RU2432650C1 - Planar antenna with controlled polarisation characteristic - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: basic radiating elements of a two-dimensional array lie in nodes of a square grid whose period is of the order of the wavelength in a planar dielectric waveguide (3), wherein the width of central orthogonal series of basic radiating elements have dimensions of the order of the period of the array, and linear arrays (1, 2) of auxiliary radiating elements which form the excitation device (5) lie orthogonal to each other, having a common central input (9), and the screen (4) is fitted with a crossed slot (8) lying under central basic radiating elements of the two-dimensional array.

EFFECT: operation of the antenna in normal radiation mode with controlled polarisation and a wider operating frequency band.

4 cl, 16 dwg

Description

 The proposed device relates to antenna technology and can be used in radio communication systems, radar systems and in security devices and systems, as well as transmission systems for satellite television and radio broadcasting of ultra-high frequency (microwave) and extremely high frequency (EHF) ranges.

Known flat antenna using a surface wave [1], made on the basis of a shielded radial waveguide with a grid of concentric metal rings, excited through a slot in the center of the screen, over which on the outer surface of the dielectric waveguide is a matching element in the form of a metal disk. An antenna is an antenna array with central power and radiation normal to the aperture plane and can provide radiation polarization control.

The disadvantage of this antenna is its low efficiency, defined as the product of the coefficient of performance (COP) and the surface utilization coefficient (KPI) of the antenna aperture, which does not exceed 50%. This is due to the fact that with the azimuthal amplitude field distribution implemented in the antenna in the aperture of its field, the instrumentation cannot be higher than 50%. In addition, the radiation of this antenna inevitably contains a significant orthogonally polarized component.

Known microstrip antenna array [2] for receiving / emitting waves with two orthogonal polarizations, which use a multilayer metal-dielectric structure with two-dimensional arrays of strip emitters, which is highly efficient in the radiation mode normal to the aperture plane.

The disadvantage of this antenna is the complexity of the design, containing 7-9 layers with various electrophysical parameters, shape and topology of metal elements.

The closest in technical essence to the proposed one is a planar bipolarization antenna with oblique radiation relative to the normal to the aperture plane [3], adopted as a prototype.

Figure 1 presents a drawing of the antenna of the prototype, where indicated:

1, 2 — linear arrays of radiating elements forming an excitation device for a planar metal-dielectric waveguide;

3 - planar metal-dielectric waveguide with a two-dimensional array of radiating elements located on a metal screen.

The prototype antenna contains linear arrays of radiating elements 1 and 2, installed at the ends of a planar metal-dielectric waveguide 3, and forming an excitation device for a planar metal-dielectric waveguide 3. When microwave oscillations are applied either to the input of linear grating 1 or to the input of linear grating 2, the antenna emits waves with orthogonal polarizations. In this antenna, an instrumentation exceeding 50% is achieved.

The disadvantages of the prototype antenna are: work in the mode of oblique radiation with respect to the plane of the radiating aperture, as well as a narrow band of operating frequencies of the antenna with its fixed orientation in space, limited by the frequency dependence of the position of the radiation pattern in the elevation plane.

The objective of the proposed technical solution is to ensure the operation of the antenna in the radiation mode normal to the plane of the radiating aperture with controlled polarization, as well as expanding the operating frequency band.

To solve the problem in a flat antenna with a controlled polarization characteristic, containing a metal screen and a flat dielectric waveguide, on the outer surface of which there is a two-dimensional array of the main radiating elements, as well as a device for exciting a flat dielectric waveguide in the form of two linear arrays of auxiliary radiating elements, according to the invention, the main radiating elements of a two-dimensional lattice are located in the nodes of a square grid with a period of the order of the wavelength in the plane m dielectric waveguide, and the width of the central orthogonal rows of the main radiating elements has a size of the order of the lattice period, and the linear lattices of the auxiliary radiating elements forming the excitation device are arranged orthogonally to each other, have a common central entrance, and the screen is equipped with a cross-shaped slot located under the central main radiating elements of a two-dimensional lattice.

Figure 1 presents a drawing of the antenna prototype; figure 2 is a General view of the proposed antenna with a cut out part of the MPE to show a cross-shaped slit; figure 3 a) is a drawing of the proposed antenna; in Fig. 3 b) - a metal screen with a cross-shaped slit; figure 4 a), b) is an example of a first excitation device of the proposed antenna; figure 5 is a diagram of the proposed antenna, explaining the principle of its operation; figure 6 is a General view of the proposed antenna with additional sides; 7 is an example of a second excitation device of the proposed antenna; on Fig - frequency dependence of the module of the reflection coefficient of the voltage (a) and the gain G of the antennas (b); in Fig.9 - the bottom of the antennas in the E- and H-planes at a frequency of 9.6 GHz: the base ("model") antenna (a) and the antenna with an excitation device based on linear arrays (b); figure 10 - frequency dependence of the module of the reflection coefficient of voltage s ₁₁ (a) and the gain G of the antennas (b); 11 - radiation patterns in the E- and H-planes of the antenna with an excitation device in the form of linear strip gratings of a stepped type at a frequency of 9.7 GHz.

In figure 2, 3A), 3B), 4A), 4B), 5 the following notation:

1, 2 - linear gratings of auxiliary radiating elements;

3 - a planar dielectric waveguide (PDW) with a two-dimensional lattice of the main radiating elements;

4 - metal screen;

5 - excitation device;

6, 7 — openings in the screen forming a cross-shaped slit;

8 - cruciform fissure;

Z, X, Y - coordinate axes;

d is the period of the two-dimensional lattice;

w is the length of the side of the emitter.

9 - a common input of the excitation device.

The proposed antenna contains a metal screen 4, a flat dielectric waveguide 3, on the outer surface of which there is a two-dimensional lattice of the main radiating elements, as well as a device for exciting a flat dielectric waveguide 5 in the form of two linear arrays of auxiliary radiating elements 1 and 2, which are located in the nodes of the square grid with a period of the order of the wavelength in a plane dielectric waveguide 3, and the width of the central orthogonal rows of the main radiating elements has a size of the order of the period lattice, and the lattice line constituting the driving device 5, arranged orthogonally to each other, have a common central inlet 9 and are connected via a cross-shaped slot 8 formed openings 6 and 7 in Figure 4 under the central main radiating elements of the two-dimensional lattice.

An example of an excitation device 5 (Fig. 4 b) can be linear gratings 1 and 2, orthogonal to each other, made on the basis of dielectric waveguides with metal strips placed in grooved metal waveguides. Lattices 1 and 2 are combined in the center and have a common entrance 9.

The operation of the proposed device is as follows.

In controlled polarization of radiation, the proposed antenna operates as follows. Microwave oscillations are fed to the input 9 of the excitation device 5 through a polarization switch (an external device that is not part of the inventive antenna), in particular, based on a ferrite polarizer (not shown in Fig. 4).

To provide radiation, for example, with linear polarization parallel to the OX axis (Fig. 3a), the polarization switch excites a linear grating 1 located along the OY axis (grating 2 located along the OX axis remains unexcited). The radiation of this grating, polarized perpendicular to the edges of the slit 8 in the screen 4, elongated along the OY axis, is led to the MPE 3, in which surface waves are excited on both sides of the OY axis, propagating to the edges of the MPE 3 in the directions ± ОХ. As a result of diffraction of surface waves by elements of a two-dimensional lattice, radiation arises along the normal to the aperture plane (OZ axis) with polarization parallel to the OX axis. A necessary condition for normal radiation at the average operating frequency of the antenna is to ensure equality of the deceleration of the surface waves of the PDV 3 and the ratio of the wavelength of the microwave oscillations to the period of the two-dimensional grating in the OX direction (Bragg resonant diffraction).

The principle of operation of the proposed antenna is further illustrated using figure 5. where 7 is one of the openings of the cross-shaped slit to which the linear grating 1 of the excitation device 5 is connected (located under the central elements and elongated along the axis OY).

When hole 7 is excited by a wave with a polarization of the electric field strength vector E perpendicular to the wide edges of the hole, a surface wave of the TM type is excited in PDV 3, propagating to both sides of slot 7. When it is scattered on a two-dimensional lattice of the main radiating elements, H-polarized radiation occurs (the vector E in the aperture plane is oriented along the OX axis, i.e., is perpendicular to the edges of the radiating elements).

The radiation directions of both halves of the antenna aperture (which lie at the central working wavelength in the XOZ plane) are determined by angles Θ _nmax relative to the normal to the aperture plane:

sinΘ _nmax = γ (λ) + nλ / d,

where γ (λ) = c / v _f - deceleration of the phase velocity of the surface wave of the MPE;

λ is the working wavelength; d is the lattice period; n is the number of spatial harmonics (GH) of the radiation field (figure 5).

Reception and emission of electromagnetic waves by the antenna are provided in the operating mode minus the first GHG (n = -1). Obviously, at the wavelength at which the deceleration of the surface wave of the PDV 3 is equal to the ratio of the wavelength to the period of the two-dimensional lattice, Θ _-1max = 0, the radiation of both halves of the _aperture is in-phase in the direction normal to its plane, i.e., along the OZ axis (second-order Bragg resonance diffraction). Due to the fact that the central elements of the two-dimensional grating have a width of the order of the grating period, and the PDV 3 thickness is selected on the order of a quarter of the wavelength in the dielectric, minimal reflection from the antenna input is ensured, so that the SWR at this wavelength can be close to 1. Moreover, good agreement is maintained in a frequency band greater than 5%. The use of surface waves PDV allows for high antenna efficiency. With a relative PDV thickness of not more than 0.2-0.3 of the maximum radiation wavelength, an almost single-mode wave propagation mode of the TM type is ensured, which makes it possible to obtain antenna radiation with a very low level of spurious (orthogonal polarization).

To ensure radiation with polarization parallel to the OY axis, a linear grating 2 is excited along the OX axis (grating 1 located along the OY axis remains unexcited).

In contrast to the prototype antenna, the claimed antenna with its fixed spatial position of the beam in the working frequency band is oriented normal to the aperture plane. In addition, this provides, with equal dimensions of the aperture of the claimed antenna and the antenna of the prototype, an almost twofold extension of the operating frequency band.

Figure 6 shows an example of a structural embodiment of the inventive antenna, in which along the perimeter of the PDV can be installed either matched loads in the form of plates 10 absorbing electromagnetic waves (which allows to expand the operating frequency band), or metal boards 10 with a height of the order of the thickness of the waveguide and having electric contact with the screen (which allows for maximum antenna efficiency). In addition, in the inventive antenna between the PDV and the metal screen, it is possible to arrange an additional flat dielectric layer, in particular, in the form of an air gap with a thickness of not more than (0.3-0.5) λ, where λ is the working wavelength. The presence of an air gap will reduce the thermal energy loss of microwave oscillations and, accordingly, increase the antenna efficiency.

The performance of the claimed antenna is confirmed by computer simulation of its operation in radiation mode. Two PA variants with controlled polarization characteristics were simulated — the base (“model”) antenna, in which the orthogonal slots were alternately excited in a single-mode mode with a cosine amplitude distribution of the electric field strength in one of the two holes forming a cross-shaped gap, and the antenna in which An exciting PDV field in the cross-shaped gap is created by switched linear gratings based on plug-in DWs with transverse metal elements. Modeling the base antenna made it possible to evaluate the potential characteristics of the antenna (operating frequency bandwidth, efficiency, level of the side lobes of the radiation pattern (UBL)) at a given maximum gain (KU).

Computer simulation of antennas is performed in the microwave range at frequencies of 9.2-10.2 GHz. Both antennas had the same size radiating aperture 23 × 23 cm ² ; polyethylene (relative permittivity ε = 2.25; PDV thickness t = 6 mm was selected as the MPD material). Normal radiation mode (second-order Bragg diffraction mode) at an average frequency of 9.7 GHz of the above range for the given MPD parameters is provided, for example, when the period of the two-dimensional grating is d = 24 mm and the width of the size of the metal emitting elements is w = d / 2. Further, the two-dimensional grating was assumed to be composed of square metal elements with dimensions w = d / 2, located with a period of d = 24 mm. to computer simulations of the antennas are shown in Fig. 8, which shows the frequency dependences of the module of the voltage reflection coefficient s11 (a) and the gain G of the antennas (b), and also in Fig. 9, which shows the antenna paths in the E- and H-planes - a base (“model”) antenna (a) and an antenna with an excitation device based on linear arrays (b).

When modeling the base antenna, it was found that switching the excitation from the slit located along the OX axis to the slit located along the OY axis leads to a change in the radiation polarization to orthogonal. The parameters of the basic PDA turned out to be quite high: the modulus of the reflection coefficient of voltage s ₁₁ at the antenna input did not exceed -10 dB in the frequency band 9.4-10.05 GHz, and the maximum gain G = 27.4 dB (antenna efficiency 0.845) was achieved at a frequency 9.6 GHz The baseline (“model”) antennas in the E- and H-planes at a frequency of 9.6 GHz are shown in figa). Thus, the relative operating frequency band at a maximum gain of 27.4 dB was 6.7%.

In the case of an antenna with a real excitation device based on linear arrays, acceptable matching took place in the frequency band 9.35-9.85 GHz with a maximum gain G = 25.8 dB (antenna efficiency 0.589) at a frequency of 9.6 GHz. The design parameters of the linear gratings were as follows: the internal dimensions of the grooved waveguides 10 × 25 × 228 mm ³ , the dimensions of the dielectric plug-in waveguides 10 × 16 × 228 mm ³ (ε = 2.0); the dimensions of the metal strips are 4 × 8 mm ² , the repetition period is 24 mm. As can be seen from figa), the frequency band of the antenna with the described excitation device, limited by the reduction of KU by 3 dB and matching, amounted to 550 MHz (5.7%). The polarization isolation was more than 20 dB.

7 shows a second example of the excitation device 5, in which linear strip gratings 1 and 2 of the step type are used on dielectric substrates placed in grooved metal waveguides; the common input 9 of the excitation device is made in the form of a round metal waveguide.

10 and 11 show the characteristics of an antenna with a second excitation device obtained by computer simulation.

The main design parameters: the dimensions of the radiating aperture 23 × 23 cm ² ; PDV material - polyethylene (relative permittivity ε = 2.25; PDV thickness t = 6 mm; width and height of grooved waveguides - 12 and 10 mm, thickness of strip grating substrates - 3 mm, relative permittivity - 2.0, strip width conductors - 1 mm, the width and length of the emitters - 4 and 10 mm, the period of the emitters - 24 mm; the inner diameter of the circular waveguide - 20 mm; the width of the holes forming a cross-shaped gap in the PDV screen - 4 mm.

As can be seen from the data shown in Fig. 10, an antenna with a second excitation device provides a frequency band limited by matching of at least 850 MHz (8.8%), and the maximum efficiency at a frequency of 9.7 GHz is 75.9%, i.e. ., close to the effectiveness of the "model" antenna. In the frequency band of 700 MHz (7.2%), the antenna gain is reduced by no more than 2 dB. Beams in the E- and H-planes at a frequency of 9.7 GHz antennas with a second excitation device are shown in Fig.11. The isolation of channels by polarization in the indicated frequency band is also more than 20 dB.

This example further confirms the performance of the claimed antenna.

Thus, the proposed flat antenna provides controlled polarization in the radiation mode along the normal to the aperture plane. Due to the fact that upon excitation of the PDV in the center, the antenna emitting aperture for any of the orthogonal polarizations is divided into two symmetric parts, the lengths of which are half the length of the entire aperture, the antenna operating frequency band is doubled compared to the case of excitation of the same exact design with end faces of the PDV. Therefore, in contrast to the prototype antenna, the claimed antenna provides an extension of the working frequency band.

LITERATURE

1. Microwave directional antenna using a surface wave (US Patent No. 4536767, 08.20.1985).

2. Dual-polarization planar antenna (US Patent No. 5510803, 04/23/1996).

3. Planar antenna (application for the invention of the Russian Federation 2003133969).

Claims (4)

1. A flat antenna with a controlled polarization characteristic, comprising a metal screen and a flat dielectric waveguide, on the outer surface of which there is a two-dimensional array of the main radiating elements, as well as a device for exciting a flat dielectric waveguide in the form of two linear arrays of auxiliary radiating elements, characterized in that the main radiating elements of a two-dimensional lattice are located in the nodes of a square grid with a period of the order of the wavelength in a plane dielectric waveguide, than the width of the central orthogonal series of basic radiating elements is of the order of size of the grating period, and linear arrays auxiliary radiating elements forming the excitation device are disposed orthogonally to each other, have a common central input, and the screen is provided with a cruciform gap situated under the central main radiating a two-dimensional lattice elements. 2. The flat antenna according to claim 1, characterized in that along the ends of the plane waveguide there are metal bumpers with a height of the order of the thickness of the waveguide and having electrical contact with the screen. 3. The flat antenna according to claim 1, characterized in that coordinated loads are installed along the ends of the plane waveguide in the form of plates absorbing electromagnetic waves. 4. The flat antenna according to claim 1, characterized in that between the plane dielectric waveguide and the screen there is a plane gap filled with a dielectric with parameters different from the parameters of the material of the plane waveguide.

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