RU2039401C1 - Cassegrainian axial-symmetry antenna - Google Patents

Abstract

FIELD: antenna equipment. SUBSTANCE: antenna feed in the form of horn and impedance cylindrical extension piece with quarter-wavelength grooves in inner surface allow axial-symmetry pattern with steep declivities and stable position of phase center to be formed. Its position does not depend on distance to points of reflection of beams from auxiliary reflector within fixed intervals of distance between aperture plane of antenna feed and center of auxiliary reflector. If this distance is less than length of wave then auxiliary reflector has parabolic shape and if it is bigger than two lengths of wave than auxiliary reflector has elliptical or hyperbolic shape. Description of invention specifies various variants of make of horn part and impedance extension piece (with ring or spiral grooves). EFFECT: enhanced efficiency of Cassegrainian axial-symmetry antenna with mixed focal plane, improved cross-polarization discrimination with minimization of antenna feed. 3 cl, 2 dwg

Description

 The invention relates to antenna technology and can be used as a transceiver antenna in microwave communication systems.

 In recent years, DZA with a shifted focal axis have become widespread.

 In antennas of this type, for example, ADE [A1] and ADP [A2], it is possible to significantly reduce the diameter of the auxiliary mirror (to 2-3 wavelengths λ) while maintaining high values of the main electrical parameters. However, the coefficient of utilization of the surface of the radiating aperture (CIP) in these DZA is much lower than it follows according to the theory (approximately 20% lower). The reasons for the discrepancy between the calculated and experimental values of the instrumentation are not studied in the literature. This does not cause any particular complaints from practice, since the standard value of the instrumentation of antennas ADE and ADP is 0.85, which in itself is a fairly high value. Nevertheless, an increase in the requirements for antenna parameters makes us look for ways to improve them.

 The invention is aimed at increasing the instrumentation with a displaced focal axis while maintaining the minimum dimensions of the irradiating system.

As shown by the analysis of theoretical and experimental data, the main way to improve the instrumentation of antennas with a shifted focal axis is to create a primary emitter with the following set of characteristics:
a) axisymmetric shape of the radiation pattern (DN);
b) the wide-angle of this form with 20 _0.5 ≃ 30-40 ^о С;
c) the position of the phase center is stable and coincides for both main polarizations of the field;
d) preservation of the above characteristics at distances corresponding to the position of the reflection points on the auxiliary mirror relative to the center of the mouth of the mouthpiece.

 DZA with such a primary emitter to the fullest extent implements the characteristics predicted by calculation.

The closest in technical essence to the proposed one is an ADE antenna with a primary emitter in the form of the open end of a circular waveguide. The open end of a circular waveguide, as is known, emits an almost spherical wave with the position of the FC coinciding with the center of its aperture. With a ratio of its diameter to the wavelength of about 0.8 days, the radiated field is approximately axisymmetric. Recall that the distance of the far zone in this case begins with a value of 1.3λ. The disadvantages of the prototype are the relatively narrow working range in which the axial symmetry of the field is preserved; the wide-angle of the MD is too large, as a result of which K _y and diffraction effects on a small mirror increase. In addition, the primary emitter cannot create an inhomogeneous flat wavefront for irradiating a small mirror with a diameter of about 2.5-3λ, at which the ADE antenna still remains operational.

 The aim of the invention is to increase the instrumentation DZA with a shifted focal axis and improve other electrical characteristics, for example, decoupling for cross-polarization while minimizing the dimensions of the irradiating system.

 This goal is achieved in that a device consisting of the horn itself and electrically connected to it and an impedance-type coaxial nozzle with quarter-wave grooves on the inner surface of the nozzle is used as the primary emitter of a DZA with a shifted focal axis, and the nozzle is made in the form of a piece of a metal cylinder ( shallow), with a radiating aperture diameter equal to 2λ, where λ is the average wavelength of the working range, and the total number of grooves cut on the inner surface of the cylinder in yato at least eight. The grooves can be either concentric or spiral.

 The proposed primary emitter creates a wide-angle beam with steep slopes and a position of the FC that does not depend on the distance to the points of a small mirror, which makes it possible to approximate the path of the rays in the antenna theoretically predicted by the laws of geometric optics (GO). In this case, the theoretical and experimental data, such as the relative positions of the antenna elements and the values of the electrical characteristics, are as close as possible to each other. It was found that at distances l <λ from the plane of the radiating aperture of the primary emitter, the radiation field is an almost inhomogeneous plane wave, since it is such a wave that is excited in the nozzle. In this case, the auxiliary mirror should have a parabolic generatrix, and the dimensions of the irradiating system are minimally possible (for devices forming a plane wave in the cylinder volume with a diameter of 2.5-3λ). At distances exceeding 2λ, the field of the primary emitter is a diverging spherical wave with a point-like phase transition. For such distances, the auxiliary mirror must have an elliptical or hyperbolic profile in order to form a plane wave in the aperture.

 The presence in the invention of a primary emitter with the described geometry (specific dimensions and the number of grooves, etc.), the profile of the auxiliary mirror, different depending on the distance to the radiating aperture of the primary emitter (parabolic if this distance is less than λ and elliptical if it is more than 2λ), distinguishes it from the selected prototype. A similar device is not described in the literature.

 The possibility of creating a positive effect is based on the analysis of the results of a theoretical study of the laws of field propagation in an endless corrugated waveguide with quarter-wave grooves on the walls (qualitative analysis). Experimental confirmation of the expected effects was obtained on several versions of the primary emitter and in an antenna of the ADE type. The use of the invention allows to design DZA type ADE, ADH or ADP with the same primary emitter having the smallest possible dimensions. In this case, closer to theoretical values of instrumentation and control devices are realized than in the prototype and analogues. Antenna of type ADP is feasible at a distance between the opening of the primary emitter and a small mirror shorter than the wavelength, and antennas of type ADE and ADH at distances greater than two wavelengths. Since each indicated type of antenna has its own positive qualities, which are most fully realized with the help of the invention, the corresponding positive effect should be correlated with the technical problem being solved.

 In FIG. 1 shows a structural diagram of the proposed DZA in an arbitrary central section using the example of the well-known ADE circuit (Fig. 1a) and a diagram of the proposed primary radiator in the embodiment with annular grooves on the nozzle walls (Fig. 1b).

Designations: D and d are the diameters of the large and small mirrors, respectively; L is the distance between the plane of the radiating aperture of the primary emitter and the small mirror (its tip) along the axis of symmetry, r _{0 is the} inner radius of the nozzle; r _{1 is} its outer radius; 1 horn part of the primary emitter (PI); 2 a cylindrical nozzle to it of length L, 3 a small mirror with a generatrix of a second-order curve, the foci of which are 0 and 0 _f , 4 a large mirror with a parabolic profile and focus at point 0 (for the symmetry of half a mirror, the same notation, but with a dash icon) The focal axis of the generatrix of the parabola is parallel to the axis of symmetry and is offset from it to the side by a distance d / 2).

 Figure 2 shows a structural diagram of the proposed PI to the antenna in the embodiment with a double-helical spiral groove on the nozzle wall.

Designations: 1 actually horn part; 2 cylindrical nozzle; 3 arbitrary central section of the nozzle 2 (the grooves of one branch of the spiral are marked with an “o”, the second, shifted along the end of the nozzle by 90 ^° with respect to the first, with an “x”; d _{in the} diameter of the supply waveguide. Starting points of the spiral branches: From the first and In the second.

 Figure 3 presents a structural diagram of the proposed PI to the antenna in the embodiment with annular grooves (concentric) on the walls of the nozzle 2. The designations are the same as in figures 1 and 2. In the circle "m" is given a callout showing the geometry of the grooves, when this t is the thickness of the metal along the wall between adjacent grooves, S is the width of the grooves, q S + t. These characteristics are the same for both annular and spiral grooves.

In FIG. 4 shows the dependence of the position of the FC L _{f of} one of the investigated variants of the proposed PI / with ring grooves on the walls and the angle of the out-of-phase part α ₂ = 45 ^о from the distance RL _f + L; figure 5 phase distribution and the bottom of one of the options PI with data: α ₁ 11 ^about , α ₂ = 55 ^about , ring grooves; in FIG. 6 is a set of phase diagrams of the same PI for different distances L (Fig.6a), the dependence of the position of its phase center on the distance (Fig.6b) and the angle sector ± θ ^o in function L, within which the phase error modulo is less than 10 ^o , in Fig.7 amplitude MD of the proposed PI in the frequency range for option α ₁ 11 ^about , α ₂ = 55 ^about , nozzle with annular grooves; on Fig amplitude and phase distribution in the aperture plane of the proposed antenna with data: ADE circuit, D 2500 mm; d 200 mm; F 575 mm; Ψ _o = 90 ^o ; α ₁ 11 ^about ; α ₂ = 45 ^about , nozzle with annular grooves, 8 pieces, L _f 13 mm; L 151.5 mm. Measurements at a frequency of 11.2 GHz.

, расстояние по металлу между соседними канавками t≅

, причем общее число канавок взято не менее восьми. Спиральная канавка является двухзаходной с точками начала каждой ветви С и В (фиг.2), сдвинутыми между собой на 90^о по торцу раскрыва. Шаг спиралей (через каждые 360^о) взят равным 2q 0,5λ Для построения рупорной части 1 может быть использован как синфазный, так и расфазированный рупор. Фокус 0 малого зеркала 3 совмещен с фокусом большого зеркала 4 (точка 0), а его второй (осевой) фокус 0_ф совмещен с фазовым центром первичного излучателя.A two-mirror antenna has axial symmetry and contains a primary (large) mirror 4 with a shifted focal axis from the parabolic generatrix, an auxiliary (small) mirror 3 with a second-order curve generatrix with foci at points 0 and 0 _f and a primary emitter 1- 2, which in turn contains the horn part 1 and the impedance nozzle 2 with quarter-wave grooves cut on its inner surface. The diameter of the inner surface 2r _about , coincides with the output diameter of the conical part of the horn 1 in the section aa ^' . In addition, this diameter is equal to two wavelengths for the average design frequency of the wavelength range. The nozzle 2 can be made with spiral grooves on the walls (figure 2), or with annular grooves (figure 3). The outer diameter of the nozzle 2r _{1 is} taken slightly more than 2.5λ, taking into account the required thickness of the metal from structural considerations. Width of each groove S≅

, the metal distance between adjacent grooves t≅

, and the total number of grooves taken at least eight. The spiral groove is two-way with the start points of each branch C and B (figure 2), shifted between themselves by 90 ^about the end of the aperture. Step helices (every ³⁶⁰ °) is taken equal to 2q 0,5λ For construction of part 1 of the horn can be used as the in-phase and misphased mouthpiece. Focus 0 of the small mirror 3 is aligned with the focus of the large mirror 4 (point 0), and its second (axial) focus 0 _{f is} aligned with the phase center of the primary emitter.

 A two-mirror antenna (option) is characterized by an elliptical or hyperbolic curve shape forming the profile of a small mirror 3, (ADE or ADH, respectively). Moreover, the distance L between the aperture plane Q of the primary emitter and the center of the small mirror 3 is taken more than 2λ.

A two-mirror antenna (option) differs in a parabolic shape of the curve forming the profile of the small mirror 3, confocal forming the parabola of the large mirror 4, but with the opposite direction of the focal axis. This DZA type ADP τ <λ
To explain the operation of the device, we note that in the aperture plane Q of the primary emitter (FIGS. 2 and 3), an almost axisymmetric plane field arises with a distribution (T) decreasing towards the edges. Such a field emits a complex wave.

в долях так называемого "расстояния Релея" R_o=

, в пределах каждой из которых структура этого поля различна. В области 0 < R < 0,5R_oизлученная волна-неоднородная плоская; в области R > R_o излученная волна-неоднородная сферическая. Так как излучающий раскрыв ПИ 2r_o 2λ, то для него R_o 2λ. Как видно из фиг.2, фазовый центр излученного поля для расстояний R < λ сильно углубляется внутрь раскрыва (L_ф > 4λ), т.е. в указанной области пространства распространяется плоская волна. В интервале расстояний 1,5λ -2λ волна нерегулярная не плоская и не сферическая. Но для расстояний R > 2λ -2,5 λ формируется регулярная сферическая волна. Кривые получены для ПИ с d_в 23 мм, α₁=11^о, α₂= 45^о, канавки кольцевые, f 10 ГГц (f частота).It is known that in the radiation field of a common-phase final aperture, two regions of space characterized by relative distance can be distinguished

in shares of the so-called "Rayleigh distance" R _o =

, within each of which the structure of this field is different. In the region 0 <R <0.5R _{o, the} emitted wave is inhomogeneous plane; in the region R> R _{o the} emitted wave is inhomogeneous spherical. Since the radiating opening PI 2r _o 2λ, then for him R _o 2λ. As can be seen from figure 2, the phase center of the radiated field for distances R <λ greatly deepens into the aperture (L _f > 4λ), i.e. a plane wave propagates in the indicated region of space. In the range of distances 1.5λ -2λ, the wave is irregular, not planar or spherical. But for distances R> 2λ -2.5 λ, a regular spherical wave is formed. The curves were obtained for PIs with d _at 23 mm, α ₁ = 11 ^о , α ₂ = 45 ^о , ring grooves, f 10 GHz (f frequency).

The described character of the radiation field of the PI remains unchanged qualitatively with different designs of the horn part 1 (close to in-phase or out-of-phase horn) and with a nozzle with concentric or spiral grooves. Depending on the nature of the grooves, differences are observed in the position of the phase center L _{f of the} emitted field, the degree of its symmetry, and the steepness of the slopes of the MD. The nozzle with a spiral groove forms a greater steepness of the slopes of the PM than with the annular ones with better matching of the waveguide input. The latter is explained by the fact that opposite the points of symmetry 0-0 ^'the opposite points of the spiral are shifted to each other by q0.25λ; therefore, the waves reflected from them in the direction of the horn part 1 travel this path twice, i.e. have a phase difference of 180 ^about . Therefore, with a spiral groove in the direction of the horn 1 of the reflected wave, the diametrically opposite surface fields on the walls of the nozzle are mutually compensated. The absence of a surface reflected wave along the walls of the nozzle with a spiral groove helps to reduce the level of spurious emitted fields, therefore, the slope of the ramps of such a nozzle is higher than that of a nozzle with annular grooves.

In FIG. Figure 5 shows the phase distributions in the horn field with d _at 19 mm, α ₁ = 11 ^о , α ₂ = 55 ^о for a nozzle with ring grooves at a frequency f of 11.2 GHz as a function of parameter 1 and depending on the angle of rotation of the probe around θ ^o The FC of the field remains practically unchanged for all the established distances, and the DNs (upper figures) are the same for both polarizations and have rather steep slopes.

Figure 6 shows the generalized measurement results for this PI. In FIG. 6a shows a set of phase distributions for E and H planes as a function of distances 50≅L≅1000 mm; on figb dependence of the position of the FC L _f on the distance L and on figv sector of the angles (-θ) ^o - (+ θ) ^o within which the deviation of the phase of the wave from the spherical modulo does not exceed 10 ^about for E and H field planes at the same time. The calculated wavelength λ = 26.2 mm, the distance of the relay R _o 53.6 mm The field was studied in the range of distances L> 0.5R _o . As can be seen from fig.6b, when L> R _{o the} radiated field very quickly becomes spherical, as follows from theory.

 It was checked the preservation of the characteristics in the frequency range (Fig.7). Measurements confirm the stability of the shape of the pattern in the frequency range while maintaining the position of the FC.

 Since the profiles of mirrors 3 and 4 are consistent with each other in order to form a common-mode wavefront in the aperture of the antenna, a plane wave with a symmetrical distribution is formed in the aperture of the antenna P based on the symmetric distribution in the aperture Q of the PI.

The device according to claim 2 works as follows. The primary emitter 1-2 in the spatial region L> 2λ emits a spherical wave, transformed by a small mirror 3 into a toroidal one with a focal ring 0-0 ^' (Fig. 1). This wave irradiates a toroidal large mirror 4 from its focal ring. Mirror 4 forms a common-mode wave front in the plane P of the aperture of the DZA. The amplitude distribution in the aperture is symmetrical and decreasing towards the edges. Such a distribution corresponds to a high instrumentation and low UPL. Since the diameter of the radiating aperture Q of the primary emitter is 2λ, the diameter d of the small mirror 3 can be taken starting from a value of 2.5λ. This ensures, if necessary, minimizing the dimensions of the irradiating system.

The device according to claim 2 was verified experimentally. Measured the distribution of the field in the aperture P DZA (Fig.8) with PI, the characteristics of which are shown in Fig.4. The measurements were performed as a function of the irradiation angle Q of the large mirror 4 from focus 0. When tuning, it was found that the distance L exactly coincided with its calculated value of 151.5 _mm in GO, which is not observed for ordinary horn emitters. There, the amount of displacement is usually about half the length of the working wave. The misphasing in the aperture is less than 10 ^about in absolute value, i.e. phase errors are not significant. The amplitude distribution of weakly oscillating without strong dips in the angular range ^of θ 0-40, as is the case with the horn radiator. Based on the measured distributions, the main characteristics were calculated, namely, obtained: instrumentation of 0.85 and UPBL -2 dB, which almost coincides with the geometrical-optical data.

 The device according to claim 3, which is an ADP type antenna, operates as follows.

The primary emitter 1-2 in the range of distances L <λ emits a plane wave (Fig. 4). A small mirror 3 with a parabolic generatrix creates a toroidal reflected wave with an annular focus of 0-0 ^' . Further transformation of this field into a common-mode wave front in the aperture of the DZA occurs similarly to that described previously with the same positive properties.

 The technical efficiency of the proposed two-mirror antenna is determined by comparison with the prototype and analogues based on direct experimental studies and by means of a mathematical experiment. As a result, the possibility of obtaining the expected positive effects was confirmed.

 Based on the technical solution described, DZAs of the ADE, ADH and ADP types can be designed with high instrumentation values and low UPL with the smallest possible dimensions of the irradiating system. Such antennas are more effective than the known ones.

 The proposed design is simple and adaptable. For example, the nozzle 2 of the primary emitter is technologically easier to manufacture with spiral grooves on the inner surface of the cylinder than a conical horn radiator with ring or spiral grooves on its working surface.

Claims (2)

1. A two-mirror axisymmetric antenna containing a main parabolic mirror with a displaced focal axis, an auxiliary mirror whose profile, formed by the rotation of a second-order curve, is aligned with the profile of the main mirror, and an irradiator made in the form of a horn and connected coaxially to its opening with a nozzle on the inside a quarter-wave formed surface of the groove, characterized in that the nozzle is designed as a segment of a metal cylinder having an inner diameter equal to the diameter 2r ₀ Coloring a horn and 2r _o = 2λ _cf. where λ _cf. average length of the working wave range, and its outer diameter 2r ₁ = 2,5λ _cf., wherein the width of each groove _cf. s ≅ λ / 6, the distance between adjacent grooves along the surface d ≅ λ _sr / 12, and the total number of grooves is at least eight. 2. The antenna according to claim 1, characterized in that the auxiliary mirror is elliptical or hyperbolic, while the distance between the aperture plane of the irradiator and the center of the auxiliary mirror is more than 2λ _cf
3. The antenna according to claim 1, characterized in that the auxiliary mirror is parabolic, while the distance between the aperture plane of the irradiator and the center of the auxiliary mirror is less than λ _cf

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