US3657656A

US3657656A - Switched high power pulsed array

Info

Publication number: US3657656A
Application number: US79182A
Authority: US
Inventors: Herbert W Cooper
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-10-08
Filing date: 1970-10-08
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18

Abstract

A time domain power divider wherein a relatively long coherent RF pulse is separated into a plurality of relatively shorter length pulses having substantially the same peak power as the input pulse by coupling a plurality of low loss type waveguide switches to a common waveguide section propagating a relatively long input pulse. The plurality of waveguide switches are selectively separated over a length of the waveguide and operated in timed relationship with respect to the input pulse wherein the pulsewidth of the relatively long input pulse is at least equal to the total span of the plurality of waveguide switches. The relatively shorter coherent RF pulses formed from the input pulse are then respectively coupled to separate antenna means through controlled phase shifters to provide a phase array output of microwave energy.

Description

United States Patent Cooper [151 3,657,656 [451 Apr. 18, 1972 154] SWITCHED HIGH POWER PULSED ARRAY [72] Inventor:

[73] Assignee:

Herbert W. Cooper, l-lyattsville, Md.

Westinghouse Electric Corporation, Pittsburgh, Pa.

122 Filed: on. s, 1970 21 Appl.No.: 79,182

[52] US. Cl ..325/130, 325/125, 325/180, 343/854 [51] Int. Cl. ..H04b 3/02 [58] Field ofSearchm ..325/l3,14,l25,128,129,

[56] References Cited UNITED STATES PATENTS 3,458,817 7/1969 Cooper ..325/l30 X Primary Examiner-Robert L. Griffin Assistant Examiner-Kenneth W. Weinstein Attorney-F. H. Henson, P. Klipfel and J. L. Wiegreffe '57 ABSTRACT A time domain power divider wherein a relatively long coherent RF pulse is separated into a plurality of relatively shorter length pulses having substantially the same peak power as the input pulse by coupling a plurality of low loss type waveguide switches to a common waveguide section propagating a relatively long input pulse. The plurality of waveguide switches are selectively separated over a length of the waveguide and operated in timed relationship with respect to the input pulse wherein the pulsewidth of the relatively long input pulse is at least equal to the total span of the plurality of waveguide switches. The relatively shorter coherent RF pulses formed from the input pulse are then respectively coupled to separate antenna means through controlled phase shifters to provide a phase array output of microwave energy.

11 Claims, 4 Drawing Figures SWITCI'IED HIGH POWER PULSED ARRAY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to microwave apparatus and more particularly to apparatus for selectively switching microwave energy being propagated along a waveguide transmission line for time dividing the power applied to the transmission line into a number of shorter timed pulses.

2. Description of the Prior Art In U.S. Pat. No. 3,323,003 granted to H. Goldie on May 30, 1967, there is described a low loss waveguide switch thyratron which is particularly adapted for application to the present invention. In brief, said waveguide switch, herein otherwise referred to as a TWS, is an externally controlled gas type switch for use in high speed, high powermicrowave applications where extremely low loss and wide bandwidths are required. The device is not RF activated and therefore a video source of triggering pulses is necessary to' operate it. The electrical characteristics are such that it is relatively insensitive to ambient temperature variations. In the TWS the control electrode is a section of microwave waveguide which is adapted to be inserted in the usual waveguide transmission line in which it is desired to control the propagation of microwave energy. The section of waveguide is sealed to the envelope that encloses the anode and electrode and the waveguide section is provided with pressure windows to complete the envelope that retains the hydrogen gas atmosphere around the electrodes. When a triggering pulse is applied between the control electrode and the cathode, a plasma is generated in the region of the cathode which causes the tube to fire and a current are to form between the cathode and the anode. This are creates a high density plasma that extends across the section of the waveguide serving as the control electrode and the plasma serves as an RF barrier to provide attenuation of microwave energy, that is, the plasma acts as a microwave short to prevent transfer of RF energy therethrough. In absence of the plasma, however, microwave energy readily passes through the TWS.

Such apparatus, moreover, is utilized in the teaching of US. Pat. No. 3,458,817, entitled Microwave High Power Short Pulse Shaper, granted to the applicant of the subject invention wherein a driver circuit is disclosed which is capable of deriving extremely short microwave pulses from a relatively longer pulse at very high power levels in rectangular waveguide. This patent as well as the subject invention has for its object the obtainment of enhanced target resolution in radar apparatus. Resolution of a target return is dependent upon the RF pulsewidth of the transmitted pulse such that the narrower the pulse the better the resolution. However, the operating range is proportional to the average power in the transmitted pulse so that in order to obtain still greater range with better resolution the peak power of the pulse must be increased. However, the peak power which can be used is limited by the component breakdown rating.

Various other techniques have been used to manipulate longer pulses from magnetrons and other tubes to achieve shorter pulses of higher peak power than generated by the tube itself. One example of this is the resonant ring wherein the amplitude of the pulse generated by the tube is built up by circulating energy within a low loss transmission line ring and then dumping it into the output by means of a fast acting low loss switch. For normal use this energy is then routed to a radiating structure such as an antenna in applications such as a radar system.

SUMMARY The present invention is directed to a time domain power divider of a relatively long input microwave RF pulse generated by means of a coherent RF pulse generator coupled to a common input waveguide transmission line for the propagation of the relatively long RF pulse so that it effectivenetic energy. A plurality of electronically controlled microwave switches are coupled to the common input waveguide, being selectively located, e.g., equally spaced, along the transmission line with the total span of the switches being at least equal to or less than the pulsewidth of the coherent input RF pulse. The plurality of microwave switches are triggered by a common video pulse fed from a video pulse generator and selectively delayed in time so that each microwave switch will provide an output in a predetermined time relationship relative to the presence of the input RF energy. The respective outputs from the microwave switches are coupled into a respective phase shifter and then to a respective antenna whereby a phased array output having relatively higher peak output is provided.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of an RF array typical of the prior FIG. 2 is a pulse diagram illustrative of the power distribution in the system shown in FIG. 1;

FIG. 3 is a block diagram of the preferred embodiment of the subject invention; and

FIG. 4 is a pulse diagram of the power distribution of the embodiment of the subject invention shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1, there is disclosed a typical prior art system for radiating a plurality of RF microwave signals from a common source of energy such as would be the case in a phased array radar system wherein scanning of the transmitted radar beam is accomplished electronically. The block diagram shown in FIG. 1 is merely illustrative of the distribution of electromagnetic energy from a common RF signal generator 10 to a plurality of substantially identical antenna elements 12 12 12 l2, via an antenna feed manifold 14. What is significant to note about the configuration as shown in FIG. 1 is that the feed manifold 14 is adapted to distribute the power output of the RF generator 10 substantially equally to all of the antenna elements 12,, 12 etc. In doing so, however, the power output from the generator 10 which is graphically shown by the pulse 16 in FIG. 2 having a peak power of P is radiated as a respective plurality of comparatively lesser peak power P/n output pulses 18,, 18 18, while maintaining the same pulsewidth of the primary pulse 16.

In order to increase the resolution of a radar system i.e., enhance its ability to distinguish targets in the reflected return signal it becomes necessary to utilize a shorter pulsewidth of the radiated RF pulses while yet having increased peak power. It is to this end that the present invention is directed. Referring now to FIG. 2 wherein the preferred embodiment of the subject invention is disclosed by way of a block diagram there is shown a source of RF microwave energy 20 shown comprising a coherent RF pulse generator. The coherent RF pulse generator 20 is adapted to be controlled from a synchronizer 22 providing a trigger signal thereto whereupon the RF pulse generator 20 produces a relatively long coherent input pulse 22 which is fed into a section of waveguide transmission line 24 terminated in a suitable RF load 26 which may be, for example, a dummy load. A plurality of externally controlled, low loss, high speed microwave switches 28,, 28 28 28, 28,, and 28,, are coupled to the common waveguide transmission line 24 and being selectively positioned with respect to one another. In the present embodiment the microwave switches 28,, 28 etc. are shown being substantially uniformly spaced but it should be understood that when desirable any other spacing may be resorted to without departing from the spirit and scope of the invention. The plurality of microwave switches 28 28, are preferably thyratron waveguide switches (TWS) of the type described in the above referenced US. Pat. No. 3,323,003. The typical characteristic of such a ly fills the input waveguide section with coherent electromag- TWS at X-band is a rise time in the order of 10-15 nanoseconds with an insertion loss in its unswitched condition in the order of 0.2db. while a 0.5-1.0db. insertion loss occurs in the fired condition. TWS 28, 28,, moreover are to be controlled from a source 30 of video trigger pulses while also receiving a control signal from the synchronizer 22 so that a common trigger pulse from the source 30 is applied to all of the switches in a timed relationship with the occurrence of the long coherent RF pulse 22 in the waveguide 24. A separate time delay circuit 32,, 32 32, is coupled between the output of the trigger pulse source 30 and respective TWS 28, 28,,. Each of the time delay circuits 32, 32, is controlled by means of a master time delay control circuit 34 which is adapted to separately control each of the time delay circuits 32, so that a video pulse output from the trigger source 30 can be applied under a controlled time of arrival to the microwave switches 28, 28,.

It should also be pointed out that the pulsewidth of the primary output pulse 22 from the coherent RF generator source is sufficiently long to span the distance between the first microwave switch 28, and the last microwave switch 28,,. When this condition occurs, the section of the waveguide 24 between the first and last microwave switch 28 is effectively filled with coherent microwave RF energy at that specific point in time as the RF pulse 22 propagates along the waveguide 24 towards the load 26. If all of the time delay circuits 32,, 32 32,, are adjusted to have substantially the same time delay, a video pulse applied to all TWS 28, 28,, simultaneously at a time when the primary RF pulse 22 spans the section of the waveguide 24 containing the microwave switches, the switches will act to slice the relatively long coherent input RF pulse 22 into an equal number n of smaller pulsewidth

secondary output pulses

34, 34,. Moreover if the pulsewidth of the video trigger from the pulse source 30 is properly adjusted, the pulse 22 can be split in the time domain such as shown in FIG. 4. It is also significant to point out that the peak power of the

output pulses

34, 34,, is substantially the same as the peak power of the input pulse 22.

A respective plurality of electrically controlled phase shifters 36,, 36 36,, couple the microwave TWS 28,. 28, to a respective plurality of radiating

antenna elements

38,, 38 38,. An electrical phase control circuit 40 is coupled to each of the phase shifters 36, 36,, so that all of the smaller

pulsewidth output pulses

34, 34,, can be controlled in phase at the arrival of the

respective antennas

38, 38,, such that a phased scanning beam of microwave energy is provided.

The advantage of the subject invention is that relatively higher power output can be obtained while obviating the necessity for the transmission line components handling the peak power which would be required in a resonant ring approach. In the present invention the microwave waveguide transmission line 24 operating at a peak power level of P transmits a peak power of n? less the losses of the transmission line and the transmission line switch. Additionally, it should be noted that in the fired condition of a transmission line switch such as described in US. Pat. No. 3,323,003, whereupon signal flow is blocked through the switch, the losses do not cascade since all of the switches in the subject invention are in parallel.

What has been shown and described, therefore, is a time domain power divider whereupon a relatively long coherent RF microwave pulse can be broken down into a number of shorter pulses to obtain higher peak power output and better resolution than heretofore obtainable. Also precise control of the respective arrival of the shorter pulses to their respective antenna elements can be provided by the time delay circuits and the phase shifters thereby providing electronic scanning of the radiated beam front which is comprised of all of the

pulses

34,, 34 34,.

Having thus described the present invention with respect to its presently contemplated preferred embodiment,

I claim as my invention:

1. An RF microwave system for deriving a plurality of very short high peak power microwave pulses from a single high power microwave pulse of a relatively long pulsewidth, comprising, in combination:

an RF pulse generator for providing a relatively long pulsewidth input microwave pulse of electromagnetic enera common waveguide transmission line connected at one end to said RF pulse generator whereby said input microwave pulse can be propagated therethrough;

an RF termination coupled to the other end of said waveguide transmission line for preventing substantially any reflection of said input microwave pulse back towards said RF pulse generator;

a plurality of low loss signal controlled waveguide switches coupled to said common waveguide transmission line along its length and having selective mutual spacing therebetween with the total span of all said spacings being at least equal to the pulsewidth of said input microwave pulse;

triggering means coupled to all of said plurality of low loss waveguide switches for operating said waveguide switches in timed relationship with the occurrence of said input microwave pulse propagating in said common waveguide transmission line for dividing the pulsewidth of said input microwave pulse into a plurality of microwave output pulses of a relatively shorter pulsewidth having a peak power in the order of the peak power comprising the input microwave pulse; and

microwave means coupled to each of said plurality of microwave switches for propagating a respective microwave output pulse therefrom.

2. The invention as defined by claim 1 wherein said RF pulse generator comprises a coherent source of microwave energy for propagating a coherent microwave pulse through said common waveguide transmission line.

3. The invention as defined by claim 2 and additionally including synchronizer means coupled to said coherent RF pulse generator and said triggering means for providing said predetermined timed relationship between the operation of said plurality of waveguide switches and the propagation of said input microwave pulse.

4. The invention as defined by claim 3 and wherein said triggering means comprises a pulse source generating a common pulse signal applied to all of said waveguide switches for rendering them selectively conducting and nonconducting.

5. The invention as defined by claim 4 and additionally including time delay means coupled between said triggering means and said plurality of microwave switches for controlling the time of arrival of said control pulse to the respective microwave switches in timed relationship with said input microwave pulse.

6. The invention as defined by claim 5 and additionally in cluding control means coupled to said time delay means for selectively altering the time delay of said control pulse to the respective microwave switches.

7. The invention as defined by claim 6 wherein said time delay means comprises a separate time delay circuit coupled between said triggering means and all of said respective microwave switches.

8. The invention as defined by claim 7 wherein said plurality of low loss signal controlled waveguide switches comprises waveguide switches of a thyratron type.

9. The invention as defined by claim 1 wherein said waveguide switches comprises thyratron waveguide switches and said microwave means coupled to the output of each of said plurality of microwave switches comprises an antenna for providing an array for selectively radiating all of said microwave output pulses.

10. The invention as defined by claim 9 and wherein said microwave means additionally includes electrically controlled phase shifter means coupled between said plurality of thyratron microwave switches and the respective antennas for providing a means of controlling radiation of said microwave output pulses from said antenna array in a selected scanned direction.

11. The invention as defined by claim and additionally including phase control means coupled to said phase shifter means for controlling the scan direction of said antenna array.

Claims

1. An RF microwave system for deriving a plurality of very short high peak power microwave pulses from a single high power microwave pulse of a relatively long pulsewidth, comprising, in combination: an RF pulse generator for providing a relatively long pulsewidth input microwave pulse of electromagnetic energy; a common waveguide transmission line connected at one end to said RF pulse generator whereby said input microwave pulse can be propagated therethrough; an RF termination coupled to the other end of said waveguide transmission line for preventing substantially any reflection of said input microwave pulse back towards said RF pulse generator; a plurality of low loss signal controlled waveguide switches coupled to said common waveguide transmission line along its length and having selective mutual spacing therebetween with the total span of all said spacings being at least equal to the pulsewidth of said input microwave pulse; triggering means coupled to all of said plurality of low loss waveguide switches for operating said waveguide switches in timed relationship with the occurrence of said input microwave pulse propagating in said common waveguide transmission line for dividing the pulsewidth of said input microwave pulse into a plurality of microwave output pulses of a relatively shorter pulsewidth having a peak power in the order of the peak power comprising the input microwave pulse; and microwave means coupled to each of said plurality of microwave switches for propagating a respective microwave output pulse therefrom.

4. The invention as defined by claim 3 and wherein said triggering means comprises a pulse source generating a common pulse signal applied to all of said waveguide switches for rendering them selectively conducting and non-conducting.

6. The invention as defined by claim 5 and additionally including control means coupled to said time delay means for selectively altering the time delay of said control pulse to the respective microwave switches.

11. The invention as defined by claim 10 and additionally including phase control means coupled to said phase shifter means for controlling the scan direction of said antenna array.