontally polarized waves with a circular radiation pattern in the horizontal plane. The technical result achieved from the implementation of the proposed invention is the expansion of the operating frequency range of the slot cylindrical antenna, providing the antenna with devices for matching with the feeder, which are not critical to size when tuning the antenna to the operating resonant frequency. Slotted cylindrical antenna contains a conductive cylindrical body with a longitudinal slot with first and second edges and a feeder, additionally comprising a first conductive clamp, a second conductive clamp and a matching cable section, wherein the first clamp is located to form a galvanic contact on the first edge of the slot, the second clamp is located to form a galvanic contact on the second edge of the slot, the feeder on the surface of the cylinder is laid along a straight line diametrically opposite to the longitudinal axis of the slot, with a bend in the vicinity of the point of excitation of the slot, laid through the first clamp with the outer conductor of the feeder forming a galvanic contact with the first clamp, a matching section of cable is laid through the second clamp , the central conductor of the feeder is galvanically connected to the central conductor of the matching cable section. 1 salary f-ly, 6 ill.

Drawings for RF patent 2574172

Field of technology to which the invention relates

The invention relates to antenna-feeder devices, namely to ultrashort radio wave antennas and microwave antennas for emitting horizontally polarized waves with a circular radiation pattern in the horizontal plane.

State of the art

The slot antenna was first proposed in 1938 by Alan D. Blumlein for use in television broadcasting in the ultrashort wave range with horizontal polarization and a circular radiation pattern (RP) in the horizontal plane [British patent No. 515684. HF electrical conductors. Alan Blumlein, publ. 1938. US patent No. 2,238,770 High frequency electrical conductor or radiator]. The antenna is a pipe with a longitudinal slot. The simplicity of the design, the absence of a protruding part above the surface in which the slot is cut, attracted the attention of specialists designing radio systems for submarines. Slot antennas do not disrupt the aerodynamics of the objects on which they are installed, which has determined their widespread use on aircraft, missiles and other moving objects. Such antennas with slots cut into the walls of waveguides of rectangular, circular or other cross-sectional shapes are widely used as airborne and ground-based antennas for radar and radio navigation systems.

So, the first slotted cylindrical antenna A.D. is known. Blumlein for emitting horizontally polarized waves of high frequencies, containing a conducting cylinder with a longitudinal slit, devices for exciting the slit at one end of the cylinder and a short circuit at the other end of the cylinder, a device for adjusting the width of the slit. The conducting cylinder has a length equal to half the wavelength in free space.

The disadvantages of the known first slot antenna are that:

The antenna does not contain devices for tuning the antenna to the resonant frequency,

The antenna has a length equal to half the free space wavelength, which makes it difficult to obtain acceptable antenna performance in terms of directional properties and antenna-to-feed matching.

A second cylindrical slot antenna is known for emitting horizontally polarized high-frequency waves, containing a conducting cylinder with a longitudinal slot, a feeder, a short circuit at one end of the slot and devices for exciting the antenna at the other end of the slot, said cylinder has a diameter of between 0.151 and 0.121, where 1 - wavelength in free space at the operating frequency. The said cylinder has a length close to nine-tenths of a quarter of the length of the standing wave established along the slot line on the cylinder (the wavelength in the slot line on the cylinder is several times greater than the wavelength in free space).

When the cylinder is vertically oriented, the antenna has an almost circular radiation pattern with horizontal polarization of the radiation field and has a high directivity coefficient (DA). The antenna is compact, convenient for installation on roofs tall buildings, its smooth surface contours prevent the accumulation of wet snow and ice formation. Due to its circular cylindrical shape, the antenna has a relatively low wind load.

The known second antenna overcomes the disadvantages of the first known antenna due to its size of half a wavelength in free space. Omnidirectional slot antenna Andrew Alford, created in 1946 and installed on the Chrysler skyscraper in New York, was used for the first broadcasts of color television.

However, the known second slot cylindrical antenna has the following disadvantages:

The antenna has a large longitudinal size in wavelengths in free space, which makes it difficult to use it as a radiating element of an antenna array that forms a radiation pattern special type in the plane of vector H;

the antenna does not have devices for matching it with the feeder.

A third slot cylindrical antenna is known for emitting horizontally polarized waves of high frequencies, containing a conducting cylinder with a longitudinal slot, short-circuited at both ends of the cylinder, excited by a coaxial cable, the outer conductor of which is galvanically connected to the first edge of the slot, and the central conductor is galvanically connected to the second edge of the slot.

The known third slot cylindrical antenna has disadvantages:

Due to the asymmetrical excitation of the antenna, a wave is excited that propagates in the line formed by the outer conductor of the coaxial cable and the cylinder, as a result of which noticeable radiation of the cable is observed (antenna feeder effect), its characteristics significantly depend on external operational factors;

There are no devices for matching the antenna with the feeder (to tune the antenna to resonance at the operating frequency),

The known third slot cylindrical antenna has a narrow range of operating frequencies, not exceeding 1% at the SWR level in the power line.

The third known slot cylindrical antenna, fed by a coaxial cable, is, in terms of its essential features, closest to the present invention. This antenna is selected by the authors as a prototype.

Disclosure of the Invention

The technical objective of the present invention is to expand the operating frequency range of a slotted cylindrical antenna, providing the antenna with devices for matching with the feeder, which are not critical to size when tuning the antenna to the operating (resonant) frequency.

This task is achieved in that a slotted cylindrical antenna containing a conductive cylindrical body (hereinafter referred to as the body) with a longitudinal slot with first and second edges and a feeder, additionally contains a first conductive clamp, a second conductive clamp (hereinafter referred to as the first clamp, the second clamp) and a matching a piece of cable, with the first clamp located to form a galvanic contact on the first edge of the slot, the second clamp located to form a galvanic contact on the second edge of the slot, the feeder on the surface of the cylinder is laid along a straight line diametrically opposite to the longitudinal axis of the slot, with a bend in the vicinity of the excitation point slot, laid through the first clamp with the formation of galvanic contact by the outer conductor of the feeder with the first clamp, the matching cable section is laid through the second clamp, the central conductor of the feeder is galvanically connected to the central conductor of the matching cable section.

The introduction of a first conductive clamp, a second conductive clamp and a matching section of cable into the antenna, their relative position and connection in the antenna as indicated above solves the following problems:

Create an antenna that, due to a symmetrical power system, provides a symmetrical radiation pattern in the plane of vector H, without bifurcation of the diagram and without deviation of the maximum of the radiation pattern from the plane perpendicular to the cylinder axis;

Create an antenna that provides a circular radiation pattern in the vector plane due to the fact that the diameter of the cylinder is much smaller than the wavelength;

To create an antenna that provides stable radiation characteristics when using both narrow slits with low wave impedance and wide slits with high wave impedance;

Create an antenna that provides compensation for the reactive component of the antenna input impedance in a wide frequency range;

Create an antenna whose radiation resistance varies within a small range over a wide frequency range;

Create an antenna that provides low SWR in the power line by matching the input impedance of the antenna with the characteristic impedance of the feeder over a wide frequency band;

Reduce the power level returning to the transmitter when the antenna is transmitting by matching the antenna with the feeder;

Reduce the level of distortion of the spectrum of the signal transmitted (received) by the antenna due to the uniform amplitude-phase characteristic of the antenna in the frequency range;

Increase the antenna's resistance to high-frequency breakdown by reducing the field strength in the radio frequency connector due to a decrease in the SWR in the power line when the antenna is operating in transmit mode;

Provide the antenna with a matching device by changing the reactance of the matching device and thereby expand the operating frequency band of the antenna;

Provide a simple method for tuning the antenna in coordination with the feeder in the frequency range;

Ensure maximum power transfer by matching the characteristic impedance of the feeder;

Increase the potential power level in a pre-selected feeder by reducing the SWR in it;

Minimize losses in the feeder and, as a result, reduce the heating of the feeder when transmitting power through it;

Minimize the emission (reception) of electromagnetic waves by the feeder ( outside outer conductor of coaxial cable);

Create a slot antenna that could be used as an independent antenna, as well as an element of an antenna array;

Create an antenna convenient for mounting on a pipe or belt of a lattice tower.

The antenna is compact; when the cylinder is oriented vertically, it emits horizontally polarized waves. Can serve as a radiating element of an antenna array. The antenna array of slot emitters can be installed both directly on the earth's surface and on the roofs of tall buildings. The smooth contours of the antenna surface prevent the accumulation of wet snow and ice formation on it. Due to its circular cylindrical shape, the antenna has a relatively low wind load.

By including a radome in the antenna, the problem of protecting the slotted cylindrical antenna in accordance with this invention from the influence of external operational factors is solved.

The solution to the above problems indicates that a new slot cylindrical antenna has been created that provides performance characteristics in a wide frequency range.

The solution to the first of these problems was obtained as a result of the fact that the proposed slot cylindrical antenna is excited symmetrically relative to the middle of the slot.

The operating frequency range of the proposed antenna on the side of shorter waves is limited by changes in the shape of the radiation pattern (DP). Use slits of such a length that the pattern has only one maximum, oriented perpendicular to the antenna axis. A decrease in wavelength with constant slit sizes can lead to the appearance of two maxima deviated from the antenna axis.

The increase in wavelength is limited by a decrease in the directivity coefficient (DA). It turns out to be significant if the diameter of the cylinder is less than 0.12 wavelengths in free space.

The proposed antenna can be tuned in the specified frequency range.

The solution to the problem of creating a circular radiation pattern in the vector plane is obtained due to the fact that the diameter of the cylinder is much smaller than the wavelength in free space.

The solution to the third problem, namely providing a wide range of operating frequencies with both narrow and wide slots, was obtained by compensating for the reactive component of the antenna input impedance.

Solving the supply problem simple method compensation of the reactive component of the antenna input impedance in the frequency range is achieved by using two series-connected capacitors for compensation.

Solution to the problem: to minimize the emission (reception) of electromagnetic waves by the feeder - obtained by rationally placing the feeder on the surface of the cylinder, introducing the first conductive clamp into the antenna, ensuring galvanic contact of the outer conductor with the first clamp along its entire circumference at the exit from the clamp.

Brief description of drawings

In fig. 1a) shows a slotted cylindrical antenna 1 in accordance with the present invention. In fig. 1b) shows a front view of a slotted cylindrical antenna, Fig. 1c) shows a top view of a slot cylindrical antenna. In fig. 1b) and fig. 1c) the following notation has been introduced:

1 - slot cylindrical antenna,

2 - cylindrical body,

4 - first edge of the slot,

5 - second edge of the slot,

7 - first clamp,

8 - second clamp,

9 - matching cylinder,

10 - matching cable section,

11 - bending of the feeder (at the turn from the vertical section to the horizontal section located in the vicinity of the slot excitation point),

A - region of excitation of the gap.

In fig. 2a) shows region A of the gap excitation. In fig. 2b) shows the connection of the outer conductor of the feeder with the first clamp and the first edge of the slot, the antenna input impedance matching device and its connection with the second edge of the slot. In fig. 2c) shows in section the connection of the outer conductor of the feeder with the second clamp and the second edge of the slot, the matching cylinder and the matching cable section. In fig. 2b) and fig. 2c) the following notations are additionally introduced:

12 - central conductor of the matching cable section,

13 - central conductor of the feeder,

14 - external conductor of the feeder.

In fig. 3 shows the equivalent circuit of the antenna; in fig. 3 new designations have been introduced:

15 - capacitance of the capacitor formed by the inner surface of the matching cylinder 9 and the outer surface of the outer conductor of the matching cable section 10,

16 - capacitance of the capacitor formed by the inner surface of the outer conductor and the central conductor of the matching section of cable 10,

17 - inductance due to the flow of currents along the inner and outer surfaces of the pipe from the first edge to the second edge of the slot (in the absence of capacitors 15 and 16),

18 - real part of the antenna input impedance (before connecting capacitors 15 and 16),

19 - conditional terminal corresponding to the point of galvanic contact of the outer conductor of the feeder through the first conductive clamp with edge 4,

20 - conditional terminal corresponding to the point at the input of the central conductor of the matching cable section,

21 - point of galvanic contact of the matching cylinder through the conductive clamp 2 with the edge 5 of the slot 3.

In fig. Figure 4 shows the experimental dependences of the real and imaginary parts of the input resistance and SWR on the frequency of the first and second samples of a slotted cylindrical antenna; in fig. 4 notation introduced:

221 - frequency dependence of the real part of the input impedance of the first sample with a matching cable section 10.5 mm long,

222 - dependence on the frequency of the imaginary part of the input resistance of the first sample with a matching cable section 10.5 mm long,

223 - dependence on the frequency of the SWR antenna of the first sample with a matching cable section 10.5 mm long,

231 - dependence on the frequency of the real part of the input resistance of the second sample with a matching cylinder 11.5 mm long and a matching cable section 20.5 mm long,

232 - dependence on the frequency of the imaginary part of the input resistance of the second sample with a matching cylinder 11.5 mm long and a matching cable section 20.5 mm long,

233 - frequency dependence of the SWR antenna of the second sample of the second sample with a matching cylinder 11.5 mm long and a matching cable segment 20.5 mm long,

241 - dependence on the frequency of the real part of the input resistance of the second sample with a matching cylinder 7 mm long and a matching cable section 24 mm long,

242 - dependence on the frequency of the imaginary part of the input resistance of the second sample with a matching cylinder 7 mm long and a matching cable section 24 mm long,

243 - frequency dependence of the SWR antenna of the second sample with a matching cylinder 7 mm long and a matching cable section 24 mm long,

251 - frequency dependence of the real part of the input resistance of the second sample with a matching cylinder 5 mm long and a matching cable section 30 mm long,

252 - dependence on the frequency of the imaginary part of the input resistance of the second sample with a matching cylinder 5 mm long and a matching cable section 30 mm long,

253 - frequency dependence of the SWR antenna of the second sample with a matching cylinder 5 mm long and a matching cable section 30 mm long,

In fig. Figure 5 shows examples of the distribution of the electric field strength along the transmission line 26, which is a longitudinal slot on the cylinder, and along the two-wire line used to excite the said transmission line: a) the frequency of the generator is less than the critical frequency of the main wave of the slot line on the circular cylinder, b) the frequency of the generator approximately equal to the critical frequency of the main wave of the slot line on a circular cylinder, c) the frequency of the generator is greater than the critical frequency of the main wave of the slot line on a circular cylinder.

In fig. 5 the following notations are introduced:

27 - concentrated voltage source,

28 - two-wire transmission line,

29 - electric field strength vectors.

In fig. Figure 6 shows the structure of the electric field at a certain moment in time in the internal and external regions of the slot cylindrical antenna in a section perpendicular to the antenna axis. In fig. 6 the following notations are introduced: 30 - electric field lines.

In fig. 7 shows an example of using a slot cylindrical antenna of the present invention as an element of an antenna array.

Carrying out the invention

Referring to FIG. 1b, which shows a slot antenna 1 in accordance with the present invention. The antenna is made in the form of a cylindrical body 2 with a slot 3 with a first edge 4 and a second edge 5, a feeder 6, a first conductive clamp 7, a second conductive clamp 8, a matching cylinder 9, a matching section of cable 10 and fasteners.

The cylindrical body 2 is made of a conductive material such as, for example, brass, aluminum alloy, steel or other metal, or a metal alloy with good conductivity. The cylindrical body with 2 in cross section has the shape of a circle. The cross-section of the body may have the form of a square, rectangle, ellipse or other curved shaped profile.

The slot 3 is made in the cylindrical body 2 to the entire depth of the body wall by milling, laser cutting or other mechanical operation to form the first edge 4 and the second edge 5, parallel to the longitudinal axis of the cylindrical body.

A serial coaxial cable can be used as feeder 6. For clarity, matching cylinder 9 is shown as a segment of a circular cylinder.

For clarity, the matching section of cable 10 is shown as a short section of coaxial line. The matching section of cable 10 is partially located inside the matching cylinder 9, and partially outside 9.

The matching cylinder 9, clamps 7 and 8 are made of highly conductive material, for example brass or aluminum alloy. To ensure soldering, they are coated, for example, with a tin-bismuth alloy.

The end of the matching cable section 10, opposite the slot, is open and not connected to anything. The central conductor 11 of the matching section of cable 10 comes out of the matching cylinder 9 and extends to the middle of the slot 3.

The above devices and parts are mutually located relative to each other and connected to each other in the following way.

The first clamp 7 is fixed to form a galvanic contact on the first edge 4 of the slot, the second clamp 8 is fixed to form a galvanic contact on the second edge 5 of the slot, the feeder 6 on the surface of the cylinder 2 is fixed along a straight line diametrically opposite to the longitudinal axis of the slot, with a bend 13 in the vicinity point of excitation of the slot, then laid through the first clamp 7 with the formation of galvanic contact by the outer conductor 14 of the feeder with the first clamp 7, the matching section of cable 10 is laid inside the matching cylinder, which is covered by the second clamp, the central conductor 12 of the feeder is galvanically connected to the central conductor 11 of the matching cable section .

The second end of feeder 6 is installed in a radio frequency connector. In this case, as a matching section of cable 10, either a section of a standard coaxial cable or a section of a special transmission line is used, consisting of an outer conductor in the form of a tube, a central conductor in the form of a rod or tube, and a hollow dielectric cylinder located between them.

To fasten the feeder 6 to the cylindrical body 2, standardized clamps, screws and nuts can be used.

Antenna operating principle

The antenna works as follows. Electromagnetic oscillations in the antenna are excited as a result of the application of a potential difference at two points 19 and 20, opposite each other on the first 4 and second 5 edges of the slot 3. To effectively excite the antenna, the diameter of the pipe 2 must be chosen such that the generator frequency is higher than the critical frequency main wave H 00 slot line on a cylindrical waveguide. To illustrate this point, three situations presented in Fig. 1 were considered (using a rigorous solution to the boundary value problem of electrodynamics) using a model problem. 5.

In fig. 5 shows a slot line on a circular waveguide, connected in series with a two-wire line, to the end of which a voltage generator is connected. In fig. Figure 5 shows examples of the distribution of electric field strength along the transmission line for the following cases: a) the generator frequency is less than the critical frequency of the main wave of the slot line on a circular cylinder, b) the generator frequency is approximately equal to the critical frequency of the main wave of the slot line on a circular cylinder, c) the generator frequency is greater critical frequency of the fundamental wave of the slot line on a circular cylinder. In fig. 5, the electric field strength is proportional to the length of the vector. As can be seen from Fig. 5, in case a) the electromagnetic wave is reflected practically from the entrance to the transmission line. The wave penetrates into the slot line to a depth that is negligibly small in the lengths of the will. In case b) an exponentially decreasing field distribution is established in the slotted cylindrical transmission line. In case c) a standing wave is established in a slotted cylindrical transmission line. In this case, the length of the standing wave in the slot transmission line is greater than the length of the standing wave in the two-wire transmission line.

It is preferable to select a pipe diameter equal to 0.14 wavelength in free space. It is advisable to choose the slit length close to half the wavelength of the main wave H 00 of the slot line on a cylindrical waveguide

The width of the slit 3 does not exceed one-thirtieth of the wavelength. Therefore, the unevenness in the distribution of current on the central conductor of the cable within the slot 3 can be practically neglected. Consequently, the unbalanced coaxial cable is introduced into the excitation region of the antenna in such a way that it does not violate either the physical or electrical symmetry of the antenna. The displacement currents arising between the outer conductor of the feeder 6 and the housing 2 in the area from the bend of the feeder to the slot are small due to the fact that the outer conductor of the feeder 6 and the housing 2 have galvanic contact with each other through the first conductive clamp 7. Galvanic contact of the outer conductor of the feeder 6 and housing 2 causes the electric field strength to be equal to zero at the point of their connection. In a section of the feeder located along a straight line diametrically opposite the axis of the slot, displacement currents between the outer conductor of feeder 6 and housing 2 are not excited, since in this section of the path the potential equal to zero. Therefore, the potential radiation from the gap formed between the outer conductor of the feeder 6 and the housing 2 can be neglected. Thus, the antenna effect of the feeder and the associated unpredictable distortions of the antenna radiation pattern, changes in the antenna input impedance, and cross-polarized field radiation are eliminated. Using a rigorous solution of Maxwell's equations under given ideal boundary conditions, the electric field lines were calculated by the time method at different times during one period of generator voltage oscillations. Field lines at some point in time are shown in Fig. 6. For the convenience of designating antenna elements by numbers, the moment in time was chosen when the electric field strength in the immediate vicinity of the slot is small, therefore there are no lines of force in this vicinity in Fig. 6. Far from the slit, already formed field vortices are observed, represented by lines of force that are not supported by charges on the walls of the cylinder. In the intermediate zone, the force lines originate on the lower half of the cylinder in the presented drawing and end their path on the upper part of the cylinder. At the point opposite the center of the slit, the line of force does not take and end its path, since the potential at this point is zero. This point is the boundary point between the lower and upper halves of the cylinder. According to the above rule, the force line should begin and end its path here. However, this turns out to be impossible, because electric field strength vectors tangent to the bottom and top power line, at this point are opposite to each other and, therefore, cancel each other. For this reason, the vicinity of the line opposite the slit axis turns out to be convenient for laying a feeder along it in order to minimize the antenna effect of the feeder.

The above antenna design provides convenient adjustment of the alignment of the antenna with the feeder. Let us consider this in more detail by referring to the equivalent antenna circuit in FIG. 3. In FIG. 3, the number 15 denotes the first capacitor with capacitance C 1, formed by the inner surface of the matching cylinder 9 and the outer surface of the outer conductor of the matching cable section 10. In this case, the cable sheath plays the role of a dielectric. The number 16 denotes the second capacitor with capacitance C 2, formed by the inner surface of the outer conductor and the surface of the central conductor of the matching section of cable 10. The number 17 denotes the inductance L, caused by the flow of currents along the inner and outer surfaces of the pipe from the first edge 4 to the second edge 5 of the slot. The number 18 indicates the resistance R, due to the radiation losses of the antenna. Terminal 19 corresponds to the point of galvanic contact of the outer conductor of the feeder through the first conductive clamp with edge 4. Terminal 20 corresponds to the point at the input of the central conductor of the matching cable section. The number 21 indicates the point of galvanic contact of the matching cylinder through the conductive clamp 8 with the edge 5 of the slot 3.

Two series-connected capacitors 15 and 16 have an equivalent capacitance C 3:

The input resistance at terminals 19, 20 Zin, due to the serial connection of an equivalent capacitance C 3 and a chain of parallel connected resistance R and inductance L, at a frequency is equal to:

At the resonant frequency, the imaginary part of the input resistance is zero, i.e.

By replacing the factor in the denominator in square brackets in (2) with its value from (3), we obtain the value of input at the resonant frequency:

Ideal matching with the feeder is achieved when the input impedance of the antenna is equal to the characteristic impedance of the feeder. For given L and R, adjustment by agreement is achieved by selecting the value of the equivalent capacitance C 3 .

In the limiting case, when there is no matching cylinder (C 1 ), the equivalent capacitance C 3 is equal to the capacitance C 2 - the capacitance of the matching cable section. Usually, to match the antenna with the feeder, it is necessary to have a small value of C 2. Sometimes, when working in the meter and decimeter wavelength ranges, a matching segment no more than ten millimeters long is required. Small absolute changes in the length of a cable section lead to relatively large relative changes in the C2 value. Therefore, when accurately tuning the antenna to the operating frequency, it is necessary to change the length of the matching segment by fractions of a millimeter. The need to select the length of the matching cable segment with an accuracy of fractions of a millimeter complicates the process of tuning the antenna.

The situation is completely different when we are dealing with two capacitors connected in series: capacitance C1 and capacitance C2. It is known that by connecting two capacitors in series, we obtain an equivalent capacitor with a capacitance less than the capacitance of each capacitor individually. Now, with a fixed value of C 1, changing the capacitance C 2 within large limits, we obtain changes in the value of the equivalent capacitance within small limits.

The initial length of the matching cable segment should obviously be greater compared to the case when this other capacitor is not present. Consequently, the change in the length of the matching cable section is now greater in relative units, and the setting is more accurate.

Those. Tuning the antenna to the operating frequency by changing the length of the matching cable section, for example, by cutting it, does not cause difficulties, because changes in length are carried out in quantities measured in millimeters.

The antenna has the following advantage, namely that with the introduction of a matching cylinder into the antenna, the electrical strength of the antenna increases. The highest electric field strength when the antenna is excited occurs in the matching section of the cable. In an antenna with a matching cylinder, the potential difference between the central conductor and the edge of the pipe is now distributed between two capacitors, the first of which is formed by the central conductor and the outer conductor of the cable, the second capacitor is formed by the outer conductor of the cable and the matching cylinder. The sum of the voltage drops across these two capacitors is equal to the potential difference between the center conductor and the edge. Those. the voltage on each capacitor is less than the total voltage, which increases the electrical strength of the antenna.

Two samples of a slotted cylindrical antenna were manufactured. The first sample contained a conducting cylinder with a longitudinal slot, a feeder and a matching cable section. The first sample did not have a matching cylinder, a first conductive clamp and a second conductive clamp. The outer conductor of the matching feeder had galvanic contact directly with edge 4. The second sample differs from the first in that it additionally contains a matching cylinder, a first conductive clamp and a second conductive clamp. The second sample uses a matching cable section that is longer than the first sample. In the second sample, the matching cable section is laid inside the matching cylinder and continues outside it. Below will be a description of the second sample corresponding to the present invention. When describing the antenna sample, we will refer to the notation of Fig. 1 and fig. 2.

The antenna sample consists of a cylindrical body 2 with a slot 3 with a first edge 4 and a second edge 5, a feeder 6, a matching section of cable 10, a matching cylinder 9, a first clamp 7 and a second clamp 8, and fasteners.

Housing 2, 720 mm long and 130 mm in diameter, is made of tinned sheet metal 0.3 mm thick. The cross-section of the body has the shape of a circle. A slot 3 with a length of 640 mm and a width of 30 mm is cut into the body to form the first edge 4 and the second edge 5, parallel to the longitudinal axis of the cylindrical body.

Serial coaxial cable RK-50-2-11 was used as feeder 6.

The matching section of feeder 10 is made in the form of a short section of coaxial cable RK-50-2-11. Section 10 of the coaxial cable is located inside the matching cylinder 9.

Matching cylinder 9 is made of a brass tube with internal diameter 4 mm. In this case, measurements were performed at three tube lengths: 11.5 mm; 7 mm; 5 mm.

The end of the matching cable section 10, opposite the slot, is open and not connected to anything. The central conductor 11 of the matching section 10 of the coaxial line comes out of the matching cylinder 9 and extends to the middle of the slot 3.

Feeder 6 is fixed on the surface of the cylinder along a straight line, diametrically opposite to the longitudinal axis of the slot, bent in the vicinity of the antenna excitation point, laid inside the first clamp 7 and then located above the slot 3, laid inside the matching cylinder 9 and then continues outside the cylinder 9. External insulation of the feeder cut and removed along the length of the slit. The outer conductor (braid) is cut along the circumference at the entrance to the second clamp 8, the braid is combed towards the edge 4. The combed braid is evenly distributed around the circle and soldered to the clamp 7. Thus, the outer conductor of the feeder 6 is galvanically connected through the clamp 7 to the first edge 4 slots, and the central conductor 12 of feeder 6 is connected to the central conductor 11 of the matching section of cable 10. The second end of the coaxial feeder 6 is embedded in a radio frequency connector.

To fasten feeder 6 to housing 2, standardized clamps, screws and nuts are used.

The values ​​of the real ReZ and imaginary ImZ parts of the input impedance of the prototype antenna and the antenna of the present invention in the frequency range measured on samples are shown in the form of graphs in Fig. 4a).

The dependences of SWR on frequency measured on the first and second antenna samples are shown in the form of graphs in Fig. 4b). Graph 22 corresponds to the first antenna sample. In this case, the length of the matching cable section is 10.5 mm. Graphs 23, 24 and 25 correspond to the second antenna sample with a matching cylinder length of 11.5 mm, 7 mm and 5 mm, respectively. In this case, the length of the matching cable section is 20.5 mm, 24 mm and 30 mm, respectively.

When tuning the first antenna sample to the resonant frequency, the length of the matching cable section was changed in increments of 0.25 mm. A change in the length of the matching segment by 0.25 mm led to a change in the resonant frequency by 0.5 MHz. When tuning the second antenna sample to the resonant frequency, the length of the matching cable section was changed in increments of 2 mm. A change in the length of the matching segment by 2 mm led to a change in the resonant frequency by 0.5 MHz. As can be seen from examining the graphs in Fig. 4, an antenna tuned to the same resonant frequency at different ratios of the length of the matching cylinder and the length of the matching cable section has almost the same dependence of SWR on frequency. It is more advantageous to use a matching cylinder of shorter length.

Indeed, the increment DC 2 of equivalent capacity C 3 can be found from the relation:

From this relationship it follows: the smaller the capacitance of the matching cylinder C 1 (the shorter the length of the matching cylinder), the less the equivalent capacitance changes with the same increments of capacitance C 2 (increment of the length of the matching cable section). In this case, it is possible to use longer matching cable sections.

With longer matching cable sections it is more convenient to tune the antenna, because you can use a traditional cable cutting tool.

Measurements of the polarization characteristics of the antenna showed that the antenna has linear polarization. Measurements taken on the antenna indicate that the antenna is free from feeder antenna effects.

Application of the invention

The invention can be used as an independent antenna, as elements of more complex antennas, radiating elements of antenna arrays, feeds of mirror and lens antennas.

The antenna can be used either as an independent antenna or as an element of a linear antenna array.

The proposed broadband dipole antenna turns out to be useful in all cases where either an independent slot antenna or a radiating (receiving) element of a more complex antenna device or antenna system is required, from which low losses in the feeder, high antenna efficiency, and a low level of cross-polarization radiation are required.

CLAIM

1. A slot cylindrical antenna containing a conductive cylindrical body in which a longitudinal slot with first and second edges is made and a feeder, characterized in that it contains a first clamp attached to the first edge of the slot to form a galvanic contact, a second clamp attached to the second edge of the slot with the formation of galvanic contact, the matching cylinder and the matching cable section, the matching cylinder is fixed on the second edge of the slot and laid through the second clamp, the matching cable section is installed on the second edge of the slot and laid through the matching cylinder, the feeder is fixed on the surface of the cylinder along a straight line diametrically opposite longitudinal axis of the slot, with a bend towards the slot in the vicinity of the point of excitation of the slot and laid through the first clamp with the formation of galvanic contact by the external conductor of the feeder with the first clamp, the central conductor of the feeder is galvanically connected to the central conductor of the matching cable section.

2. Slot cylindrical antenna according to claim 1, characterized in that the matching cylinder is made in the form of a circular conducting cylinder.

in a supercritical mode when they propagate between parallel metal plates you can determine the distance between the protrusions; d 0 (Fig. 5.12), their length is 1(/and thickness - \ - ., \ ^

In Fig. 5.13 and 5.14 show examples of the design of waveguide-slot non-resonant

antennas with inclined slots on a narrow waveguide wall when the antenna is fed by a rectangular waveguide (Fig. 5.13) and with longitudinal slots on a wide wall when fed by a coaxial cable (Fig. 5.14).

An example of the design of a waveguide slot antenna with electromechanical beam swing (with a removable upper slot wall) is shown in Fig. 5.15. The purpose of the individual antenna elements is indicated in the same figure.

In Fig. 5.1-6a shows one of the variants of a two-dimensional waveguide-slot antenna [L 11], consisting of eight parallel aluminum waveguides, in each of which ten dumbbell slots are cut. Dumbbell slots have a greater bandwidth than conventional rectangular slots [LO 9]. A special feature of the antenna is that the even and odd waveguides are fed from different sides using power dividers and the entire aperture is used to form four beams, the spatial arrangement of which is shown by the dotted line in Fig. 5.16.6, Such antennas are used, for example, * in aircraft Doppler autonomous navigation devices designed to determine the speed and drift angle of the aircraft.

A set of several linear*waveguide-slot antennas located along the generatrices of the conical part of the aircraft (Fig. 5.17) / can be used to form the required shape of the radiation pattern [LO 7]..

To protect from atmospheric precipitation and dust, the opening of the waveguide-slot antenna must be covered with a dielectric plate, or the entire radiating system must be placed in a radio-transparent radome. /у.-"-; ;7 ";;>■-■

5.9. Approximate procedure for calculating waveguide-slot

When developing or designing slot antennas, the initial data can be:

Width of pattern in two main planes or in one

20q 5 and side lobe level;

Directional coefficient £) 0 ;

Amplitude: or amplitude-phase distribution over the antenna and the number of emitters N; frequency range

Let's look at the calculation procedure for the following two options:

Option 1. The amplitude distribution over the antenna aperture and the number of emitters N are specified.

Option 2. The width of the radiation pattern in one or two main planes and the level of lateral radiation are specified.

First, the type of waveguide-slot antenna is selected. If the angular position of the main maximum DN 0 GL is specified and the antenna must ensure operation in the frequency band, a non-resonant antenna is selected. If, according to the design instructions, the antenna is narrow-band, but must have a high efficiency value, a resonant antenna is preferable.

Option 1. For a given law of amplitude changes according to the antenna aperture, the distance between the emitters d in the waveguide of a given frequency range selected for constructing the antenna is initially determined: In a resonant antenna with variable-phase slots In a non-resonant antenna, the value of d can be chosen in two ways. If the position of the main maximum of the pattern in space 6 No. is given, then the required value of rf is found using formula (5.26). If the Angle angle is not specified, then the distance between the emitters is selected d^\"k B /2 and, moreover, so that at the extreme frequencies of the given range there is no resonant excitation of the antenna [formula (5.22)]: Next, the calculation is carried out in the following order.

Ts Taking into account the general equivalent circuit of the antenna (see Fig. 5.8.6), the equivalent normalized conductivities g n (or resistance g n) of all N slots of the antenna are calculated (see § 5.4).

2. Knowing the value of gv or g p / by: formulas table. 5.1 (§ 5.2) determine the displacement of the center of the slits relative to the middle of the wide wall of the waveguide, or the angle of their inclination 6 in the side wall.

P 3. Having calculated the conductivity of the radiation of the slot in the waveguide (i.e., external conductivity), f from the known value of the power at the input, (in the case of a transmitting antenna) determine the voltage at the antinode of the slot U m [formula (5.3)], and therefore, and slit width di [formula (5.4)].

4. Given the known location of the slits on the wall of the waveguide and their width, according to the data in § 5.2, find the resonant length of the slits in the waveguide.

5. Calculate the antenna pattern (see § 5.7) ^ its k.n. d. and k.u.

Option 2. First, find the distance between the emitters similar to the first calculation option. Then the amplitude distribution over the antenna is selected, ensuring

10* 147 starting pattern with a given level of side lobes. Next, using the now known amplitude distribution, the length of the antenna (and, accordingly, the number of emitters) is found, providing the required width of the pattern at a level of 0.5 power (formulas in Table 5.2 § 5.7). Further calculation coincides with paragraphs. 1-5 of the previous calculation option.

In addition to the electrical calculation of the antenna itself, the supply line and exciter are calculated, required type rotating joint, when required by design specifications, and determine its main characteristics.

Literature

G. Kyu n PV Microwave antennas. TTur. With; German edited by M. P. Dolukhanova. Publishing house "Shipbuilding", 1967.

"2. Pietol'kor with A.A. General theory of diffraction antennas. ZhTP, 1944, vol. XIV, No. 12, ZhTF, 1946, vol. XVI, (Nb 1.

3. "Manual for course design of antennas." VZEYS, 1967.

4. Yatsuk L.P., Smirnova N.! B. Internal conductivities of non-resonant slits in a rectangular waveguide. “News of universities”, Radio engineering, 1967, vol. X, 4.

"5. Veshch"Nikova I.E., Evetroiyov G.A. Theory of matched slot emitters. "Radio engineering and electronics", 1965, vol. X, No. Ш

6. E in s t r. o i o in G. A., Ts a p k i n S. A. Study of waveguide-slot antennas: with identical resonant emitters. "Radio Engineering and Electronics", 1965, vol. X, no. 9.

7. Evstropov G.A., Tsarailkin S. “A: Calculation of wave-bottom-slot antennas taking into account the interaction of emitters along the fundamental wave. “Radio Engineering and Electronics”, 1966, vol. XI, no. 5.

8. Shubarin Yu. V. Antennas of ultrahigh frequencies. Kharkov University Publishing House, 1960.

9. "Microwave Scanning Antenna Systems", vol. I. Transl. from English, ed. G. T. Markov and A. F. Chaplin. Publishing house "Soviet Radio", 1966.

10. Shyrman Ya. D. Radio fiber guides and volumetric resonators. Svyazizdat, 1959.

11. Reznikov G. B. Aircraft antennas. Publishing house "Soviet Radio", 1962.

HORN ANTENNAS

6.1. Main characteristics of horn antennas

Waveguide horn antennas are the simplest antennas in the centimeter wave range.

They can form radiation patterns with a width from 100-140° (when opening a special shape) to 10-520° in pyramidal horns. The possibility of further narrowing the horn pattern is limited by the need to sharply increase its length.

Waveguide horn antennas are broadband devices and provide approximately one and a half range coverage. The possibility of changing the operating frequency within even greater limits is limited by the excitation and propagation of higher types of waves in the supply waveguides. The efficiency of the horn is high (about 100%). Horn antennas are easy to manufacture. A relatively minor complication (inclusion of a phasing section in the waveguide path) ensures the creation of a field with circular polarization.

The disadvantages of horn antennas are: a) bulky design, limiting the possibility of obtaining narrow radiation patterns; b) difficulties in regulating the amplitude-phase distribution of the field in the aperture, which limit the possibility of reducing the level of side lobes and creating radiation patterns special form.

Horn radiators can be used as independent antennas or, like the open ends of waveguides, as elements of more complex antenna devices. As independent antennas, horns are used in radio relay lines, in weather service stations, very widely in radio measuring equipment, as well as in some special-purpose stations. Widely - small horns are used. and open ends of waveguides as feeds

parabolic mirrors and lenses. Feeders in the form of a line of horns or open ends of waveguides can be used to form specially shaped radiation patterns, controlled patterns, or, for example, using the same paraboloid to create -pencil and cosecant] diagrams!® orientation. A four-horn or eight-horn emitter can be used for: Monopulse direction finding method. Sectorial horns with higher pitches can be used for the same purpose. : wave types (#yu, Nsch #zo). To form narrow radiation patterns, two-dimensional arrays made from the open ends of waveguides or small horns can be used. It is possible to construct flat or convex phased arrays.

Paragraphs 6.2-6.9 are devoted to consideration of methods. calculation of horn emitters. Paragraphs 6.10-6.12 outline some features of the design of horn-waveguide phased arrays.

6.2. Calculation method

The calculation of horn antennas is based on the results of their analysis, i.e., they are initially tentatively specified; " the geometric dimensions of the antenna, and then determine its electrical parameters. If the dimensions are unsuccessful, then the calculation is repeated again.

Radiation field of a horn antenna; like all microwave antennas, it is determined by an approximate method. The essence of approach; is that despite the connection between the field inside and outside the horn, the internal problem is solving the external one, and obtained from. this

solving the field value in the horn opening plane is used to solve the external Problem [DO 1, LO 13].

The amplitude distribution of the field in the horn aperture is assumed to be the same as in the waveguide feeding it. For example, . when excited.;, horn with a rectangular WAVEGUIDE WITH wave #10, along the X-axis (passing in the H plane) the distribution of the field amplitude is cosine, and along the Y axis (passing in the E plane) the amplitude distribution is uniform. Due to the fact that the wave front in the horn does not remain flat, but is transformed into a cylindrical one in a sectorial horn and into a spherical one in a pyramidal and conical one, the phase of the field along the opening changes according to a quadratic law.

The described amplitude and phase distributions of the field along the aperture are approximate. Some clarification is provided by taking into account reflection from the opening of at least only the main type of wave. It should be borne in mind that the reflection coefficient G decreases with increasing aperture.

The radiation pattern of a horn antenna based on a known field in the aperture can be calculated by the wave optics method based on the Huygens principle and the Kirchhoff formula [LO 13, JIO 11, J10 1]. The application of Kirchhoff's formula to the electromagnetic field is not strict. A number of authors made clarifications taking into account the peculiarities electromagnetic field antennas. Because of this, in the literature for calculating the radiation pattern there are several different, but similar formulas that give similar results. Calculation formulas will be given below in § 6.5. Having an expression for the radiation pattern, one can find the directional coefficient of the antenna, the dependence of the width of the radiation pattern on the size of the aperture, and other characteristics of the antenna.

6.3. Selection of geometric dimensions of the horn and waveguide emitter

Horn antenna (Fig. 6.1) consists of horn I, waveguide and exciting device 3

If the generator feeding the antenna * has a coaxial output, then the antenna waveguide 2 is most often excited by a pin located perpendicular to the wide wall j of the waveguide; the excitation is supplied to the pin by a coaxial cable. If the generator feeding the antenna has a waveguide output, then the feeder path is usually made in the form of a rectangular waveguide with an H 10 wave. The waveguide feeder directly passes into the waveguide 2, exciting the horn. Calculation of the exciting device in the form; an asymmetrical pin will be given in the next paragraph.

Selecting Waveguide Sizes

The choice of cross-sectional dimensions of a rectangular waveguide a and b is made from the condition of propagation of only the main type of wave #у in the waveguide:

Relationship (6.1) is presented in the graph in Fig. 6.2, which can be used to find the dimensions of a. Dimension b must satisfy condition b

Let us present some considerations for calculating probe transfer (see Fig. 6.3).

The input impedance of a pin in a waveguide, as well as an asymmetrical vibrator in free space, is in the general case a complex quantity. The active part of the input resistance depends: mainly on the length of the pin, the reactive part - on the length and thickness. In contrast to free space, the input impedance of a pin in a waveguide depends on the structure of the field in the waveguide near the pin.

Calculation; the reactive component of the input resistance gives inaccurate results and does not make sense. To ensure matching, the reactive component of the input resistance must be equal to zero. The active component of the input resistance can be considered equal to the resistance of the Radiation pin in the waveguide. It should; be equal!

The radiation resistance of a pin in a rectangular waveguide in the traveling wave mode is determined by the following relation:

In the presence of a reflected wave in a rectangular one; waveguide, the pin resistance changes slightly:-

wave impedance of the feeder.

reactive parts of conductivity to the right and left of the pin, namely:

In the given formulas, the following notations are adopted: a and bSh are the dimensions of the cross-section of the waveguide; X\ - position of the pin on the wide wall of the waveguide, more often; In total, the pin is located in the middle of the wide wall, i.e. Xi = a/2; Zi.-- distance from the pin to the short-circuiting wall of the waveguide; dsh is the distance from the pin to the nearest voltage node; k.b. V. - coefficient of the traveling wave in the waveguide; X^f is the wavelength in the waveguide; r in -4 waveguide impedance

/g d - effective height of the pin in the wave

water, the geometric height of which is /, is determined by the formula

Given the values ​​x\ and, using formulas (6.18), (6.19) and (6.21) we can find the height of the pin / at which the required /? In x.

For complete coordination, the designs must provide two adjustment elements. For example, you can adjust the height of the pin / and the position of the short-circuiting wall in the waveguide U (see Fig. 6.3) or the dimensions k and S (see Fig. 6.4,6). In some cases, to simplify the design, they are limited to one; adjustment and allow some* mismatch in the supply coaxial.

6.5. Calculation of reflection coefficient

Reflection in a horn antenna occurs in two sections: in the horn aperture (1\) and in its neck (G 2).

Let us briefly consider each of the reflection coefficients. The reflection coefficient from the aperture T\ is a complex value; its modulus and phase depend on the size of the aperture. A rigorous solution to the problem for the open end of a waveguide sandwiched between two infinite planes, carried out by L. A. Weinstein; allows us to establish that the modulus of the reflection coefficient decreases with increasing size of the aperture, and the phase approaches zero.

Approximately the modulus of the reflection coefficient from the aperture for the main type of wave can be determined from the relation

Propagation constant in a rectangular waveguide, the cross section of which is equal to the horn aperture;/" d*// r: . ? \ ^

The propagation constant in a circular waveguide whose diameter is equal to the diameter of the aperture of a conical horn.

The reflection coefficient along the length of the horn from the aperture to the neck changes not only in phase, but also in amplitude. With opening sizes of several lengths

The reflection coefficient fi from the open end of a rectangular waveguide (23X10) mm 2 at a wavelength of 3.2 cm, measured experimentally, is equal to

Let's consider the reflection coefficient from the throat of the horn G2.

When determining the coefficient G2, it is assumed that

a traveling wave was established in the horn. The problem is solved by combining fields >at the junction of the waveguide

Selecting Horn Sizes

The dimensions of the opening of a pyramidal or sectorial horn a p and b p (see Fig. 6.1) are selected according to the required width of the radiation pattern in the corresponding plane or according to the k.n. d.

The width of the radiation pattern is related to the aperture dimensions a v and b v by the following ratios:

a short-circuited quarter-wave section of a two-wire line is formed. Having a high input resistance, it does not allow currents to branch off to the outer shell of the feeder. Since the resistance between points “a” and “b” is high, the arms of the vibrator at the radiation frequency are electrically isolated, despite the galvanic connection between them. The edges of the slots are usually made widening to ensure matching of the wave impedance of the feeder with the input impedance of the vibrator.

the input impedance of the vibrator is 4 times. In this regard, it is convenient to use it to power the Pistelkors loop vibrator, the input impedance of which is 300 Ohms, with a standard feeder with ρ f = 75 Ohms.

3. 2. Slot antennas

3.2.1. Types of slot antennas. Features of their design

A slot antenna is a narrow slit cut into the metal surface of a screen, resonator shell, or waveguide. Slot width d<<λ , длина обычно близка к половине волны. Щели прорезаются так, чтобы они пересекали линии поверхностного тока, текущего по внутренней стенке волновода или резонатора (рис. 3.21). Возможны различные положения щелей (см. рис. 3.21): поперечная (1), продольная (2), наклонная (3), и разнообразные их формы: прямолинейные, уголковые, гантельные, крестообразные (рис. 3.22).

A high-frequency surface current, crossing the gap, induces alternating charges (voltage) along its edges, and on the reverse (outer) side

It is not the surface that currents are excited. The electric field in the gap and currents on the surface are sources of radiation and form in space

and in decimeter - using a coaxial transmission line. In this case, the outer conductor is connected to one edge of the slot, and the inner conductor is connected to the other. To match the transmission line with the antenna, the feed point is shifted from the middle of the slot to its edge. Such an antenna can radiate into both hemispheres. In the centimeter range and the adjacent part of the decimeter range, resonator and waveguide-slot antennas are used (see Fig. 3.21, 3.22). In coaxial waveguides, only transverse or inclined slots are excited; in rectangular waveguides, various slot placement options are possible (see Fig. 3.21).

The slot width affects the active and reactive parts of the input resistance. Both components increase with increasing slit width. Therefore, to compensate for Xin, it is necessary to reduce the length of the slot (shorten it). An increase in Rin leads to an expansion of the slot antenna's bandwidth. Typically, the slot width d is selected in the range (0.03...0.15)λ. To further expand the bandwidth, dumbbell slots and special designs of exciting devices are used.

In addition to the range, the choice of slot width is influenced by the condition for ensuring electrical strength. The concentration of electric charges at the edges of the gap leads to local overvoltages and the occurrence of electrical

where E ь max is the electric field strength at the antinode. Taking E ь max = E μ (breakdown voltage, for dry air E μ = 30 kV/m), we find

In practice, choose d ≥ K spare d min, where K spare =2…4 is the reserve coefficient

Slots of more complex shapes than rectangular ones can be considered as combinations of simple ones. They are used to produce electromagnetic waves with the required polarization properties. For example, a cross-shaped slot allows you to obtain an antenna with elliptical and circular polarization. The direction of rotation depends on the direction of displacement of the slit from the axis of the wide wall of the waveguide.

Slot antennas are distinguished by their simple design, high reliability and the absence of protruding parts, which allows them to be used in aircraft and ground antenna systems as independent antennas, feeds for complex antenna systems and elements of antenna arrays.

3.2.2. Single slot. Pistelkors' principle of duality

Let's consider the characteristics and parameters of the so-called ideal slot antenna, i.e. a single slit cut into a perfectly conducting flat screen. Calculating the field of such an antenna using the equations of electrodynamics presents significant difficulties. It is greatly simplified if we use the principle of duality formulated by Pistelkors in 1944. This principle is based on the permutational duality of Maxwell's equations, known from the theory of the electromagnetic field. For a gap these equations have the form:

If the screen is removed and the slit is replaced by an ideal flat vibrator of the same dimensions as the slit (Fig. 3.23), and with the same current distribution as the voltage distribution along the slit (an equivalent vibrator cut from the screen to form the slit), then the field emitted they also bu-

Comparing the boundary conditions of the slot (3.27) and the equivalent vibrator (3.29), we can verify that the structures of the electric field near the slot and the magnetic field near the vibrator coincide. The boundary conditions for the equivalent vibrator are obtained from the boundary conditions for the slot by rearranging E ↔ H. Taking into account the above, for the complete field in the entire space we can write:

where C 1 and C 2 are constant coefficients.

In practice, half-wave slits are usually used. In this case, regardless of the excitation method, the amplitude of the electric field in the gap is maximum in the center and decreases towards the edges, i.e. corresponds to the law of current distribution in a half-wave vibrator. For a narrow slit (thin vibrator), the boundary conditions, and therefore the constant coefficients, can be expressed as

voltage at the center of the slot U 0 and current at the center of the vibrator I 0 (see Fig. 3.23):

Then the first expression in (3.31) will be rewritten as:

Thus, the principle of duality as applied to slot antennas is formulated as follows: the electric field of a slot antenna, up to a constant factor, coincides with the magnetic field of an additional vibrator of the same dimensions as the slot and with the same amplitude distribution.

This means that the EMF of the slot and the equivalent vibrator are different

between themselves only by rotating the corresponding vectors E r ы and E B by 90°,

H r sch and H B .

Applying the principle of duality, we can write for the radiation patterns:

F u (θ ) H = F B (θ ) E ;

F u(θ) E = F B (θ) H,

where F sch (θ ) H , F sch (θ ) E - normalized DN gaps in the planes H and E corresponding

responsibly; F B (θ ) H , F B (θ ) E are the corresponding normalized patterns of the half-wave vibrator.

When the angle θ is measured from the normal to the slit plane, the radiation pattern of the half-wave slit will be written in accordance with equality (3.33) in the form:

The resistance of the slit, as well as the vibrator, is complex and depends on its dimensions (length 2l and width d). The values ​​of Rw in and X w in are calculated for different values ​​of l / λ and are given in the form of graphs in reference and educational literature. The reactive component of the gap is capacitive in nature. However, the gap can also be adjusted by shortening it. The amount of shortening is calculated using the formula:

As follows from (3.35), wider slits are shortened by a larger amount.

The input resistance of the slot is related to the input resistance of the vibrator complementing it. It is more convenient to express this relationship in terms of the complex input gap conductivity:

Complex input conductance of a half-wave slot