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Publication numberUS3768025 A
Publication typeGrant
Publication dateOct 23, 1973
Filing dateNov 18, 1971
Priority dateNov 18, 1971
Publication numberUS 3768025 A, US 3768025A, US-A-3768025, US3768025 A, US3768025A
InventorsHreha M
Original AssigneeBunker Ramo
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Microwave sampling device
US 3768025 A
Abstract
A broadband microwave sampling device employing a balanced arrangement of matched semiconductor sampling diodes mounted in a waveguide adjacent a step recovery diode across which sampling pulses are generated for coupling to the sampling diodes by propagation through the waveguide. The microwave signal to be sampled is coupled to the sampling diodes by a transmission line which passes through the waveguide. The waveguide is chosen to have a cut off frequency greater than that of the microwave frequency so that there is no propagation thereof within the waveguide.
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United States Patent 1 1 Hreha 1 51 Oct. 23, 1973 1 MICROWAVE SAMELING DEVICE [75] Inventor: Michael A. Hreha, Redondo Beach,

Calif.

[73] Assignec: Bunker Ramo Corporation, Oak Brook, [11.

221 Filed: Nov. 18, 1971 211 Appl. No.: 199,898

[52] US. Cl 328/151, 307/240, 333/7 [51] Int. Cl. [103k 17/00 [58] Field of Search 328/151; 333/7, 7 D; 324/95; 332/52; 307/240 [56] References Cited UNITED STATES PATENTS 3,278,763 10/1966 Grove 328/151 X 3,007,123 10/1961 Andrew et a].

3,479,528 11/1969 Fisher 328/151 FROM 3/1967 Hutchins et a1 328/151 x Primary Examiner1John W. Huckert Assistant Examiner-B. P. Davis Att0rneyFrederick M. Arbuckle 57 I ABSTRACT I 17 Claims, 5 Drawing Figures I Tamas/11551014 LlNE PATENTEDflm 23 ms REFERENCE P U LSE GEN SHEET 1 OF 2 PRlOR ART.

REFERENCE 5AMPUNC':

SAMPLING DEViCE GUNN OSC,

TUN\NC: 2 vArzAcToR P ULsEs 50o.

MICHAEL A. HREHA MICROWAVE SAMPLING DEVICE BACKGROUND OF THE INVENTION The present invention relates generally to means and methods for sampling high frequency electronic signals, and more particularly to improved means and methods for providing broadband sampling at microwave frequencies.

A typical application which requires broadband sampling of a microwave signal arises, for example, where it is desired to provide for automatically controlling the tuning of a Gunn oscillator which may typically operate at a frequency of GI-lz. Although semiconductor diodes having appropriate frequency response for sampling at microwave frequencies have been available for some time, such as epitaxially grown Schottky-barrier junctions in low parasitic packages, it has nevertheless remained a most difficult problem to design a sampling device using such diodes which is capable of providing satisfactory microwave sampling, particularly at X- band and higher frequencies. The primary reason for this difficulty is that the frequency response of a sam pling device employing semiconductor diodes is determined not only by the frequency characteristics of the sampling dioes and the sampling pulse, but'also by the frequency characteristics of the-coupling structure employed to connect them to one another. It has been the provision of such coupling structure which has presented the greatest difficulty in the design of a broadband sampling device. Further considerations in this regard and an example of a typical prior art approach will be found in the article Sampling for Oscilloscopes and Other RF Systems: Dc Through x band, W. M. Grove, IEEE Transacions on Microwave Theory and Techniques, Vol. MTT-l4, No. l2, December, 1966, pages 629-635. I

SUMMARY OF THE PRESENT INVENTION pling device in accordance with the foregoing objectswhich is relatively simple, reliable, and'economical.

A further object of the invention is to provide a sampling device in accordance with theforegoing objects which employs semiconductor diodes.

A still further object ofthe-present invention is to provideimproved means and methods for obtaining broadband coupling at microwave frequencies. An additional object of the invention is to provide improved means and method for automatically controlling the tuning of a bulk-effect oscillator and other electronic oscillators.

The above objects are accomplished in an exemplary embodiment of thepresent invention by the provision of a novel broadband sampling device which achieves broadband microwave samplingby taking advantage of the properties of a waveguide to provide the required coupling between the sampling pulse, sampling diodes and the microwave signal to be sampled. Morespecifically, in the exemplary embodiment of the invention, a microwave sampling device is provided in which a waveguide is employed to provide broadband coupling of reference sampling pulses generated by a step recovery diode generation circuit to a balanced configuration of sampling diodes mounted in the waveguide along with the step recovery diode. The microwave signal to be sampled is coupled to the sampling diodes by a transmission line which passes through the waveguide and is terminated in its characteristic impedance. The waveguide is chosen to have a cut off frequency greater than that of the microwave signal to be sampled so that there is no propagation thereof within the waveguide. Also, the cut off frequency of the waveguide is further chosen in conjunction with the reference sampling pulses applied to the step recovery diodes to provide for the propagation of energy from the step recovery diode to the sampling diodes via the waveguide so as to result in the application of appropriately shaped driving pulses to the sampling diodes.

The specific nature of the invention as well as other objects, uSes, advantages-and features thereof will become apparent from the following description of an exemplary embodiment in conjunction with the accompanying drawings in which:

FIG. 1 is an electrical block diagram illustrating a conventional circuit arrangement including a sampling device for automatically controlling the tuning of a Gunn oscillator.

FIG. 2 is a graphical representation illustrating the operation of the circuit arrangement of FIG. 1.

FIG. 3 is. an electrical circuit diagram illustrating a typical embodiment of the reference pulse, generator in FIG. 1.. 1 .FIGS. 4 and 5 are schematic and electrical diagrams illustrating the construction and arrangement of a preferred embodimentof a sampling device in accordance with the. invention.

Lik e designations referto like elements throughout the figures of the drawings.

Referring initially to FIG. 1, illustrated therein is a typical prior art circuit arrangement which may be employed for automatically controlling the tuning of a Gunn oscillator 10, an associated electronically adjustable tuning varactor 12 being provided in the oscillator cavityfor this purpose. As illustrated in FIG. 1, a signal 10a representative of the Gunn oscillator output signal is applied to a sampling device 20 for-a comparison with reference sampling pulses 50a provided by a refer.- ence pulse generator 50, a typical relationship between the Gunn oscillator signal 10a and the reference sanipling pulses 50a being illustrated in FIG; 2. It will be understood from FIG. 2: that operation of the sampling device 20 is typically such-that, if the pulse repetition rate .of the reference sampling pulses 50a is coherent with the frequency of the Gunn oscillato'r signal 10a, the sampling pulses 50a will occur at substantially the same point on the Gunn signal waveform for each cycle sampled, resulting in an average or direct current value being obtained at the output 20a of the sampling device 20, On the other hand,. if the pulse reptition rate of the reference sampling pulses 50a is not coherent with the Gunn oscillator frequency, then theperiodic sampled value will be random so that the resulting average value provided at the sampling device output 20a will thenessentially be zero. The sampling device output 20a is applied via a suitable am plifier 22 to the tuning varacter 12 which responds thereto in a conventional manner to maintain the desired phase and frequency relationships between the Gunn oscillator signal a and the reference sampling pulses 50a.

Referring next to FIG. 3, illustrated therein is a typical embodiment which may be employed for the reference pulse generator 50 in FIG. 1 for generating the reference sampling pulses 50a. An oscillator 52, which typically includes a crystal oscillator for high stability, provides a large amplitude sine wave at the frequency desired for the output reference sampling pulses. The output of the oscillator 52 is applied to a transmission line 57 via a shaping network comprised of capacitors 53, 54 and 55 and inductance 56. The transmission line 57 is terminated by a step recovery diode 58 across which the resulting reference sampling pulses appear.

The design of the reference pulse generator circuit of FIG. 3 is such that the step recovery diode 58 conducts during the forward half cycle of the sine wave provided by the oscillator 52 and for a fixed time during the negative half cycle. When the stored change in the diode 58 is depleted, the diode 58 snaps off, producing a fast negative wavefront which travels in both directions on the transmission line 57. The wavefront component traveling down the transmission line 57 towards the oscillator 52 inverts upon encountering the capacitor 55 and travels back clown the transmission line 57 towards the diode 58, thus forming the trailing edge of the resulting output pulse appearing across the step recovery diode 58. The width of the resulting output pulse is determined by appropriate choice of the total delay time provided by the transmission line 57. The values of the capacitors 53 and 54 and the inductance 56 are chosen to achieve maximum pulse amplitude.

Reference is now directed to FIGS. 4 and 5 which illustrate the manner in which the coupling characteristics of a waveguide 70 may advantageously be employed in accordance with the present invention to provide an unusually broadband and unexpectedly simple and inexpensive sampling device for use, for example, as the sampling device in the system illustrated in FIG. I.

As illustrated in FIG. 4, which is a side view of the waveguide 70, a pair of matched semiconductor diodes 80 which are to serve as sampling diodes are mounted in the waveguide 70 in a balanced configuration parallel to and spaced from the step recovery diode 58 which is also mounted within the waveguide 70 for injection of the samplingpulses therein. These diodes 58 and 80 are preferably 'epitaxially grown Schottkybarrier diodes provided in low parasitic packages and their mountings in the waveguide 70 may be conven-' tional with appropriate care being taken to minimize any stray inductance in the diode-to-waveguide connections. Also, sampling capacitors 84 required for sampling are advantageously incorporated into the waveguide mountings of the sampling diodes 80 in a conventional manner so as to provide an appropriate sampling capacitance with respect to ground, as indicated by the dashed line capacitors 84'. As illustrated in FIG. 5, the sampling diodes 80 and sampling capacitors 84 are coupled via respective summing resistors 86 to an output junction 88 at which the resulting sampling output signal 20a is provided.

As also illustrated in FIG. 5, which is an end view of the waveguide 70, a small portion of the microwave output signal from the Gunn oscillator signal is extracted for application to the sampling diodes 80 using a probe 72 extending into the ,Gunn oscillator cavity 13. The probe 72 is coupled to a transmission line 75, such as a coaxial line, for example, which passes through the waveguide and is terminated by a load 80 having an impedance equal to the characteristic impedance of the transmission line 75. Appropriate care is taken to keep the line impedance of the transmission line 75 constant to minimize reflections. As also shown in FIG. 5, the transmission line 75 passes through the waveguide 70 perpendicularly to the sampling diodes and intersects the junction 82 therebetween, thereby providing balanced coupling of the microwave signal to the sampling diodes 80.

The waveguide 70 is chosen to have a cut off frequency greater than that of the microwave signal output of the Gunn oscillator so that there is no propagation of the sampling pulses through the transmission line 75. The cut off frequency of the waveguide 70 is also chosen so that each reference sampling pulse appearing across the step recovery diode 58 will cause energy to be propagated via the waveguide to the sampling diodes 80 so as to cause each sampling diode 80 to be driven from cut off into forward conduction for an appropriate predetermined sampling time. As will be understood from FIG. 2, this predetermined sampling time is chosen so as to be relatively short as compared to the Gunn oscillator period, but sufficiently long to permit the charging capacitors 84 to be charged to a value representative of the amplitude of the sampled portion of the Gunn oscillator waveform appearing at junction 82. The magnitudes of the sampling capacitors 84 and the charging resistors 86 are appropriately chosen so that the average or direct current value of the resulting output signal 20a obtained at the output junction 88 indicates the coherency relationship between the Gunn oscillator frequency and the pulse repetition frequency of the reference sampling pulses. As will be understood from the previous consideration of FIGS. 1 and 2, if coherency exists, a corresponding average or direct current output voltage signal will be obtained at the output junction 88, but if they are not coherent, then the periodic voltage at junction 88 will be random and an essentially zero output voltage signal willthen be obtained.

A particular embodiment of a sampling device in accordance with the invention was constructed and successfully tested forGunn oscillator microwave signals ranging from 4 to 20 GHz using reference sampling pulses of approximately MHz repetition rate with the pulse generator circuit 50 in FIG. 3 being designed to provide a reference pulse width of .less than 50 psec. The particular waveguide employed for the waveguide 70 in FIGS. 4 and 5 was a 1% inch section of WR-28 waveguide having a cut off frequency of about 22 GHz. The sampling capacitors 84 each had a value of approximately 25 pico farads. The step recovery diode 58 and the sampling didoes 80 were centrally mounted in this waveguide section with a spacing of about 0.25 inch. The spacing between the diodes was not found to be critical.

Although the present invention has been disclosed with reference to a particular exemplary embodiment thereof, it is to be understood that varoius modifications in the construction, arrangement and use of the invention are possible without departing from the true spirit of the invention contribution. For example, an alternative way to couple the Gunn oscillator signal to the sampling diodes 80 would be to mount the sampling device directly on the Gunn oscillator cavity with a probe extending into the cavity from the junction 82 within the waveguide 70. Such a modification is merely one example of various alternative possibilities which may be employed. The invention is accordingly to be considered as encompassing all possible variations and modifications coming within the scope of the invention as defined by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a microwave sampling device for sampling a microwave signal, the combination of:

a waveguide having a cut off frequency greater than that of the microwave signal to be sampled, first and second diodes mounted in said waveguide in a balanced configuration,

means for providing balanced coupling of a microwave signal to be sampled to said first sand second diodes,

a third diode mounted in said waveguide spaced from said first and second diodes and across which sampling pulses are generated for coupling to said first and second diodes by propagation through said waveguide.

2. The invention in accordance with claim 1, wherein said waveguide is chosen so hat the generation of a sampling pulse across said third diode will cause energy to be propagated via the waveguide to said first and second diodes for providing sampling of said microwave signal.

3. The invention in accordance with claim2, wherein capacitors are incorporated in the waveguide mountings provided for said first and second diodes for detecting the microwave signal sampled thereby.

4. The invention in accordance with claim 2, wherein said means for providing balanced coupling of said microwave signal to said first and second diodes includes a transmission line passing through said waveguide and coupled between said first and second diodes.

5. A microwave sampling device for sampling a microwave signal, said device comprising:

a waveguide having a longitudinal axis and a cut off frequency greater than the microwave signal to be sampled,

a pair of sampling diodes mounted in said waveguide in a balanced configuration with respect to the waveguide, longitudinal axis,

transmission means for providing balanced coupling of a microwave signal to be sampled to said sampling diodes, I

means external to said waveguide for generating sampling pulses of predetermined width and repetition rate appropriate for sampling of said microwave signal,

means for injecting said sampling pulses into said waveguide at a location longitudinally paced from said sampling diodes for coupling to said sampling diodes via longitudinal propagation in said waveguide so as to cause sampling of said microwave signal by said samplingdiodes in response to said sampling pulses, and

output means coupled to said sampling diodes for providing an output signal in response to the sampling of said microwave signal provided by sai sampling diodes.

6. The invention in accordance with claim 5, wherein said transmission means for providing balanced coupling of a microwave signal to raid sampling diodes includes a transmission line passing through said waveguide.

7. The invention in accordance with claim 6, wherein said transmission line is coupled to a point between said diodes.

8. The invention in accordance with claim 7, wherein said transmission line receives said microwave signal at one end and is terminated by its characteristic impedance at its other end.

9. The invention in accordance with claim 5, wherein said means for injecting sampling pulses into said waveguide is chosen in conjunction with the frequency characteristics of said waveguide so that each sampling pulse injected into the waveguide causes energy to be longitudinally propagated in the waveguide to said sampling diodes for driving thereof between conductive and non-conductive states for a predetermined period of time appropriate for providing sampling of said microwave signal.

10. The invention in accordance with claim 9, wherein said means for injecting sampling pulses into said waveguide includes an injecting diode mounted in said waveguide adjacent said sampling diodes.

11. The invention in accordance with claim 10,

wherein said means for injecting comprises a step re-.

covery diode generation circuit in which said injecting diode serves as a step recovery diode across which the sampling pulses are generated. I

12. The invention in accordance with claim 5, wherein said output means is constructed and arranged so that said output signal is representative of the coherence between the pulse repetition rate of said sampling pulses and the frequency of the microwave signal'being sampled.

13. The invention in accordance with claim 5, wherein said output means includes sampling capacitors respectively coupled to said sampling diodes for detecting the microwave signal sampled thereby.

14. The invention in accordance with claim 13, wherein said sampling capacitors are respectively incorporated'in the waveguide mountings provided for said sampling diodes.

:15. A method for providing broadband sampling of a microwave signal comprising the steps of:

- mounting sampling diodes within a waveguide in a balanced configuration, said waveguide having a longitudinal axis and a cutoff frequency greater than the microwave signal to be sampled,

Ic'ouping the microwave signal to be sampled to said sampling diodes in a blanced manner,

generating sampling pulses externally to said waveguide having a pulse width and repetition rate appropriate for sampling of said microwave signal,

injecting said sampling pulses into said waveguide at a location longitudinally spaced from said sampling diodes and so that each sampling pulse will cause energy to be longitudinally propagated in the waveguide to drive said sampling diodes in a manner appropriate for providing sampling of said microwave signal, and

generating an output signal in response to the sampling of said microwave signal provided by said sampling diodes.

wherein the step of generating an output signal is such that the generated output signal is representative of the coherency between the pulse repetition rate of the sampling pulses and the frequency of said microwave signal.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3007123 *Mar 28, 1960Oct 31, 1961Bell Telephone Labor IncTraveling field sampler
US3278763 *Aug 23, 1965Oct 11, 1966Hewlett Packard CoTwo diode balanced signal sampling apparatus
US3308352 *Jun 1, 1964Mar 7, 1967Tektronix IncTransmission line mounting structure for semiconductor device
US3479528 *Feb 13, 1967Nov 18, 1969Bell Telephone Labor IncHigh speed sample and hold circuit
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4259743 *Dec 1, 1978Mar 31, 1981Hitachi, Ltd.Transmit/receive microwave circuit
US5440283 *Jun 14, 1994Aug 8, 1995Sierra Microwave TechnologyInverted pin diode switch apparatus
US6900710 *Nov 2, 2001May 31, 2005Picosecond Pulse LabsUltrafast sampler with non-parallel shockline
US7084716Apr 10, 2001Aug 1, 2006Picosecond Pulse LabsUltrafast sampler with coaxial transition
US7170365Jan 27, 2005Jan 30, 2007Picosecond Pulse LabsUltrafast sampler with non-parallel shockline
US7358834Aug 29, 2002Apr 15, 2008Picosecond Pulse LabsTransmission line voltage controlled nonlinear signal processors
US7612628Sep 28, 2005Nov 3, 2009Picosecond Pulse LabsUltrafast sampler with coaxial transition
US7612629May 26, 2006Nov 3, 2009Picosecond Pulse LabsBiased nonlinear transmission line comb generators
DE2908961A1 *Mar 7, 1979Sep 13, 1979Sits Soc It Telecom SiemensSchaltungsanordnung zum stabilisieren eines mikrowellensignals
DE4021846A1 *Jul 9, 1990Jan 16, 1992Ant NachrichtentechMicrowave oscillator with simple frequency sand modification - has frequency divider between output of VCO and phase detector
Classifications
U.S. Classification327/91, 327/124, 333/103
International ClassificationH01P1/10, G11C27/00, H01P1/15, G11C27/02
Cooperative ClassificationG11C27/024, H01P1/15
European ClassificationH01P1/15, G11C27/02C