RU2321111C1 - Frequency-scanned antenna arrangement - Google Patents

Abstract

FIELD: microwave radio engineering, route surveillance radars.

SUBSTANCE: proposed antenna arrangement incorporating power splitters and array of waveguide-slot stripline radiators (strips) has its power splitter disposed in plane parallel to that incorporating strips; it is made in the form of E-plane folded serpentine waveguide that has coupling members with strips. Power splitter longitudinal axes incorporating even- and odd-numbered coupling members with strips are spaced apart through integer odd number of quarter-wavelength in power splitter waveguide. Power splitter waveguide line section between adjacent coupling members is twice bent through 180 deg. and its length is chosen to be a multiple of integer odd number of half-waves in power splitter waveguide. Even- and odd-numbered strips are different in length. Half-wave phasing section affording phase shift required for matching even- and odd-numbered outputs of power splitter is inserted in input section of each strip by changing size of strip waveguide wide wall.

EFFECT: reduced level of side lobes, standing-wave voltage ratio at normal-frequency power splitter input, enhanced amplifier gain, directive gain, and antenna sheet surface utilization factor.

4 cl, 3 dwg

Description

The invention relates to radio engineering of microwave frequencies (hereinafter referred to as microwave), and in particular, to the design of antenna arrays with frequency scanning used in radars, for example, in survey track radars, and intended for viewing air, surface and ground space.

Widely known and used in radiolocation, frequency-scanning antennas are a flat array of waveguide-slot linear emitters (hereinafter referred to as the rulers) connected to a power divider containing a slow-wave structure in the form of a serpentine waveguide folded in the E-plane and communication elements with rulers. A description of the design and principle of operation of such antennas is provided in many sources, in particular, in “Scanning Microwave Antenna Systems,” Vol. 3, ed. G.T. Markov and A.F. Chaplin, ed. "Soviet Radio", M., 1971 and "Antennas and Microwave Devices", ed. D.I. Voskresensky, ed. Sovetskoe Radio, M., 1972. In addition, analogues of the present invention are frequency scanning antennas of the AN / SPS-48 radar company ITT Gilfillan, USA (Foreign Military Review No. 5, 1980, Aviation Wee No. 24, 1984, TIER T.73, No. 2) and antennas used in three-coordinate radars (patents RU 35688, RU 2254593, RU 51754, SU 1597986 and GB 2051486). A significant drawback of the known antennas is that the standing wave voltage coefficient (hereinafter referred to as VSWR) at the input of the power divider at the normal frequency (signal frequency corresponding to the formation of a radiation pattern with a maximum in the direction normal to the longitudinal axis of the line of the snake waveguide of the power divider) increases sharply as a result in-phase addition of a large number of reflections from the bends of the serpentine waveguide of the power divider and couplers (elements of communication between the power divider and the rulers). This phenomenon is commonly referred to in the literature as the “normal effect” (see “Antennas and microwave devices,” edited by D. I. Voskresensky, ed. “Soviet Radio”, M., 1972, p. 41, 42). The matching at the input of the power divider at the normal frequency is degraded, and therefore, the operational characteristics of not only the antenna device, but also the radar as a whole, are deteriorating.

As a prototype of the proposed technical solution, the frequency scanning antenna of Patent No. RU 2284079, made in the form of a planar array of waveguide-slot linear emitters connected through communication elements to a power divider, can be adopted. The power divider is made in the form of a serpentine waveguide folded in the E-plane. The length of the line of the serpentine waveguide of the power divider in the gap between adjacent communication elements of the power divider is selected from the condition of providing a given sector of beam scanning in a plane perpendicular to horizontally located rulers. The elements of communication of the power divider with the rulers are divided into two groups - even and odd. The separation of the power divider communication elements into two groups is carried out by spreading in space the longitudinal axes of the power divider, containing even and odd communication elements, relative to each other by a distance equal to an odd integer number of quarters of the wavelength in the waveguide of the power divider at the normal frequency. This technical solution along with advantages also has significant disadvantages. The design of the prototype contains a power divider with one 180-degree bend in the gap between adjacent communication elements (see Figure 2 to patent No. RU 2284079). This design of the power divider is large and increases the total weight of the antenna due to the large mass of metal in the spaces between the bends of the waveguide. In addition, the disadvantage of the prototype with rulers made on waveguides with a rectangular cross section is that when the dimensions of the wide walls of the waveguides of the rulers and the waveguide of the power divider are not equal, achieving phase matching of the even and odd outputs of the power divider is difficult and, possibly, only due to the curvature of the rulers, which significantly complicates the design of the antenna and its manufacturing technology.

The problem to which the invention is directed, is the creation of an antenna device with frequency scanning (hereinafter referred to as an antenna) operating in a given frequency range and having the lowest level of side lobes at a given width of the main lobe of the radiation pattern.

The technical results achieved by the implementation of the claimed invention are, in particular, a low level of side lobes (from minus 40 to minus 30 dB); reduction of VSWR at the input of the power divider at the normal frequency; improved alignment; gain increase; increase in directional coefficient; increase in utilization of the surface of the antenna sheet; simplicity and manufacturability of manufacturing and maintenance of the antenna; reducing the overall dimensions of the antenna.

The essence of the invention lies in the following features affecting the achievement of the claimed technical results in the implementation of this technical solution. An antenna device with frequency scanning contains a power divider and a flat array of waveguide-slot linear emitters (rulers), each of which is a rectangular waveguide, in a narrow wall of which alternately inclined slots are made. The power divider is made in the form of a serpentine waveguide, folded in the E-plane, and is located in a plane parallel to the plane containing the rulers. Each output of the power divider is connected through a communication element to the input section of the corresponding line. The line of the snake waveguide of the power divider in the gap between adjacent communication elements has two 180-degree bends, and its length is selected as a multiple of an integer odd number of half-waves in the waveguide of the power divider. The power divider coupling elements are divided into two groups so that the longitudinal axis of the power divider containing all the even coupling elements is offset relative to the longitudinal axis of the power divider containing all the odd coupling elements by an integer odd number of quarters of the wavelength in the waveguide of the power divider. The difference in the lengths of even and odd rulers is equal to the value by which the longitudinal axes of the power divider are offset, containing even and odd coupling elements. In this case, the centers of all slots with the same serial numbers (counting from the output of the power divider in the line) of each line are located on the same vertical axis. The direction of inclination of the slots of even lines is mirrored with respect to the direction of the slots of odd lines. A phasing section is introduced into the input section of each ruler with a long length, providing such a change in the size of the wide ruler wall so that within the length of the phasing section the phase shift is carried out, which is required to match the phases of the even and odd outputs of the power divider at the average frequency of the operating frequency range of the antenna frequencies, the length of the phasing section is chosen equal to half the wavelength in the waveguide of the ruler with the size of the wide wall, modified taking into account the introduction of the phasing section into it.

Figure 1 presents a diagram of the construction of an antenna device with frequency scanning.

Figure 2 presents the design of the antenna device with frequency scanning (front view).

Figure 3 AA shows a frontal section of an odd ruler connected through a communication element to a power divider, and Figure 3 BB shows a front section of an even ruler containing a phasing section and connected through a communication element to a power divider.

As shown in Fig.1, 2, the antenna device with frequency scanning contains a power divider 1 and a flat waveguide slot antenna array of horizontally arranged lines divided into two groups: even lines 2 and odd lines 3. Each line 2, 3 represents a rectangular waveguide, in a narrow wall of which alternately inclined slots 5 are made.

The power divider 1 provides scanning of the beam in a vertical plane and contains a slowdown structure in the form of a serpentine waveguide, rolled in the E-plane, and communication elements 4. The longitudinal axis a of the power divider 1, containing communication elements 4 with all even lines 2, is offset in space relative to the longitudinal axis b of the power divider 1, containing coupling elements 4 with all the odd rulers 3, by a distance Δ equal to an integer odd number of quarters of the wavelength in the waveguide of the power divider at the normal frequency. The offset of the longitudinal axes a and b of the power divider 1 by the distance Δ ensures coordination, that is, a low level of VSWR at the input 6 of the power divider 1 at the normal frequency and mutual compensation of the reflections coming to the input 6 of the power divider through communication elements 4 from even lines 2 and odd rulers 3 and appearing in antiphase in relation to each other.

The serpentine waveguide of the power divider 1 contains 180-degree bends, straight sections with communication elements 4, and straight sections without communication elements 4 (idle channels). In this case, the straight sections of the power divider 1 containing communication elements 4 and idle channels in the waveguide of the power divider 1 are located through one. In the interval between adjacent communication elements 4, the waveguide of the power divider 1 contains two 180-degree bends, and the line length of the snake waveguide of the power divider 1 in this interval is selected as an integer multiple of an odd number of half-waves in the waveguide of the power divider 1 at the normal frequency. At the end of the power divider 1, a matched load 7 is installed.

A waveguide-slot antenna array with a frequency scanning antenna device comprising bars 2 and 3 forms a radiation pattern in horizontal and vertical planes. Each ruler 2, 3 is made on the basis of a rectangular waveguide with a cross section of c × d, in one of the narrow walls d of which alternately inclined slots 5 are cut, the number of which is the same in even and odd rulers (Figs. 1-3). Even rulers 2 and odd rulers 3 have different lengths. The indicated difference in the lengths of even and odd rulers is equal to Δ by which the longitudinal axes a and b of the power divider 1 are offset, containing even and odd coupling elements 4. Moreover, the centers of all slots 5 with the same serial numbers (counting from the output of the power divider to the line) each ruler 2, 3 are located on the same vertical axis. The number of vertical axes on which the centers of the slits are located is equal to the number of slots in each line 2, 3. The connection of the inclined slit 5 with the field inside the waveguide of line 2, 3 is characterized by the value of the normalized conductivity, equal to the ratio of the power radiated by the gap to the power passed beyond this gap:

Where

g is the normalized conductivity of the gap;

P _rad - power radiated by the gap;

P _under - power brought to the section with a gap;

R _prosh is the power that passed beyond the gap.

To obtain a linear phase distribution, the slope of the slots 5 is alternated, while the direction of the slopes of the slots of the even lines 2 is mirrored with respect to the direction of the slopes of the slots of the odd lines 3. The resonance setting at the coupling maximum in a given operating frequency range is controlled by the depth of incision of the slot 5 into wide walls with waveguide of rulers 2, 3. The distance between the slits is selected from the condition of preventing the appearance of secondary main maxima when the beam sways in the working frequency range and preventing the manifestation of the normal effect in lineups. Thus, the pitch of the slits is approximately equal to half the wavelength in the waveguide of the rulers 2, 3. To seal the slots, a fluoroplastic overlay is installed on each of the rulers.

The input of each of the lines 2, 3 is made in the form of a waveguide H-plane 90-degree angle with a 45-degree bevel, designed to connect to the corresponding output of the power divider through the communication element 4. At the end of each line 2 and 3, a matched load 8 is installed.

To ensure the required scanning sector and its position relative to the normal to the antenna device with frequency scanning, the size of the wide wall k of the waveguide of the power divider 1 is made smaller than the size of the wide wall from the waveguide of the rulers 2, 3 (Figure 3 A-A, B-B). The size of the narrow wall m of the waveguide of the power divider 1 in a straight section with communication elements 4 coincides with the size of the narrow wall d of the waveguide of lines 2 and 3 (Figure 2). The size of the narrow wall n of the waveguide of the power divider 1 in a straight section without communication elements 4 is made smaller than size d and smaller than size m. Due to the inequality of the dimensions of the wide walls k and c, a stepwise phase error is formed at the input sections of the rulers 2, which leads to an increase in the level of the side lobes and, as a result, to a worsening radiation pattern.

Compensation of the indicated phase error is realized by introducing into the input section of each ruler 2 a phasing section 9 correcting the phase, that is, increasing or decreasing the electric length of the input section of the ruler 2 by an amount equal to the resulting phase error (Fig. 1, Fig. 3 B-B ) The phasing section is a device due to the use of which a constructive change in the size of the wide wall from line 2 to the size of the wide wall from the _{FS of} line 2 is realized (Fig. 3 B-B). The conditions for calculating the dimensions of the phasing section 9 is that the size of the wide wall with the _{FS of the} waveguide of line 2 should be such as to provide the phase shift required to match the phases of the even and odd outputs of the power divider at the average frequency of the operating frequency range of the antenna frequencies. The length L _{FS of the} phasing section 9 is chosen equal to half the wavelength in the waveguide of line 2 with the size of a wide wall with _FS at the average frequency of the operating frequency range of the antennas.

The required beam width in horizontal and vertical planes in a given operating frequency range depends on the size of the antenna sheet and its utilization rate. Based on technological reasons and the conditions of transportation and storage, each ruler 2, 3 is assembled from several segments of the waveguide connected by waveguide flanges 10, each of which is placed instead of one of the slots 5 (Fig.2, 3). At the same time, in order to avoid an unacceptable increase in the level of side lobes, the flanges 10 on the antenna sheet are placed in columns in the field of decay of the amplitude-phase distribution of the field along the antenna opening, i.e. at the edges of the antenna sheet, which reduces their influence on the radiation pattern.

The proposed design of the antenna device with frequency scanning has been tested experimentally. The antenna device operates in the frequency range 2710-2850 MHz. The size of the antenna sheet was 4 × 7 m. The antenna array consists of 54 waveguide-slotted lines, each of which is made on the basis of a rectangular waveguide with a cross section of 72 × 34 mm, 87 alternately inclined slots are cut in one of its narrow walls with a step of 73 mm . Moreover, each line is assembled from three segments of the waveguide, the middle of which is 5 m long, and connected by two waveguide flanges. The waveguide flanges are arranged in columns instead of 10 and 77 slits of each line, therefore, each line contains 85 radiating slots. The longitudinal axes of the power divider containing even and odd coupling elements are offset relative to each other by ¼ wavelength in the waveguide of the power divider at the normal frequency. The length of the line of the snake waveguide of the power divider in the gap between adjacent communication elements is made equal to 2.5 wavelengths at the normal frequency. The size of the wide wall k of the waveguide of the power divider was 62.4 mm, the size of the narrow wall m of the waveguide of the power divider in a straight section with communication elements was 34 mm, and the size of the narrow wall n of the idle channel was 24 mm. The phasing section, which is a metal plate mounted in the input section on the narrow wall d of the waveguide of each even line, has a length of 93 mm. The level of the side lobes was minus 34 dB, the VSWR at the input of the power divider in the operating frequency range has a value of no more than 1.5.

Claims (4)

1. An antenna device with frequency scanning, containing a power divider and a flat array of waveguide-slot linear emitters, each of which is a rectangular waveguide, in the narrow wall of which alternately inclined slots are made, and the power divider is made in the form of a serpentine waveguide folded in E- plane, and is located in a plane parallel to the plane containing the waveguide-slot linear emitters, each output of the power divider is connected through a communication element to the input section of the corresponding its waveguide-slot linear radiator, while the power divider communication elements are divided into two groups so that the longitudinal axis of the power divider containing all the even communication elements is offset from the longitudinal axis of the power divider containing all the odd communication elements by an odd integer number of quarters the wavelength in the waveguide of the power divider, characterized in that the line of the serpentine waveguide of the power divider in the gap between adjacent communication elements has two 180-degree bends, and its length is selected an odd integer multiple of half-waves in the waveguide power divider; the difference in the lengths of even and odd waveguide-slot linear emitters is equal to the value by which the longitudinal axes of the power divider are offset, containing even and odd coupling elements, while the centers of all slots with the same serial numbers (counting from the output of the power divider into the waveguide-slot linear radiator) of each waveguide-slot linear radiator are located on one vertical axis, the direction of inclination of the slots of even waveguide-slot linear radiators is mirrored with respect to the direction of it cracks odd-gap linear waveguide radiators; a phasing section is introduced into the input section of each waveguide-slot linear radiator having a large length, providing such a change in the size of the wide wall of the waveguide-slot linear radiator so that the phase shift is achieved within the length of the phasing section, required to match the phases of the even and odd outputs of the divider at the average frequency of the operating frequency range of the antenna device with frequency scanning, while the length of the phasing section is chosen equal to half the wavelength in the wave ode linear waveguide slot radiator with a wide size wall modified with the introduction into it phasing section. 2. The device according to claim 1, characterized in that the waveguide-slot linear emitters consist of several parts connected by waveguide flanges, which are placed instead of slots with the same serial numbers (counting from the output of the power divider in the waveguide-slot linear radiator) of each waveguide slot linear emitter in the field of decline of the amplitude-phase distribution of the field by the opening of the antenna device with frequency scanning. 3. The device according to claim 1, characterized in that for each waveguide-slot linear radiator a sealing plate is installed made of a material having hydrophobic properties, for example, fluoroplastic. 4. The device according to claim 1, characterized in that the input of each waveguide-slot linear emitter, designed to connect to the corresponding output of the power divider, is made in the form of an N-plane 90-degree angle with a 45-degree bevel.

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