Short position i
US 3258721 A
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Description (OCR text may contain errors)
J1me 1966 F. J. LA RUSSA ETAL MICROWAVE PHASE SHIFTER Filed March 26, 1962 5 Sheets-Sheet 1 -16 FIG. 2
SHORT CIRCUIT- f .5. 132 1 [SHORT CIRCUIT 1 r34 28 3o b .v x x H INVENTORS T FRANCIS J. LuRUSSA BY ERNEST J. WILKINSON ATTORNEY June 1966 F. J. LA RUSSA ETAL 3,258,721
MICROWAVE PHASE SHIFTER Filed March 26, 1962 I34 5 Sheets-Sheet 2 FIG. 8
INVENTORS FRANCIS J. LGRUSSA BY E NEST J. WILKINSON 5. 74 ATTORNEY June 28, 1966 F. J. LA RUSSA ETAL 3,258,721
MICROWAVE PHASE SHIFTER Filed March 26, 1962 5 Sheets-$heet 5 3 SHORT POSITION IL (INCHES) D v 0 l l l J 0 0.5 |.5 2 2.5 .D -m
6; DJ LIJ I80 DJ 2 LL! (0 2; a 90 FIG. 6
LL! (9 Z 2 o l l l 4| 0 0.5 L5 2 2.5
SHORT POSITION 11, (INCHES) 75 LL! LU 5 360 [LI 0 m 270 (I) E I80 l-IJ so 1. I 2: o l
SHORT POSITION 1L (INCHES) INVENTOR. FIG 7 FRANCIS J. LclRUSSA BY ER EST J. WILKINSON ATTORNEY United States Patent "ice 3,258,721 MIQROWAVE PHASE SHTFTER Francis .1. La Russa, South Boston, and Ernest J. Wilkinson, Westwood, Mass., assignors to Sylvania Electric Products llnc., a corporation of Delaware Filed Mar. 26, 1962, Ser. No. 182,343 8 Claims. (Cl. 333-11) This invention relates generally to microwave phase shifters and is more particularly concerned with phase shifters which are controlled by varying the amplitude of an electrical signal.
There is a requirement in many electronic systems for a pair of equal amplitude signals whose relative phase can be continuously varied. A particular application having this requirement is a phased antenna array in which the relative phase of adjacent elements in the array must be varied in order to scan the beam. Heretofore, duplicate phase shifters have been required to produce a dual output with relative phase shift. Although duplicate phase shifters are suitable for some purposes, they have several disadvantages which limit their applicability, such as a need for careful balance between the two phase shifters to insure that the outputs are of equal amplitude. Moreover, the size and weight of duplicate phase shifters limits the applications in which they can be used.
With an appreciation of the foregoing limitations of the prior art, applicants have as a primary object of the present invention to provide apparatus for producing a pair of equal amplitude output signals the relative phase of which can be varied.
Another object of the invention is to provide apparatus in which the relative phase of a pair of output signals is varied in response to the relative amplitude of a pair of signals.
Another object of the present invention is to provide an amplitude controlled variable phase shifter in which the total power delivered to the device remains constant.
A further object of the invention is to provide apparatus in which the relative phase of the output signals is varied with a single control.
Briefly, the invention resides in the novel combination of a power divider and a hybrid junction, the power divider providing a pair of constant phased voltages of variable amplitude which are applied to the input terminals of the hybrid junction. Energization of the hybrid by the constant phased voltages from the power divider causes a pair of equal amplitude voltages at the output terminals of the hybrid whose relative phase is varied in direct relation to the relative amplitude of the input signals, which, in turn, are determined by the setting of the power divider.
The power divider may be constructed of either coaxial line, waveguide, stripline or a combination of these types, all of which are well known in the art. The hybrid may also be any one of several well-known types, for example, coaxial line, stripline, waveguide or lumped parameter. The only limitation on the power divider is that its total output power must be constant in order for constant amplitude voltages to appear at the output terminals of the hybrid. That is, it is necessary to use a power divider which does not absorb energy in the process of dividing the power between the two outputs.
The foregoing and other objects, features and advantages of the invention, and a better understanding of its construction and operation, will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a pictorial view, partly diagrammatic, of one embodiment of the present invention;
FIGS. 2 and 3 are schematic diagrams of a hybrid junction and a power divider, respectively, useful in ex- 3,258,721 Patented June 28, 1966 plaining the theory of operation of the present invention;
FIG. 4 is a pictorial view of another embodiment of the present invention;
FIG. 5 is a graph of the amplitude characteristic of a coaxial line power divider of the type shown in FIG. 4;
FIG. 6 is a graph of the phase characteristic of a coaxial line power divider of the type shown in FIG. 4;
FIG. 7 is a graph of relative phase of the output signals from the hybrid junction versus the position of the short of the power divider for the embodiment shown in FIG. 4;
FIG. 8 is a partially cut-away pictorial view of another embodiment of the invention.
A waveguide version of the present invention, which is by way of illustration only, is shown in FIG. 1 consisting of a hybrid junction 10, commonly known in the art as a magic T, which is connected by waveguides 12 and 14 here indicated diagrammatically, to a power divider 16. The hybrid junction is well known in the microwave art and is described, for example, in United States Patent 2,593,120, issued April 15, 1952 to R. H. Dicke. It is well known that a voltage applied to the sum port 18 of a hybrid will produce equal amplitude in-phase voltages at output ports 20 and 22, and a voltage applied to the difference port 24 will produce equal amplitude voltages of opposite phase at ports 20 and 22. An interesting property of a hybrid not generally recognized, however, is that the simultaneous application of quadrature phased voltages to ports 18 and 24 will produce equal amplitude output voltages at ports 20 and 22 whose relative phase is dependent upon the relative amplitude of the input voltages.
The power divider 16 is equally well known, being described, for example, in United States Patent 2,605,356, issued July 29, 1952 to G. L. Ragan. While it is known that the position of the short circuits in stubs 32 and 34 determines the relative amplitude of the output signals from ports 28 and 30, it is not commonly known that the output signals from ports 28 and 30 maintain a constant relative phase shift of independent of their relative amplitude. While the phase shift of the individual signals varies with the amplitude, the difference in phase between the two signals remains constant at 90. The foregoing properties of the hybrid and power divider, together with their operation in combination will be more fully appreciated by considering the following mathematical development.
Referring now to the schematic diagram of the hybrid in FIG. 2, it is known that a voltage V applied to sum port 18 will produce output voltages at ports 20 and 22 which can be expressed as If a voltage V, which is in phase quadrature with V is applied to difference port 24, the output voltage at port 20 will be V '=j.7o7V, (2
and the output voltage at port 22 will be V '=j.707V (3) Now, if voltages V and V, are applied simultaneously to ports 18 and 24, respectively, the output voltages V at port 20 and V at port 22, will be the sum of the input voltages, namely,
It is seen, therefore, that the magnitudes of the output voltages at ports 20 and 2 2 are equal, and depend only on the sum of the squares of the input voltages, or stated another way, the magnitude of the output voltages is dependent only on the total power into the hybrid. As long as the total input power remains constant, the amplitude level at the output ports will remain constant.
The phase of the output voltages at ports 20 and 22, however, is dependent on the relative amplitude of the input voltages, as shown by Equations 4 and 5. Dividing Equations 4 and 5, we obtain which is the relative phase angle of the output signals at ports 20 and 22 and is seen to be directly related to the input voltages.
Referring now to FIG. 3 which is a schematic diagram of a power divider of the type described by Ragan, it will be shown that the power divider is capable of supplying to the hybrid a pair of voltages of variable magnitude but whose relative phase remains constant at 90.
It is well known, as exemplified by page 556 of the fourth edition of the ITT Handbook, Reference Data for Radio Engineers, that the voltages at terminals 26, 28 and 30 of the power divider are related by V V J (8) where Yb w cot a 1 Q-ld-j tan A where l is the distance to the short circuit on stub 34, as shown. From Equations 7 and 8, it follows that nan and from Equations 9, 10 and 11 Y /Y can be expressed as which clearly indicates that the relative phase angle of the signals appearing at output ports 28 and 30 remains constant at 90.
The input admittance Y, at port 26 can be written as 21rl 1-1 cot 1+tan which indicates that the input admittance Y,, is always matched to the characteristic admittance of the line, and
is independent of stub length l.
When the power divider output ports 28 and 30 are connected to the input ports 18 and 24 of the hybrid, V /V is the same as V /V and Equation 6 can be written XL Vs'r 6 (1 from which it is apparent that the relative phase of the signal at the hybrid output ports 20 and 22 varies linearly with the length l of the short circuited stubs 32 and 34 of the power divider. Thus it is evident that the relative phase angle of the signals at ports 20 and 22 of the hybrid can be varied by a single control arranged to alter the length l of stubs 32 and 34.
FIG. 4 illustrates another embodiment of the invention wherein a coaxial line power divider 60 of the type shown in the Ragan patent is connected by equal length coaxial cables 62 and 64 to a hybrid 66 of the type known in the art as a rat race. A voltage applied to the input port 76 of the divider is divided between output ports 78 and 80 in accordance with the position of the short circuits in stubs 82 and 84, as adjusted by ganged arm 86, and applied through the coaxial cables to input ports 88 and 94 of the hybrid. As has previously been discussed, the variable amplitude voltages applied to'the hybrid input port-s are in phase quadrature thereby causing equal amplitude output voltages to appear at ports 92 and 90 whose relative phase is directly related to the ratio of the voltages at ports 78 and 80 of the power divider.
FIGS. 5 and 6, respectively, show the measured amplitude and phase characteristics of a power divider of type shown in FIG. 4. A 2400 me. signal was applied to terminal 76 of the power divider and the amplitude and phase of the output signals at terminals 78 and 80 were measured using standard slotted line techniques. FIG. 5 shows that the ratio V V varies according to the function tan T as has been expressed by Equation 12, while FIG. 6 shows the phase angle between the output signals is substantially constant over a relatively large range of short positions.
The slight departure of the amplitude characteristic of FIG. 5 from a true tangent curve, and the gradual, rather than instantaneous change in phase at the quarter wave points of the characteristic of FIG. 6 are probably due to leakage past the less than ideal short circuits between the conductors of the power divider, and the interaction between the output voltages in the slotted line measuring equipment.
The linear phase variation with stub position I, predicted by Equation 14, is depicted by the dotted line curve in FIG. 7. The solid line curve indicates the values obtained when a 2400 me. signal was applied to terminal 76 and the relative phase angle of the output signals at ports 92 and 94 measured as the stub position I was varied. The slight non-linearity of the measured curve is due to the causes which have already been noted.
FIG. 8 illustrates a further embodiment of the invention wherein the power divider and hybrid are combined in a compact integral unit. The hybrid, again of the stripline rat race type, comprises a ring-shaped strip conductor sandwiched between dielectric plates 102 and 104 with metal plates 106 and 108 forming the ground planes. The output terminals 110 and 112 extend radially outward and are circumferentially spaced by an integral number of half wavelengths at the frequency of operation. In the disclosed configuration, the hybrid is not provided with input terminals in the usual sense, the input signals instead being coupled directly to the ring at points 114 and 116 respectively located the same integral number of quarter wavelengths counterclockwise from output con-.
nections 110 and 112, with point -114 being midway between terminals 110 and 112.
The power divider is partially contained in the stripline structure, the input terminal thereof being coupled to an L-shaped conductor having arms 120a and 12% which extend radially outward to points 114 and 116 at which they are joined with ring-shaped conductor 100. A pair of coaxial line stubs 122 and 124 extend perpendicularly upward from the plane of the stri-pline structure, with their inner conductors joined to ring 100 and points 114 and 116 and their outer conductors electrically connected to ground plane 106. The stubs are provided with movable shorting disc-s 126 and 128 which are ganged for movement in unison by a pair of rods 130 and 132 cross-connected by a suitable handle 134. The rods may be formed of a dielectric material, as shown, in the interests of reducing weight and wear, or they may be formed of conducting material, if desired. It will be seen that the output terminals of the power divider are also at points 114 and 116, and thus coincident with the input terminals of the hybrid. A signal applied to input terminal 118 produces equal amplitude output signals at terminals 110 and 112 the relative phase of which may be varied by adjustment of the position of the shorting discs 126 and 128.
While there has been described what are now believed to be preferred embodiments of the invention, many modifications and changes can be made without departing from the spirit and scope of the invention. For example, a variety of power dividers and hybrid junctions can be used, such as waveguide, coaxial line, stripline, lumped circuit or a combination thereof; Also, the two devices can be integrated in many way-s which will occur to those skilled in the art. Further, a hybrid of the type' described requiring input signals with a constant 90 phase shift is illustrative only, as other types of hybrids having different input requirements can be used to produce the desired re sult. For example, a branched line coupler, of the type described on page 866 of volume II of the Massachusetts Institute of Technology Radiation Laboratory Series, can be used if constant in-phase signals, which are required to energize this hybrid, are provided. The in-phase signals could be provided by adding a quarter wavelength transmission line to one of the arms of the power divider. Accordingly, it is not intended to limit the scope of the present invention by what has been particularly described except as indicated in the appended claims.
What is claimed is:
1. Microwave phase shifting apparatus comprising the combination of a power divider having two stubs with slidable short circuits thereon for varying the relative power'between a pair of outputs while maintaining a constant relative quadrature phase, and a hybrid junction having two input terminals and two output terminals, said input terminals connected to said power divider outputs whereby a pair of equal amplitude signals are produced at the output terminals of said hybrid junction whose relative phase is dependent on the position of said slidable short circuits.
2. Microwave apparatus comprising ring-shaped transmission line having two output terminals connected thereto and an integral number of half wavelengths apart, two impedance changing means connected to said ring shaped line, said impedance changing means being separated by an integral number of half wavelengths with one of them located midway between said output terminals, and an input terminal connected to said ring-shaped line to points of connection common with said impedance changing means, said input terminal being connected to said ringshaped line by transmission lines each an odd number of quarter wavelengths long.
3. Microwave apparatus comprising a ring-shaped conductor having two output terminals connected thereto an integral number of half wavelengths apart, two coaxial lines connected to said ring conductor, said coaxial lines being separated by an integral number of half wavelengths with one of them located midway between said output terminals, a slidable short circuiting contact on each of said coaxial lines, said contacts arranged an integral number of quarter wavelengths apart, means for moving said contacts in unison such that the quarter wavelength spacing between said contacts is maintained, and an input terminal connected by quarter wavelength conductor to said ring-shaped conductor at points of connection common with said coaxial lines.
4. Microwave apparatus comprising a ring-shaped conductor having two output terminals connected thereto an integral number of half wavelengths apart, two shortcircuited stubs connected to said ring-shaped conductor, said stubs being spaced apart an integral number of half wavelengths with one of them located midway between said output terminals, means for altering the length of said stubs while maintaining a quarter wavelength spacing between said short circuits, and an input terminal connected by quarter wavelength conductors to said ringshaped conductor at the same points of connection as said stubs.
5. Microwave phase shifting apparatus comprising a ring-shaped conductor having four terminals connected thereto at points spaced from each other by an integral number of quarter wavelengths, two coaxial lines each having a slidable short circuit thereon, said coaxial lines being connected to an alternate two of said terminals, an input terminal also connected to said alternate two terminals by quarter wavelength conductors, and means for slidably adjusting said short circuits while maintaining a quarter wavelength spacing between said short circuits, whereby a signal applied to said input terminal will cause equal amplitude signals to appear at the other two of said terminals whose phase is variable in response to adjustment of the positions of said slidable short circuits.
6. Microwave phase shifting apparatus comprising a ring-shaped conductor supported between and electrically insulated from two parallel conducting plates, two output terminals connected to said ring conductor at points separated by an integral number of half wavelengths, two coaxial lines having inner and outer conductors, the inner conductors of said lines being connected to said ring conductor and the outer conductors thereof being connected to one of said conducting plates, the points of said coaxial lines to said ring-shaped conductor being spaced apart an integral number of half wavelengths with one of them located midway between said output terminals, a slidable short-circuiting contact on each said coaxial lines spaced from each other an odd number of quarter wavelengths, means for moving said contacts in unison while maintaining said quarter wavelength spacing, and an input terminal connected to said coaxial lines by quarter wavelength conductors supported in the plane of said ring-shaped conductor, wherein a change in the position of said slidable contacts will cause a change in the relative phase between the signals appearing at said output terminals.
7. A microwave phase shifter operative to produce a pair of signals having equal amplitude and variable rela tive phase said phase shifter comprising, means for producing a pair signals of variable relative amplitude and constant relative quadrature phase, and hybrid means directly connected to said first mentioned means for producing in response to said pair of signals a pair of output signals of equal amplitude and whose relative phase is dependent on the relative amplitude of said pair of quadrature phased signals.
8. Microwave phase shifting apparatus comprising the combination of a power divider having an input terminal, two output terminals, and means for varying in response to a signal applied to said input terminal the relative amplitude of signals appearing at said output terminals while maintaining the relative phase between said signals in quadrature, and a hybrid junction having two input 7 terminals and two output terminals, said input terminals connected to said power divider output terminals whereby a pair of equal amplitude signals are produced at the output terminals of said hybrid junction whose relative phase is dependent on the relative amplitude of the quadrature phased signals from said power divider.
References Cited by the Examiner UNITED STATES PATENTS Fox 33311 Tillotson 333--9 Grieg et a1 33311 Pan 333-9 Wheeler 333--7 Petrich 333-11 Marcatili 3339 Budenbom 3339 10 HERMAN KARL SAALBACH, Primary Examiner.
C. BARAFF, Assistant Examiner.