US2408033A - Coupling system - Google Patents

Description

Sept. 24, 1946. A. c. Em

COUPLING- SYSTEM Filed March l7,' 1942 v INVENTOR A. C. BECK I BYQ A TTOR/VEV Patented Sept. 24, 1946 COUPLING SYSTEM Alfred 0. Beck, Red Bank, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. 2., a corporation of New York Application March 17, 19h, Serial No. 435,016

(Cl. 17s-44) 4 Claims.

This invention relates to microwave coupling devices and more particularly to wave-guide transmission line coupling arrangements.

As disclosed in the copending application of H. T. Friis, Serial No. 435,017, filed concurrently with the instant application, impedance matching over a band of frequencies between a coaxial line or conductive channel and a main wave guide, and unilateral wave propagation in the wave guide, may be effected without the use of a piston. reflector by means of a rectangular wave guide folded or looped in the plane of its short transverse dimension, that is, in the plane of polarization of the propagated electric wave component. In this arrangement the end apertures of the folded guide are superimposed and joined to an end orifice of the main guide and the coaxial line is connected to the longitudinal center point of the looped guide. Also, for multifrequency operation, each of the two branches of the folded guide includes a twisted 90 degree polarity changer for securing colinearly polarized wave components in the superimposed folded guide apertures. While the folded guide coupling is suitable for use in many microwave systems, the polarity changers aside from being more or less difficult to manufacture, cause a certain amount of loss and it now appears desir. able to employ folded wave guide coupling sections having no quadrature polarity changers of l the twisted type. In this connection applicant has discovered that, contrary to the teaching of the prior art, rectangular wave guides may be bent or curved in the plane of the long transverse dimensions or, stated differently, in a plane perpendicular to the polarization plane of the electric component utilized in the wave guide, without substantial loss and, in fact, with only slightly greater loss than that sustained in guides folded or curved in the plane of polarization.

It is one object of this invention to secure in single frequency and multifrequency systems, each comprising a wave guide coupled to a transmission line, unilateral propagation in the wave guide without utilizing a reflecting piston and with minimum loss.

It is another object of this invention to match the impedances of a dielectric channel and a line channel Without using auxiliary adjustable apparatus or quadrature polarity changers of the twisted wave-guide type.

It is still another object of this invention to obtain a multifrequency folded wave-guide coupler which does not include twisted portions and which is simpler in construction than the couplers heretofore utilized.

As used herein the term quadrilateral generically includes the terms rectangular and square, and the term rectangular excludes square.

In accordance with the preferred embodiment guide having a considerably larger impedance as,

for example, l-Z, through a rectangular wave guide having characteristic impedance of 22 and folded in the plane containing its long transverse dimension which plane is perpendicular to the plane of polarization of the electric vector. The end apertures of the'folded wave guide section are superimposed so that their short trans verse dimensions are aligned. The coaxial line is coupled through aimultifrequency matching device of the type disclosed in applicants copending application, Serial No. 429,358, filed February 1942, to the longitudinal center point of the rectangular folded wave guide; and the superimposed end apertures are joined to an end orifice of the main quadrilateral wave guide. In operation, the wave components or wavelets in the two branches of the loop section have, at the longitudinal center point mentioned above, equal phase angles and are similarly polarized. Since the end apertures of the loop are equally distant from the center point and since the folded guide is not bent in the plane of polarization, the wavelets at the superimposed apertures are in phase angle agreement and are similarly polarized, whereby a wave of maximum intensity is propagated unilaterally in the main quadrilateral guide. Friis application, the coaxial line impedance equals th combined parallel impedance of the branches or folded guide sections, and the serially connected apertures of the loop section have a total impedance equal to that of the quadrilateral guide. Hence, the folded guide section functions as a transformer for matching the impedances of the coaxial line and the main Wave-guid over a band of microwave carrier frequencies.

Th invention will be more fully understood from a perusal of the followingspecification taken in conjunction with the drawing on which like reference characters denote elements of similar function and on which:

a conductive channel or coaxial line connected thereto. The line channel 2 is connected through a rectangular wave guide section 3 folded or looped in the plane of its long, transverse dimension b to a quadrilateral main wave guide or dielectric channel l and a radiating or receiving antenna such as a horn 5. The inner conductor 6 of coaxial line 2 is attached to the folded guide Moreover, as explained in the copending' section 3 at the longitudinal mid-point I of the looped guide through a multi-frequency coupling device of the type disclosed in applicants copending application mentioned above and comprising an adjustable sleeve member 8. As explained in my application mentioned above, the sleeve is adjusted and a particular value for the short transverse dimension a of the loop 3 selected such that the exposed. exciter portion 9 of the inner conductor 6 has the proper length and impedance for matching over a carrier band of frequencies the characteristic impedance Z of line 2 to the total folded guide impedance comprising the impedances of the two loop branches I and I I connected in parallel. Thus, assuming the line 2 has a characteristic impedance Z equal to 100 ohms, each of the loop branches II] and I I has a characteristic impedance 22 equal to 200 ohms, and the two impedances in parallel equal the line impedance. The main dielectric channel has a characteristic impedance, IZ, which may be taken as th value of its input or send end impedance since the length of the main guide 4 is great relative to the wave-length employed and may be considered infinite. Inasmuch as the apertures l2 and I3 are superimposed with their transverse dimensions a aligned, the characteristic impedances of the apertures are serially associated and their total impedance, GZ, equals the send end im edance and the characteristic impedance of guide 4.

In operation, assuming device I is a transmitter, while the energies conveyed between the device I and the horn 5, and propagated in the branches I0 and I I, flow relative to point 1 in opposite or bilateral directions, the combination including looped section 3 functions to produce only unilateral propagation in the dielectric channel 4. Arrows I4, I5, I6 and I1 denote the directions of propa ation in line 2. branch I0, 'branch I I and guide 4. respectively. The wavelets propagated in directions [5 and I6 have, at center point I, the same (zero) phase angle and are similarly polarized as shown by arrows I8 and IS in a'direction ali ned with the short transverse dimension a and the exposed exciter 9. that is. in a vertical direction in the plane of the drawing. Contrary to the effect secured in a system of the copending Friis application, the curvature in the coupling section 3 does not shift the polarity of these wavelets since the curvature is only in a plane perpendicular to the direction of polarization. Moreover. the branches I i) and II are of equal length so that in apertures I2 and I3 the wavelets are similarly polarized, as shown by arrows 20 and 2!. and combine to form a maximum vector. resultant 23 in the main wave-guide channel 4.

Thus. in accordance with the invention the system or combination illustrated by Figs. 1 and 2 and comprising a multi-frequency coaxial lineto-wave guide. cou ling device, a wave-guide coupling section folded in the plane perpendicular to the plane of polarization of the electric vector and a ma dielec ric channel. functions to match the impedances of a line channel and a dielectric channe without reflection losses and without losses due to chan ing the polaritv of the wave component. over a h nd of carrier fre uencies including several hundred me acycles. At the same time the combination functions to produce ,unilateral or one way propagation in the quadrilateral wave guide 4.

Although the invention has been explained in connection with a certain embodiment thereof, it should be understood that it is not to be limited to this arrangement inasmuch as other apparatus may be employed in successfully practicing the invention. More particularly, the folded wave-guide coupling section and the main wave guide may each have a square instead of a rectangular cross section. Also, any other type of line, such as a balanced line, and even a dielectric wave-guide channel, may be employed in place of the coaxial line; and the invention may be utilized for coupling a balanced line to a dielectric channel or for coupling two dielectric channels.

What is claimed is:

1. A dielectric channel-transmission line coupling device comprising a rectangular wave-guide section for conveying wave components polarized in the plane of one transverse dimension, said section being looped or curved in the plane of the nel and an aperture at an intermediate point for junction with said line, the two paths connecting said intermediate point with said channel being electrically equal, said guide being energized with waves polarized in the plane of its short transverse dimension and folded in the plane of its long transverse dimension.

3. In combination, a quadrilateral wave guide having a given impedance and an end orifice, a transmission line having a difierent impedance, and means for matching said impedances and for producing unilateral propagation in said guide comprising a rectangular wave-guide section having an impedance intermediate said impedances and a curvature in the plane'of its long transverse dimension, said section having superimposed end apertures joined to an end orifice of said quadrilateral guide, said line projecting into said section at its mid-point in a direction coincident with the short transverse dimension of said section. a

4. In a system for transmitting transverse electric waves. a quadrilateral wave guide having an end orifice. a coaxial line, and means for connecting said guide and line and matching their ime nedances over a band of frequencies several hundred megacycles wide, said means comprising a rectan ular wave guide folded in the plane of the transverse dimension perpendicular to the polarization of the transverse e ectric wave and havin superim osed end apertures joined to an end orifice of said quadri ateral uide. the c aracteristic impedance of t e rectan ular guide bein equal to twice t at of said line and to one-half that of the cuadrilateral guide, a multifreouency impeda ce ou er co nectin said line to the mid-point of said fo ded guide. whereby corn-

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