US 3777284 A Abstract A coupling technique for selectively obtaining, within limits, any amplitude and phase relationship between the coupled and through ports of a stripline coupler.
Claims available in Description (OCR text may contain errors) United States Patent Schultz [1 11 3,777,284 1 Dec. 4, 1973 DIRECTIONAL PHASE-SHIFTING COUPLER [75] Inventor: Richard V. Schultz, China Lake, Calif. [73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC. [22] Filed: Mar. 27, 1972 211 App]. No.: 238,266 [52] US. Cl. 333/10, 333/34, 333/84 M [51] Int. Cl. H0lp 5/14, HOlp 3/08 [58] Field of Search 333/9, 10, 11, 84 M, [56] References Cited UNITED STATES PATENTS 3,626,332 Barbatoe 333/10 3,440,570 4/1969 Kasper 333/10 3,528,038 9/1970 Tresselt.... 333/10 3,617,952 11/1971 Beech 333/10 OTHER PUBLICATIONS Levy-General Synthesis of Asymmetric Multi-Element Coupled-Transmission-Line Directional Couplers in [BE Transactions On Microwave Theory and Techniques July, 1963; pp. 226-237. Primary Examiner-Rudolph V. Rolinec Assistant ExaminerMarvin Nussbaum Attorney-11. S. Sciascia etal. [57] ABSTRACT A coupling technique for selectively obtaining, within limits, any amplitude and phase relationship between the coupled and through ports of a stripline coupler. 5 Claims, 8 Drawing Figures PATENTEUBEE 41w 3,777,284 sum 1 0r '4 COUPLING COEFFICIENT I I I I POSITION FIIG. lc PAT-ENTEDUEB 4197s FIG 2 PATENTED 4 I973 SHEET 3 BF 4 mp OP I OOF m GE ONOO O 1- O l EISVHd VWWVD OFOO ONOO OmOO DIRECTION AL PHASE SI-HFTING COUPIZER BACKGROUND OFTH-E IN VENT ION In the field 'of stripline-couplers; prior'-'techniques have been able to obtain only a selectable output sign'al: 5 amplitude "relationship with" the phase '-'of the1coupled port signal relative to *the tht'ough' port isigna'l bein'g fixed at a multiple of 90 1'" That 'is-,- no 'pr'ior' -device-or-'= technique provided-for the arbitrary selection of bbth the amplitude and-phasearelationshipsbtween-the-cou l pled and thi'ough ports ln' thepresent:in'ventiomlthe amplitude and phase relationshipsbetween-the*coupledfi and through ports are selectable; and-.the selectedphase relationship need 'not be'=a multiple"-of 90 i by Carl-P3 Tresselt; and fifisynthesis -and Desigrr of 'Wid' Band Equal R:ipple- TEM Directionalcouplers and- Fixed-Phase Shifters an article by 'J.- P"Shelton and-'J A: Mosko appearing in i IEEE Tr'ansactionson' "Micro wave Theory "and-Techniques; Volume M lT 1 4, No. analysis: of stripline couplers,""to which gr'oup the';presbackground material; SUMMARYOF TI-IEINVENTIQNQ 10, October, 1 96'6; provide description;'=discussion;and ent invention belongs;- and arei in'corporated herein 'as A 'coupling te'chiiique'wh'erein striplinescomprising? two lines in' closeproximity are"tape'red or steppedandzf both the amplitude-and'phase relationships are' choseri" and obtained by geometrically 'arrangingthe lines in ac cordance with ithe following equationsw v the lines might be "unsymmetrical; :Thatds; th'e portionof the lines" to the left'of,for-example; their crossover sections might be longer and of different:shape-thanther portion to the rightrThe steps'for obtaining thede'sired coupling are:' 1. Taking VE(6) ye('-0) and V0(0)"= 0(0); 2. calculate 'a,, and a andb vwhere'm- -l, 2, M;' 3. compute the reflection "coeffi'cients' (F5), where'n 5. examine=the valueofli if they arenot small adjust the impedances 'Z; and 6: using afor example,- Cohnsequations, determine the "physical layout: BRIEF DESCRIPT ION OF THE DRAWINGS FIGS. l(A)," 16B and 1(0) show the plan diagrams foranonsymmetr'ic, stepped-crossover coupler (A) and a nonsyimnetric, tapered crossover coupler (B), and' the coupling-position graph of couplers (A) and (B) of the present invention; FIG.'2isaplanview'of the preferred embodiment of a phise'shifting; tapered coupler of the/present in ventioti'y F IG. -3 is a graph showing the gamma-position rela tionsh'ipi of thecoupler of FIG. 2; F IG'..-' 4'-is' a graph showing .the phase-frequency relationshipbefdre-and after adjustm'ent of the coupler of F IG. :2;"i FIGJSJis'a graph showing .the impedance-position relationshipbeforeand after'adjustmentpf the coupler of FIG. -6 is a graph showing the voltage-frequency relationshipbefdre and-after adjustment of the coupler of- FIG. 2. v DESCRIPTION 'OF PREFERRED EMBODIMENT FlG.'l "(A-)- and'(B discloses the possibly unsymmetrical t'tharacter of the present invention'in 'a crossover configuration; The'present'invention'is likewise appli- .:cable-to other types of coupling configurations, such as parallelcouplingxAs'showri in (A), eachline has three stepsto-the left of the cross 'over section and only two stepsto thearight. Likewise -inltB) the length of each line to the le'ft'of the crossover section isgre ater than to .therig'ht; Asa result; the coupling'coefficient shown in* C) is unsymmetrical. The-present invention provides means to synthesize a matched-stripline device that'will couple a fixed spec ified relative voltageiam'plitude and will allow the phase "relationshipof the coupled port-voltage relative to the through "port' voltage to be specified. Additionally, using the present "invention," the relationships will be substantially maintained'over. the frequency range of 7 operation: As an example, if port 10 of the tapered coupl'errshownin' FIG. 1 (B) is the inputport, port 16 will bewthe-'through' port and 'port '12 -willbe the coupled port, and-the1voltage1amplitude and phase relationships of the-signahatlport12 with respect to the signal at port l6rnay* be'preselected and maintained over the frequency range of -ope'ration:' Although matrix representation is an exact method for analyzing stripline couplers, the" approach becomes unmanageable and'alb intuitive feel' fo r theresults is lost.In' 'the discussion that follows all'impedances will be the-normalized-even mode impedances unless otherwise specifiedjth'e number N of different impedance levelspossible throughout the device will inherentlybe an 'eveninteger, and the electrical'length'of each and every section'of impedance will"bel such-that the totaldevice lehgth'will be N Assume a matched transmission line with N contiguous-sections-, each section having impedance Z, l and being of electrical length l Defining the and assuming small reflections at each interface, i.e., the reflection coefficient amplitude at each interface is much less than 1, the application of one volt at 0 at port FIG. 1 (B) will'result in a relative reflected voltage at coupled port 12 of approximately 0 1 r,, l e f lye- +r ep If 0 is defined by 6 2 1 the relative reflected voltage V can be written as which can be reduced to V e [C(49) +jS (6)] or 12 H M1 where tan [01(0)] S(0)/C(0) The approximate relative transmitted voltage, the voltage at port 16, is similarly described by where A is a value between 0 and 1. As a result, the relative coupled voltage amplitude at port 12 for a unit applied voltage at port 10 is and the relative phase of the coupled port signal with respect to the through port, port 16, is If the input signal is applied to port 14 the signal ap pearing at coupled port 16 becomes and the signal appearing at through port 12 becomes V12 Be where the value of B is between 0 and l, and B is approximately equal to A. Thus, the relative amplitude of the coupled voltage is the same for an input at port 10 or port 14. However, a phase difference between the coupled ports and the through ports of a in one direction yields a phase difference of rr a in the opposite direction. The designed technique of the present invention which allows the selection of the amplitude and phase relationships of the stripline coupler will now be discussed. If M is defined as equal to N/2 where N is the number of contiguous sections and 0 is defined as equal to 24') where is the electrical length of each section, the coupled port voltage can be written as where a,, 2F, m M-m ltH-m mid I b,, I Fm m The relative amplitude of the coupled port voltage is described by the quantity Defining VE andVO as: M V0= E b sin 7, In?! it the coupled port voltage becomes V e' [VE=jV0]. Any function that is periodic with period 2w can be written as a Fourier Series in the form: Periodic Even and Odd Functions If the pattern shown in the sketch immediately above is periodic with period 211', its even function is and its odd function is 370(9) =ib sin n8 resulting in 0 v b,,= f 11 (0) sin n0d0 also?! Note the similarity between the even function ye(6) and VE, and the odd function y0(0) and V0. As a result, VE and V can be considered the truncated Fourier cosine and sine series, respectively, for the associated functions ye(0) and yo(0). Thus the relative amplitude of the coupled port voltage 18 we) W and the relative coupled port voltage phase angle is 01(0) arctan (VO/VE). As a result, VE(0) V(()) cos 01(0) VO(0) V(6) sin 04(0) As indicated by the equations, the desired coupling of V(6) /a(6) where the value of V(0) is less than 1 but equal to or greater than 0 and the value of 01(0) is in the range 0 to 21:, inclusive, can be obtained by causing the even and odd functions VE(0) and VO(0) to satisfy VE(0) V(0) 005040) V0(0) V(0) sina(0) for the 0 values of interest. If VE(0) and VO(0) satisfy the equations for the 0 values of interest, a,, and b, can be calculated using the above equations. The corresponding coefficient of reflection values l", can then be computed, which values determine the impedance profile. Applying Cohns equations to the impedance profile, the physical layout of the coupler will be determined. A reasonably accurate result can be obtained using the above procedures. However, the results may be improved by forcing the condition that all I"s be small. If they are not alreay small, the impedances can be adjusted to achieve small values of F according to One method of adjusting the impedances which provides satisfactory results is to divide the impedance profile into sections such that each section includes, for example, one peak-root pair. Each root value that is below the realistic minimum of one is multiplied by the appropriate number to increase the value to one. The adjacent peak is multiplied by a similar, not necessarily same, and preferably smaller, amount. It should be noted that this approach does not attempt to force the peaks down to a value of one. The results of the above method are: the adjusted impedance profile is smoothed; no values on the curve are less than the realistic value of one; the respective reflection coefficient of l on each side of a sharply peaked maximum. And, finally, note in FIG. 6 that the relative voltage value of the adjusted design is maintained substantially constant over a wide frequency range. What is claimed is: l. A coupler having first and second substantially parallel, electrically conductive lines including at least one portion in which the lines are in close proximity to one another: comprising a a first line having first and second ports wherein said first port is the coupler input port and said second port is the through port; a second line having first and second ports wherein said first port is the coupled port; and means for preselecting the phase relationship of the output signal at said coupled port to the output signal at said through port, wherein any value chosen from the range of values 0 to 21r radians, inclusively, may be preselected as the phase relationship, and for preselecting the amplitude relationship of the output signal at said coupled port to the output signal at said through port, wherein no energy is transferred from said input port to the second port of said second line. 2. The coupler of claim 1 wherein said first and second lines are substantially in parallel planes and cross within said at least one portion in which the lines are in close proximity to one another. 3. The coupler of claim 1 wherein said first and second lines are tapered. - 4. The coupler of claim 1 wherein said first and second lines consist of a plurality of abutting sections, and adjacent sections are offset, such that a step is formed where two adjacent sections abut. 5. A coupler having first'and second substantially parallel, electrically conductive lines including at least one portion in which the lines are in close proximity to one another: comprising a first line having first and second ports wherein said first port is the coupler input port and said second port is the through port; a second line having first and second ports wherein said first port is the coupled port; and means for preselecting the phase relationship of the outputsignal at said coupled port to the output signal at said through port, wherein any value chosen from the range of values 0 to 211' radians, inclusively, may be preselected as the phase relationship, and for preselecting the amplitude relationship of the output signal at said coupled port to the output signal at said through port, wherein no energy is transferred from said input port to the second port of said second line; wherein said first line and said second line are each unsymmetrical around their mid-point within said at least one portion. 1 Patent Citations
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