US2641648A

US2641648A - Directional coupler

Info

Publication number: US2641648A
Application number: US72591A
Authority: US
Inventors: Sensiper Samuel
Original assignee: Sperry Corp
Current assignee: Sperry Corp
Priority date: 1949-01-25
Filing date: 1949-01-25
Publication date: 1953-06-09
Anticipated expiration: 1970-06-09
Also published as: GB668927A

Description

June 9, 1953 s. SENSIPER DIRECTIONAL COUPLER Filed Jan. 25, 1949 xrxx III? llrr XXIX xxlx INVENTOR SAMUEL SENS/PER Patented June 9, 1953 UNITED STAT DIRECTIONALTCOUPLEB Samuel Sensiper, Cambridge, Mass assignor to The Sperry Corporation, Great Neck, N. Y., a corporation of Delaware 1 Application January 25, 1 949, senrm). r2591 The present invention relates to electromagnetic energy couplers between ultra high frequency energy transmission lines, such as wave guides, coaxial lines, or the like, and in particular relates to directional couplers between two such ultra high frequency transmission lines.

In order to connect measuring apparatus to an ultra high frequency energy transmission system, some means of radio frequency energy coupling must be provided. Such coupling means operate independently of the standing waves which may exist in the transmission line, and the amount of power which is extracted from the transmission line should preferably be a definite fraction of the power which is to be transmitted along the main transmission line. To obtain these advantageous conditions, it ishighly desirable that the coupler operate in such a manner that an electromagnetic wave travelling in a single direction along the main line induce a wave travelling in a single direction along the coupling line. Likewise, a wave travelling in the opposite direction in the main line should induce a wave travelling in the opposite direction in the coupling line. 'A coupler which has these properties is known as a directional coupler. The performance of a directional coupler may be described in terms of three quantities:

(1) Attenuation The attenuation of a coupler is the strength of the travelling wave in the main line relative to the strength of the travelling wave which it induces in the auxiliary or coupling line. This is a power ratio, usually expressed in decibels.

(2) Directi'uz'ty o (3) Bandwidth The bandwidthover which the coupler pro- I 3 Claims. (01. 178-44) Typical directionalcouplers of the priorarti'or coaxial lines and wave guides are shown by Tervides maximum directivity with minimum. atv tenuation is important in many installations. It is particularly desirable to'iprovide a wide bandwidth of operation to extend the useful operating range of the coupler so that one coupler can do the same job that a number of difierent couplers formerly did.

man in Radio Engineering, published 1947, by McGraw-Hill, pages 112 to 141. One type or these couplingscomprises a pair of parallel wave guides having two couplingholes spaced one-quarter wavelength apart. In the secondary wave guide, propagation is reenforced in a desired direction and cancelled in theopposite direction dueto the half wavelength difference in path of travel; The disadvantages of this type coupler is that it is frequency sensitive, and has a narrow 'usee ful bandwidth due to the quarter wavelength limitation. Y i Another typical prior art coupler shown in the Terman reference is the single hole, or Bethehole, coupler in which both electrical and magnetic coupling takes place through the same opening. In this type coupling the electric field produces energy flow in both directions in the secondary line, where the waves in the secondary line travelling away from the coupling point are essentially in phase at the coupling point; the magneticfield produces energy fiow in both directions in thesecondary line, but the waves in the secondary line travelling away from the coupling point are essentially 180 out of phase at the coupling point. The magnetic coupling 1s proportional to the cosine .of the angle at which the primary and secondary guides cross, whereas the electrostatic coupling is independent o1 this angle. Therefore the ratio of the couplings may be controlled so that they reenforce each other in one direction andcancel each other in the opposite direction by adjusting the angle between the primary and secondary guides. Good dlrectivity in the secondary guide is obtained at an angle of approximately 63 degrees. This single hole coupler has the disadvantage of havmg a bulky and inconveneint wave guide joint due to the required large angle between the guldes. The coupler'i s merely a single hole and there are no parameters to adjust.

Accordingly, the principal object of the invention is to provide an improved wide band directional coupler for ultra high frequency transmission lines.

Another object of the invention is top'rovide an improved directional coupler which is not frequency sensitivei a Another object of the invention is to provide a directional coupler having substantially independent magnetic and electric coupling.

Another object ofthe' invention is to proand the magnetic cou ling bye slots; opening;

Both or these couplings are in the same trans! verse plane of the guides, and. they are substane tially independent of each other. Thus, the frequency sensitive space factor of a multi hole; coupler is eliminated. In the present invention n9: irequencysensitiv ty-res lts from; ila eeparation; I v

he. fact. ...at the ele tric; and. ma ih tieplihgs. are subs t ally ind p ndent? prov d s parametersforz a j s ment for frequ ncy i sensitivity. V V

The single, hole, or, Bethe directional coupler is, W611..K QWI in the, art, and. i analyzed in the Principles oiQBadaL, by the M.. I. Tl. Radar cho S Li, hublished sc Mc aw-Hill. chanter 10, page 33, but t will be briefly reviewed here for thepurpose. of explaining the, presentinvention.

"Figs. lA-lC illustrate a conventional single hole or Bethe directional coupler, Fig. in being the side view showing thc main. and. auxiliary wave guides I and 2, whichfare joined, togetheralong' their wi'defside; and; the single coupling hole 3. The electric field is illustrated by the electric vectors 4: and the direction of energy flow in the main guide I shown by the arrow 5'. The-electric vectors 4 fringe through the hole 3 and excite the auxiliary guide 2 in; both directions as shown by thearrowEA.

Fig: 1B is the same side view ofthe guides showing the portion of the magnetic field, illustrated by the dots and? crosses, which is transverse to thelongitudinal axis of the guides Ij and 2,. This: magnetic: field creates an electric field I across the couplingrholet due to the charge 4 is the cross-section of Fig. 2A showing how probe I5 is mounted. Probe I5 is preferably insulated as by washer II.

Fig. 2C shows the action of the probe I5 coupling the electric vector into the auxiliary guide I2. The probe I5 acts very much like an antenna exciting waves in the auxiliary guide I2. in both directions as;show,n-.by-:arrows-:Eni The slot l4 couples the magnetic field into the. auxiliary guide I2 in the same manner as the single hole coupler of Figs. lA-1C. However, the fringing of, thfieldqtric fields is minimized due to the narrownessof" the slot.

Therefore, the; present invention acts similartn. the. single hole coupler but has the advantages. of? the additional probe which provides (381 113 parameters, such as size of probe and slot magnitudes of the coupled fields.

currents 9 caused by; the; magmaticfields which flow; alongthe walls of; the. guides. This excitation. results, i waves travelling in. both directions -as; shown; by" anrow; Ear and E1 2 butthe phasehf h leo rio fields is pp site; as shown. by the electric: vectors: I8.v and I9.

Fig. 1C showsthe two coupled. electric field'sof Figs. 1A and} 1B superimposed, and illustrates that they reenforce; each other 11 he e and tend to cancel each; other to the; right, thereby prod ing h d red irec io al; Wave. A previously. mentioned. the two fields do. not: com-. pletely cancel and it is necessary to skewthe longitudinal axes of the guides to thereby vary the magnetic. coupling for complete cancellai The pr sent. inrention. obta ns this; can;- ell oh. without skewing the:- guides.

Fig. 2A illustrates the directional. eouplergqof the present, invention which, operates. Similarly to the conventional single hole coupler. Qf Fi .5. lA-lC'. It comprises main and. auxiliary wave guides II and t2, direction or power f ew being shown by the. arrow I3, a slot- I4, anda, probe I5 coupling thejtwo. guides being in the same n rse. plan r lat re to the guide 2 and their spacing for choosing of the relative By properly choosing the size of the slot I4, probe I5, the cahgel at on of e fie s; the; u iliary 7 gu hd; he ore direet vi v max e; Q -ta' d, w he cut sk w n he: wave. guides.- t n. inconv nient.

n le. uch. as is requ ed; e; 0ll ritismalv singleholecoupler. '1 The probe; may. be made; justable by making it ortelescoping portionsyas shown in Fig; 2D; I

The advantage is that themagnetic and electric coupling adjustments have been; separated; This, invention avoids frequency sensitivity re,- sulting from separation. The. invention isnot limited to wave guidesbutamay also beused with coaxial lines. I

Since many: Qhangescouldbemadein the above ructi a d many ap ren y dely din rs e em ments Qfi h -s inv ntione uld'. bema e W hout depa ti rom the-scope thereo itzis intendedthat all; matter-contained the above.

desc ip i or: shown hth accompa yi g d aw-' i s shall be: terp ted a iilu trati e-a dxnht other and centered in the same transverse plane relative to the longitudinal axes of the wave guides.

2. Av wide band directional coupler comprising a pair of rectangular hollowwave g-uides exe tending, in parallel relationship with v a common broad wall therebetween, said; common broad wall having first and second, separate openings therein centered along ajline, extending in a rectio p rpe i ar. t e ng tu inal ax 'sei. each of said wave guides, the second opening. be,- ing an elongated slot having its longitudinalaxis aligned with the center'oi said first opening, and a. co ductive pro e l ment xtend ng throu h said first pe ing a diproiec g a apprecia e d ance int th nte io o each oi aid ere,

' guides. th en s o sa d. pro e: el ment bei g spaced, from the. Walls of therespeotiye Wave guide thev Probe. lement. bein unhnt ed hr andinsulated fr m. sa d cm moh r adwal 3. A Wide band directional coupler compr References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Korman July 1, 1947 Sontheimer July 1, 1947 Landonv July 8, 1947 Bradley June 14, 1949 Purcell Aug. 9, 1949 Tiley Aug. 23, 1949 Bethe Aug. 22, 1950 Watson Nov. 6, 1951 Doherty et al Nov. 20, 1951 Hansen A Jan. 1, 1952