US2476885A - Mixer for microwave receivers - Google Patents

Description

July 19, 1949. c. E. M CLELLAN MIXER FOR MICROWAVE RECEIVERS Filed July 28, 1 943 INVENTOR Cyril f. McClellan BY I ATTORNE mun 1 m LI mumuu mum Patented July 19, 1949 MIXER FOR MICROWAVE RECEIVERS Cyril E. McClellan, Catonsville, massacr Westinghouse Electric Corporation, East Pitts burgh, Pa., a corporation of'Pennsylya'nia' Application July28, 194.3, Serial No. 4 96.519

My invention relates to ultra high frequency circuit elements and, in particular, relates to arrangements for producing beat frequencies by combining the effects of two higher frequencies for purposes well known in the radio art, such as the demodulation of modulated carrier waves. Arrangements for this purpose are frequently termed mixers. I

As is well known in the radio art, it is frequently desirable to transform the power of a high frequency carrier current to alternating power of a lower frequency; and one expedient for doing this is to provide a local source of alternating currents which differs from the abovementioned carrier frequency by the frequency to which it is desired to transform the power. Circuit elements are then provided on which both the carrier current and the locally-generated current impress voltages, this step being referred to as mixing. By now providing a circuit tuned to the desired difference frequencies of the carrier and the locally-generated currents and embodying a detector on which the resultant mixed currents impress voltages, power of the desired lower frequency will be derived.

In attempting to apply the foregoing expedient to ultra high frequency carrier waves, the practice has been to provide a single tuned transmission line, acting as a resonant circuit, on whichv the carrier voltage and local oscillator voltage were impressed; the tuned line being tuned to the carrier frequency. I have found that when this is done the fact that the tuned line is tuned to a frequency other than that of the local oscillator results in an inefficiency in power transfer from the latter. The invention which I herein describe greatly improves the efficiency of this,

power transfer.

One object of my invention is, accordingly, to

high frequency circuits.

Another object of my invention is to provide an arrangement for efiiciently transforming the frequency of ultra high frequency power.

provide a mixer, particularly adapted for ultra Still another object. of my invention is to provide an arrangement embodying tuned resona;

tors of the concentric transmission line type in of myinvention will become ap- 5 Claims! (01.250 20) parentafupon reading-the following description, taken in connection with the drawings in which:

Figure 1 is a diagrammatic illustration of an arrangement embodying the principles of my invention in a tunableconcentric-line type of resonator; and

Fig. 2 is a cross-sectional View of a resonator of the cavitytype adapted to be used in place of the tunable concentric line in the Fig. 1 arrangement.

Referring particularly to Fig. 1, there is diagrammatically shown an antenna I adapted to receive ultra short radio waves. The antenna l is connected through a suitable inleading conduct-or. 2 to a-loop 3 disposed within the chamber i in the interior of a segment of a transmission line of -.the concentric type. The transmission line segment may suitably consist of a cylindrical sheath 5 of conducting-material having an insulating passage for conductor 2 and divided into two chambers land 6 by a conducting partition i. In the axis of the sheath 5 is positioned a core 8 of conducting material on which are slidably mounted a pair of pistons 9 and H which are capable 'of moving independently of each other. The pistons 9 and I i may make contact with either or both the core 8 and the sheath 5 or may be separated from either of these elements by narrow insulating gaps. When the latter construction is used, the pistons should have sufflciently long projecting rims so that the narrow annular space separating these rims from the sheath 5-or core 8 will constitute capacitors having a negligibly small reactance at-the frequency of the'carrier-wave coming in over the antenna i. The lead from the antenna I to the loop 3 constitutes lnitself a concentric transmission line, inasmuchas it is-centrally positioned inside a conducting sheath l2 which is connected to the sheath 5 at one end. The piston 9 is provided with adjustingmeansfnot shown) by which the chamber 4 may be tuned to the wave length of the incoming carrle'r wave. On the opposite side of the partition 'l-is provided a loop is from which a conductor {passes'through an insulating passage in sheath. 5 into a sheath l4 projecting from the sheath S-and constituting a concentric transmission line leading to a local source of electrical oscillations diagrammatically illustrated at l5. The sheath 5 and one terminal of the oscillator l5 .are connected together, for example, by round connections lGand I.'!. The oscillator l5-is preferably arranged so that its frequency can be regulated at; will to difier from the frequenoyof the-"incomin carrier waves incident adapted to insulatingly pass a conductor 19 which has one end attached to the sheath within the chamber 6 in such a way as to form a loop therein and which forms another loop within the chamber 4 before it passes through an insulating pas sage in thesheath 5 to the work icircuit in which it is desired to use the lower or fmixed frequency output. A conducting'sheath 2|, form ing with the conductor IS a concentric line l'e'afd ing to the load apparatus, projects from the sheath 5.

The mode of operation of the above-described arrangement is as follows: Carrier waves incident uponthe antenna I act through the loop 3 to set up resonant vibrations oftheir own frequency within the chamber l the latter being tuned to resonate at 'th-at fre uency. Oscillations of the frequency of the local oscillator fl 5 react through the loop H to produce resonant vibrations within the chamber 6, the piston ll being moved so as to tune the chamber-etc such frequency. The.

portion 'of the conductorj"i9 forming a loop inside th'e' cha'm-ber 6 and the portion of that con;- ductor forming a loop within the chamber 4 impress voltages of the combined frequency of the resonant chamber 4 and the resonant chamber 6 onthe load apparatus. The latter may conveniently be provided with afdetector; and circuit [tuned to thefd ifference between the carrier frequency and the rreque ey of the oscillator 15. thereby eriving p we'r or substantial magnitude atf 's-u'ch diiferer'ic'e requehcy; I

R eferring'to Fig.2," he latter shawsa resonator of the cavity was theconcentric tr'a mission line type-of resonator descr'i'bedfinoonnection with Fig. 1. Many of the elements er structure i'n th'e resonator of Fig. 2 are'sirnilarfto those of Fig. 1, and in such cases they bear t e same reference numeral. I I II eholesure a l of 'cohduchhg material which may, rot; eisa mple, comprise 'a rectangular parallelo pi ed has a e'eh'trai partition 1 which divides it into two chambers lfa n'd is analogous to the chambers 1 Q6 of Fig. An in-leading condiletbr passin -through the conducting sheath '2 of a concentric transmission line leading from the source of barrier rreueney formsa loop 3 with-iii the chainbr 4 nalo'g'oiis to the 10010 3 Fig. '1. A second 166i) l aianalogous to the loop [3 in Fig. '1, mass to 'thefcentral conductor within a sheath M, fcirm-ing therewith a con centr'ic transmission the anam ous to the transmission I-ii'le "l4 i'n Fig. 1', ah1 which, like the lat t'er, leads to a source of ldcalescinauons. A conductor l9 having one oi-id connected to the walls of the chamber-3i and passingthrough an insulating aperture in the partition 1 leads to the central conductor passing through '-a sheath 2 I and forming therewith a concentric transmiss'io'n line leading to the --lo'a'd circuit." The conductor 19 forms-loops'withih the chambers 6 and 4, analogous to the loops already described in connection withtlie conductor 19 in Fig. '1. I

The resonant'cha-ihbers l {and 6 are arranged to be tuned to resbriate respecuveiy at the carrier frequency and the local" oscillator 'rreq ehcy y two screws 32 and -33 which areFthr'eaded in cert-- tral positions ill the eild VVaIIS of the I chamber 31.. By inwardly or cutwa' eiy displacing these hi-eh may be substituted for 4 screws 32 and 33, the respective chambers 4 and 6 may be tuned to the frequency of the carrier wave and of the local oscillator.

While I have described two specific embodi- 5 mentsof my invention, it will be evident that the principles thereof may be employed in many different ways which will be clear to those skilled in the art.

I claim as invention? I 1. A mixer for deriving beat frequency currents from two sources of alternating current having a frequency difference which comprises an enclosure having conductive walls divided by a conductive partition into two chambers, a transmis-f sion' line leading irom one of said sources and forming a closed loo within one said chamber, a transmission line leading from the other said source and forming a closed loop within the sec- 0nd chamber, a third transmission line forming.

loops in both said chambers and a detector and circuit tuned to said heat firequehcy cor-messed to said third transmiss I 2. A mixer for rents from twosourc'e's of attenuating cur ent having a frequency difiei'fio =cornprises an enclosure 'hav i ucti've walls divided by .a conductive partition into two enters, a

transmission line leading from one said source and forming a clos'ed'lo'op 'w ithin'jorie s'a'id chamber, a transmission line leading rrom the other said source and forming a closed'loop within the second chamber, a third transmission line forming loops in both "said en-anthers, a detector and circuit tuned to said heat if-requ ncy connected to said third transmission line, an-

desired rrequehcy. I I II I I I I '3.'Ami X-er-forde vihg beat-rrea' Treat 'av-ihg from two sources 0 a erna-"t-ing closure havin'gconduotive *walls divided by a conductiv'e partition into two -=ohan*ibers, a trans- .c\ 7 7 through an msiiiatmgriassage through said partition into the other chamber, and rmm'm latter l-ine, and'adetector and I II I eat;frequehty co hecteii to said'thirdtrans-mission line. I

"4. A mixeriarthr vingbeatirrequehcy -eo mhts from two sources of fa citing cur ent having a frequency deference which comprises an en closure "having cohdu'ctiv'e walls Eliv'ide'dby a con ductive partition into two chambers, jaftifansmission line leading frorn-onesaid source and forming a Closed loop whim conductor leading from the therjsaidsource and forming-a 1psea-1bppwi hes'e'c' I a third conductor havi I I a connected t the wall of said chamber and passing through an B I I, I I o resonate at "the frequency of the secon d mentio'ned source. 4

5. In combinationwith an alternating 'currerit 'inpiitl'ihetraverseilbyadirst "alterhatihg'curreht,

O n I deriving heat rre uehcy car-- I eahs't each said chamber for it to r'es'e'nainoe {Eta a freq enc airrereheeiwhich corriprises an em ,ohiicharriber, I

insulating passage through said partition into roe and for a mixer comprising a, central conductive core and a conductive outer sheath, a conductive partition interconnecting said sheath and core, a conductive piston movable along said core on one side of said partition, a second piston movable along said core on the other side of said partition, a conductor connected to said input line and insulatingly passing through the Wall of said mixer to form a loop on the first-mentioned side of said partition, a second conductor insulatingly passing through said Wall and connected to an alternating-current source of frequency different from that of said first alternating current and forming a loop on the second=mentioned side of said partition, and a third conductor having one end connected to said sheath on one side of said partition and insulating 1y passing through said partition to form loops on each side thereof, and means for insulatingly passing said third conductor through said sheath to a detector and circuit tuned to the difference of the above-mentioned frequencies.

CYRIL E. MCCLELLAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS iiumber Name Date 2,141,242 George et a1 Dec. 27, 1938 2,202,035 Trevor May 28, 1940 2,216,964 Stepp Oct. 8, 1940 2,223,835 Smith Dec. 3, 1940 2,236,004 MacLean Mar. 25, 1941 2,247,217 Braaten June 24, 1941 2,253,589 Southworth Aug. 26, 1941 2,272,066 Peterson Feb. 3, 1942 2,280,026 Brown Apr. 14, 1942 2,293,151 Linder Aug. 18, 1942 2,312,919 Litton Mar. 2, 1943 2,419,557 Friis Apr. 29, 1947

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