US3230481A - Method for segregating harmonic power in a waveguide system - Google Patents

Description

Jan. 18, 1966 D. J. LEWIS METHOD FOR SEGREGATING HARMONIC POWER IN A WAVEGUIDE SYSTEM 2 Sheets-Sheet 1 Original Filed Nov. 19 1959 INVENTOR an /0 J1 151/45 Jan. 18, 1966 D. J. LEWIS 3,230,431

METHOD FOR SEGREGATING HARMONIC POWER IN A WAVEGUIDE SYSTEM Original Filed Nov. 19, 1959 2 Sheets-Sheet 2 E Ti: 1173;; 6 fly? 25 w J/ 2'! 27 4 l i::; k 27 25' 2 7 J7 INVENTOR 6 2 4; a zz/ms United States Patent 3,230,481 METHOD FOR SEGREGATING HARMONIC POWER IN A WAVEGUIDE SYSTEM David J. Lewis, Culver City, Calif., assignor to the United States of America as represented by the Secretary of the Air Force Original application Nov. 19, 1959, Ser. No. 854,216, now Patent No. 3,078,423, dated Feb. 19, 1963. Divided and this application Nov. 6, 1962, Ser. No. 235,900 The portion of the term of the patent subsequent to Feb. 19, 1980, has been disclaimed 1 Claim. (Cl. 3336) This application is a divisional application of applicants copending' application, Serial No. 854,216, filed November 19, 1959, now US. Patent No. 3,078,423, granted February 19, 1963.

This invention relates to waveguide transmission systems for the transmission of electrical wave energy, and more particularly to a method of segregating the total energy being propagated at any discrete harmonic frequency of the fundamental wave in a waveguide system.

The theory relating to electromagnetic propagation in waveguides is well established in the microwave transmission art; therefore, only such basic principles as are germane to the present invention will be recited here.

Any hollow rectangular waveguide may propogate energy by an infinite number of possible modes which are characterized by particular field configurations. The configuration of such fields within the waveguide must be a solution of Maxwells equations and satisfy the boundary conditions.

The possible modes may be further divided into two fundamental types. In the first type, the electric field lies in a plane at right angles to the longitudinal axis of the guide and has no component anywhere in the direction of said longitudinal axis, while the magnetic field at the same time has components in the direction of said longitudinal axis as well .as at right angles to it. These waves are termed transverse electric or TE waves. In the second type the electric field has components in the direction of the longitudinal axis and the magnetic field is everywhere only transverse to said longitudinal axis. These waves are termed transverse magnetic or TM waves.

The ditferent types of configuration under each class are designated by the subscripts mn where m' represents the number of half period variations of the transverse component encountered tin passing across the width of the waveguide cross-section and n represents the number of half periods of transverse components encountered in passing across the height of the waveguide. As an example, TE (m=1, n=0) represents a wave having a one half electric field variation across the width of the guide, and since the field is uniform there is no variation across the height of the guide.

It is also noted that a wave guide acts as a high pass filter and has a cut-cit frequency deter-mined by the dimensions of the guide and the particular field configurations involved. All waves having a frequency higher than the cut-off frequency will be propogated down the waveguide with the resultant transmission of energy.

The preferred mode of operation of a waveguide is at the lowest cut-off frequency. This is called the dominant mode and has the longest cut-off wave length of an infinite series of possible field configurations that can be propagated down the waveguide. The next higher modes include Waves of both the transverse magnetic type and the transverse electric type. These higher order modes are ordinarily produced whenever energy is delivered to or abstracted from a waveguide.

It is oftentimes necessary in the microwave art to measure the energy present in some discrete harmonic of the fundamental wave being propogated in a waveguide system. The measurement of energy in such a harmonic is complicated by the fact that energy is propagated in every mode consistent Wit-h the frequency and the waveguide dimensions. Conventional means for coupling to a primary waveguide to measure the energy of a particular harmonic usually results in coupling to several modes simultaneously thereby making useful and reliable measurements impossible.

The present invention provides a novel and improved method of segregating the energy in any particular harmonic wave being propagated in a waveguide system.

In the drawings:

FIGURE 1 illustrates a plan and side view of one auxiliary waveguide used in one embodiment of my invention.

I FIGURE 2 illustrates a plan and side view of a second auxiliary waveguide used in said embodiment of my invention.

FIGURE 3 illustrates a plan and side view of a third 'auxiliary waveguide used in said embodiment of my invention.

FIGURE 4 illustrates a plan and side view of a fourth auxiliary waveguide used in said embodiment of my .invention. FIGURE 5 illustrates an isometric view of said embodiment of my invention in which all of said auxiliary waveguides are shown in their proper relation to the primary waveguide.

My invention is a method designed to segregate, for the purpose of measurement, the energy present in each discrete mode of a preselected group of modes propogating in a rectangular waveguide. A novel combination of mode suppression methods ensures accurate detection of the energy propogated in the desired mode only, with all unwanted modes being effectively rejected.

The measuring apparatus utilizing my method consists of a plurality of secondary waveguides, said secondary waveguides having particular geometric configurations and means for coupling to the primary waveguide in accordance with the principles of my invention as hereinafter described.

A certain amount of selectivity of the modes which will propogate in a given waveguide is possible by taking advantage of the electromagnetic field configuration to discriminate against one or more modes of propagation.

In a rectangular waveguide for any particular mode of transmission the cut-oft" wavelength h is given in terms of the waveguide dimensions a (width) and b (height) by In this formula m and n are the subscripts denoting the particular mode under consideration. The equation holds for either IE or TM modes of transmission The dimensions of the aforementioned secondary waveguides are therefore determined for any given mode by the solution of Equation 1.

Further selectivity is possible by orienting the apertures which couple said secondary lwaveguides to the primary waveguide in the manner taught by the present invention wherein either transverse magnetic or transverse electric modes are admitted.

A hole or aperture in a waveguide wall will enable energy to leak from the guide into space or another guide or cavity. The coupling thus introduced by a hole or aperture in the guide wall may be either to the electric or magnetic fields. Electric coupling occurs when electrostatic flux lines that would normally terminate on the guide wall are able to pass through the hole. Magnetic coupling results when the hole interferes with the current O flowing in the guide wall. The nature and magnitude of the coupling in any particular case depend upon thesize;

shape, and orientation of the coupling hole. An elongated slot which is oriented transverse to the magnet c field inside the primary waveguide produces a mlnlmum of interference with current in the guide wall and introduces little or no magnetic coupling. It will, however, readily permit electric coupling. An elongated slot which is orientated parallel to the magnitude field in the pnmary waveguide on the other hand permits easy escape of magnetic flux lines and interferes to a maximum extent with the guide wall current. Coupling permits maximum magnetic coupling while causing little or no electric coupling. (A more detailed background discussion of the general principles of operation of slot mode couplers may be found in 11 Radiation Laboratory Series 854-897, particularly pages 88589l, McGraw- Hill Book Co. Inc., New York 1947).

Still further selectivity is possible by applying the well known duplexing principle to phase out unwanted modes. This is accomplished in the present invention by the use of two coupling apertures being so located with respect to each other that unwanted modes admitted by the said coupling apertures are in phase opposition and cancel out.

Since substantially all of the second harmonic energy is an S Band rectangular waveguide will travel in the TE TE TE and TM modes an accurate measurement of said energy is obtained, in accordance with my invention, by the application of secondary waveguides illustrated in FIGURES 15.

FIGURE 1 illustrates auxiliary waveguide 7 which is coupled to primary waveguide 6 by elongated coupling apertures 10 and l' l. Auxiliary waveguide 7 is dimensioned such that the fundamental mode present in primary waveguide 6 is rejected. Coupling apertures 10 and 11 are oriented to admit only energy present in the TM mode to auxiliary waveguide 7.

To prevent reflection of said T-M mode back into primary waveguide 6 auxiliary waveguide 7 is terminated with absorbing material 9. Measurement of TM energy present in auxiliary waveguide 7 is made through coaxial to waveguide coupler 8.

FIGURE 2 illustrates auxiliary waveguide -17 having coupling apertures '20 and 21, termination absorbing material 19 and coaxial to waveguide coupling 18. The dimensions of auxiliary waveguide'17 and orientation of coupling apertures 20 and 21 are such that the T E mode is coupled to the auxiliary waveguide while all others are rejected.

FIGURE 3 illustrates auxiliary waveguide 27 having coupling apertures 30 and 31, terminationabsorbing material 29 and coaxial to waveguide coupling 28. Said auxiliary waveguide 27 as illustrated couples strongly to the TE mode.

FIGURE 4 illustrates auxiliary waveguide 37 having coupling apertures 39 and 40, termination absorbing material 38 and output ports 41'and 42. Auxiliary waveguide 37 couples to :both TE and TE modes depending upon which output port is used.

FIGURE 5 presents an isometric view of primary waveguide 6 showing the relative location of auxiliary waveguides 7, 17, 27 and 37.

The outputs of auxiliary waveguides 7, 17, 27 and 37 may be taken by any conventional means and summed either analytically or electronically to determine the total second harmonic energy present in the primary Waveguide system.

It is to be understood that the above-described arrangement is illustrative of the principles of my invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of this invention.

What is claimed is:

In a Wave guide harmonic measuring system, the method of segregating the fundamental Wave from certain desired modesof said harmonic, comprising (1) the step of preventing, by cut-01f frequency dimensioning, the spurious propagation of said fundamental wave, (2) the step of separating and propagating a transverse magnetic mode of said harmonic, (3) the step of separating and propagating at a subsequent position in said wave guide system a pair of transverse electric modes of said harmonic by phase opposition coupling oriented with respect to the ambient fields in such manner as to exclude undesired modes, and (4) the step of separating and propagating an, additional pair of transverse electric modes of said harmonic by causing said additional pair of transverse electric modes to be selectively segregated by way of separate output ports.

References Cited by the Examiner UNITED STATES PATENTS 2,197,122 4/ 1940 Bowen 33398 2,684,469 7/1954 Sensiper 3338l 2,748,350 5/1956 Miller 33310 2,785,381 3/1957 Brown 3337 2,869,085 1/ 1959 Pritchard 333-98 2,961,619 11/1960 Breese 3'33-10 3,078,423 -2/ 1963 Lewis 3336 HERMAN KARL SAALBACH, Primary Examiner. C. BARAFF, Assistant Examiner,

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