US2762973A - Matchmeter - Google Patents

Description

Sept. 11, 1956 H. E. KALLMANN MATCHMETER Filed Jan. 24, 1946 PROBE AUDIO FULL-WAVE DIRECT INDICATING FREQUENCY PEAK CURRENT DETECTOR I AMPLIFIER DETECTOR AMPUF'ER INSTRUMENT I i l2 so 4o so 6o *KSI m A E 52 4| INVENTOR.

HEINZ E. KALLMANN ATTORNEY United States Patent MATCHlVIETER Heinz E. Kallmann, New York, N. Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application January 24, 1946, Serial No. 643,159

7 Claims. (Cl. 324-58) This invention relates to a standing wave ratio detector,

and more particularly, to an automatic standing wave pling section of transmission line connected between a source of radio frequency energy and the component being measured. The voltage amplitudes of the successive maxima and minima produced by the standing waves existing along the transmission line are recorded. The voltage standing wave ratio and the absolute value of the reflection coefficient of the component are then calculated from these data. Production testing of components' by this conventional method involve the loss of considerable time.

It is an object of this invention to provide a standing Wave ratio detector.

It is another object of this invention to provide a means for determining rapidly the standing wave ratio existing along a transmission line.

It is another object of this invention to provide a means foindicating directly the standing Wave ratio existing along a transmission line.

It is a further object of this invention to provide a means for changing periodically the velocity of propagation along a transmission line.

These and other objects will be more apparent upon consideration of the following description together with the-accompanying drawings, in which:

Fig. l is a perspective view of an embodiment of this invention;

Fig. 2 is a block diagram of the amplifying and detecting apparatus comprising a part of the invention; and

Fig. 3 is a schematic circuit diagram of a special fullwave peak detector included in the apparatus of Fig. 2.

By means of the apparatus shown in Fig. 1, the effective electrical path length of a waveguide transmission line between its ends is changed periodically by the alternate insertion into and withdrawal from the waveguide of a dielectric material, thereby changing periodically the velocity of propagation of electromagnetic energy therein.

As is illustrated, a rectangular waveguide 11 is bent into a U-shape. Electromagnetic energy introduced into the Waveguide at the input end 10 is propagated along the waveguide and is partially absorbed by a load (not shown) coupled to the output end 22. Energy reflected back from the load results in the production, as is well known, of standing waves having voltage maxima and minima. These maxima and minima are periodically displaced along the Waveguide by the dielectric disk 20. This disk, of any suitable dielectric material such as polystyrene and preferably having a beveled edge, is supported eccentrically upon a shaft 21 which in turn is coupled to a driving motor (not shown). A longitudinal slot 15, cut into the inner wall of the U-shaped section of waveguide, permits the entry of the disk into the wave- "ice guide. Due to the eccentricity, the disk is inserted. into and withdrawn from the waveguide once during each revolution of shaft 21.

Strips-16 of a lossy material such as conducting rubber, are fastened along the edges of the slot 15 to absorb energy radiated through the slot. A piece 14 of lossy material, such as molded polyiron powder, is fastened at the end of the slot to absorb spurious standing waves set up between the two edges of the slot. A similar piece, not visible, is fastened to the other end of the slot. Polyiron is a powdered iron mixed in a phenolic binder.

A probe detector 12 of conventional design, fastened to the waveguide, produces at its terminal connection 13 an output which is a function of the amplitude of the voltage existing. within the waveguide at. the location of the probe. The periodic shifting of the maxima and minirna of the standing waves past the probe produces a voltage at the output of detector 12 which is a function of the standing wave ratio existing along the waveguide .11.

Referring now to Fig. 2, the output of probe detector 12 is amplified by an audio frequency amplifier 30,, the output of which is impressed upon a full-wave peak detector 40, shown in detail in Fig. 3 and described below. The output of peak detector 40 is impressed upon a direct current amplifier 50, preferably one having a high input impedance, such as a cathode follower. An indicator 60, such as a moving coil direct current. instrument, connected to the output of amplifier 50,. can .be calibrated to indicate directly the standing wave ratio existing, along the waveguide.

The accuracy of indication of the indicating instrument 60 is directly related to the: degree of perfection of the peak detector 4%. The detector 40 must be .of the full-wave type and must produce equal loading of both positive and negative peaks of the input wave. Both input and output circuits of the detector should preferably be unbalanced to ground to simplify the design problems of the associated amplifiers.

The circuit diagram of a detector 40 which meets these specifications is shown in Fig. 3. The alternating current signal produced at the output of amplifier 30 is impressed. between terminals. 41 and 42. The rectified direct current component appears between output terminals 51 and 52 and has an amplitude substantially equal to the peak-to-peak voltage impressed between terminals 41 and 42.

In operation, during that period of time when terminal 42 is positive with respect to terminal 41, charging current flows through the series combination of coupling capacitor 43, rectifier 46 and filter capacitor 49, causing capacitors 43 and 49 to assume acharge. During the negative excursion of the input voltage, charging current flows through the series combination of coupling capacitor 43, rectifier 44, and filter capacitor45, causing capacitor 43 to assume a charge opposite to that received during the positive excursion of the input voltage. During the succeeding positive excursion, the voltage acting upon the first-mentioned series combination is :that of the input voltage plus the voltage appearing across capacitor 43 due to the residual charge. As can readily be seen, an equilibrium condition will be reached in which the open-circuit voltage appearing across filter capacitor 49 and the output terminals 51 and 52, will be equal approximately to the peak-to-peak amplitude of the input voltage impressed between terminals 41 and 42. If resistor 48 has a high resistance, such as several megohms, approximately equal loading of the positive and negative peaks will be obtained. Resistors 47 and 48 in series combination function as the load resistance for rectifier 46 while resistor 48 serves as the load resistance for rectifier 44,

Since certain changes may be made in the above described apparatus and difierent embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense, and therefore, that the invention is to be limited only by the prior art and the spirit of the appended claims.

What is claimed is:

1. A standing wave ratio detector comprising, a generator of radio frequency energy, a waveguide, said generator energizing said waveguide, a longitudinal slot cut into a wall of said waveguide, the edges of said slot being covered with a lossy material, a piece of dielectric material, means for periodically introducing into and withdrawing said dielectric material from said waveguide through said slot, and means for measuring at a predetermined fixed point the amplitude of electromagnetic waves within said waveguide.

2. A standing wave ratio detector comprising, a generator of radio frequency energy, a waveguide, said generator energizing said waveguide, said waveguide having a rectangular cross-section and being bent into a U-shaped section, a longitudinal slot cut into the inner wall of said U-shaped section of waveguide, the edges and ends of said slot being covered with a lossy material, a motor, a

disk of dielectric material, said disk being supported eccentrically upon the shaft of said motor, said shaft being positioned so as to cause said disk periodically to enter into and be withdrawn from said waveguide through said slot, a probe detector, said probe detector being fastened to said waveguide between said generator and said slot, an audio frequency amplifier, said amplifier being energized by the output of said probe detector, a full wave peak detector, said peak detector being energized by the output of said amplifier, a direct current amplifier, said direct current amplifier having a high input impedance and being energized by the output of said peak detector, and an indicating instrument, said instrument being energized by the output of said direct current amplifier.

3. The apparatus of claim 2 in which said peak detector comprises, first and second input terminals, first and second output terminals, an electrical connection be-' tween said second input terminal and said second output terminal, a coupling capacitor connected to said first input terminal, a first rectifier, the anode of said first rectifier being connected to said coupling capacitor, the cathode of said first rectifier being connected to said first output terminal, a second rectifier, the cathode of said second rectifier being connected to the anode of said first rectifier, a first filter capacitor, said first filter capacitor being connected between the anode of said second rectifier and said second input terminal, a second filter capacitor connected between said first and second output terminals, a first load resistor connected between said first output terminal and the anode of said second rectifier and a second load resistor connected between the anode of said second rectifier and said second input terminal.

4. Apparatus for periodically varying the velocity of propagation of electromagnetic waves in a transmission line having a longitudinal slot cut in the outer wall thereof'comprising, in combination, an eccentrically rotatable dielectric disk disposed adjacent said outer wall, and means for rotating said disk for causing said disk periodically'to penetrate said wall.

5. A standing wave detector comprising, a wave guide bent into a U-shaped section, a longitudinal slot cut in the inner wall of said U-shaped section, an eccentrically rotatable dielectric member disposed between the legs of said U-shaped section, means for rotating said dielectric member such that said member is periodically inserted and withdrawn from said longitudinal slot, and means for measuring the amplitude of energy within said wave guide at a fixed point.

6. A standing wave detector comprising, in combination, a section of transmission line, means for coupling electromagnetic energy to one end of said transmission line, means for terminating the other end of said transmission line with a load whose characteristics are to be investigated, a probe detector coupled to said transmission line, means for cyclically varying the effective electric length of that portion of said transmission line between said detector and said load by at least one-half the wave length of the electromagnetic energy coupled to said transmission line, whereby said detector measures the amplitude of at least one maxima and one minima of the standing wave developed in said transmission line as a result of any impedance mismatch of said lead, and means for providing an indication of the difference between the amplitudes of the maxima and minima 50 measured by said probe detector.

7. Apparatus for use in determining standing wave ratios comprising, in combination, a section of hollow transmission line, means for coupling electromagnetic energy to one end of said transmission line, means for terminating the other end of said transmission line with a load, a stationary probe detector coupled to said transmission line, means for cyclically varying the effective electric length of that portion of said transmission line between said detector and said load by at least one-half the wave length of the electromagnetic energy coupled to said transmission line, whereby said detector measures the amplitude of at least one maxima and an adjacent minima of the standing wave produced in said transmission line as a result of any impedance mismatch of said load, said last-mentioned means comprising a longitudinal slot cut in an outer wall of said hollow transmission line and a dielectric disk eccentrically mounted adjacent said transmission line and adapted to be inserted through said longitudinal slot into said coupled transmission line by variable amounts upon rotation, and means for providing an indication of the difference in amplitudes of the maxima and mjnima so measured by said probe detector.

References Citedin the file of this patent UNITED STATES PATENTS 2,087,063 McCutchen July 13, 1937 2,270,697 Clark Jan. 20, 1942 2,400,597 Peterson May 21, 1946 2,403,289 Korman July 2, 1946 2,412,393 Ghosh Dec. 10, 1946 2,415,242 Hershberger Feb. 4, 1947 2,433,368 Johnson et al. Dec. 30, 1947 2,605,413 Alvarez July 29, 1952

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