US3599215A - Leaky waveguide-antenna combination - Google Patents

Abstract

A leaky waveguide-antenna combination employing a leaky waveguide having a coextending ground plate attached thereto and an elongated antenna positioned in parallel over the leaky coaxial cable to receive waves therefrom. Metallic plates extend from both sides of the antenna in parallel to the ground plate and are provided with parallel grooves which extend longitudinally and have a depth of about one-fourth the cutoff wavelength of the antenna so that the input impedances for the modes propagating in space between the grooved plates and the ground plate is infinite thereby preventing stray interferences.

Description

linited States Patent 'Zl t l l l UN lmentors Kenichi Ynshida Sakai: lliroshi Kitani, Taketsuki. both of. Japan App! No 831.093 Filed June 6. [969 Patented Aug. 10, I97! Assignee Surnitorno Electric Industries. Ltd.

Osaka, Japan Priority June 1 l. 1968 Japan 43/40l72 LEAKY WAVEGUIDE-ANTENNA COMBINATION 3 Claims.4 Drawing Figs.

U.S.CL 343/767, 343/772. 343/78l, 333/73 M Int. 13/10, HOlq 13/22 FieldofSear-ch IBIS/L98 M, Ll; 343/775, 785, 767. 770, 77!, 772, 781; l79l82 156} References Cited UNITED STATES PATENTS 2993.205 7/l96l Cooper. 343/785 X 3.221.331 11/1965 Spitz. 343/785 3.44-7.58 5/!969 Sunderland .r 343/775 X Primary Examiner- Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon. I r. Attorney-Carothcrs and Carothers ABSTRACT: A leaky waveguide-antenna combination ernploying a leaky waveguide having a coextending ground plate attached .thereto and an elongated antenna positioned in parallel over the leaky coaxial cable to receive waves therefrom. Metallic plates extend from both sides of the antenna in parallel to the ground plate and are provided with parallel grooves which extend longitudinally and have a depth of about one-fourth the cutoff wavelength of the antenna so that the input impedances for the modes propagating in space between the grooved plates and the ground plate is infinite thereby preventing stray interferences.

Ll-LAIQ WA\ EGLlDE-ANTENNA CUMBINATION BRIEF EXPLANATION OF THE DRAWING FIG I and FIG. 2 are diagrammatic perspective views of a transmitting and receiving device using a leaky waveguide. FIG. 3 is a diagrammatic perspective view of a transmitting and receiving device using a waveguide according to the present invention. FIG. 4 is a diagrammatic front sectional view of the device.

DETAILED EXPLANA'ITON OF THE INVENTION This invention relates to a leaky waveguide device in which unwanted radiation is suppressed.

When employing electromagnetic waves radiated from a leaky waveguide and received by an antenna aboard a vehicle in its vicinity, it has already been suggested to place an ex posed antenna 4 facing the leaky waveguide l on the ground as shown in FIG. I, or to use an antenna 4 provided with an arcil'orm focusing reflector plate 8 as shown in FIG. 2. In the case of the device shown in FIG. I, it is not effective for suppressing unwanted radiation because the antenna is exposed, so that unwanted electromagnetic waves are radiated into free space, interfering with other communication systems and incurring interference from other systems. This type electromagnetic interference is strictly controlled by Government Wave Regulations. In the case of the device shown in FIG. 2. electromagnetic waves from leaky wave apertures in an antenna 4 are focused toward the apertures 3 of leaky waveguide l by means of a focusing reflector plate 8 placed over the antenna 4, so that, as compared with the device shown in FIG. I, this device has a suppression effect on unwanted radiation to some degree. However, this suppression can by no means be said to be satisfactory.

According to the present invention. metal plates having groo es are placed on both sides of an antenna in parallel to a ground metal plate of a leaky waveguide for the purpose of obraining a leaky waveguide device free from the aforesaid drawbacks, Le. a device which suppresses unwanted radiation. The depths of the grooves in the metal plates are made such that the input impedance becomes infinitely great for mode waves transmissible in the transverse direction of the antenna.

This will be explained in a concrete form with reference to the attached drawings. FIG. 3 shows a perspective of a leaky waveguide of the present invention. In FIG. 3, 1 denotes a leaky waveguide of ground potential, 2 denotes a flat metal plate attached to said leaky waveguide l. 3 denotes leaky wave apertures provided in said leaky waveguide l and through plate 2, 4 and antenna located in parallel to the leaky waveguide I. 5 metal plates attached to the antenna and hav ing grooves which are attached to said antenna 4, 6 and 7 grooves provided on said metal plates 5 in parallel to said antpma Each groove has a width 12" and is placed apart from an adjacent groove or the antenna by a dtance which is determined by structural condition. FIG. 4 is a cross section of what is shown in FIG. 3. A metallic plate 2 has ground potential, the metallic plates 5 are provided on both sides of the antenna 4, the distance between metal plates 2, 5 is a." The depths of the grooves 6, 7 are respectively d,, d,, and the impdences of the first, the second. grooves are 2,, Z respectively.

An electromagnetic wave propagating in a space determined by some boundary can be expressed with phase constanls as follows:

pl-v fiy -izll l l fir-t-fiy*+flz=k=wcu (2) where, fix, By, B: are phase constants in the r, y-, 1- directions, respectively, and w is an angular frequency.

If any one of fix, By and Bz is an imaginary number. the Wave becomes evanescent in the corresponding direction. For example, when Bx is an imaginary number jx (where Ex is a real number), e.rp(-jBrX) becomes arm-E90 and the wave exponentially attenuates in the x-direction.

In the present case, Bz can be determined by the propaga tion constant in fl veguide of the antenna, and therefore ,6: is then Vk 21r/Ac) where, A, is a cutoff wavelength of the waveguide for an antenna 4. On the other hand, B, can be determined by the spacinga and its value can be given by mr/a wherein n represents an integral number. These values for By and fiz give Bx by using eg. (2) as follows:

l J(EI) (2E) Bx J Bx: (a) he a where A,- is the cutoff wavelength when the antenna is regarded as a waveguide.

In consequence, the group of modes which satisfy the condition its 21' 7%? namely n 2alM attenuate in the x-direction transverse to the direction of the leaky waveguide as, B)" becomes imaginary That is to say, if the metallic plates 5 and 2 are extended for some length larger than AJZ in the transverse direction, whether the metallic plate 5 has grooves or not, the amount of unwanted radiation of the group of modes of n 2alM becomes very small. On the other hand, the group of modes which has the condition risk/Ac does not attenuate in the transverse direction in the space bounded by metallic plates 5 and 2, and unwanted radiation is not suppressed by no matter how long the metallic plates 5 and 2 are extended in the xdirection. In this case, it is necessary to provide grooves 6 and 7, etc. as shown in FIGS. 3 and 4 on said metallic plate 5. The phase constants in the groove can be determined in such a anner that Bz is m as per the above discusion, fir is expressed by m'lrlb with an integral number m, and then fiya flrrlhd -(mrrlb) If the width of the groove 6 is smaller than Ac/2, only one mode (m=0) can propagate in the y-direction in the groove. Then, the input impedance becomes infinite under the assumption that the top end of the groove is short circuited,

when the depth d is kcl4+An.

The correction term, An is related to the propagation mode number n in the spacing between the metal plates 2 and 5 as above mentioned, and is necessary for compensating the fringing effect to each mode and the spacing distance between adjacent grooves is not restricted by electromagnetic conditions, but is determined rather by structural conditions. The unwanted radiation of the group of the modes wherein n 2a/ltc is choked by these grooves. This prevents useless energy propagation in the transverse direction.

In other words, the total impedance between the grooved metallic plate and the ground plate for energy propagated in the transverse direction. is the impedance of the grooves plus the impedance between the two opposed plates. As the impedance of the groove or grooves is infinite, so therefore, is the sum of these two impedanccs. If there are n mode waves according to the condition of d: 241M, then it grooves should be provided on either side metal plate of the antenna and the depths of the grooves are so deterin'ned such that the input impedances 2,, 2 for the modes correspondin to them respectively becomes infinitely great.

In the foregoing explanation, the depths of the grooves o, 7 in the metallic plate 5 were shown as d,, d,, however, the present invention is merely not restricted by this. It is sufficient to say that grooves are provided for the transmissible modes and arranged to make their input impedance infinitely great.

As the invention places metallic plates having grooves on both sides of an antenna and makes the depths of the grooves such that the input impedance is infinitely great for their corresponding modes, it suppresses the radiation in the transverse directions on both sides of the antenna and can remarkably improve the coupling between the antenna and the leaky waveguide.

We claim:

grooves having depths of about Air/4 so that the input impedances for the modes propagating in space between said grooved metallic plate and said ground plate is infinite.

2. The leaky waveguide-antenna combination of claim 2 characterized by a plurality of said grooves on each side of said antenna.

3. The leaky waveguide-antenna combination of claim 3 characterized in that said antenna is tubular with apertures facing said waveguide.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 Dated August 10 r 19 71 Inventor(s) Kenichi Yoshida and Hiroshi Kitani It is certified that error a ppears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, Claim 2, line 4, "claim 2" should read -claim l--;

Claim 3, line 7, "claim 3" should read -claim 2--.

Signed and sealed this 25th day of January 1972.

jSEAL) Attest:

EDWARD M.FLETCHER, JR. BERT TTSCHALK M testing Officer Commissioner of Patents PO-105O i10-691 USCOMM-DC 60376-PG9 U 5. GOVERNMENT PRINTING OFFICE 7969 O35S33d

Claims (3)

1. A leaky waveguide-antenna combination comprising a leaky waveguide having a coextending ground plate extending laterally therefrom on both sides and attached thereto with leaky wave apertures of said leaky waveguide extending through said plate, an elongated antenna positioned in parallel with said leaky waveguide and in receiving proximity thereto to receive waves leaking from said apertures, a metallic plate extending laterally from both sides of said antenna and having parallel grooves extending in the longitudinal direction with their valleys extending away from said ground plate, said grooves having depths of about lambda c/4 so that the input impedances for the modes propagating in space between said grooved metallic plate and said ground plate is infinite.

2. The leaky waveguide-antenna combination of claim 2 characterized by a plurality of said grooves on each side of said antenna.

3. The leaky waveguide-antenna combination of claim 3 characterized in that said antenna is tubular with apertures facing said waveguide.

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