US3795915A

US3795915A - Leaky coaxial cable

Info

Publication number: US3795915A
Application number: US00299192A
Authority: US
Inventors: K Yoshida
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1972-10-20
Filing date: 1972-10-20
Publication date: 1974-03-05
Anticipated expiration: 1991-03-05

Abstract

A leaky coaxial cable is disclosed, which is a very preferable transmission line for use in vehicular communication system. It has an outer conductor having a slot array in the direction of the cable axis such that each slot is arranged periodically at a fixed interval and a fixed shape, but with the dimensions thereof or other radiation factors of the slot being changed sinusoidally in another periodicity different from the periodicity of the slots. The leaky coaxial cable according to the present invention has very broad band characteristics in the radiation properties of the leaky wave.

Description

atent 1191 Yoshida ar. 5, 1974 [5 LEAKY COAXHAL CABLE 3,560,970 2/1971 Kamimura et al 333/84 1. [75] Inventor: Kenichi Yoshida, Osaka, Japan Primary Examiner-Eli Lieberman [73] Asslgnee: Sumltoma Electric lindusmes, Attorney, Agent, or FirmCarothers and Carothers Osaka, Japan [21] Appl' 299,192 A leaky coaxial cable is disclosed, which is a very Related Application Data preferable transmission line for use in vehicular com- [63] Communion of Ser No 106 343 Jan 14 munication system. It has an outer conductor having a abandoned slot array in the direction of the cable axis such that each 'slot is arranged periodically at a fixed interval 52 us, Cl. 343/771, 333/84 R and e fixed Shape, but Wiih the dimensions thereof or 51 .Int. Cl. H01q 13/10 other iedieiieh feeieie of the slot being changed [58] Field of Search 333/84 L; 343/770 771 soidally in another periodicity different from the periodicity of the slots. The leaky coaxial cable according [56] References Cited to the present invention has very broad band characteristics in the radiation properties of the leaky wave.

14 Claims, 9 Drawing Figures Pmmmm sum 3.795915 SHEET 1 0? 2 Para 2P0 61% P72 IN vemrok KEN/cm YOSH/DA Y AEO TH'ES CQEOTHEES mmmm 5 1914 3mm 1 s /N vawoz. KEN/CH1 YosH/m 5 Y C A120 THEKS Oworwaes Ms A rro @NE Y5 LEAKY COAXIAL CABLE CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. THE FIELD OF THE INVENTION The present invention relates to a leaky coaxial cable having broad band characteristics particularly suitable for use in vehicular communication systems.

2. The Description of the Prior Art In recent times great progress has been made in the art of vehicular communication systems. In such communication systems, open type transmission lines installed along the vehicle track which transmit electromagnetic waves while radiating a part of the transmitted wave into the space around the line, play an important role in vehicular communication. 7

Among various kinds of open type transmission lines available, a leaky coaxial cable is considerable-to be the most suitable for this purpose.

Conventional leaky coaxial cables as shown in FIG.

I, however, have generally an array of slots of identical 1 shape arranged with a simple periodicity. The radiation property frequency band of a leaky wave of such a leaky coaxial cable is so narrow that broad band communication would not be possible. Recently, however, as considerably more information for transmission is required than ever in vehicular communication, the broader band characteristics of the leaky coaxial cable became of greater necessity SUMMARY OF THE INVENTION BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is a perspective view showing a leaky coaxial cable of the prior art.

FIG. 2 is a cylindrical coordinate diagram used in the explanation of the invention.

FIG. 3 is a graph which is used in the explanation of the invention. a

FIGS. 4,5,6,7,8 and 9 are perspective views showing different embodiments of the leaky coaxial cable of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION.

As shown in FIG. 1 of a prior art, the typical slot layout in leaky coaxial cables heretofore in use is one having a simple periodicity. In FIG. 1, (1) denotes the inner conductor of the coaxial cable, (2) the outer conductor, and (3 (3 the slots, respectively. These slots (3 (3 are located periodically, so that the electromagnetic field in the external space may be given by Equation (1).

L 2 F= E (A -cosine where r, d) and z are the cylindrical coordinates defined in FIG. 2, Hm ('y,,-r) the m-th order Hankel function of the second kind, 'y,, the propagation constant of the n-th harmonic wave, exp the exponential function, p the pitch of slots (the repetition interval), and Amn, and Bmn are certain constants.

As is well known, there is also the following relationship in regard to the n-th propagation constant 7,, in such a periodic structure of slots as shown in FIG. 1;

where k and B are the propagation constants in the free space and in the waveguide, respectively, and A and Ag are the wavelength in free space and in the waveguide, respectively.

When 'y,, is positive in Equation (2), the n-th harmonic wave can radiate out superiorly. Conversely when 7,, is negative, it becomes a surface wave which exists only in the neighborhood of the cable. A surface wave, in other words, does not play an important role in coupling with a vehicular antenna. Therefore, it is necessary to make y positive, at least, so as to obtain good coupling between the leaky coaxial cable and the vehicular antenna. Furthermore, not only must y,. but basically it is also required that only one such leaky wave satisfying the condition 'y,, 0 be transmitted at a time. The reason for this is that if two component waves satisfy the condition y,, 0 are transmitted at the same time, beating occu rs, because their phasecgr stants in the z-direction (Bz=B+27m/p) are different with each other (since n is different), so that a great fluctuation occurs in the coupling level which greatly obstructs communication.

When the required conditions for good coupling as discussed above are satisfied, the pitch of slots p must become subject to the following restriction in view to Equation (2).

the required conditions may not be satisfied. In consequence, the ratio of k/ p having a value 1.5 2 may actually be effective. In other words, the effective frequency range is limited as follows;

C/2 p C/k C/l.5p

C light velocity The present invention is concerned with the basic concepts for extending the limitation of the effective frequency band for communication by a leaky coaxial cable. The leaky coaxial cable of the present invention is characterized by its double periodical slot array configuration. That is, the wave source intensity and phase of the l-th slot are made so as to satisfy the following equation.

Sl=[A-cos 21rze/p B exp (J B z e) where z, I-p,, (p denotes the slot interval), and A and B are arbitrary constants. Equation means that the radiation intensity of each slot changes sinusoidally along the axis of the cable.

In this case, the n-th propagation constant y, can be deformed as shown below.

According to the condition (7), the permissible range of A/ p is enlarged as compared with the condition (3). That is to say, A/ p can take an arbitrary value within the range of O 2, because of v z 1. When p is suitably small as compared with p, the condition (8) is satisfied. Accordingly, the present invention is able to obtain a broad band radiation property, over a wide frequency band.

FIG. 4 shows an example of an embodiment of the present invention. In the figure, (4,), (4 denote slots. All of these straight line slots have the same slot length, and have the small periodicity p and the large periodicity p. In such a double periodical slot structure, every slot inclination angle with respect to the cable axis is changed discretely one after another in order to realize the sinusoidal distribution of the wave source intensity as shown in Eq. (5 It is well known that wave source intensity of a slot increases according to slot inclination angle with respect to the cable axis, and a slot in parallel to the cable axis will not radiate. In the figure, (4 (4 and (4 corresponds to a positive half cycle of the sinusoidal change in the wave source intensity distribution, (4 (4 and (4 a negative half cycle of the sinusoidal change in said intensity distribution, and (4,), (4 and (4 to zero points of the sinusoidal change in said distribution. The slots (4 (4 and (4 corresponding to the zero amplitude points may be eliminated because they do not contribute to the required sinusoidal distribution of radiation intensity indicated in Eq. (5 FIG. 5 shows another example of a slot array whose slots corresponding to the zero amplitude of the sinusoidal change in the radiation intensity distribution are eliminated.

FIG. 6 shows another example of an embodiment of the present invention. In the figure, all of the slots (4 (4 in each group have the same slot inclination angle with respect to the cable axis, but every slot length is changed discretely one after another for realizing the sinusoidal distribution of the wave source intensity as shown in Eq. (5). It is well known that wave source intensity of a slot increases according to slot length. In FIG. 6, slots corresponding to the zero amplitude points of the sinusoidal change in the wave source intensity distribution indicated by Eq. (5) are eliminated.

FIG. 7 shows another example of an embodiment of the present invention which mixes the above mentioned two example embodiments. That is, the required conditions in the wave source intensity distribution indicated by Eq. (5) is accomplished by changing the slot length and slot inclination angle simultaneously. Similarly, slots corresponding to the zero amplitude points of the sinusoidal change in the wave source intensity distribution may be eliminated.

FIGS. 8 and 9 shows other example embodiments of the present invention using another slot shape. Exemplarily shown in the figure, the shape of the slot is a bent line, whose straight part (5) is inclined in relation to the cable axis to effect the radiation, and bent parts (6 at both ends, which are parallel with the cable axis, are subsidiary to the radiation effect. These two examples utilize the basic concept of the present invention to provide a sinusoidal distribution in the radiation intensity at each slot along the cable axis. In FIGS. 8 and 9, this concept is accomplished by changing slot length and the slot inclination angle one after another along the cable axis, respectively. This concept characterizing the present invention can be realized in any radiation structure using slot elements in any leaky coaxial cable.

I claim:

1. A leaky coaxial cable comprising an inner conductor, a coaxial tubular outer conductor and a longitudinal leaky slot array in said outer conductor with a fixed slot center-to-center spacing, characterized in that the slots in said array at least in part extend in length other than transverse to the axis of said cable and the radiation intensity factors of said slots are successively varied in a sinusoidal fashion such that a plurality of slots are present in each sinusoidal half cycle with the slot configuration and direction of slot length extension for one half cycle alternately reverse from one half cycle to the next.

2. The leaky coaxial cable of claim 1 wherein said slot radiation intensity factors which are varied are selected from one or more factors in the group consisting of slot size and slot angle of inclination to the cable axis.

3. The leaky coaxial cable of claim 1 wherein slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

4. The leaky coaxial cable of claim 1 wherein each slot has the same angle of inclination to the cable axis and the slot length is successively varied.

5. The leaky coaxial cable of claim 4 wherein the slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

6. The leaky coaxial cable of claim 1 wherein each slot has the same length and the slot inclination angle to the cable axis is successively varied.

7. The leaky coaxial cable of claim 6 wherein the slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

s. The leaky coaxial cable of claim 1 whr'iiiihe slot length and inclination angle to the cable axis are successively varied simultaneously.

The leaky coaxial 5551a of claim 8 wherein t he slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

10. The leaky coaxial cable of claim 1 wherein each slot in said sinusoidal array has a bent line configura- 11. The leaky coaxial cable of claim 10 wherein the slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

' whereby the wave source intensity and phase of the lth slot satisfy the equation wherein z =l -P,,, P is the slot pitch, B is the propagation constant in the waveguide, and A and B are arbitrary constants.

13. The leaky coaxial cable of claim 12 wherein said slot radiation factors which are varied are selected from one or more factors in the group consisting of slot size and slot angle of inclination to the cable axis,

14. The leaky coaxial cable of claim 12 wherein the slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

Patent 3,795,915 Dated March 5, 1974- Inventor(s) KENICHI OSHIDA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 1, cancel beginning with "12. A leaky" to and including "arbitrary constants." in line 14, and insert the following claim:

12. A leaky coaxial cable comprising an inner conductor, a coaxial tubular outer conductor and a longitudinal leaky slot array in said outer conductor with a fixed slot center spacing Po, characterized in that the radiation intensity factors of the slots in said array are successively varied in a sinusoidal fashion with the periodicity p whereby the wave source intensity and phase of the SL-th slot satisfy the equation S2 [A-cos 2'nz /p B] exp (-JBz wherein 2 JL'P p is the periodicity of the radiation intensity factor of the slot array varied sinusoidally,

B is the propagation constant in the waveguide, and A and B are arbitrary constants. I

-Signed and sealed this 17th day of September 1974,

(SEAL) Attest: V

McCoy M. GIBSON JR. 7 c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM P071050 (1069) USCOMM-DC scan-ps9 I I V 1.5. GOVERNMENT PRINTING OFFICE I559 D365'334,

Claims

8. The leaky coaxial cable of claim 1 wherein the slot length and inclination angle to the cable axis are successively varied simultaneously.

9. The leaky coaxial cable of claim 8 wherein the slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

10. The leaky coaxial cable of claim 1 wherein each slot in said sinusoidal array has a bent line configuration.

11. The leaky coaxial cable of claim 10 wherein the slots corresponding to zero radiation amplitude in said sinusoidal array are eliminated.

12. A leaky coaxial cable comprising an inner conductor, a coaxial tubular outer conductor and a longitudinal leaky slot array in said outer conductor with a fixed slot center spacing Po, characterized in that the radiation intensity factors of the slots in said array are successively varied in a sinusoidal fashion whereby the wave source intensity and phase of the l-th slot satisfy the equation Sl (A.cos 2 pi ze/P + B) exp (-J Beta ze) wherein ze l.Po, P is the slot pitch, Beta is the propagation constant in the waveguide, and A and B are arbitrary constants.

13. The leaky coaxial cable of claim 12 wherein said slot radiation factors which are varied are selected from one or more factors in the group consisting of slot size and slot angle of inclination to the cable axis.