US2879485A - Broad band electronic switch - Google Patents

Description

March 24,1959 J. CART ER ETAL 2,879,485.

BROAD BAND ELECTRONIC SWITCH Filed April 6. 1956 DUPLEXER ITTlNG SOURCE TRANSM RECEIVER INVENTORS, JOHN 1.. 04mm BY 4 IRVING RsllvaoLb.

A TTORNE Y BROAD BAND ELECTRONIC SWITCH John L. Carter, Neptune, and Irving Reingold, West Deal,

N.J., assignors to the United States of America as represented by the Secretary of the Army Application April 6, 1956, Serial No. 576,747 3 Claims. (Cl. 333--13) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to a broad band electronic switching device particularly useful in high level energy microwave apparatus where a transmitter and receiver must be alternately connected to an antenna at high speeds such as in the operation of a radar system. In many such systems it becomes either necessary or desirable that the operating frequency be shifted thru a relatively wide band. In microwave systems having conventional switching devices it is difficult or impossible to maintain normal operating conditions thruout a wide band of frequencies unless a complicated tuning system is empioyed in the switching device. The present invention enables a system to be operated successfully and eliiciently thru a wide range of frequencies with no physical change in the switching device. The range of operating frequencies may be as broad as the spectrum embraced by the waveguide or other carrier of energy employed in the system.

The invention has Wide application for use in various circuits and in conjunction with numerous microwave energy generating devices, the energy outputs of which are tunable thruout a relatively wide range of frequencies, such as magnetrons, carcynotrons, traveling wave tubes, klystrons and similar devices. An important capability of the invention lies in the fact that it is especially well adapted for use in connection with electronically tunable generators such as the voltage tunable magnetron.

The device of the invention consists of two main elements within a waveguide or other energy conducting structure. The first element is abroad band cavity resonator such as a pre-transmit-receive tube commonly designated a pre-TR tube. Tubes of this type have various forms and for purposes of the invention this tube may be of that type known as the multi-iris encapsulated window type. However, any resonant broad band pre- TR tube can be used such as a pre-TR tube having two multi-iris windows separated by a quarter wavelength tube body. For purposes of description the encapsulated window type will be described and illustrated herein.

The pre-TR tube above referred to is exposed to high level energy from a generator or any source of such energy and functions in the conventional manner to transmit the major portion of the energy into one channel and block the passage of energy to a second channel. At the same time this tube passes a small amount of leakage energy into the second channel. It is the function of a second element in the second channel to attenuate or absorb this leakage energy and to prevent all or substantially all of the leakage energy from flowing therein.

The second element must be capable of attenuating the leakage energy thruout a broad band of frequencies at least as great as the band of frequencies embraced by the first element. This second element is a gas filled nited States Patent M 2,879,485 Patented Mar. 24, 1959 attenuator tube situated within the second channel of the energy conducting system in such position that it will receive all of the leakage energy from the first element and must have a gas content so adjusted as to break down at the energy level of the leakage component and moreover the attenuator tube must respond to energy thruout the stipulated broad frequency band of the system. A further component of the attenuator tube is a magnetic element designed to embrace the tube and apply a field of varying strength along the tube to efiect ionization of the. gas therein. This magnetic element insures that gyromagnetic resonance will occur thruout the he quency band in use. An alternative structure for the second element would provide an attenuator tube having external triggering means. Thus energy in the system is under control of the switch which functions efficiently thruout a wide band of frequencies.

It should be particularly pointed out that the applied magnetic field reduces the energy level at which the attenuator tube may be made to fire by a large factor compared to its breakdown point without the field. This ratio may be as high as fifty to one; The action of the magnet therefore contributes in large part to the success of the invention by enabling the attenuator tube to respond to the relatively low energy level of the leakage energy.

it is a primary object of the invention to provide electronic switching of microwave energy over a broad band of frequencies.

A further object of the invention is to provide broad band microwave switching capable of controlling high level microwave energy to an extent which affords complete protection and permits operation of sensitive low power devices connected in the system.

A still further object of the invention is to provide an electronic switching device substantially uniformly effective thruout the operating frequency of the waveguide or other energy conducting means in which it is used.

A further object of the invention is to provide an electronic switching means having an attenuating device capable of being activated at very low energy levels thereby to attenuate leakage energy passed by a pre-TR tube.

A still further object of the invention is to provide a switching device reliable in operation and exceptionally rugged and long-lived.

Other objects and features of the invention will more fully appear from the following description and will be particularly pointed out in the claims.

To present a better understanding of the invention a particular embodiment thereof will be described and illustrated in the accompanying drawings, wherein Fig. l is a diagrammatic representation of one type of apparatus in which the device may be used.

Fig. 2 is a longitudinal cross-section on line 22, Fig. 3.

Fig. 3 is an end elevation of the device.

The invention may be utilized in many applications requiring microsecond switching of high level microwave energy. As a typical example of the use of the invention the following description presents the invention in connection with radar systems. In the design of radar systems the problem of the inherent operating bandwidth thereof presents certain limiting conditions which are diflicult to overcome. In many radar systems and also in systems. other than radar, it is highly advantageous to operate the apparatus at diflferent frequencies at different times. This fact coupled with the fact that conventional switching or duplexing devices function efiiciently within a narrow frequency band only restricts conventional systems to narrow band operation. The

invention, on the other hand, affords efiicient switching and the necessary protection to delicate receiving elements or other devices in the system thruout a wide band of operating frequencies.

Referring to the drawings in Fig. l a switch or duplexer 5 constructed in accordance with the invention is shown as inserted in a conventional radar circuit containing a magnetron 6 or other microwave generator, an antenna 7 and a receiver 8. As in conventional duplexing devices power generated by the magnetron, in pulsed form, acts to short-out that portion of the circuit leading to the receiver thus affording protection for the receiver during the transmitting period. The echo pulse picked up by the antenna is then prevented from traveling to the magnetron and is switched into the receiver 8 in the con ventional manner passing freely thru the duplexer.

The switching unit or duplexer 5 is of special construction as illustrated in Figs. 2 and 3 of the drawings and is composed of two main elements arranged in series in the waveguide 9. The first element is a broad band resonant pre-TR device constructed and arranged to be exposed to high level energy in the system and becomes ionized by such energy. The gas content and the physical conformation of this device is adjusted to function over a wide band of frequencies and moreover the gas content should be such that a predetermined leakage current will pass therethru for reasons to be pointed out hereinafter. This first element may be a multi-iris gas filled encapsulated window. Any resonant broad band pre-TR tube may be used. As shown in the drawings the first element consists of a multi-iris window 10 extending laterally across the waveguide 9. The window is composed of a metal plate 11 desirably made of Kovar or similar material having suitable thermal expansion characteristics matching that of the glass windows 12 which are sealed into openings in the plate 11. The edges of a glass member 13 are fused into contact with the plate 11 to form a chamber 14 embracing the windows 12.

The chamber 14 is exhausted and filled with an appropriate gas filling such as argon plus water vapor at a pressure between and 50 mm. of mercury. The gas content should be adjusted to permit leakage energy to pass therethru at a level sufficient to ionize the gas content in the second element. The level of this leakage energy should not, however, exceed that which the second element may safely absorb.

The second element is an attenuating device capable of absorbing the leakage energy which passes thru the first element and comprises an attenuator tube 15 within the waveguide and spaced a short distance from the first element. This attenuator tube can be an externally triggered, broad banded, cold cathode device or it may be a self-triggered device in which the frequency at which breakdown occurs therein is controlled by a shaped magnetic field. The latter type of device is shown in the drawings and utilizes either a solenoid type electromagnet or a permanent magnet. For best operation it has been found that when the operating frequency is less than 3000 me. an electromagnetic solenoid may be used having windings designed to produce a tapered magnetic field extending along the flow of energy within the tube and energized from an external source. At frequencies exceeding 3000 me. a more suitable means for supplying the magnetic field has been found to be a permanent magnet 16 shown in the drawings. This magnet may have a horse-shoe shaped cross-section as shown in Fig. 3 and embrace the full length of the attenuator tube preferably extending somewhat beyond the ends thereof to eliminate fringing field effects. The magnet also is tapered in its dimension parallel to the waveguide thereby to impose a shaped or tapered magnetic fieeld upon the gas within the tube. Such a structure may be designed to produce proper gyromagnetic resonance over a broad frequency band. This relationship of the field strength of the magnet and operating frequency may be expressed as follows:

where H is the field strength in gauss required for gyromagnetic resonance to occur and f is the transmitter signal frequency in megacycles. The length of the magnetic field should be of the order of two wavelengths of the nominal resonant frequency of the waveguide in use.

The invention functions as follows. A high energy RF pulse from the magnetron or other source of power acts to ionize the gas in the first element; namely, the pre-TR tube thus cutting off substantially all of the flow of energy into the waveguide 9. The amount of leakage energy which passes the first element is controlled by the particular gas content of the element and moreover since the first element is a broad band device it will fire at any frequency within its particular spectrum and consequently the leakage frequency may also be of any value within that spectrum. The second element is adjusted to break down or fire at the level of the leakage energy. The attenuator tube 15 also has the necessary capacity to absorb all or substantially all of the leakage energy. This control is effective at any wavelength within the band embraced by the device which, as suggested above, may be substantially equal to that of the bandwidth of the waveguide itself. The magnet 16 acts to permit gyromagnetic resonance at any frequency within the band.

What is claimed is:

1. A duplexer for microwave energy connected in a system where it is exposed to the maximum energy output level of a microwave generator comprising, a waveguide, a transmit-receive electronic switching means in said waveguide having a resonant broad band cavity with a gas content adjusted to ionize at the generator output energy level, attenuating means in said waveguide on the low energy level side of said transmit-receive switching means, said attenuating means consisting of an elongated energy permeable inclosure having a gas content adjusted to ionize at the low level of the leakage energy from said transmit-receive switching means and a magnet embracing said inclosure, said magnet having a tapering flux density along its length whereby the varying field intensity applied to the leakage energy present in the inclosure will expand the band of frequencies which are absorbed within the inclosure.

2. In combination with means to conduct microwave energy from a source of energy to at least two channels, an electronic switching device comprising a transmitreceive resonant cavity exposed to the maximum energy from said source, said cavity having a predetermined high ratio of incident to leakage energy, said transmit-receive cavity acting to pass all but a small portion of the energy to a first channel and to stop all except a small amount of leakage energy from passing to a second channel, attenuating means positioned in said second channel to receive leakage energy only from said transmit-receive cavity consisting of an elongated attenuator tube of energy permeable material having a gas content ionizable at the leakage energy level and having an absorption capacity sufiicient to attenuate the leakage energy and an elongated magnet embracing said attenuating tube said magnet acting to apply a field to said tube varying in intensity along the path of energy flow, said gas content and magetic field being calculated to cause ionization of the gas content through-out a broad band of frequencies.

3. In combination with a microwave energy conducting system operable to conduct energy from a source to at least two channels, an electronic switching device comprising a first transmit-receive resonant cavity exposed to the maximum energy from said source said resonant cavity being constructed to function thruout a broad band of frequencies of the order of the operating band of frequencies of said conducting system said cavity having a predetermined high ratio of incident to leakage energy, said transmit-receive cavity acting to pass most of the high level energy to a first channel and to stop all but the leakage component thereof which passes to the second channel, attenuating means in said second channel on the low energy side of said first resonant cavity consisting of an elongated attenuating tube of energy permeable material in said second channel containing a gas content ionizable at the leakage energy level and having an absorption capacity at least sufficient to absorb the leakage energy and an elongated magnet constructed to produce a field of varying intensity thruout its length,

said magnet being positioned to apply its varying flux along the direction of energy flow in said attenuator tube.

References Cited in the file of this patent I UNITED STATES PATENTS 2,519,795 Smullin Aug. 22, 1950 2,748,35l Varnerin May 29, 1956 2,776,412 Sparling Jan. 1, 1957 OTHER REFERENCES Ararns: Microwave Applications of Gas Discharges, Electronics, November 1954, pages 168 72. Copy in R0. Library.

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