US2760162A

US2760162A - Waveguide amplitude modulator

Info

Publication number: US2760162A
Application number: US282962A
Authority: US
Inventors: Miller Theadore
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1952-04-18
Filing date: 1952-04-18
Publication date: 1956-08-21
Anticipated expiration: 1973-08-21

Description

Aug. 21, 1956 T. MILLER 2,760,162

WAVEGUIDE AMPLITUDE MODULATOR Filed April 18, 1952 Modulating WITNESSES: INVENTOR MWZW E fTTQRNEY Theodore Miller.

United tates Patent house Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 18, 1952, Serial No. 282,962

3 Claims. (Cl. 332-51) My invention relates to waveguide amplitude modulators, and particulary to a waveguide amplitude modulator having a broad frequency response.

It is known to modulate electromagnetic energy bein propagated in a hollow metallic waveguide by applying a magnetic field to a section of the waveguide containing a material having a transmission loss dependent upon the intensity of the magnetic field. However, losses caused by eddy currents induced in the waveguide walls limit the frequency response of such modulators to less than 1,000 cycles, While at the same time tending to heat the waveguide walls and load the wave energy source.

It is an object of my invention to provide an improved waveguide amplitude modulator having a broad frequency response.

It is another object of my invention to provide a Waveguide amplitude modulator which is responsive to a wide range of modulation frequencies.

It is another object of my invention to provide an improved waveguide modulator of the type in which a modulating signal varies the intensity of a magnetic field, and in which eddy current problems are obviated.

The features of my invention, which I consider novel, are set forth in the appended claims. The invention, together with additional objects and advantages thereof, will be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which the single figure is a schematic diagram showing a preferred embodiment of the invention.

In the drawing, two rectangular waveguide sections 11, 13 are shown coupled together by means of a dielectric waveguide section 15. The ends of the rectangular waveguide sections 11, 13 have tapered

portions

17, 19 forming a transition to

circular waveguide portions

21, 23. The dielectric waveguide section 15 has a pair of

cylindrical portions

25, 27 which are fitted inside the circular portions of the rectangular waveguide sections 11, 13. The

end portions

29, 31 of the dielectric waveguide section are tapered to insure a low reflection match between the dielectric and metallic waveguide sections. The center portion 33 of the dielectric waveguide section is in the form of a cylindrical rod having a small diameter. The center portion 33 of the dielectric Waveguide 15 is joined by a pair of

tapered portions

35, 37 to the

cylindrical portions

25, 27 which fit inside the

circular portions

21, 23 of the metallic waveguides.

Transitions from rectangular metallic waveguides to dielectric waveguides of the type just described, and of other types applicable to my invention are known in the art. Transmission efliciencies comparable to those of ordinary waveguide are obtainable with the types of dielectric waveguides used in these transitions. For a detailed discussion of low-loss dielectric waveguides and transitions of types suitable for use with my invention, reference is made to the article entitled An Investiga- "ice .2 tion of Dielectric Rod as Waveguide, by C. H. Chandler, Journal of Applied Physics, December, 1949.

Referring again to the drawing, there is shown an electromagnet 39 having acoil 4'1 wound on a powdered "iron core 43. The electromagnet 39 is disposed around the center portion 33 of the dielectric waveguide section 15 so that the powdered iron core 43 will intercept electromagnetic energy being propagated along the dielectric waveguide section. A source of bias, shown as a battery 45, is connected in series With an impedance, shown as a resistor 47 between the

terminals

49, 51 of the electromagnet. The modulating signal is impressed across the resistor 47.

In operation, when the waveguide is being excited by energy of the carrier frequency, most of the electromagnetic energy being propagated by the dielectric waveguide section will exist outside its center portion. A modulating signal applied to the electromagnet will vary the intensity of its magnetic field. Variations in the intensity of the electromagnet field will cause like variations in the permeability of the powdered iron core, which in turn will absorb varying amounts of the electromagnetic energy being propagated along the waveguide. Modulation of the carrier energy is thus accomplished.

With an arrangement such as that shown in the drawing, the modulating magnetic field is entirely separated from metallic waveguide sections and so no eddy currents are induced in the waveguide walls. Consequently, this type of modulator is much more efficient than those known in the prior art, and it will respond to a wide range of modulation frequencies.

It will be apparent to those skilled in the art that other types of waveguide transitions could be used as well as the specific one shown in the drawing. It will also be apparent that other types of core material could be used for the electromagnet. The only limiting factors are that the modulating magnetic field should be applied to a dielectric waveguide section, so that no eddy current losses are involved; that the dielectric waveguide section be of a low-loss type; that the transition between the metallic waveguide sections and the dielectric waveguide section should be an efficient one; and that the core material be of a type which will absorb the high frequency electromagnetic energy in accordance with the variations in intensity of the modulating magnetic field. It will further be apparent that various dispositions of the electromagnet with relation to the dielectric Waveguide section could be utilized. The only limiting factor in this respect is that the core material be disposed to intercept a suitable portion of the high frequency electromagnetic energy being propagated along the waveguide. The electromagnet should of course be appropriately based for substantially linear operation.

While I have shown my invention in only one form, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit thereof.

I claim as my invention:

1. A high frequency modulator comprising a low-loss solid dielectric waveguide section interposed between and properly matched to a pair of hollow metallic waveguide sections, a ring of powdered iron material disposed in the path of Wave energy propagated by said solid dielectric section, a winding associated with said powdered iron material, means for applying a bias potential to said winding, and means for applying a modulating voltage to said Winding.

2. A high frequency modulator comprising a lowloss solid dielectric waveguide section, a ring of powdered iron material surrounding said section and disposed in 3 4 the path of Wave energy being propagated by said secsion loss of said material in accordance with a modulattion, and means for varying the transmission loss of ing signal.

said material in accordance with a modulating signal.

R fer n es C'ted in the file of this atent 3. A high frequency modulator comprising a low-loss e e c l p solid dielectric waveguide section interposed between and 5 UNITED STATES PATENTS properly matched with a pair of hollow metallic wave- 2,286,428 Mehler June 16, 1942 guide sections, powdered iron material disposed in the 2,483,818 Evans Oct. 4, 1949 path of Wave energy being propagated by said solid di- 2,607,031 Denis et a1. Aug. 12, 1952 electric section, and means for varying the transmis- 2,610,250 Wheeler Sept. 9, 1952