US2855569A - Phase shifter - Google Patents

Description

Oct. 7, 1958 w. SICHAK 2,855,569 I PHASE SHIFTER Filed Nov. 22, 1955 RESONAMR INVENTOR WILL/AM s/cl/AA BY dyad/pl! AesN'T ttes PHASE SHIFTER Application November 22, 1955, Serial No. 548,357

9 Claims. (Cl. 333-9) This invention relates to microwave phase shifters and more particularly to a high-speed continuous rotary phase shifter providing two outputs which are conjugate.

In many microwave system applications, phase shifters are needed, generally, for such applications as shifting the angular position of an antenna radiation beam. Heretofore, various means and methods of shifting the phase of an output wave with respect to the input wave have been proposed.

Previously, microwave phase shift arrangements capable of relatively high power transmission generally com: prised circular waveguide structures, an input antenna for radiating a circularly polarized wave through the waveguide and an output antenna to receive the transmitted wave. As one or both of the antennas is caused to rotate about a given axis, the transmitted electromagnetic energy is shifted in phase when received at the output antenna. These prior art arrangements become extremely large for some applications when scaled down for frequencies of 1,000 me. or lower and have no real practical usefulness. For example, at 100 mc., a wavelength is approximately ten feet and a half wavelength is approximately five feet. When microwave energy is transmitted in a circular waveguide of the prior art phase shifter, it is necessary that the diameter be in excess of one-half wavelength, and thus the cut-ofi diameter would be five feet at 100 mc. and the preferable diameter would be seven feet with a correspondingly greater length.

Therefore, it is an object of this invention to provide an improved phase shifter of practical physical dimensions and weight and which is capable of relatively high power transmissions at microwave frequencies below 1,000 mc.

Another object of this invention is to provide a phase shifter which utilizes a coaxial resonator having a practical physical dimension and weight at microwave frequencies below 1,000 mc.

Still another object of this invention is to provide a phase shifter providing two output signals which are in a conjugate relationship, that is, equal in magnitude but, with equal and opposite phases.

A feature of this invention is the provision of a cavity resonator of the coaxial type, means to couple continuous signal energy to the resonator and a pair of output coupling means for the resonator disposed in orthogonal relation to each other. The output coupling means are synchronously rotated in the same direction tojproduce signals at the output coupling means respectively varying in accordance with the sine and cosine of the angle of rotation of the pair of output coupling means. The sine and cosine varying output signals are coupled through output lines which differ by a quarter wavelength to two terminals of a four-terminal network of the bridge or hybrid type to combine these signals in a manner to provide two signal outputs from the other terminals of the four-terminal network which are in a conjugate relationship.

The above-mentioned and other features and objects of this invention will become more apparent by reference atent O to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic illustration of one form of phase shifter following the principles of this invention;

Fig. 2 is a cross-sectional view of one form of cavity resonator which may be utilized in the phase shifter of Fig. 1;

Fig. 3 is a cross-sectional view taken along 3-3 of Fig. 2, and

Fig. 4 illustrates equivalent circuit diagrams of the phase shifter of this invention.

Referring to Fig. 1, the phase shifter of this invention is illustrated diagrammatically as comprising an input line 1 coupling wave energy in any convenient manner to resonator 2. Resonator 2 provides two output signals, one of which varies as cosine 0, where 0 equals the angle of rotation of the output coupling means, and the other of which varies as sine 0. These outputs are connected to opposite ends of a four-terminal combining network 3, illustrated diagrammatically herein to be a bridge or hybrid junction type waveguide network, through transmission lines 4 and 5 that differ in length by a quarter wavelength at the mean operating frequency of the phase shifter. As illustrated in Fig. 1, line 5 is coupled to the output varying in accordance with sine 0 and has a length greater than line 4 by one-quarter wavelength. This difference in length imparts to the output varying as sine 0 the j factor or a -degree phase shift as illustrated at input 6 of network 3. Thus, network 3 has coupled thereto at one input terminal a voltage varying as cosine 0 and at the other input terminal a voltage varying as sine 0.

Network 3 includes four legs or arms 7, 8, 9 and 10 of waveguide configuration. Three of these legs are of equal length while the fourth leg has a length one-half a wavelength longer than the other three legs at the mean operating frequency of the phase shifter. For the example illustrated in Fig. 1, leg 10 is one-half a wavelength longer than the length of legs 7, 8 and 9. The cosine varying input at terminal 11 is coupled along legs 7 and 8 to the output terminals 12 and 13, respectively. The 1' sine varying input at terminal 6 is coupled along leg 9. to output terminal 13 for addition with the cosine varying voltage. At the same time, the j sine varying input is coupled along leg 10 to output terminal 12 for subtraction from the cosine varying voltage. The subtraction results since leg. 10 has the one-half a wavelength additional length. The resultant output from terminals 12 and 13 will therefore be conjugate, that is, equal in magnitude but having equal and opposite phases where the phase between the input signal to the resonator and the output signals from the network 3 depends upon the angle of rotation of the resonator output coupling means.

Referring now to Figs. 2 and 3, there is illustrated in cross-section one form of cavity resonator which may be utilized as resonator 2 of Fig. 1. Resonator 2 is illustrated as comprising a coaxial cavity resonator 14 of the reentrant cylindrical type, but it is to be understood that other types of coaxial resonators may be employed. This reentrant type of coaxial resonator may be considered as a coaxial line having a short circuit 15 between the inner conductor 16 and the outer conductor 17 at one end thereof and a capacitive load at the other end thereof between inner conductor 16 and plate 18 disposed to close outer conductor 17. While other forms of cavity resonators may in theory be employed, the coaxial-type cavity resonator is the most practical for those frequencies below 1,000 mc. For instance, the resonator of Fig. 2 need be only a quarter wavelength which at mc. is two and one-half feet long and has a diameter 3 comparable with the diameter of standard coaxial cables, or roughly one inch.

The outer conductor 17 of resonator 14 is provided with an input aperture 19 and two output apertures 20 and 21. As illustrated, output apertures 20 and 2 1 are disposed substantially on the same diameter and input aperture 19 is disposed on a diameter substantially perpendicular to the diameter on which are disposed apertures 20 and. 21. The input line 1 comprising a coaxial transmission line 22 is received in aperture19 and secured to the edge thereof. The center conductor of transmission line 22 is extended into resonator 14 and formed into a loop 23 or another form of coupling probe. Through the means of loop 23, continuous wave energy is coupled into resonator 14.

Output apertures 20 and 21 have fitted therein bearings 24 and 25, respectively, such as oilite or graphited-bronze bearings, to rotatably receive coaxial transmission line sections 26 and 27. Sections 26 and 27 are coupled to transmission lines 4 and 5, respectively, by rotary joints 28 and 29. Rotary joints 28 and 29 may be any conventional rotary joint permitting continuous rotation of sections 26 and 27 in either direction about the longitudinal axis thereof which provide a good impedance match for all rotations and minimize the R.F. leakage from the rotation components to prevent interference with the succeeding equipment and to prevent damage from sparking to the moving mechanical parts.

The center conductors of sections 26 and 27 are each formed to provide a loop-type coupling probe as indicated at 30 and 31. Loops 39 and 31 are oriented 90 degrees apart or in orthogonal relationship as indicated in Figs. 2 and 3. Sections 26 and 27 and their associated coupling loops 30 and 31 are synchronously rotated in the same direction by means of motor 32 and mechanical linkages 33 and 34. Thus, the signal coupled by rotating loop 30 from resonator 14 will follow a cosine law with rotation and the signal coupled by rotating loop 31 from resonator 14 will follow a sine law with rotation. The cosine and sine 0 varying outputs will be acted upon as discussed with respect to Fig. 1 to provide two phase shifted outputs which are in a conjugate relationship with each other.

Referring to Fig. 4, there is illustrated the schematic representation 35 of the circuit of Fig. l and its equivalent circuit form 36, ignoring resonator losses which affect only the insertion loss. The value of the resistors in the equivalent circuit 36 is obtained by recalling from elementary physics that the resistance on one side of a coupling transformer is equal to the square of the turns t ratio times the resistance on the other side of the transformer. In the present case, let n equal the coupling from the generator, n equal the coupling from the cavity into one output path which is proportional to sin 0 and n equal the coupling from the cavity into the other output path which is proportional to cos 0. Therefore, we will obtain the resistance values as shown in equivalent circuit 36 from the schematic circuit 35. The resistance seen by the equivalent generator is then given by The ratio of the output powers is Substituting 11 :11 tan 0 in the first equation, weobtain =m sin 9R Therefore, if

n sin 0R :n R

the input is always matched while delivering the required sin 0 and cos 0 outputs. For R =R (the usual case) this requires i sin 0 This law is the one normally followed by loops and similar coupling means.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A phase shifter comprising a cavity resonator, means to couple signal energy to said resonator, a pair of output coupling means for said resonator disposed in orthogonal relation to each other, means to synchronously rotate said coupling means in the same direction to produce signal energy outputs varying in accordance with the sine and cosine of the angle of rotation at said pair of output coupling means, respectively, and means to combine the output signal energy of said pair of coupling means to provide two additional output signals which are in a conjugate relationship.

2. A phase shifter according to claim 1, wherein said cavity resonator is of the coaxial cavity type.

3 A phase shifter according to claim 1, wherein said pair of output coupling means includes a pair of loops oriented to be disposed in a -degree relationship with each other.

4. A phase shifter according to claim 1, wherein said means to combine includes a network having two input terminals, two output terminals and transmission lines coupling said output terminals in parallel to each of said input terminals, one of said transmission lines differing in length from the other of said transmission lines by one-half a wavelength or multiple thereof at the mean operating frequency, and means coupling the output sig-. mail of each one of said pair of output coupling means to a separate one of said input terminals.

5. A phase shifter according to claim 1, wherein said cavity resonator is of the coaxial cavity type and said pair of output coupling means includes a pair of loops oriented to be disposed in a 90-degree relationship with each other.

6 A phase shifter according to claim 1, wherein said pair of output coupling means includes a pair of loops oriented to be disposed in a 90-degree relationship with each other and said means to combine includes a network having two input terminals, two output terminals and transmission lines coupling said output terminals in parallel to each of said input terminals, one of said transmission lines differing in length from the other of said transmission lines by one-half a wavelength or multiple thereof at the mean operating frequency, and means coupling the output signal of each one of said pair of loops to a separate one of said input terminals.

7. A phase shifter according to claim 1, wherein said cavity resonator is of the coaxial cavity type and said means to combine includes a network having two input terminals, two output terminals and transmission lines coupling said output terminals in parallel to each of said input terminals, one of said transmission lines differing in length from the other of said transmission lines by one-half a wavelength or multiple thereof at the mean Operating frequency, and means coupling the output signal of each one of said pair of output coupling means to a separate one of said input terminals.

8. A phase shifter according to claim 1, wherein said cavity resonator is of the coaxial cavity type, said pair of output coupling means includes a pair of loops oriented to be disposed in a 90-degree relationship with each other and said means to combine includes a network having two input terminals, two output terminals and transmission lines coupling said output terminals in parallel to each of said input terminals, one of said transmission lines differing in length from the other of said transmission lines by one-half a wavelength or multiple thereof at the mean operating frequency, and means coupling the output signal of each one of said pair of loops to a separate one of said input terminals.

9. A phase shifter comprising a coaxial-type cavity resonator, an input loop coupling continuous signal energy into said resonator, a first output loop and a second output loop for said resonator, said first and second output loops being oriented in a 90-degree relationship with each other, means to synchronously rotate said output loops in the same direction to produce in said first output loop signal energy varying in accordance with the cosine of the angle of rotation and in said second output loop signal energy varying in accordance with the sine of the angle of rotation, a bridge-type network having first and second input terminals, first and second output terminals, a first arm extending from said first input terminal to said first output terminal, a second arm extending from said first input terminal to said second output terminal, a third arm extending from said second input terminal to said second output terminal and a fourth arm extending from said second input terminal to said first output terminal, said first, second and third arms having a given length and said fourth arm having a length one-half a wavelength longer at the mean operating frequency than said given length, a first transmission line coupling the output of said first loop to said first input terminal, and a second transmission line coupling the output of said second loop to said second input terminal, said second transmission line having a length one-quarter wavelength longer at the mean operating frequency than said first transmission line whereby the signal energy of said coupling loops is combined in said bridge-type network to provide a signal output at each of said first and second output terminals thereof, said signal outputs being in a conjugate relationship.

References Cited in the file of this patent UNITED STATES PATENTS 2,422,601 Tashjian June 17, 1947 2,442,597 Greenough June 1, 1948 2,619,635 Chait Nov. 25, 1952 2,759,099 Olive Aug. 14, 1956 FOREIGN PATENTS 711,752 Great Britain July 7, 1954

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