US2641702A - Control of wave length in wave guide and coaxial lines - Google Patents

Description

June 9, 1953 N. col-IEN ET AL 2,641,702

CONTROL OF WAVE LENGTH' IN WAVE GUIDE AND COAXIAL LINES mea oct. 22. 194s A T TOJPA/EY Patented June 9, 1953 vCONTROL OF WAVE LENGTH IN WAVE GUIDE AND COAXIAL LINES Nathaniel L. Cohen, Teaneck, Ladislas Goldstein, 1

Weehawken, vand William Sichak, Lyndhurst; N. J., assignors, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application October 22, 1948, Serial No. 55,862

. 1 f This invention relates to wave transmission systems and more especially to the art of controlling thewave length of propagated waves in a' transmission medium.

In wide band transmission media such as coaxial transmission lines or dielectric Wave guides the wave length of electric energy is generally determined by the dimensions of the conductors and the insulating media. The speed of transmission is substantially constant so that at a Y given frequency the nodes and loops will be differently distributed along the line than at any other frequency. In many instances it is desired to have the wave distribution constant along a line with changes in frequency of energy in the line. A particular example of such systems is when it is desired tofeed the antennas of an array, or' other loads, with a given phase relationship, regardless of wave length, over arelatively wide band. With the usual transmission system, an elaborate tuning means to vary the inductance or capacitance of the line is required to achieve this purpose.

It is an object of this invention to.- stabilize the Wave length of Waves propagated along a wave transmission line even though the frequency of the impressed wavesris varied.

Another object is to provide an arrangement for producing a stabilized directional radiation pattern fro-m an antenna array fed from a Wave transmission line, even though the frequency of the waves impressed on said line is varied.

Another object is to provide a method of controlling the Wave length of waves propagated along a transmission line of the coaxial or waveguide type, by constituting a gaseous discharge plasma as part of the line, and controlling the 2 Claims. (CL. Z50-33.63)

electron density of the plasma to control thereby i the dielectric constant of the said line.

A feature of the invention relates to a Wave transmission line having incorporated therein a gaseous discharge of controllablecurrent density Y for stabilizing the wave length of variable frequency Waves impressed on said line.

Another feature relates toa Wave transmission line of the coaxial type or Wave guide type, havl reference to. the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. l is awschematic representation of a typical radiation system to which theA invention is applicable.

Fig. 2 is a longitudinal central cross-section of a coaxial transmission line embodying the invention.

Fig. 3 is a sectional view of Fig. 2, taken along the line 3-3 thereof. l

Fig. 4 is a longitudinal central cross-section of a Wave guide embodying the invention.

In certain kinds of Wave transmission systems such, for example, as radiating antenna systems and the like, it is highly desirable to produce a field or radiation pattern which has substantially constant directional properties, even though the impressed Waves are varied in frequency. Thus,

there is sho-Wn in Fig. 1, a typical antenna array comprising a coaxial feed line With its central conductor l and its outer concentric conductor or pipe 2. Connected at suitable spaced points along the length of conductor I, are the several radiator elements 3. Likewise, connected to the conductor 2 at the samespaced intervals are the complementary radiator elements 4. vThe showing of Fig. 1 is intended to be generically schematic, in that the radiator elements are arranged to extract wave energy from the coaxial transmission line at appropriate numerous points along its length. It will be understood, of course, that the radiator elements may be coupled to a Wave guide instead of a coaxial line, for the same purpose. The theory of such an arrangement is that each set of radiator elements extracts small packets of energy content from definitely phased points along' the line. Thus, for

example, the spacing interval between the sucing of the several radiator elements, or of the frequency of the source 5 from Which the Waves objects of this invention and the manner of attaining themv Will become more apparentand the invention itself Will .be best understood,v by

are impressed on the line, will result in a shift in the direction of radiation.

In certain cases, it is desirable to be able to operate such a system over a wide range of impressed frequencies, for example from 1,0'00 megacycles to 2,000 megacycles. Therefore, in

order to avoid any substantial shift in the radiation direction for the different impressed frequencies, it is necessary to maintain the wave length of the waves propagated along the line at l a stabilized selected Value. The present invention provides a method and arrangement of apparatus for securing this desirable objective.

It has been determined hereto-fore, that at high frequencies, the dielectric constant of a conductive gaseous discharge plasma depends on the electronic charge density contained in the plasma, the plasma as is well-known, constituting the largest portion of the discharge column. Y

between the anode and cathode of agaseous con-` duction tube. The relation between thisY dielec-4 tric constant and the electronic charge density is given bythe following formula.;A Y

where Y eg is the effective dielectricv constant at frequency w/Z1r;

E is the dielectric'constantof free space;

Ne is the electronic charge densi-ty; and

is the ratio of charge to mass of the electron. In the case where the electronic collisional frequency v in the discharge plasma is of the order of or larger than the signal frequency w/21r, this expression becomes:

41|-Ne2 Elf- 1 However, for purposes of this discussion, we will omit this case.

It is` also known that the wave length of a wave in dielectric medium is related to its free space wave length by: Y

where he, is the free space wave length;

M isjthewave length in the dielectric medium;

EdY is the relative dielectric constant of the medium.

In accordance with the present invention, the transmission feed lineY has incorporated in the wave propagating spaced thereof a gaseous discharge plasma of controllable electronic charge density. For example, in the case of a coaxial If we set M as a constant and with eo=l, We have Near-(til o That is, N, the electrondensity, is azfunction of frequency for a constant wave length )\=?\d. Now, it is known that N is a function of the current density, and hence the current in the discharge, for a given set of conditi-ons of gas pressure, nature of the gas and gas purity and geometry. y

Referring to Figs. 2 and 3, there is shown a suitable .arrangement whereby the wavelength of a signalin a coaxial line can be held constant over a wide range of transmitted frequencies. The line comprises the usual central conductor `6 and its coaxial guide or pipe conductor 1, a1'- ranged to be connected to a suitable high frequency source 8. Surrounding the conductor 6 and located within the wave propagational space ofthe coaxial line, is an elongated tubularglass container 9, having side seals I0 and II. Suitably mounted in the side seals I0 and I I, are respective electrodes I2, I3, which are connected Y sure of a few millimeter of mercury. When theV electrodes I2' and I3 are thus energized, there is set up a gaseous conduction column extending throughout the length of the tube 9, the greater part of this column being constituted of ther plasma. By means of the source I4 and the adjustable resistor I5,v the current density inV the plasma can be adjusted to-flt the requirements of the above-noted formula #6. As a typical. example, if the impressed frequencies from source 8 are variable between 1,000 mega-cycles and 2,000 megacycles, and it is desired maintain the wave length in the line at 30 centimeters, which is a free space wave length of 1,000- megacycle signals, then from Formula #6 it can be seen that for f=1,000 meg acycles,'N=0- For a frequency of 2,000 megacycles, N`=3.68 1010 electrons per cubiccentimeter within the plasma. Then for different frequencies between 1,000 megacycles and 2,000v megacycles, the relation of the impressed frequency andl stabilized wave. length and the number of electrons per cubic centimeter in the plasma is given in thev follow--V ing table:

f M Y electrons/cc.

Cms. Cms.

Thus, it will be seen that by adjusting the current density in the plasma, the wave length can be stabilized at any particular value in accordance with Formula #6.

In the event that the stabilization,l is to be ef-l fected.r automatically, a sample of the energy propagated through the line can be applied` to anyV well-known frequency discriminator I6 whose output can control a variable resistor tube I'I connected acrossresistor I5'. VBy this arrange--A menttherefcre, the propagated Wave length in;

the coaxial line will be automaticallystabilized at the predetermined value.

It will be clear that the invention is not limited to a transmission liney of the coaxial type. Thus, there is shown in Fig. 4 a transmission line of the Wave guide type wherein the Wave guide I9 has on the interior thereof an elongated gaseous conduction tube i9 which may be similar to tube 9 of Fig. 2. Here again, the current density in the plasma within the tube I9 can be adjusted by potential source 20 and variable resistor 2i in accordance with the above-noted Formula #6 to stabilize the Wave length of the propagated Waves Within the Wave guide. It will also be understood that the transmission line with which the controlled plasma cooperates may be of any other Well-known type. v

While We have described abo-ve the principles of our invention in connection with specific apparatus, it is to-y be clearly understood that this description is made only by Way of example and not as a limitation to' the scope of our invention.

What is claimed is:

1. A high frequency Wave transmission line, comprising a hollow member dening a wavepropagating vline upon which high frequency Waves are impressed, an enclosed gas-tight device extending along a predetermined length of the interior of said member, said device containing a filling of an ionizable gaseous medium, electrodes at opposite ends of said device, means to adjust the potential between said electrodes to control the density through said medium to stabilize the physicalwave length of the Waves propagated along said linev Within said medium, and a plurality of radiator elements'coupled to said Wave propagatingline through the ionizing device at spaced points along said device, said means to adjust being controlled to present the high frequency energy at the same'relativephase to said radiators over av range of frequency of` said high frequency source.

2. Apparatus according to cla-im 1, in which said line is of the coaxial type. NATHANIEL L. COI-IEN. LADISLAS GOLDSTEIN.

WILLIAM SICHAK.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,064,582 Wolff Dec. 15, 1936 2,106,770 Southworth Feb. 1, 1938 2,142,648 Linden Jan. 3, 1939 2,159,937 Zworykin May 23, 1939 2,203,807 Wo-ln June 11, 1940 2,210,666 Herzog Aug. 6, 1940 2,407,250 Busignies Sept. 10, 1946 2,408,425 Jenks et al. Oct. 1, 1946 2,408,435 Mason Oct. 1, 1946 2,477,510 Chu July 26, 1949 2,480,208 Alvarez Aug. 30, 1949 2,557,961' Goldstein et al. June 26, 1951 2,577,118V Fiske Dec. .4, 1951

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