US2462893A - Modulator - Google Patents

Description

March E, 1949.

P. J. PONTECORVO MODULATQR Filed March 7, 1946 Patented ai'. 1, 1949 MODULATOR Paul J. Pontecorvo, Cambridge, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation .of Delaware Appiicaton March 7, 1946, Serial No. 652,738

3 Claims.

This invention relates to modulating apparatus, and more particularly to apparatus for modulating electromagnetic energy in the microwave region of the spectrum.

While not limited thereto, the present invention is admirably adapted for use as a balanced modulator in the local frequency-controlling section of the terminal station disclosed in the copending application oi George G. Bruck, Philip E. Vois, Paul J. Pontecorvo and Malcolm C. Vosburgh, entitled Radio communication system, Serial No. 650,716, led February 27, 1946.

One of the objects of the present invention is to provide a suppressed-carrier modulator in which impedance-matching problems, normally difficult of solution, are considerably simplified.

Another object of the present invention is to provide a balanced modulator capable of handling a relatively wide frequency band with a minimum of distortion.

These, and other objects of the present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner:

rEhe invention contemplates the provision oi means, for example, a wave-guide section, having a perpendicularly extending' branch arm receptive ci a carrier wave, for deriving from said carrier wave two constituent waves of opposite phase. Said constituent waves are applied to ineens, for example, a pair of series-connected, non-linear impedan es which terminate the opposte ends of said wave-guide section, which are also receptive, in parallel, of a modulation wave, whereby two additional constituent waves of opposite phase are derived and combined, respectively, wlth said rst-named constituent waves to produce sideband waves. Said sideband waves, together with portions of said first-named constituent waves reflected from said non-linear impedances, are fed to means, for example, a second branch arm extending perpendicularly from said wave-guide section, perpendicularly to said first-named branch arm, whereby said sideband waves are combined and transmitted to a load, and said reflected portions of said firstnamed constituent waves are combined so as to suppress the same in the direction of said load.

In the accompanying specication there shall be described, and in the annexed drawing shown, an illustrative embodiment I the modulating apparatus ci the present invention. It is, however, to be clearly understood that the present invention is not to be limited to the details herein shown and described for purposes of illustration il only, inasmuch as changes therein may be made without the exercise of invention, and within the true spirit and scope oi the claims hereto appended.

In said drawing, the single ligure is a schematic diagram of a modulating device `assembled in accordancewith the principles cf the p osent invention.

Referring now more in detail to the aforesaid illustrative embodiment oi the p;.'eseut invention, with particular reference to the drm ing illustrating the same, the numeral it? genn erally designates what may be termed a double T-shaped wave-guide assembly. Such an assembly includes a cross-arr il from the center of which, or from what will hereinafter be called a common junction l2, extend two branch arms i3 and ill, said cross-arm being common to both Ts,

and said branch arms being perpendicular to said cross-arm, and to each other. .as herein shown, the branch arm lli recedes from the observer for a short distance from the common junction it, then bends downwardly, and is then twisted through an angle of The opposite ends of the cross-arm terminate, respectively, in non-linear impedances, for example, rectiiying crystals l5 and it, said crystals being oppositely disposed with respect to cach other, and connected in series through resistor ll and a source lil of direct current. The conductors connecting said crystals pass through insulators i9 to 22, inclusive, unted in the cross-arm H, the insulators i3 and ii being of such construction (not specifically shown) to present capacitances 23 and 2li between one side of each of said crystals and the crossai'm itself, the latter being grounded as shown. The crystals l5 and i6 are further connected to provide parallel inputs to ground through capacitor an d the primary winding of an output transfer; ier 2l having a secondary winding The source I8 of direct current constitutes a bias for the purpose of enabling operation of the crystals at favorable points alongtheir characteristic curves, and t .e .series circuit is for the purpose of passing equal currents through said crystals to assure their similar behavior even though both be mismatched to the wave-guide assembly.

For an understanding of the operation oi the device, assume that a carrier wave we is traveling down the branch arrn I3 toward the common junction l2 with its electric vector pointing, arbitrarily, to the right. As this wave reaches the junction I2, it splits into two constituent waves,

one, having its electric vector pointing downwardly, traveling along the cross-arm wave-guide section Il toward the crystal I5, and the other, having its electric vector pointing upwardly, traveling along said wave-guide section II toward the crystal I6.

Now, further assume that a modulation wave om is applied to the transformer 21, and that the two constituent waves derived therefrom by reason of the parallel connection thereof across the crystals I5 and I6 have their electric vectors pointing in the same direction, arbitrarily, down- Wardly.

Thus, there arrives at the crystal I5 two similarly-phased constituent waves, and there arrives at the crystal I6 two oppositely-phased constituent waves. However, because of the opposite disposition of the crystals I5 and H5 with respect to each other, it can be considered that the modulating constituent wave arriving at that crystal with respect to whose conducting direction said constituent wave is out of phase, in the case under consideration, the crystal I6, is, in effect, phase shifted 180. Therefore, effectively, the Waves at said crystal I6 are of like phase, although their phase is opposite to that of the similarly-phased constituent waves at the crystal I5. As a result, the phases of the sideband waves 1c-:wm produced, respectively, at the crystals I5 and l may be considered positive inasmuch as the component waves of each are of like phase.

The similarly-phased sideband waves thus produced, together with the out-of-phase portions of the carrier constituent waves reflected from the crystals I5 and I6, travel along the waveguide section Il toward the common junction I2. At said junction, the sideband waves combine and are propagated along the branch arm I4. The crystal-reflected carrier waves combine and are propagated back along the branch arm I3 from whence the initial carrier wave came, but since these crystal-reflected carrier Waves are of opposite phase, they are suppressed in the direction of the branch arm i4. Thus sideband and carrier waves are effectively separated.

While the branch arm I3 has, in the foregoingr descrip-tion, been considered as the input for the carrier wave, it is desired to point out that the branch arm i4 may be used as the input for the carrier, in which case the branch arm E3 becomes the output for the sidebands.

This completes the description of the aforesaid illustrative embodiment of the present invention. Objects and advantages thereof, in addition to those set forth in earlier portions of this specification, will readily occur to'those skilled in the art to which the same relates.

What is claimed is:

l. Modulating `apparatus comprising: a waveguide section, having a perpendicularly extending branch arm receptive of a carrier wave, for deriving from said carrier wave two constituent waves; a pair of series-connected, non-linear impedances terminating the opposite ends of said wave-guide section, receptive, in parallel, of a modulation wave and receptive of said constituent waves, for deriving from the former two additional constituent waves of opposite phase, and combining the same, respectively, with said first-named constituent waves whereby sideband waves are produced; and a second branch arm` extending perpendicularly from said wave-guide section, perpendicularly to said first-named branch arm, receptive of said sideband waves and receptive of portions of said frst-named constituent Waves reflected from said non-linear impedances, for combining said sideband waves and transmitting the same to a load, and combining said reflected portions of said first-named constituent waves and suppressing the same in the direction of said load.

2. A balanced modulator comprising: a waveguide section having series-connected, non-linear impedances terminating the opposite ends thereof; a carrier-receiving branch arm extending perpendicularly from said wave-guide section; a source of modulation; an impedance, receptive of said modulation, connected, in parallel, across said non-linear impedances; and a sidebandreceiving branch arm extending perpendicularly from said wave-guide section, perpendicularly to said carrier-receiving branch arm.

3. A balanced modulator comprising: a waveguide section having crystal detectors terminating the opposite ends thereof; a carrier-receiving br-anch arm extending perpendicularly from said wave-guide section; a source of modulation; an impedance, receptive of said modulation, connected, in parallel, across said crystal detectors; and a sideband-receiving branch arm extending perpendicularly from said wave-guide section, perpendicularly to said carrier-receiving branch arm.

PAUL J. PONTECORVO.

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

UNITED STATES PATENTS Number Name Date 1,673,002 Fearing June l2, 1928 FOREIGN PATENTS Number Country Date 116,110 Australia Nov. 4, 1942

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