GB2221799A

GB2221799A - Slot array antenna

Info

Publication number: GB2221799A
Application number: GB8917699A
Authority: GB
Inventors: Kunitaka Arimura; Fumio Takenaga; Akira Tsukada; Hiroshi Kasuga
Original assignee: Arimura Giken KK
Current assignee: Arimura Giken KK
Priority date: 1988-08-08
Filing date: 1989-08-02
Publication date: 1990-02-14
Also published as: KR900004062A; GB8917699D0; DE3926187A1; AU614651B2; KR920002441B1; JPH0246006A; CN1040890A; AU3908789A

Description

2- Z21 17 9.001

DESCRIPTION OF INVENTION

Title: "Slot array antenna" THE PRESENT INVENTION relates to a slot array antenna having a rectangular waveguide, and more particularly to a slot array antenna for communication, broadcasting and other purposes.

Figure 17 shows a conventional slot antenna having a circular waveguide. The electromagnetic wave is propagated in a space S' of the waveguide in TEM coaxial mode which is represented by cylindrical coordinates as shown in Figure 18. In Figure 18, reference e designates a direction of electric field and h designates a direction of magnetic field. Since the wave propagates coaxially about a central feeder opening 41, radiation slots lal are coaxially or spirally disposed in a metal plate 11.

Such a circular antenna is suitable for circularly polarised waves. However, there are problems when used for radiating the linear polarisation, since the side lobe becomes large and the antenna gain reduces compared with the circularly polarised wave.

The object of the present invention is to provide a slot array antenna having a rectangular waveguide which may radiate not only the circularly polarised wave, but also the linearly polarised wave at high efficiency.

According to the present invention, there is provided a slot array antenna having a rectangular waveguide with a space having-a rectangular sectional shape and a power feed opening, a power f eeder means connected to the rectangular waveguide at the power feed opening, the rectangular waveguide having a plurality of wave radiation slots formed in one of the metallic plates forming long sides of the rectangular sectional shape, the width of the rectangular waveguide being four times as large as wavelength in the space or more, the height of the rectangular waveguide being one-fourth of the wavelength or more, and the ratio of the wdith to the height of the rectangular waveguide being 10:1 or more.

The rectangular waveguide may have a terminal resistor at an end plate which is opposite to the power feed opening. The power feeder means may comprise a feeder waveguide having a plurality of feeder openings communicating with the space for dispersing power and feeding the power to the rectangular waveguide.

The feeder waveguide may be laterally attached to the rectangular waveguide.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings, wherein:

- Zt - Fig. 1 is a perspective view showing a slot array antenna according to the present invention; Figs. 2a to 2d show various arrangements of electric power radiation slots of the antenna; Fig. 3 is a graph showing a power density distribution in a space of the antenna; Figs. 4a and 4b are illustrations showing radiation directions of the antenna; Fig. 5 is a perspective view showing a first modification of the antenna of Fig. 1; Fig. 6 is a graph showing a power density distribution of the first modification; Fig. 7 is a perspective view showing a second embodiment of the present invention; Fig. 8a is a perspective view showing a third embodiment; Fig. 8b is a perspective view showing a fourth embodiment; Fig. 8c is a perspective view showing a fifth embodiment; Fig. 9a is a front view showing a power feeder means for a second modification of the first embodiment; Fig. 9b is a front view showing a power feeder means for a third modification; Fig. 9c is a perspective view of the power feeder means; Fig. 10a is a perspective view showing an antenna provided with the power feeder means of Fig. 9a; Fig. 10b is a perspective view showing an antenna provided with the power feeder means of Fig. 9b; Fig. 11 is a perspective view showing a sixth embodiment of the present invention; Figs. 12a and 12b are illustrations showing directivity of the antenna of the sixth embodiment; Fig. 13 is a perspective view showing a seventh embodiment; Fig. 14 is a perspective view showing an eighth embodiment; Fig. 15 is a perspective view showing a ninth embodiment; Fig. 16 is a perspective view showing a tenth embodiment; Fig. 17 is a sectional perspective view of a conventional circular slot of a coaxial cable type; and Fig. 18 is a diagram explaining the wave propagation in the conventional slot antenna shown in cylindrical coordinates.

Referring to Fig. 1 showing a first embodiment of present invention, a slot array antenna according to the present invention comprises a rectangular waveguide G having a power feed opening 4 formed at an inlet side 4 thereof, and a waveguide 6 connected to the rectangular waveguide G at the power feed opening 4. The rectangular waveguide G comprises opposite rectangular metallic plates 1 and 2, and metal side plates 3 secured to the three sides of each plate 1(2) to form a rectangular waveguide space S having a rectangular sectional shape. The width W of the rectangular waveguide is four times as large as the wavelength Xg (Xg is the wavelength in the waveguide) in the space S (4Xg) or more, and the length úe is 4Xg or more. The height d is one-fourth of the wavelength Xg (Xg/4) or more. The ratio of the width.W to the height d is 10:1 or more. The metallic plate 1 has a plurality of electric power radiation slots la, arranged in a matrix. Each slot la is disposed perpendicular to the axis of the waveguide G. On the inside of the end side plate 3 of the rectangular waveguide G, a terminal resistor 7 is provided. A dispersing feeder waveguide 6 having a plurality of feeding openings 5a on a metallic plate 5 thereof is laterally attached to the rectangular waveguide G as power feeder means. The power is dispersed by the openings 5a and fed from the openings 5a to the space S. Consequently, electric power propagates in the waveguide G, with phase fronts being a plane. Thus, the power is fed to the rectangular waveguide G in the form of the plane wave. The power of equiphase radiates from the slots la. Remaining power in the rectangular waveguide G - is absorbed in the terminal resistor 7, thereby preventing influence of reflected power.

Figs. 2a to 2d show various arrangements of the slot la. The slots of Fig. 2a are arranged at the distance P1 of lg/4 and at the distance P2 of Xg. The direction of a slot is perpendicular to that of an adjacent slot. The resultant electric field of the wave radiated from a pair of slots becomes a circularly polarized wave.

The other slot array antennas shown in Figs. 2b to 2d radiate linear polarizations. Since tens of slots are arranged on each column and row, the gain is raised and the directivity is sharpened. For example, if the width W is 50 cm, length te is 50 cm and height d is 0.8 cm, the gain is about 34.8 dBi at 12 GHz.

In the above described arrangement of slots, the beam radiates in the vertical direction to the metallic plate 1. If the distance between the slots la is deviated from Xg, the direction of the beam inclines, as described hereinafter with reference to Figs. 4a and 4b.

Fig. 3 shows a power density distribution in the space S of the waveguide G according to the first embodiment. The power density reduces toward the terminal resistor 7 because of the radiation of the power from slots la. Consequently, the power distribution is irregular so that the antenna gain reduces.

A first modification shown in Fig. 5 is to uniformly radiate the power. The distance d is reduced to the terminal resistor 7 in a line or in a curve. Thus, the power is substantially uniformly distributed as shown in Fig. 6, thereby increasing the antenna gain.

Since the area of the plate 1 which is perpendicular to the direction of the electric field is sufficiently large compared with the wavelength 1 in the free space, the wavelength 1g becomes substantially equal to the wavelength X, which causes reduction of gain because of a large grating lobe. However, if the length of each slot la is determined below the resonance length so that the reactance of the slot may become negative, the phase of the propagating power is delayed by the slot. Accordingly, the interval between slots is set to a value between 0.95X and 0.98X in order to radiate the equiphase power, which makes it possible to suppress the generation of the grating lobe without providing a slow-wave device.

If the slow-wave device is provided in the space S of the waveguide G, the phase constant of the propagating power is suppressed to reduce further the wavelength Xg. Therefore, the density of the slot is increased to improve the antenna efficiency.

Fig. 7 shows the second embodiment of the present invention. The antenna has a T-shaped feeder waveguide 6 so as to make a right angle with the metallic plate 5. A reflector member 10 as a matching means is provided on the plate 5 so as to distribute the power. The operation and effect of the second embodiment are the same as the first embodiement.

The third embodiment shown in Fig. 8a has a pair of 7 horn waveguides 9 as a power supply means and a branching T-shaped feeder waveguide 6. The other parts of the antenna are the same as the first embodiment in construction. The first modification of Fig. 5 may be used for the third embodiment.

Referring to Fig. 8b showing the fourth embodiment the present invention, waveguide G has a horn waveguide having a median partition 11. This embodiment has the same operation and advantage as the second embodiment.

Fig. 8c shows the fifth embodiment of the present invention. The branching feeder waveguide 6 comprises multiple stages forming a multi- stage disperse waveguide. This embodiment has the same operation and advantage as the first embodiment. The waveguide of Fig. 5 as the first modification may be applied to the power supply of 9 means.

Figs. 9a and 9b show a power feeder means for a second modification and a power feeder means for a third modification of the first embodiment, respectively. Each power feeder means is a microstrip line comprising a substrate 12b of dielectric, a branching strip 12 in intimate contact with one side of the substrate 12b, and a grounding plate 13 (Fig. 9c) provided on the other side of the substrate. The strip 12 has a feeding end 12a. As shown in'Fig. 9c, the grounding plate 13 has a plurality of radiating slots 13a, each being opposite to a feeder end 12c of the strip 12. A reflector plate 14 is provided opposite the grounding plate 13 with a space through 8 - spacers (not shown). Distance h between the reflector plate 14 and the grounding plate 13 is about X/4 so that the power radiates from the slots 13a in a predetermined direction.

Fig. 10a and 10b show antennas provided with the power feeder means shown in Fig. 9a or 9b. The feeder means is attached to the antenna so as to open the slots 13a to the power feed opening 4 of the rectangular waveguide G. The antenna of Fig. 10b comprises a pair of adjacent rectangular waveguides G. The power feeder means consisting of a pair of microstrip lines is attached to a central portion of the antenna accordingly. This embodiment has the same operation and advantage as the first embodiment. The waveguide of Fig. 5 as the first modification may be applied to the power supply means. Although the slot 13a is employed as a radiation element in the above embodiment, other elements may be used.

Referring to Fig. 11 showing a sixth embodiment of the present invention, the antenna comprises a pair of adjacent rectangular waveguides G each having the power feed opening 4 at a central portion of the antenna, and the feeder waveguide 6 connected to the antenna so as to communicate with the power feed openings 4.

Referring to Fig. 4a showing a radiation direction in the first embodiment, if the wavelength X 1 of the power fed to the space S of the rectangular waveguide is shorter than the set wavelength X 0 (distance between slots la), the phase of the power radiated from the slot la-1 is in advance of the phase of the power radiated from the slot la-2 by the difference between X 0 and X 1 (X0-xl). Consequently, the.main lobe P inclines toward r as shown in Fig. 4b. When the wavelength X 1 is longer than the 5 wavelength Xot the main lobe P inclines toward ú.

Figs. 12a and 12b show directivity of the antenna of the sixth-embodiment shown in Fig. 11. The power fed from the power feeder means 6 is divided into the right and left spaces S of the rectangular waveguide G. The divided powers propagate symmetrically in the right and left spaces S. Therefore, if the wavelength of the power changes, the left main lobe P1 and the right main lobe P2 incline symmetrically as shown in Fig. 12b. Consequently, the direction of the resultant main lobe P becomes perpendicular to the surface of the antenna advantageously.

Referring to Fig. 13 showing the seventh embodiment of the present invention, the rectangular waveguide comprises a pair of adjacent rectangular waveguides and a pair of feeder waveguides 6 provided on opposite sides of the rectangular waveguide. The rectangular waveguide has power feed openings at both ends thereof and the terminal resistor 7 at a central portion thereof. The feeder waveguides 6 are symmetrically attached to the rectangular waveguide so as to communicate with the power feed openings. In a central portion of the feeder waveguide 6, the reflector member 10 is provided for reflecting the power to both waveguides. Other construction, operation and advantage than the above description are the same as the fifth embodiment. The modified rectangular waveguide of Fig. 5 may be used for the antenna of the seventh embodiment.

Referring to Fig. 14 showing the eighth embodiment of the present invention, the rectangular waveguide comprises a pair of adjacent rectangular waveguides and the feeder waveguide 6 provided on the underside of a center portion of the rectangular waveguides. In the waveguide 6, the 10 reflector member 10 is provided.

Figs. 15 and 16 show the ninth and tenth embodiments of the present invention. The antennas are similar to the eighth embodiment of Fig. 14. The parts corresponding to the parts of Fig. 14 and other embodiments are identified with the same references as those prior embodiments.

From the foregoing, it will be understood that the antenna of the present invention provides a slot array antenna having a rectangular waveguide which may radiate not only the circularly polarized wave, but also the linear polarization at high efficiency.

While the invention has been described in conjunction with preferred specific embodiments thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.

Claims

1. A slot array antenna having a rectangular waveguide with a space having a rectangular sectional shape and a power feed opening, a power feeder means connected to the rectangular waveguide at the power feed opening, the rectangular waveguide having a plurality of wave radiation slots formed in one of the metallic plates forming long sides of said rectangular sectional shape, characterized in that width of said rectangular waveguide is four times as large as wavelength in said space or more; height of said rectangular waveguide is one-fourth of said wavelength or more; and the ratio of said width to the height of said rectangular waveguide is 10:1 or more.

2. The slot array antenna according to claim 1 wherein the rectangular waveguide has a terminal resistor at an end plate which is opposite to said power feed opening.

3. The slot array antenna according to claim 1 or 2 wherein the space is reduced toward the end plate.

4. The slot array antenna according to claim 1, 2 or 3 wherein said power feeder means comprises a feeder waveguide having a plurality of feeder openings- communicated with said space for dispersing power and feeding the power to the rectangular waveguide.

5. The slot array antenna according to claim 4 wherein said feeder waveguide is laterally attached to said rectangular waveguide.

6. The slot array antenna according to claim 4 wherein said feeder waveguide is a T-shaped waveguide.

7. A slot array antenna substantially as hereinbefore described with reference to, and as shown in any one or more of Figures 1 to 16 of the accompanying drawings.

8. Any novel feature or combination of features described herein.

-G- Published 1990 athe Patent Office, State House. 6671 High Holborn. LondonWC1R4TP.Further copies maybe obtainedfrom The PatentOfficeSales Branch, St Mary Oray. Orpingtor. Kert ERS 3F.D. Prired by Mliltiplex techniques ltd, St Mary Cray, Kent. Con- 1'87