AU620426B2

AU620426B2 - Slot array antenna

Info

Publication number: AU620426B2
Application number: AU39085/89A
Authority: AU
Inventors: Kunitaka Arimura; Hiroshi Kasuga; Fumio Takenaga; Akira Tsukada
Original assignee: Arimura Giken KK
Current assignee: Arimura Giken KK
Priority date: 1988-08-08
Filing date: 1989-07-28
Publication date: 1992-02-20
Anticipated expiration: 2009-07-28
Also published as: JPH0246004A; AU3908589A; GB2221800A; KR920002440B1; FR2638025A1; KR900004063A; CN1040288A; GB8917701D0; DE3926188A1

Description

COMMONWEALTH OF AUSTRALIA Patent Act 1952 6 2 0 4 2 6 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number Lodged Complete Specification Lodged Accepted Published Priority 8 August 1988 Related Art Name of Applicant :ARIMURA GIKEN KABUSHIKI KAISHA 9 0 Address of Applicant Actual Inventor/s Address for Service 2 -lu, 2-chome, Matsunami, Chigasaki-shi, Kanagawa-ken, Japan :Kunitaka Arimura; Fumio Takenaga Akira Tsukada, Fumio Kasuga RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN 2041.

0 0 0 C6mplete Specification for the invention entitled: SLOT ARRAY ANTENNA The following statement is a full description of this invention including the best method of performing it known to us/3e:- BACKGROUND OF THE INVENTION The present invention relates to a slot array antenna for the communication, broadcasting and others.

The slot array antenna comprises a plurality of slots formed in a plate of a rectangular waveguide. Fig. 21a shows distributions of an electromagnetic field in a 0 0 .so @rectangular waveguide and Fig. 21b shows a pattern of 09 o o0 10 current. As a wave propagation mode in the rectangular oo00 waveguide, a dominant mode (TE 1 0 or TE1 wave) the 10 01 attenuation of which is the smallest in orthogonal 0 0 coordinates is used. If the cut-off frequency is fc, the speed of light is c, the length of the long side of the oo?"o 15 waveguide is a, the waveguide is used in the frequency 0.*00 range between fc=c/2a and fc 2 0 =c/a at which attenuation of another higher order mode occurs. Accordingly, the a to e long side length a is between a A/1.06 and a' A/1.56 00 20 where X is the free space wavelength, and the short side o 0 length b is about a/2.

The slots of the conventional slot array antenna are formed in a plate of the above described waveguide. As shown in Fig. 22, the direction of the current becomes inverse at every one-half wavelength Xg/2 (Xg is the wavelength in the waveguide). The direction of the inclination of the slot is opposed to the adjacent one 1Aaccordingly. Thus, all of the Z-component of the resultant electric field of the wave radiated from each slot is oriented in one direction, and Y-components are in opposite phase to be offset. As a result, the linear polarization is radiated from the slots. The width of the beam in the x-y plane is between 160 and 20° and that in the x-z plane is between 1° and 2* which is in proportion to the number of the slots and hence narrow.

Since the beam width in the horizontal plane is t I 10 narrow and the beam width in the vertical plane is wide, the gain of the above described slot array antenna is small. Consequently, the antenna is improper to use as an antenna for the communicacion, broadcasting and the like, although it is useful in the radar system.

15 SUMMARY OF THE INVENTION The object of the present invention is to provide a ,j t I slot array antenna which is useful as an antenna for the communication and broadcasting, simple in construction and light in weight.

According t *hP nt a slot array antenna having a rectangular wavega with a space having a rectangular sectional sh and a power feed opening formed by metallic es, a power feeder means connected to the r angular waveguide at the power feed opening, th ectangular waveguide having a plurality of wave lation slots formed in one of the metallic .d a f my lE s uf 1=Lai g tail latal 2 2a According to the present invention, there is provided a slot array antenna having a rectangular waveguide, formed by metallic plates, defining an internal 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 i said rectangular sectional trt h r

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t t t ((9

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i shape.

The width of the rectangular waveguide is four times as large as wavelength in the spa-P or more, the height of the rectangular waveguide is one-h lif of the wavelength or more, and the power feeder means ha,: means for feeding power to the space in a form of plane wave.

In an aspect of the present invention, the rectangular waveguide has a terminal resistor at an end plate, and slow-wave means. The space is reduced toward 10 the end plate. Further, the rectangular waveguide comprises a plurality of rectangular waveguides connected with each other, and a matching member is provided for directing the power fed from the power feeder means to the rectangular waveguides.

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

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a perspective view showing a slot array I 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 3 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 modification; Fig. 8 is a perspective view showing a third modification; 4 t 10 Figs. 9a and 9b are perspective views showing horn r waveguides of the antenna; Fig. 10 is a perspective view showing a second embodiment of the present invention; Fig. 11 is a perspective view showing a third embodiment; Fig. 12 is a perspective view showing a fourth embodiment; Fig. 13 is a plan view showing a fifth embodiment; Fig. 14a is a plan view showing a sixth embodiment; Fig. 14b is a plan view showing a seventh embodiment; Fig. 14c is a plan view showing an eighth embodiment; Fig. 15a is a front view showing a power feeder means for a fourth modification of the first embodiment; Fig. 15b is a front view showing a power feeder means for a fifth modification; Fig. 16a is a perspective view of the power feeder means; Fig. 16b is a perspective view showing an antenna 4

I

provided with the power feeder means of Fig. Fig. 16c is a perspective view showing an antenna provided with the power feeder means of Fig. Fig. 17 is a perspective view showing a ninth embodiment of the present invention; Figs. 18a and 18b are illustrations showing directivity of the antenna of the ninth embodiment; Fig. 19 is a perspective view showing a tenth embodiment; 10 Fig. 20 is a perspective view showing an eleventh embodiment; Fig. 21a is an illustration showing distributions of electromagnetic field in the antenna; Fig. 21b is an illustration showing a pattern of current; and Fig. 22 is a perspective view showing a conventional slot array antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1 showing a first embodiment of the 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 thereof, and a horn waveguide 5 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 5 rectanc lar waveguide space S having a rectangular sectional shape. The width W of the rectangular waveguide is four times as large as the wavelength Ag in the space S (4Xg) or more, and the length £e is 4Xg or more. The height d is one-half of the wavelength Ag (Xg/2) or more.

The ratio of the width W to the height d is 5:1 or more.

The metallic plate 1 in the E-plane has a plurality of electric power radiation slots la, arranged in a matrix.

On the inside of the end side plate 3 of the rectangular S 10 waveguide G, a terminal resistor 7 is provided. The horn waveguide 5 has a horn shape in the E-plane and has a lens antenna 6 therein. The lens antenna 6 may be made of dielectric or metallic plates, or corrugated metallic plate. In the horn waveguide 5, a partition 5a is axially disposed at a central position, for preventing disorder of Sphase.

Vi .Electric power propagates in the horn waveguide with phase fronts being coaxial with an ideal origin. The power is converted to a plane wave when passing through the lens antenna 6. Thus, the power is fed to the 7 rectangular waveguide G in the form of the plane wave the I electric field of which is laterally directed. 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. If the waveguide G is so designed that the power fed from the horn waveguide 5 is exhausted by the 6

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radiation from the slots la, the terminal resistor 7 is unnecessary.

Slots may be formed in the H-plane (x-z plane in Fig.

21a) which is perpendicular to the direction of the electric field. Since current on the H-plane is sinusoidally distributed, slots are also sinusoidally distributed. Such distributions render the current and radiation of power irregular, so that the antenna efficiency reduces.

4 t 10 In the slot array antenna of the present invention, o slots are formed on the E-plane which is parallel with the direction of the electric field in the waveguide G, where the current flows uniformly. Accordingly, the slots are uniformly disposed, so that the antenna efficiency is increased.

Figs. 2a to 2d show various arrangements of the slot la. The slots of Fig. 2a are arranged at the distance Pl of Xg/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 Le is 50 cm and distance d is 2 cm, the gain is about 35.5 dBi at 12 GHz.

In the above described arrangement of slots, the beam

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7 i, I_ -7 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 10 irregular so that the antenna gain reduces.

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

it However, in such an antenna, the height d must be at d>Xg/2 so as not to cut off a certain frequency. In addition, the wavelength Xg in the space also changes with the height d (Xg=X/ (1-(X/2d) 2 where X is the wavelength in the free space). Accordingly, it is necessary to design the distance between slots in accordance with the change of the wavelength xg. Other operation and advantages than the above description are the same as the first embodiment.

Fig. 7 shows a second modification of the present invention. The width W of the E-plane is reduced to the end in a line or in a curve, thereby providing a 8 substantially uniform distribution of the radiated power.

Since the height d is constant, the wavelength Ag does not change. Thus, it is unnecessary to change the slot distance, so that the design of the antenna is facilitated.

Since the height d is not permitted to be largely increased, the wavelength Xg in the space S becomes large compared with the wavelength A in the free space, so that the slot distance becomes large. Other operation and advantages than the above description are the same as the first embodiment.

S't iThe antenna shown in Fig. 8 as a third modification, is to reduce the slot distance. In the space S, a slow-wave device 8 such as dielectric or corrugated metallic plate is provided. In the drawing, the space S is filled with foam polyethylene as dielectric. The phase c constant of the power propagated in the space S of the 'rectangular waveguide G can be controlled by the slow-wave device 8 to reduce the wavelength Ag in the space S. Thus, it is possible to increase the density of the slots to increase the efficiency of the antenna. If the wavelength Agis substantially equal to the wavelength X, the grating lobe becomes large to reduce the antenna efficiency. It is necessary to design the phase constant so as not to equalize the wavelength Ag with the wavelength A accordingly. Other operation and advantages than the above description are the same as the first embodiemnt.

Fig. 9a shows the horn, waveguide 5 as a power feed 9 :I I 1~ means for the above described antennas. The opening angle 6 of the horn waveguide is less than 30' so as to provide the dominant mode wave. If the length L is shortened, the opening angle 6 increases. When the opening angle e exceeds 40', a high order mode generates as shown in Fig.

9b, causing the disorder of the phase.

The second embodiment shown in Fig. 10 has a horn waveguide which prevents the disorder of the phase. The horn waveguide comprises a pair of parallel waveguides 10 and a branching T-shaped feeder waveguide 5c. The other Sparts of the antenna are the same as the first embodiment in construction. By such construction, the opening angle is reduced, so that the power fed in the horn waveguide becomes a virtual plane wave. Thus, the lens antenna 6 can be omitted, and the high order mode can be prevented.

i 'f the lens antenna 6 is used in the horn waveguide 5' to flatten the phase front, the length of the horn waveguide is further reduced. The first to third modifications may be used for the horn waveguide of the second embodiment, so that operations and advantages due to Srespective modifications can be obtained.

A power feed end guide 5b for T-shaped feeder waveguide 5c may be provided at another position, for example, at the underside thereof, or at the top surface, or at the inside as shown by dot-dash lines. It should be noted that the phase in the feede'- waveguide 5c becomes reverse when the power is fed from the top surface or from the underside of the waveguide 10 Referring to Fig. 11 showing the third embodiment of the present invention, a waveguide 10 having feeding openings 9a on a metallic plate 9 thereof is attached to the rectangular waveguide G as power feeder means. Other constructions are the same as the first embodiment. The power is propagated from the openings 9a to the space S as a plane wave.

The shape of the opening 9a may be round or rectangular. By changing the diameter of the round opening, or changing the lengths of the long side and the |i short side of the rectangular opening, or changing the inclination and position of the rectangular opening, the directions of the electric field and magnetic field in the ~space S of the rectangular waveguide can be adjusted.

Furt:her, the distribution of the radiated power can be :V equalized. Other operation and advantages than the above description are the same as the first embodiment. The first to third modifications shown in Figs. 5, 7 and 8 can also be connected the power feeder means with the waveguide having openings, so that operations and advantages due to respective modifications can be obtained.

Fig. 12 shows the fourth embodiment cf the present invention. The branching feeder waveguide 5c comprises multiple stages forming a multi-stage disperse waveguide.

Other constructions are the same as the first embodiment.

The first to third modifications shown in Figs. 5, 7 and 8 can also be applied to the antennas of this embodiment.

11 Referring to Figs. 13 to 14c showing the fifth to eighth embodiments of the present invention, the antenna of the fifth embodiment has an offset reflector 12, the antennas of sixth and seventh embodiments have Cassegrain reflector 13 and Gregorian reflector 14 respectively, and the antenna of eighth embodiment has a parabolic reflector The power feeder waveguide means is provided on each reflector. These embodiments have the substantially same operations and advantages as the first embodiment. The first to third modifications shown in Figs. 5, 7 and 8 can also be applied to the antennas of the fifth to eighth embodiments, so that operations and advantages due to respective modifications can be obtained.

Figs. 15a and 15b show a power feeder means for a fourth modification and a power feeder means for a fifth modification of the first embodiment, respectively. Each power feeder means is a microstrip line comprising a substrate 16b of dielectric, a branching strip 16 in intimate contact with one side of the substrate 16b, and a grounding plate 17 (Fig. 16a) pro- ided on the other side of the substrate. The strip 16 has a feeding end 16a. As shown in Fig. 16a, the grounding plate 17 has a plurality i of radiating slots 17a, each being opposite to a feeder end 16c of the strip 16. A reflector plate 18 is provided opposite the grounding plate 17 with a space through spacers (not shown). Distance h between the reflector plate 18 and the grounding plate 17 is about X/4 so that the power radiates from the slots 17a in a predetermined 12

I_

direction. The distance L between the feeder ends 16c is X/2, and adjacent slots are inclined in the opposite directions with each other. Thus, the resultant electric field direction of the power radiated from the slots is directed shown by an arrow in Fig. 16a.

Fig. 16b and 16c show antennas provided with the power feeder means shown in Fig. 15a or 15b. The feeder means is attached to the antenna so as to open the slots 17a to the power feed opening 4 of the rectangular i 10 waveguide G. The antenna ofi Fig. 16c 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. The first to third modifications shown in Figs. 5, 7 and 8 can also be applied to the antennas of -his embodiment. Although the slot 17a is employed as a radiation element in the above embodiment, other elements may be used.

Peferring to Fig. 17 showing a ninth embodiment of the present invention, the antenna comprises a pair of adjacent rectangular waveguides G. Each rectangular i' 'waveguide G comprises opposite rectangular metallic plates 2 5 1 and and metal side plates 3 secured to the three sides of each plate to form a rectangular waveguide space S. The metallic plate 1 in the E-plane has a plurality of electric power radiation slots la, and power feed opening 4 is formed at an inlet side of the space S. Both the waveguides are connected with each other, forming a space there-between. The horn waveguide 5 is perpendicularly 13

B

I I i connected to the underside of the antenna so as to communicate with the space between the powe- feed openings 4. The electric field plane of the waveguide is sufficiently increased compared with the wavelength in the space S. A matching member 11 as a reflector member is provided in the space between the openings 4. The horn waveguide 5 has a horn shape in the E-plane and has a lens antenna 6 therein. The lens antanna 6 may be made of dielectric or metallic plates, or corrugated metallic plate. In the horn waveguide 5, median partition 5a is I axially disposed.

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 1 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 and X 1 Consequently, the main lobe P inclines toward r as shown in Fig. 4b. When the wavelength X 1 is longer than the wavelength X 0 the main lobe P inclines toward Pigs. 18a and 18b show di.rectiv'ty of the antenna of the ninth embodiment shown in Fig. 17. The power fed from the power feeder means 5 is divided by the matching member 11 to 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 14 I Ithe right main lobe P2 incline symmetrically as shown in Fig. 18b. Consequently, the direction of the resultant main lobe P becomes perpendicular to the surface of the antenna advantageously. Other constructions are the same as the first embodiment. The modified rectangular waveguides of Figs. 5, 7 and 8 and other power feeder means may be selectively used for the antenna of this embodiment.

Referring to Fig. 19 showing the tenth embodiment of A 10 the present invention, the rectangular waveguide G t ]comprises a pair of adjacent rectangular waveguides and a pair of horn waveguides 5 provided on the underside of the rectangular waveguides G. The rectangular waveguide G has power feed openings 4 at both ends thereof and the terminal resistor 7 at a central portion thereof. The horn waveguides 5 are parallelly and symmetrically provided to the rectangular waveguide G so as to communicate with the power feed openings 4. In the both ends of the rectangular waveguide G, matching members 11 as reflector means are provided for reflecting the fed power to the space S. The lens antenna 6 of dielectric is jprovided in each horn waveguide 5. Thus, the substantially same operation and advantage as the first and ninth embodiments can be obtained. The modified rectangular waveguides of Figs. 5, 7 and 8 and other power feeder means may be selectively used for the antenna of this embodiment.

Referring to Fig. 20 showing the eleventh embodiment 15 of the present invention, the antenna compr..ses a pair of parallel rectangular waveguides G. Since the opening angle of each horn waveguide 5 can be reduced, the power propagated in the waveguide becomes a substantially plane wave, so that a high ord mode can be prevented. Other constructions are the same as the first embodiment. The modified rectangular waveguides of Figs. 5, 7 and 8 and other power feeder means may be selectively used for the antenna of this embodiment.

i 10 From the foregoing, it will be understood that the antenna of the present invention has following advantages.

Since slots are formed on the E-plane which is I t, parallel with the direction of the electric field in the waveguide G, the current flows uniformly. Accordingly, the slots are uniformly disposed, so that the antenna t l efficiency is increased.

The phase constant of the power propagated in the space of the rectangular waveguide can be controlled by the slow-wave device to reduce the wavelength in the space. Thus, it is possible to increase the density of the slots to increase the efficiency of the antenna.

Since the distance between the H-planes is reduced to the terminal resistor, .the power is substantially uniformly distributed.

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.

16

Claims

1. A slot array antenna adapted to operate at an operating wavelength and having a rectangular waveguide, formed by metallic plates, defining an internal space having a rectangular sectional shape and a power feed opening, a power 9: It ttcr Irr I.

9. #9 9 9 I I LI It I. CL C 17 THE CLAIMS DBSiMING TI Aw'AMo DFNG RE.3 AS LL&gWZ 1. A slot array antenna adapted to o Ee an operating wavelength and h arectangular waveguide with a space a a rectangular sectional shape and a 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 at least four times as large as said wavelength; height of said rectangular waveguide is at least one-half of said wavelength; said power feeder means has means feeding power to said space in the form of a plane wave, having its electric field directed laterally and parallel to the metallic plates. 2. The slot array antenna according to claim 1 wherein the rectangular waveguide has a terminal resistor at an S end plate which is opposite to said power feed opening. 3. The slot array antenna according to claim 1 or 2 wherein the rectangular waveguide has slow-wave means. I.r 4. The slot array antenna according to claim 1 or 2 wherein the space is reduced toward the end plate. The slot array antenna according to claim 1, 2, 3 or 4 wherein said rectangular waveguide comprises a plurality of rectangular waveguides connected with each other. 6. The slot array antenna according to claim 5 further comprising a matching member for directing power fed from said power feeder means to said rectangular waveguides. Dated this 9 th day of July 19 91 ARIMURA GIKEN KABUSHIKI KAISHA SPatent Attorneys for the Applicant F.B. RICE CO.