GB2208969A

GB2208969A - Slot antenna

Info

Publication number: GB2208969A
Application number: GB8819376A
Authority: GB
Inventors: Kunitaka Arimura; Akira Tsukada; Hiroshi Kasuga; Fumio Takenaga
Original assignee: Arimura Giken KK
Current assignee: Arimura Giken KK
Priority date: 1987-08-18
Filing date: 1988-08-15
Publication date: 1989-04-19
Anticipated expiration: 2008-08-15
Also published as: DE3827956A1; KR890004467A; FR2619658A1; GB8819376D0; GB2208969B; CN1031451A; CN1014572B; KR910008948B1

Description

SLOT ANTENNA

BACKGROUND OF THE INVENrION

The present invention relates to a slot antenna having a rectangular waveguide, for the communication, broadcasting and others.

Referring to Fig. 44 showing a conventional slot antenna having a circular waveguide, the electromagnetic wave is propagated in the waveguide in TEM coaxial mode which is 19 represented by cylindrical coordinates as shown in Fig. 45. Since the wave propagates coaxially about a central feeder opening, radiation slots are coaxially or spirally disposed.

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

SUMMARY OF THE INVENTION

An object of the present invention is to provide a slot antenna having a rectangular waveguide which may radi ate not only the circularly polarized wave, but also the linear polarization at high efficiency.

Another object of the present invention is to provide an antenna which may compensate a phase difference of an electric field in a waveguide.

According to the present invention. there is provided a slot antenna comprising a rectangular waveguide surrounded by metal plates to form a rectangular waveguide space,.-a horn waveguide connected to the rectangular waveguide so as to communicate a horn waveguide space therein with the rectanqular waveguide space, and having a power fee(i inlet opening at an end thereof, the rectangular waveguide having a plurality of wave radiation slots on one of the metal plates.

By adjusting the disposition of the slots, both the circularly polarized wave and linear polarization can be 10 radiated from the slots.

In an aspect of the invention, the rectangular waveguide has a terminal resistor at an end plate thereof, and has matching means at an end plate thereof, for increasing the power of wave radiated from slots adjacent the end plate.

In another aspect, a metal plate opposite to the metal plate having the slots has slow-wave means such as a corrugated metal plate for delaying the propagated wave.

Further, the present invention provides a slot antenna comprising a rectangular waveguide surrounded by metal plates to form a rectangular waveguide space, a horn waveguide connected to the rectangular waveguide so as to communicate a horn waveguide space therein with the rectangular waveguide space, and having a power feed inlet opening at an end thereof, the rectangular waveguide having a plurality of wave radiation slots on one of the metal plates, a parabolic reflector provided between the horn waveguide space and the rectangular waveguide space, for reflecting wave to the rectangular waveguide so that an equiphase plane of the wave may be flattened.

2 - 1 These and other objects and features of the preseAt invention will become more apparent from the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Fig. I is a perspective view showing a slot antenna as a first embodiment of the present invention; Fig. 2 is a sectional perspective view of the slot antenna taken along a line A-A' of Fig. 1; Fig. 3 is a diagram explaining wave propagation modes in the slot antenna shown in orthogonal coordinates; Fig. 4 is a diagram explaining wave propagation phases in a horn waveguide of the slot antenna; Fig. 5 is a graph showing a characteristic of power density at a longitudinal section of a rectangular wave- guide-, Fig. 6 is a diagram showing an electric field distribution at a cross section of a rectangular waveguide of the slot antenna; 20 Fig. 7a is a perspective view of a horn waveguide provided in a second embodiment of the present invention; Fig. 7b is a perspective view of a modification of the horn waveguide 0, Fig. 8 is a perspective view of another modification 25 of the horn waveguidel, Fig. 9 is a plan view of the slot antenna of the second embodiment; Fig. 10 is a sectional perspective view of a slot antenna as a third embodiment of the present invention;

3 - Fig. 11 is a graph showing a characteristic of power density at a longitudinal section of the slot antenna of the third embodiment:

Figs. 12 to 15 show examples of section of a slot antenna as a fourth embodiment of the present invention:

Fig. 16 is a sectional perspective view of the slot antenna shown in Fig. 15; Fig. 17a is a fragmentary perspective view of a slot antenna as a fifth embodiment of the present invention:

Fic. 17b is an explanatory diagram showing an electric field distribution in the slot antenna of Fig. 17a;

Fig. 18a is a fragmentary sectional view of a slot antenna as a sixth embodiment of the present invention:

Fig. 18b is a plan view of a metal plate used in the slot antenna of Fig. 18a:

Fig. 19 is a fragmentary sectional view of a slot antenna as a seventh embodiment of the present invention:

Fig. 20 is a fragmentary sectional view of a slot antenna as an eighth embodiment of the present invention; Fig. 21 is a sectional perspective view of a slot antenna as a ninth embodiment of the present invention:

Figs. 22 and 23 are schematic sectional views of the modifications of the slot antenna of the ninth embodiment:

Fig. 24 is a sectional perspective view showing another modification of the slot antenna of the ninth embodiment; Figs. 25 to 28 are diagrams showing slots and radiated electric fields of slot antennas:

Fig. 29 is a perspective view of a horn wavegUide; 4 - 1 Fig. 30 is a sectional perspective view of a modification of a horn waveguide; Fig. 31a is a perspective view of a slot antenna as a tenth embodiment of the present invention, having para5 bolic reflectors; Fig. 31b is a sectional perspective view of the slot antenna of the tenth embodiment:

Fig. 32 is a plan view of a horn waveguide of 'the slot antenna:

Fig. 33a is a perspective view of the slot antenna shown in orthogonal coordinates:

Figs. 33b and 33c are explanatory diagrams of the slot antenna; Fig. 34 is an enlarged perspective view showing a part of the slot antenna:

Fig. 35 is a sectional view of the slot antenna; Fig. 36 is a sectional perspective view of a slot antenna as an eleventh embodiment., Figs. 37 and 38 show sectional perspective views of modifications of the eleventh embodiment:

Fig. 39 is a sectional perspective view of a slot antenna as a twelfth embodiment:

Figs. 40 to 43 are plan views of the examples of dispositions of slots; Fig. 44 is a sectional perspective view of a conventional circular slot of a coaxial cable type: and Fig. 45 is a diagram explaining the wave propagation in the conventional slot antenna shown in cylindrical coordinates.

- DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figs. 1 and 2, a slot antenna according to the present invention comprises a rectangular waveguide W and a horn waveguide 5 connected to the rectangular wave guide W at a power feed opening 2 thereof. The rectangular waveguide W comprises opposite rectangular metal guide plates 3 and 4. and metal side guide plates 1, 7 and 8, to form a rectangular waveguide space S. The upper guide plate 3 has a plurality of wave radiation slots 15, arranged in rows. The rows are coaxially arranged, and each slot is disposed perpendicularly to the axis of the waveguide W.

On the inside of the side plate I of the rectangular wave guide W, a terminal resistor 6 is provided as shown in Fig. 2.

In the rectangular waveguide W, the electromagnetic wave is propagated in TE10 mode represented by orthogonal coordinates as shown in Fig. 3. In Fig. 3, dotted lines H represent lines of magnetic force and lines E represent lines of electric force at every one-half wavelength (1/2>,O).

Since lines of electric force having the same direction generate at every one wavelength (,,0), it is easy to form slots for radiating the electric force. In accordance with the antenna, not only the circularly polarized wave, but also linear polarization can be radiated at high efficiency.

If slots are formed on the side plate 8, the magnetic force is radiated from the slots. In such an antenna, slots are disposed in parallel to the axis of the rectangular wave guide.

In the horn waveguide 5, the wave is propagated in 1 coaxial wave about a center 0 in a power feed inlet a# shown in Fig. 4. Accordingly, there is a phase difference S between the wave traveling distance L from the center and an outlet opening 22 along the axis (B-B') and the wave trav eling distance along a side 21. In order to compensate the phase difference, the slots 15 are arranged along co axial circular lines, about the center 0. Thus, electric forces having the same phase can be radiated from the slots.

The remaining power in the waveguide W is absorbed in the terminal resistor 6 at the end side plate 1.

Referring to Fig. 7a showing a second embodiment of the present invention, the horn waveguide 5 has, at the outlet thereof, a lens antenna 19a of dielectric. The lens antenna has a semicircular shape in plan view, so that the phase difference of the wave can be compensated. The operation and effect of the embodiment is the same as the first embodiment.

The horn waveguide 5 shown in Fig. 7b has a lens antenna 19b made of a plurality of metal plate, and the horn waveguide 5 of Fig. 8 has a slow-wave device 13 in the form of a corrugated metal plate. By such means, a plane passing equiphase portions becomes flat. Thus, slots 15 may be arranged in parallel as shown in Fig. 9.

Fig. 5 shows a power density distribution of the antenna according to the f irst embodiment shown in Fig. 1. The power density reduces toward the end side plate 1 because of the radiation of the power from slots 15, so that the antenna gain reduces. A third embodiment shown in Fig. 10 is to uniformly radiate the power. The guide plate 4 without slots is inclined to the guide plate 3 to reduce the pidth of the space S in the waveguide toward the side plate 1. Thus, the power is substantially uniformly distributed as shown in Fig. 11, thereby increasing the antenna gain.

Referring to Fig 6, a dotted line D shows a distribu- tion of the electric field in the transverse plane in which the electric force reduces toward both sides 7 and S. Each of waveguides as a fourth embodiment shown in Figs. 12 and 14 has a V-shaped guide plate 4, and each waveguide shown in Figs. 13, 15 and 16 has a circular guide plate 4. so that the distribution of the electric field may be unified.

In a fifth embodiment of Fig. 17a, a pair of metal plates 18 are provided in the waveguide W adjacent the side plates 7 and 8. Each plate 18 is secured to the plate 4 forming a gap between the plate 3, so as to effect choking the waveguide to provide a proper impedance. Thus, the distribution of the electric field may be unified as shown in Fig. 17b.

A waveguide of sixth embodiment shown in Fig. 18a hasan intermediate metal plate 17 having a large number of slots and holes 16. By adjusting the form and density of the holes as shown in Fig. 18b, the power density in a space S I and electric field can be uniformly distributed.

In a seventh embodiment shown in Fig. 19, a matching member 11 is provided on the end plate I instead of the terminal resistor 6 in the first embodiment. The wave striking the matching member is reflected to be added to waves radiated from end slots, thereby equalizing the distribution of the power.

m A waveguide according to an eighth embodiment shpwn in Fig. 20 has a slow- wave device 13 formed by a corrugated plate or made of dielectric. By controlling the phase constant of the wave, it is possible to adjust the direction of the radiation and density of the power to improve the directivity and gain of the antenna.

An antenna shown in Fig. 21 as a ninth embodiment, the rectangular waveguide W is superimposed on the horn waveguide 5 to form a compact construction - The guide plate 4 is shortened, so that the opening 22 of the horn waveguide 5 is connected to the opening 2 of the rectangular waveguide W, thereby forming a U-shaped connection. Figs. 22 and 23 show U-shaped connections, respectively. In each of the connections, an inclined guide member 12 is provided at each corner, so that the wave is turned 180 degrees without reflecting the wave, thereby effectively radiating the power.

Fig. 24 shows a modification of the antenna of Fig. 21. The antenna has a parabolic reflector 23 at the U-shaped connection. By reflecting the wave by the parabolic reflector 23, the phase difference is compensated to form a flat equiphase wave plane. Thu,,:;, slots 15 can be disposed in parallel.

Fig. 25 shows the disposition of slots at intervals of the wavelength)-O. Slots 15 shown in Figs. 26 and 27 are formed at intervals of one-half wavelength Ni, 0 /2 and at 45 degrees with the axis of the waveguide. Slots 15 an adjacent rows are inverted to make 90 degrees with each other. Thus, components P having the same direction are added to each other, thereby increasing the radiated power.

9 Since the density of the slot is increased, aperture etficiency can be increased to improve the antenna gaIn.

The slots shown in Figs. 25 to 27 are disposed for the linear polarization. Slots shown in Fig. 28 are arranged 5 for circularly polarized wave.

Fig. 29 shows a modification of the horn waveguide 5. The horn waveguide has a bent guide 14. The horn waveguide 5 shown in Fig. 30 has a coaxial cable 24 as a feeder. Another feeder such as a ridge waveguide and a loop coupling may be used.

Referring to Figs. 31a and 31b showing a tenth embodiment, the antenna comprises a pair of rectangular waveguide W1, W2 and a pair of horn waveguides. The rectangular waveguides are formed by opposite guide plates 31, 32, side plates 33, 33a and a partition 37 having terminal resistors on opposite sides thereof, so that a pair of waveguide spaces S 1 and S 2 are formed. The horn waveguide comprises guide plates 32 and 34a to form a pair of horn waveguide spaces A, and A2 which are separated by a matching member 35. Thus, a pair of antennas are symmetrically formed. A feeder waveguide 34 having a waveguide space A is connected at a central portion of the antenna which is communicated with the spaces A 1 and A2 through symmetrically separated by the matching power feed openings. Each connection C having a gap D has side plate 33a having a semicircular or polygonal sectional shape. and has a parabolic reflector. The parabolic reflector is formed by moving a parabola along the semicircular plate 33a. In other words, the parabolic reflector has a-parabola at every cross section of the semicircular plate 33a.

Accordingly, the parabolic reflector is different frornthe 7 parabolic antenna which is formed by rotating a parabola.

Wave in the space A (A2) in the horn waveguide propaaates in circular mode about 0 as shown in Fig. 32, having a phase difference. The wave is reflected by the parabolic reflector, so that the phase difference is compensated to provide equal traveling distances with respect to the Y-axis as shown in Fig. 33b. In addition, as shown in Fig. 33c, the wave is reflected at the U-shaped reflector in parallel. The traveling distances with respect to the Z-axis are equalized. Thus, the slots 31a can be parallelly disposed.

Since the wave reflected at the U-shaped reflector passes the space S1 different from the space AI(Fig. 33c), it is possible to prevent the reduction of the gain due to blocking which occurs in a double reflect parabolic antenna.

As to the dimension of the slat 31a, the length of the slot is about onehalf wavelength (1/2',,O) and the width is smaller than the wavelength. it is preferable that the interval h between slots is smaller than one free space wavelength X 0 in order to reduce the side lobe of the antenna, for example 0.9 X0 to 0.5'-O. However, it is impossible to radiate the wave from the slots disposed at such intervals.

In order to radiate the wave, a corrugated plate 36 as a slow-wave device is mounted on the guide plate 32 as shown in Fig. 35. By delaying the wave, the same phase waves can be radiated from the slots disposed at small intervals. Although the interval h is reduced, the length of the slot 31a is 11 about one-half wavelength. It is possible to increase:P the ratio of the available area of slots 31a to the sectional area of the rectangular waveguide having a parabolic reflector, thereby improving the aperture efficiency. For example, if a rectangular waveguide with a parabolic reflector has the axial length of 80 cm and the rectangle long side length of 60 cm, the interval h is 0.8),,0, and the frequency of the wave is 12GHz. 1600 parallel slots can be provided on the radiating plane.

Referring to Fig. 36 showing an eleventh embodiment, a single horn waveguide having a connection C disposed in parallel with the rectangular waveguides W1 and W2. The connection C has a parabolic reflector and the wave is fed from a central portion between the waveguides W1 and W2.

Accordingly, the terminal resistors 37 are provided opposite ends of the antenna. Figs. 37 and 38 show modifications of the eleventh embodiment, in which each connection C is disposed perpendicular to the rectangular waveguide.

Fig. 39 shows a modification of the tenth embodiment of Figs. 31a and 31b. A coaxial cable 38 is connected to the antenna at a central portion between the horn waveguides for radiating waves to horn waveguide spaces Al and A2 through power feed inlet openings.

Figs. 40 to 43 show dispositions of slots 31a. The antenna of Fig. 40 is provided for radiating the linear polarization and antenna of Fig. 41 is for radiating the circularly polarized wave. In the antenna shown in Fig. 42. f our slots encircled by a line is an unit f or radiating a linear polarization and a plurality of units are arranged t along rows and columns.

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.

13 -

Claims

1. A slot antenna comprising:

a rectangular waveguide having metal plates to form a rectangular waveguide space:

a horn waveguide connected to the rectangular waveguide so as to communicate a horn-waveguide space therein with the rectangular waveguide space, and having a power feed inlet opening at an end thereof:

the rectangular waveguide having a plurality of wave radiation slots on one of the metal plates.

2. The slot antenna according to claim 1 wherein the rectangular waveguide has a terminal resistor at an end plate thereof.

3. The slot antenna according to claim 1 wherein the rectangular waveguide has matching means at an end plate thereof, for increasing the power of wave radiated from slots adjacent the end plate.

4. The slot antenna according to claim 1 wherein a metal plate opposite to the metal plate having the slots 20 has slow-wave means for delaying the propagated wave.

5. The slot antenna according to claim 1 wherein the rectangular waveguide space is reduced toward an end plate in width between the metal plate having the slots and an opposite metal plate.

6. The slot antenna according to claim 1 wherein the rectangular waveguide has a pair of metal plates adjacent side plates. each of which is secured to a plate opposite the plate having the slots so as to effect choking the rectangular waveguide to provide a proper impedance, thereby R 1 uniformly distributing the electric field.

7. The slot antenna according to claim 1 wherei n the slots are disposed perpendicularly to the axis of the rectangular waveguide. 5

8. The slot antenna according to claim 1 wherein the rectangular waveguide and the horn waveguide are disposed such that axes of both waveguides are arranged on an axial line.

9. The slot antenna according to claim 1 wherein the rectangular waveguide and the horn waveguide are superimposed with each other.

10. A slot antenna comprising:

rectangular waveguide surrounded by metal plates to form a rectangular waveguide space:

horn waveguide connected to the rectangular waveguide so as to communicate a horn waveguide space therein with the rectangular waveguide space, and having a power feed inlet opening at an end thereof:

the rectangular waveguide having a plurality of wave radiation slots on one of the metal plates:

a parabolic reflector provided between the horn wave guide space and the rectangular waveguide space, for reflect ing wave to the rectangular waveguide so that an equiphase plane of the wave may be flattened.

11. The slot antenna according to claim 10 wherein the rectangular waveguide has a terminal resistor at an end plate thereof.

12. The slot antenna according to claim 10 wherein a metal plate opposite to the metal plate having the slots has slow-wave means for delaying the propagated wave. - 15 -

13. A slot antenna substantially as d.escribed herein with reference to the accompanying drawings.

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

iR T Published 1988 a- Tne Patent W:1CE. E-.z-ie Hc---cú 6e7. H_- 47P CC-,Iez ing De ob,:,a, f=- M.e Pa-C= offcc Sales Branch. St Ma:y Cray. Orpingtc-n. Kent BR5 3RD Print--'- bv Multiplex techmques ltd. St. Ma--y Crky. Kent. Con. 187