US3562674A

US3562674A - Broadband microwave phase shifter utilizing stripline coupler

Info

Publication number: US3562674A
Application number: US737745A
Authority: US
Inventors: Carl W Gerst
Original assignee: Anaren Microwave Inc
Current assignee: Anaren Microwave Inc
Priority date: 1968-06-17
Filing date: 1968-06-17
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09

Abstract

A TWO-PORT MICROWAVE-SIGNAL PHASE SHIFTER UTILIZES STRIPLINE TECHNOLOGY. THE PHASE SHIFTER COMPRISES A FIRST SIGNAL CONDUCTOR PRINTED IN THE FORM OF A CLOSED LOOP ON ONE SIDE OF A DIELETRIC SHEET. PRINTED ON THE OTHER SIDE OF THE SHEET IS A SECOND SIGNAL CONDUCTOR OVERLYING THE FIRST SIGNAL CONDUCTOR AND SIMILARLY CONTOURED. HOWEVER, THE SECOND SIGNAL CONDUCTOR IS AN OPEN LOOP. THE ENDS OF THE SECOND SIGNAL CONDUCTOR ARE THE SIGNAL TERMINALS. DISPOSED AGAINST EACH OF THE SIGNAL CONDUCTORS IS A SHEET OF DIELECTRIC MATERIAL HAVING A CONDUCTIVE LAYER ON ITS FACE REMOTE FROM THE SIGNAL CONDUCTOR.

Description

C. W.*GERST Feb. 9, 1971 BROADBAND MICROWAVE PHASE SHIFTER UTILIZING STRIPLINE COUPLER Filed June 17, 1968 2 Sheets-Sheet 1 PRIOR ART 4 i coUPLERgg FIG.3

B 4 @Q TIMM m M" f /B M 1 7 B a 3 M LNIL m Y -,/J MY 6 6 T R A R. m D D.

PHASE SHIFTER 130 INVENTOR. Carl W. Germ` ATTORNEY C. W. GERST Feb. 9, 1971 BROADBAND MICROWAVE PHASE SHIFTER UTILIZING STRIPLINE COUPLER Filed June 17, 1968 2 Sheets-Sheet 2 Flag FIG.1 I

nited States Patent BROADBAND MICROWAVE PHASE SHIFTER UTILIZING STRIPLlNlE COUPLER Carl W. Gex-st, Skaneateles, NX., assignor to Anaren Microwave Incorporated, Syracuse, NX., a corporation of New York Filed June 17, 1968, Ser. No. 737,745

Int. Cl. HOIp 1/18, 5/14 U.S. Cl. S33-10 1l Claims ABSTRACT F THE DISCLOSURE This invention pertains to microwave-signal phase Shifters and more particularly to microwave-signal phase Shifters ideally suited for stripline technology.

Microwave signal processing relies heavily on the use of phase shifters and hybrids. In fact, the bulk of the signal processing is done with 90 hybrids and 180 hybrids. Usually a 90 phase shifter is used to convert a 90 hybrid to a 180 hybrid. Therefore, in reality, most microwave signal processing apparatus can be performed by 90 hybrids and 90 phase-Shifters. However, in order to get broadband operation, certain 90 hybrids and certain 90 phase-Shifters are desirable. With respect to the hybrids, the most desirable is a backward-wave transmission-line coupler because of its broad band characteristics. This device has various names in the art, i.e. 3 db coupler, quadrature coupler, coupled transmission line coupler, etc. A 90 phase-shifter with the desired dispersive characteristics is a Schiffmfan phase-1 shifter. In fact, the Schiffman phase-shifter is obtained from modifying a backward-wave transmission-line coupler.

While it is true that the backward-wave transmissionline coupler and the Schiffman phase-shifter readily lend themselves to stripline technology, a problem arises with the Schiffman phase-lifter when photo-etched or printed circuit techniques are used to realize the stripline technology. In stripline technology two signal conductors are disposed in separate parallel planes between two parallel ground planes. Now the Schiffman phase-shifter requires that the signal conductors overlie each other for a given coupled path distance, usually one-quarter of the center frequency wavelength and that they be physically short circuited together at one point. In order to maintain the bandwidth and minimize reflections the short circuiting point is extremely critical. The distance which the actual point deviates from the desired point should be an as small as possible fraction of the coupled path distance. It should be apparent that the higher the operating frequency (the shorter the operating wavelength), the more likelihood of error. In fact, for millimeter wavelenths extreme precision is required.

When printed circuit techniques are employed the signal conductors are printed or photo-etched on opposite sides of a sheet or dielectric material. While the printing operation results in siganl conductors having the desired precision for the geometry there is a serious problem concerning the short circuiting. In order that one 3,562,674 Patented Feb. 9, 197i ice of the signal conductors be connected to the other, a cut must be made through the sheet of dielectric material at the desired point and a metallic tab inserted and soldered to both signal conductors. This operation is costly and is subject to error since it requires a worker to precisely make the cut at the required point with a blade of finite thickness and often with the aid of a microscope.

It is accordingly a general object of the invention to provide an improved microwave-signal phase-shifter.

It is another object of the invention to provide an improved microwave-signal phase-shifter which accomplishes the same end result as a Schiffman phase-shifter but which does not require that the two signal conductors be physically short circuited.

It is another object of the invention to replace the Schiffman phase shifter by a stripline phase shifter employing printed circuit or photo-etched techniques wherein no mechanical cut need be made in the dielectric sheet between the signal conductors so that the construction of the phase shifter is only a printing operation.

It is a further object of the invention to satisfy the cited objects with a broadband microwave-signal phase shifter which is extremely simple, reliable and inexpensive to fabricate.

Briefly, the invention contemplates a two-part microwave signal phase-shifter utilizing a backward-wave transmissionline coupler. The coupler includes at least one ground plane element and rst and second non-intersecting conductors which are substatially parallel to the ground plane element. The ground plane element and the signal conductors are in electromagnetically cooperative relationship so that at least a portion of the microwave energy being guided by one signal conductor is coupled to the other. Each end of each signal conductor is a signal transfer port. One of the signal transfer ports of the first signal conductor is short circuited to the other signal transfer port of the first signal conductor, while one signal transfer port of the second signal conductor is adapted to receive microwave signals and the other signal transfer port of the second signal conductor is adapted to transmit the received microwave signals.

It should be noted that such a phase-shifter is usable in stripline technology by utilizing two ground plane elements and by disposing the signal conductors in different planes or in microstripline technology by utilizing one ground plane element and by disposing the signal conductors in the same plane.

Alternately, the microwave-signal phase-shifter can be viewed as comprising a first signal conductor in the form of a closed loop which is disposed in a rst plane and a second signal conductor disposed in a second plane parallel to and displaced from the second plane. The second signal conductor has a signal transfer port at each of its separated ends. In addition, the second signal conductor at least partially overlies the first signal conductor and has a similar path contour so that the signal conductors are electromagnetically coupled. Both signal conductors are displosed between a pair of parallel ground plane elements to provide a stripline configuration.

It should be noted while the invention is ideally suited to printed circuits or photo-etched realizations, it is also applicable to conventional microwave plumbing realizations.

Other objects, features and advantages of the invention will be apparent from the following detailed description of the invention when read with the accompanying drawings which show, by way of example, and not limitation the now preferred embodiment of the invention.

FIG. l shows a top view of a prior art backward-wave transmission-line coupler using stripline technology;

FIG. 2 is a sectional View taken along the line 2-2 in FIG. l;

FIG. 3 is a sectional view taken along the line 3 3 of FIG. l;

FIG. 4 is a sectional view taken along the line 4 4 of FIG. l;

FIG. 5 is a top View of a prior art Schiffman phase shifter using stripline technology;

FIG. 6 is a sectional view taken along the line 6 6 of FIG. 5;

FIG. 7 is a sectional view taken along the line 7 7 of FIG. 5;

FIG. 8 is a top view of a phase shifter in accordance with the invention utilizing stripline technology;

FIG. 9 is a sectional view taken along the line 9 9 of FIG. 8;

FIG. 10 is a sectional view taken along the line 1(9 10 of FIG. 8;

FIG. ll is a top view of the phase shifter of FIG. 8 with the top ground plane element removed; and

FIG. l2 is a bottom view of the phase shifter of FIG. 8 with the bottom ground plane element removed.

By way of background a stripline embodiment of a backwardwave transmission-line coupler is shown in FIGS. l to 4 as coupler 30. The coupler 30 is linear and reciprocal. The coupler also has a given bandpass and has a characteristic impedance at its signal transfer terminals. Normally, the microwave-signal energy being processed has frequencies within the passband of the coupler and devices connected to the coupler have input and output impedances which match the characteristic impedance of the couplers. For the sake of deniteness the

terminals

31 and 32 are considered to be the input terminals of the coupler and the

terminals

33 and 34 are considered to be the output terminals of the coupler. Because of the reciprocal nature of the coupler, the input terminals and output terminals can be interchanged.

If a microwave signal is received at the rst input terminal 31 the power or energy of the signal is split into two equal quantities. One quantity is fed to the rst output terminal 33 and the other is fed to the second output terminal 34. The signal phase of the power transmitted from output terminal 33 is advanced by 9() electrical degrees from the signal phase of the power transmitted from output terminal 34. Thus, if the microwave power received at input terminal 31 is represented by the quantity A, the

terminals

33 and 34 transmit microwave energy having voltages represented by the quantities A/\/2 and ]'A/\/2 respectively. Similarly, if a microwave signal is received at thev second input terminal 32, the power of the signal is split into two equal quantities, one half of the power is fed to each of the

output terminals

33 and 34. The signal phase of the power transmitted from output terminal 34 is advanced by 90 electrical degrees from the signal phase of the power transmitted from output terminal 33. Thus, if the microwave power received at input terminal 32 is represented by the quantity B, the

terminals

33 and 34 transmit wave power having voltages represented by the quantities iB/V2 and B/\/ 2, respectively. If microwave-signal power is simultaneously applied to input

terminals

31 and 32, signal super-position occurs because the coupler is linear. Therefore, by using the above indicated terminology, when microwave power received at input terminal 31 is represented by A and the microwave power received at input terminal 32 is represented by B, output terminal 33 transmits microwave power having a voltage represented by (-J'B) V2 and output terminal 34 transmits microwave power having a voltage represented by 4 Hence, the names 3 db coupler or 90 degree hybrid. Two points are worth repeating: (l) any power received at an input terminal is divided equally between the output terminals, and (2) the signals transmitted by the output terminals have a degree difference.

Coupler 30 comprises a central sheet of dielectric material 50. On the top surface of the sheet 50 is a first signal conductor 52 having three

continguous portions

52A, 52B and 52C angularly disposed with respect to each other. Conductor 52 is indicated by dot-dash lines in FIG. l. On the bottom surface of sheet 50 is a second signal conductor '54 having three

contiguous portions

54A, 54B and 54C, angularly disposed with respect to each other. Conductor 54 is indicated by dash lines in FIG. l,

Portions

52B and 54B are in parallel opposed relationship. T he energy transfer between the two conductors 52 and 54 occurs only via these portions. The lengths of these portions are odd-integral multiples of quarter operation wavelengths. The angular disposition of the other portions is to prevent coupling at other regions. (It should be noted that the angles are exaggerated.) It should be noted that the active region or the coupler per se is actually the

portions

52B and 54B, the remaining portions are primarily signal leads. This fact is important for the subsequent discussions of the phase Shifters. The ends of the

portions

52B and 54B are signal transfer ports which are connected to the input and output terminals. In particular, one end of portion 52B is connected via portion 52A to terminal 31; the other end of portion 52B is connected via portion 52C to terminal 34. Similarly, one end of portion 54B is connected via portion 54A to terminal 32; the other end of portion 54B is connected via portion 54C to terminal 33. Disposed on top of conductor 52 is a sheet of dielectric material 56. On the top of sheet 56 is a ground-plane element 58 in the form of a layer of conductive material. Disposed below conductor 54 is a sheet of dielectric material 60. Below sheet 60 is a ground-plane element 62 also in the form of a layer of conductive material.

Conductor 52 electromagnetically cooperates with groundplane elements 58 and 62 to provide a transmission line of the shielded-stripling type; conductor 54 electromagnetically cooperates with ground-plane elements 58 and 62 to provide a transmission line of the shielded-stripline type. Input terminal 31 is connected to one end of conductor 52; and input terminal 32 is connected to one end of conductor 54. The

output terminals

33 and 34 are coupled to the other ends of conductors 54 and 52 respectively.

The coupler 30 can be fabricated by photo-etching the conductors 52 and 54 on opposite sides of a dielectric substrate having surfaces of a conductive material using conventional printed-circuit techniques and sandwiching this substrate between two other substrates having conductive material on their outer surfaces. With such a coupler at 2:1 bandwidth is easily obtained and with moderate care an 8:1 bandwidth can be achieved.

The Schiffman phase sifter 130 shown in FIGS. 5, 6 and 7 is readily derived from the coupler 30 of FIGS. 1 to 4. In fact, it is only necessary to apply feedback between terminals `31 and 33. Actually, the feedback path shown can be minimized. Since the active region of the coupler 30 is that associated with the

opposed portions

52B and 54B, the feedback is best applied by connecting together the ends of portions "52B and 54B which are closest to

terminals

31 and 33. When this is done,

terminals

31 and 33 and

portions

52A and 54C of signal conductors 52 and 54 can be eliminated. With these facts in mind phase-shifter 130 will now be described. However, because many of the elements of phase-shifter 130 are similar to the elements of coupler 30, reference characters incremented by will be used for such similar elements and only the difference will be described.

In particular signal conductor 154 comprises

only elements

154A and 154B and signal conuctor 152 comprises

only elements

152B and 152C. The end of the portion 154B of signal conductor 154 which is remote from terminal 132 is connected by short-circuiting link 153 to the end of the portion 152B of signal conductor 152 which is remote from terminal 134. These ends are signal transfer ports. It is because of the need for shortcircuiting link 153 which must traverse the central sheet 150 that fabrication problems arise when the phase shifter 130 is realized by using photo-etching or printed circuit techniques. Again, it should be realized that the other ends of the

portions

154B and 152B are also signal transfer ports which are connected via

portions

154A and 152C to

terminals

132 and 134 respectively.

Applicant has discovered that substantially the same desirable dispersive characteristics which result in a broad passband response can be obtained if feedback is applied between signal terminals y31 and 34 of coupler 30. Again it should be recognized that the feedback path should be short and that the active portions of the coupler is associated with

portions

52B and 54B of the signal conductors 52 and 54, with the remaining portions only serving as signal conduits.

With these facts in mind the phase shifter 230 according to the invention is shown in FIGS. 8 to l2. Again elements similar to those of coupler and phase shifter 130 bear reference characters prefixed by the number 2.

In particular, coupler 230 compirses a sheet of dielectric material 250. On the top face of sheet 250, as viewed in the drawings, is printed or photo-etched signal conuctor 254 comprising

portions

254A, 254B and 254C (see FIG. ll). It should be noted that there is a gap between the ends of portion 254B. These ends are signal transfer ports. On the other face sheet 250 is printed or photo-etched a second signal

conductor comprising portions

252B and 253 connected to form a closed loop. While the geometry shown is a circle, other closed-loop geometries can equally well be employed, subject to the following criteria:

portions

252B and 254B should have relatively similar contours and lengths as required by the need for electromagnetic coupling therebetween. Now, the junction of

portions

254A and 254B can be considered as a signal transfer port with portion 254A and terminal 232 comprising a signal path for access to the signal transfer port; similarly, for the junction of

portions

254B and 254C. In addition, one junction of portion 252B and portion 253 can be considered as a signal transfer port, while the other junction can also be considered as a signal transfer port. In such a case the portion 253 is a short circuiting element between the signal transport ports associated with the coupled portion 252B. It should be noted that portion 253 lies below the gap between the ends of portion 254B. The amount of electromagnetic coupling is controlled by the thickness of sheet 250, (the thinner the sheet the tighter the coupling) by the amount of overlaying congruence between the

portions

252B and 254B (off-setting the overlie decreases the tightness of the coupling), and by the length of the gap betweenv the ends of portion 254B (and consequently the length of portion 253).

Just as with coupler 30 and phase-shifter 130, the remainder of phase-shifter 230 comprises two

other sheets

256 and 260. Each sheet is of dielectric material. Each of the sheets is fixed against one of the faces of sheet 250. The outer faces of each of

sheets

256 and 260 are covered with a layer of

conductive material

258 and 262, respectively, to provide ground plane elements.

In order to enhance the coupling between the

portions

252B and 254B of the signal conductors, the thickness and dielectric constant of the sheet 250 is less than the thickness and dielectric constant of the

sheets

256 and 260. In addition, in order to provide impedance matches between the various portions of the signal conductors their characteristic impedances are controlled by varying the width of the various portions. It should be noted that the

uncoupled portions

254A, 254C and 253 have substantially the same width which is approximately twice the Width of the coupled

portions

252B and 254B.

In operation, microwave signals can be applied between terminal 232 and ground plane element 258 and transmitted after a phase shift from terminal 233 and ground plane element 258, and vice versa.

There has thus been shown an improved phase-shifter having a dispersive characteristic lwhich is substantially identical with the Schiffman phase-shifter and consequently nearly constant phase shift over a broad band. However, the phase shifter of the invention has no crossovers between different planes and therefore is ideally suited to stripline techniques requiring only printed circuit or photo-etching operations and no mechanical intervention by a worker during fabrication.

While only one embodiment of the invention has been shown and described in detail, there will now be obvious to those skilled in the art many modifications and variations, satisfying many or all of the objects of the invention which do not depart from the spirit thereof.

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

1. A microwave-signal phase shifter comprising a first signal conductor in the form of a closed loop and disposed in a first plane, a second signal conductor having a terminal at each of the separated ends thereof and disposed in a second plane parallel to and displaced from said first plane, the second signal conductor at least partially overlying said first signal conductor and similarly contoured, said first and second signal conductors being electromagnetically coupled, a iirst ground-plane element disposed in a third plane parallel to and displaced from said first plane on the side thereof remote from said second plane, a second ground-plane element disposed in a fourth plane parallel to and displaced from said second plane on the side thereof remote from said first plane.

2. The microwave-signal phase-shifter of claim 1 wherein said second signal conductor has a given width, the portion of said first signal conductor opposite said second signal conductor has said given width, and the remaining portion of said first signal conductor has substantially twice said given width.

3. The microwave-signal phase-shifter of claim 1 wherein the spacing between said first and second planes is less than the spacing between said first and third planes.

4. The microwave-signal phase-shifter of claim 3 wherein the spacing between said second and fourth planes is equal to the spacing between said first and third planes.

5. The microwave-signal phase-shifter of claim 1 further comprising a sheet of dielectric material disposed between said first and second signal conductors.

6. The microwave-signal phase-shifter of claim 5 wherein said first and second signal conductors are printed on said sheet of dielectric material. 'd

7. The microwave-signal phase-shifter of claim 1 further comprising a first sheet of dielectric material disposed between said first signal conductor and said first ground-plane element, and a second sheet of dielectric material disposed between said second signal conductor and said second ground-plane element.

8. The microwave-signal phase-shifter of claim 7 further comprising a third sheet of dielectric material disposed between said iirst and second signal conductors.

9. The microwave-signal phase-shifter of claim 8 wherein the dielectric constant of the dielectric material of said third sheet is less than the dielectric constant of the dielectric material of said first and second sheets.

10. The microwave-signal phase-shifter of claim 9 wherein the dielectric constant of the dielectric material of said second and third sheets is equal.

References Cited UNITED STATES PATENTS 1/1960 Cohn 333-10 8/1949 Tiley 333--10X 8 8/1958 Kock 333-1OX 2/ 1959 Sferrazza S33-10 HERMAN KARL SAALBACH, Primary Examiner 5 P. L. GENSLER, Assistant Examiner U.S. C1. X.R.