IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, HairPin-Line VOL. MTT-20, and Hybrid NO. 11, NOVEMBER Abstract—A new class hybrid hairpin-line/half-wave ported. This class and TEM printed-circuit is generally into its input filter realizations output filters, is particularly not two types. and microwave first to yield at their FRANKEL is have I re- ~[ been INPUT OUTPUT by having ends. impedance SIDNEY of the filt er filters A) is characterized practical Filters for microstrip grounding Half-Wave and filters, Hairpin-line (Type AND hairpin-line suited because required. The well limes open-circuited has been found CRISTAL parallel-coupled-line of filters resonators divided of G. 719 HairF)in-Line/ Parallel-Coupled-Line EDWARD 1972 The levels Type (a) A for narrow + to approximately 25-percent bandwidths. The second (Type B) is char. acterized by having its input and output lines short-circuited at their ends. However, filter are not design because equations mental data of space presented in this for Type for several widths are given. circuit (MIC) stripline details Theoretical A bandpass Experimental filters limitations, paper. filters filters results of the Type background are presented. of 5- and B and INPUT Experi- 20-percent band- for two microwave-integrated- Fig. of USE stripline grated-circuit T tems methods costs, ticularly and systems ground, since most filter filter filters and unavailable. present The an filters narrow data for The the the above image reported [1]. for to is awkward A. (b) Type B. of the for filters present theory filter for 3) to 1) to and hybrid circuits have for at the hairpin-line/ constant been several for Type y for the and filters These circuits negligible (i.e., of are used and neighbors based difficult a 2(a) on the the sparse assumption tlhat neighbors is assumption). geometries than beyond capacitance-matrix using be the the differs usual one nearest assunnp- Physically, terms of’ the basic definitions of the coupling parameters. case of the admittance (capacitance) parameters, the can the respec- assumption to satisfy, difference by (b), tion). In the sche- Equivalent derived nearest this coupling exact reported. shown and inductance-matrix capacitive (i.e., are been Fig. arrays, is more negligible 1 have microwave-filter coupled-line been respectively. in beyond a sparse commonly from, of Fig. were How- neither have filters (b), presented coupling parallel. and line, [2]. filters, equations B hairpin-line 1 (a) are inductive For Manuscript received November 8, 1971; revised June 8, 1972. This work was conducted at the Stanford Research Institute, Menlo Park, Calif. 94025, and supported principally by the U. S. Army Electronics Command Laboratories under Contract DAAB07-70-C0044. The revised paper was financially supported by the National Research Council of Canada under Grant A8242. E. G. Cristal was with the Stanford Research Institute, Menlo Park, Calif. 94025. He is now with the Department of Electrical Engineering and the Communications Research Laboratory, MclMaster University, Hamilton, Ont., Canada. S. Frankel is at P.O. Box 126, Menlo Park, Calif. 94025. A and circuits A hairpin 6 Conference hairpin-line design y in Fig. authors the Type Region finite-length matically tively. previously periodical for including IEEE approximate The experimental propagation line lines, discussed nor filters. hairpin terminated ever, of very 2) to present present and are . been hairpin-line bandwidths Equivalent circuits for hairpin-line filters. C; represents the 2. open-circuited transmission line of chara~ter@tic impedance C,. Li represents the short-circuited transmission hne of characteristic imped mce L,. UE represents the umt element of character stic impedance Z~,i+l. (a) Equivalent circuit for hairpin-line filter of Fig. 1 la). (b) Equivalent circuit for hairpin-line filter of Fig. 1(b) to date, have paper 20 to 25 percent; and (b) Fig. Hairpin-line although, these design impedance Equivalent pre- parallel-coupled- hairpin-line periodic C would connections condition. parallel-coupled-line infinite (a) Type ,N:T)l,fm...+jlliuTuT is par- transmission-line condition, purposes equations; several or MI size, Circuits half-wave equations to approximately half-wave lbl IC circuits. connections above is satisfactory design filters. (a) to numerous the approximate that filter the the design respect requiring of such available, also satisfy theory not sys- manufacturing with in stripline Among microwave other integrated realization satisfies to reproducibility. hybrid geometries cases. designs line usually in in advantages constructed utilize Hairpin-line ‘N;I!!tdmT”’~ ”’pu’ microwave-inte- designs preferred of and useful ferably in often because weight, and/or (N!I I C) is 1. are discussed. 1. INTRODUCTION HE OUTPUT (b) understood in IEEE TRANSACTIONS ON MICROWAVE 720 lr4PuT— ‘“’”’~ 2 while . six . Three . . . 3. filter of Fig. half-wave 4(b) consists NOVEMBER of one 1972 hairpin and resonators. . . Fig. the THEORY AND TECHNIQUES, . of the design 1701ding procedure forobtainillg ahairpiIl-lille from a half-wave parallel-coupled-line filter. filter lows. line theory 1) In the limiting case filters), the go from [5]. all OUTPUT INPUT ~ manner. 3) stituting hairpin and be individually may The the half-wave between resonators paralleland pairs may previ- designer hairpin-line/half- all a straightforward coupling as fol- those allows hybrid to in with theory to are parallel-coupled- are identical hairpin-line approximate herein (half-wave 2) The designs of the presented parallel-coupled-line coupled-line (a) equations published wave [ — advantages and ously to principal equations be adjusted of chosen at simple lines con- arbitrarily any point in the design. OUTPUT In the — (b) Fig.4. Examples of hybrid parallel-coupled-line hairpin-line/half-wave filters. nearest tween neighbors a conductor act as partial the next-nearest and between impedance-parameter conductors netic (inductive) only field electric slightly lines to case, effect spread the out shields neighbor. over the be- In the “floating” tendency of the coupled entire mag- line reason for in the filters. since circuits the basis mental results. sented that both trix compare folding pair line the of resonator The first hairpin, giving hybrid allel-coupled-line filter sired, half-wave second second hairpin and continued Clearly, possible. tween as a large It has turns accounted for same illustrates consists of by two one the having the hybrid and all into The filter hairpin a linear cor- half-wave for cp will given experimental trial and Type M I C. in Section are a may wishes. results A filters Design con- procedures II 1. In Section IV a stated. coupling must Fig. be filters were first 2(a) very graph and RESULTS results closer VSIVll w = 0.05 and in coupling computed picted 5 for using by the solid used, and tions of Cristal 4(a) and 2(a) and to the for method [3] sponses based on line for one that the The computed responses fractional are of The value would filters Also, the by more for response 2(a) of cp. This be obtained the for design halfequa- of Fig. transformation cp = ~. accurate is de- response circuit graph are resonator of Fig. using of 1.355, hairpin equivalent the of theoretical circuit any hairpin- bandwidth ripple values identical the give a four-resonator equivalent obtained are by [3]. typical passband three [5]. accurate derived below. parallel-coupled-line that a more should in decibels). the these circuit on a sparse-capacitance- A few theoretical Fig. using of equivalent using a nominal (cp value cirhaving designed responses circuit therefore responses having of filters were the is based discussed of validity equivalent of Sat~Cristal to experiment. and filter, using recalculated and range and I I 1. The equivalent circuit assumption, the a number method equivalent is identical 4(a) then transformation The [2], Section complex) wave resonators, and calculated matrix Iine check equations 5 to 20 percent in than of Fig. 2(a) of from same the be be- EXPERIMENT.4L design procedures shown is AND theoretically in Fig. presented if de- greater may four a giving process cases results. pairs correspond- definition and conclusions to given latter the par- process couplings herein filters. the line the in (and of cp = ~ words, for stripline approximate of Fig. by Next, order (but realizations folding in a extent designer that performance half-wave The physical However, presented electrical as the half-wave be folded, filter. determined in designs equations basic hybrid times 24 dB. from be obtained right. between into discussed THEORETICAL bandwidths ma- judge In cuit based is folded the “coupling” A value In other This sense Theory of the pre- 3 illustrates may of hybrid introduced approximately design been on line a new many are hairpin-line/half-wave shown number on experi- to what resonator of spacing) theoretical are and of resonators. III. II, equations degree the in decibels qualitative mathematical and in both II. A. approach, parallel-coupled Fig. structed a degenerated in Section Section and unsatisfactory. may filters. half-wave the and has A precise presented summary responses becomes filters resonators process. the point B are hairpin in resonators. ing to very sparse-capacitance method hairpin-line open-circuited (b) closeness hairpin to no coupling. capaci- and may relative responds In re- be judged examples reader at what design Conceptually, the the equations, coupling likelihood either filter and judge constituting Ultimately, theoretical computed viewpoint approximate in several so that any must between sparse-inductance theoretical be necessary Nevertheless, assumptions, preclude initially design the constituting used consequently lat- A and leads procedures. assumption of comparisons Type of negligible that are of either the that neighbors design approximations than the assumption practical practicality for the nearest equivalent the the The rather simplification circuits beyond achieving former enormous equivalent coupling complex the is the hairpin-line tive on making assumption sults of to be given The ter pairs and to denote is resonator. array. discussions cp is used parameter order the following parameter Theoretical equivalent recircuit CRISTAL AND FRANI03L : MICROWAVE 711 ~lLTE1?S 40 -–—- -XT I— ep.m \ dB \ F‘., \\ C-Z;p:: : \ \ \ \,\ \/l ; ,,,, +;‘r: b’ ,30}>’ ---+ ,\l’ “’&- gzo, .__:!,(>, ‘; ~ --* ; ‘$ 10 -——- —-- j \\” J&.— - ~ ‘,\ ‘! I ;:- ,\i ~-. ~ , .-m ,,+...J. .- ,_. ~.LL!L .1. 1 J -- 89 88 o- 90 __–L~v *- –J 84 85 8s O-DEGREES Fig. for cp = 8 and curate 12 dB curves, analysis a function predicts remains out for that coupling the nearly stripline for practice, so of practical that decibel curve. Fig. the effects of the diminished cases. Figs. 5 and bandwidth for of third curve curve will 1.355, of ally N, possible function done cp But, later.) again 8-OEGREES tighter than cp value. to plot the 8, which of VSWR 12 and the Computed VSWR responses using approximate exact equivalent circuits (N =4, w =0.15). de- passband is also VSWR in the the the co dB. shown. more (A This accurate from is nearly the equi- was was value found universal computed and to for This 0.01- a the and it contraction curve. was be virtu- bandwidth Consequently, bandwidth the equiva- however, design resonators. manner, accurate nominal nominal relative above more Surprisingly, contraction of filter narrow- having contraction using of the for 7. bandwidth. less batidwidth Fig. reflect the filters Again, examined of cp in a single in for calculated A” the diminished cases the number values bandwidth was independent the curves. theoretical as “Curve calculated circuit percefitage and a the of the bandwidth function w = 0.15, be discussed value. lent of denoted over infinite- merely results hairpin-line nominal all typical 7 presents reveals In be approxi- the selectivity Fig. analysis ripple In usually lie bandwidths ‘EI!III”H=E1 Thus case. would curves 4 resonator bandwidths VSWR’S is 8-dB a worst would Computed selectivity responses using approximate and exact equivalent circuits (N=4, w = 0.05). be pointed cp = 12 and in the ac- Fig. filters. responses the 6 represent 89 VSWR realization. corresponding differences coupled sign the the the geometries, responses between 6 presents cases 10 to 20 dB typical in the range k ~ 88 and more that It should is essentially of from the as cp decreases planar limit mately As expected, all cp = 8 dB cp values selected, in M IC long-dash that larger equiripple. and the the 6. Fig, contraction becomes However, is near curve by Note a bandwidth which coupling). response depicted respectively. of cp, (tighter are “. O–DEGREES 5. Computed VSWR responses using approximate and exact equivalent circuits (N= 4, w =0.05). short-dash -.. 07 \“ is as a has been and O.1O- Fig. 8. Relative bandwidth contraction versus coupling parameter cp. and 722 IEEE TRANSACTIONS ON MICROWAVE TABLE SUMMARY OF EXPERIMENTAL Filter : 5 ripple cases, filters analyze lent for The N= from the may a hairpin-line circuit bandwidth to by fractional a l—the substituting in Section A in Fig. by simplified value filter w first the result into the of the latter technique design - to- ! : nominal z ; . . nominal 8, and -30- : then equations -20- 2 8, and the Fig. -40- given -50 13625 7. In this bandwidth case, filter is illustrated in order with 0.15 used in the design VSWR A) a 0.15 a design in frac- value Fig. to III. be 9. Measured for trial of 0 Section is seen I 45 150 FREQuENcY = 0.168 equations (Curve 140 by Curve to achieve cp = 12 dB, 1 – 0.112 resulting e,= 9.7 e,= 9.7 in in in in 10 pin in 10 pin than a specified dividing from b =0.250 b =0.250 b =0.250 h= O.025 lz=O.025 0 1) to Fig. have Tellite, .,=2.32 Tellite, c,= 2.32 Rexohte, e,= 2.54 99.6-percent alumina, 99.6-percent alumina, all equiva- the from to value WI= was the less ways: multiplying ordinate ordinate were in two In Ground Plane Spacing or Substrate Thickness and Roughness Dielectric III. A result tional curve using hairpin-line bandwidth by 11 resonators. be utilized by first l—the design value 2(a) 0.1 0.1 7 plotted filter of Fig. 0.1 2 1972 SPECIFICATIONS stripline stripline stripline MIC MIC 0.1 NOVEMBER 1 FILTER Media 0.1 4 4 4 through curve Passband Rlpple (dB) Resonators 0.05 0.05 0.20 0.05 0.20 deviations 0.5 percent. 2) Type Hairpin-line Hybrid Hairpin-line Hairpin-line Hairpin-line ; dB Fractional Bandwidth THEORY AND TECHNIQUES, I 155 I I loss I I 1 1 s WAVE Mom + I The quite I5 5 GHZ attenuation and return stripline filter 1. 1 I — $“.,.. satis- factory. B. Experiment In order of the trial with cal to experimentally theory and stripline and widely differing and material mental on the A filters bandwidths. in results Filters of validity a number were The for summarized Filters: range equations, Type experimental Str@ine 1) M IC are the design specifications filters ments check filter of constructed nominal electri- several of the Table 1. Some expericom- follow. 1, 2, and 3 were I 10 con- I I 1 I ,0 1 I 30 I 1 40 1 I 50 60 FREO” ENC, — G., structed Filter Fig. in stripline, 1 was 1 (a). quency nominal were return 12 dB. loss This Using the contraction is The shown points approximately 0.044 designed data of with of Fig. between dB. The are 10-dB and could 0.035, a cp value 8, the 0.05 x (1 – 0.112) determined believed results from that the = of antici- 0.044. bandwidth the finite additional length line not be slightly A to be bandwidth ccmnections pairs wide-band hairpin-line frequency response filter 1. for between in the Fig. 10, responses, typically plane-wave by wave mode. experimental This resonators dB down there that mode hairpin-line is has been was the of the or nearly filters. filter. for more, by always However, filter 1, spurious which tuning a noticeable identified this coupling low-level excited that practice, response numerous modes additionally In increasing frequency shows resonators theory. by interior 40 at 2.8 GHz hairpin the for swept caused response in compensated wide-band shown constituting accounted However, is seen Measured of stripline at- 9. and 10. freThe Fig. 2,5 Fig. in center measured in approximately was depicted and 1.5 GHz. contraction experimentally It type spacing. is w = The are plane of the between filter bandwidth smaller. is ground bandwidth 10SS are measured respectively. pated and return attenuation bandwidths 12-dB filter design 5 percent and midband 0.25-in a hairpin-line Its tenuation with were screws. spurious as a surface- excited its in the magni- CRISTAL AND FRANKEL : MICROWAVE 0 -,0 .20 -3” % z ~ -40 -m .60 I I 0 I I [ I I ,SUR, I I ‘- N] wAVE1 I I ACE WAVE S“.,ACE MODE MODE \ -,0 --REDUCE. ,0 -m dB w,,. ADDITION OF DIELECTRIC .2, F,LLER \ & 1 1 1 -50 ti[ 1 1 , Fig, Fig. I I 723 — 1 .70 1 I FILTERS 12. 11. 1 I 3 1 1 ! 4 F,, CLIENT” --l I 1 1 5 , G 2 FRE(XJENCY hairpin-line/half-wave response Fig. parallel-coupled-line filter 13. Measured of stripline could using line be substantially hybrid inate air sult of the or 2) by gaps response between first for tions as filter filter the in Fig. 1, but 11. Fig. was of filter method at 2~0 is that by 11 gives identical the hybrid the surface-wave mode does mode was Results couple at by of the second given filter 3, whose bandwidth. while reduced data in Fig. The reduce the nating air gaps shows that was second coupling Note that method 25 dB are attempts surface-wave dielectric the path and (but spurious 10 down. dB Fig. I 1,9 1.7 return and response 1.9 2 GHZ loss for trial for stripline filter 3. of 12-dB sults or elimiFig. with 13 the for 2) the JZIC design filters, tested. 0.20 filters was the a about a dielectric reduced filler spurious and 14-dB cp value (1 – narrower bandwidth Filters: In theory and Photographs is order again these this filter was would be 0.149. smaller with the than the previous re- filters. to experimental equations 5 of Table of loss are 0.1144 for bandwidth = pws- bandwidth return 0.255) is consistent loss in the fractional The bandwidth 4 and return fractional X which the of 2.5) measured the expected measured c,= measured respectively. “theoretical,” 20-percent by The the points w = there was only — 26 dB. 3. The so that together), = 2j0, which insertion jelly, filter 0.135, at However, to about case. the clamped passband petroleum spurious by tightly 14 presents band 8 dB, the TEM to eliminate mode planes narrow between of hairpin-line interfaces. filler reason in this illustrated are for the dielectric a the Measured ground response A response the time 14. (Vaseline hairpin- spurious of 5 resonators to the between without data specifica- interrupts approximately method re- attenuation 12. The at the same 2f0. 13. These design the geometry mode, not reduces Fig. 1,s 1.5 FREQUENCY - Fig, measured in a hybrid in freq[]ency filter 3. to elim- configuration. 2 is shown — (i”, wide-band hairpin-line 1) by The the electrical constructed greatly the filler interface. parallel-coupled-line photograph this dielectric had ways: a dielectric is illustrated 2, which line/half-wave that in two parallel-coupled- using technique shown data reduced hairpin-line/half-wave geometries, 6 5 2. 304 !,4 tude 4 3 — . . . Measured wide-band frequency of hybrid strip line filter 2. Hybrid ~ with I were filters y evaluate regard to constructed are shown MI C and in Fig. lEEETRANSACTIONS 724 of the ON MICROWAVE filters. face-wave These mode cussion always strongly for when the In stripline (c, = 9.7), only only The well-known tables and Fig. 15. 15(a) MIChairpin-line and (b), that of differing even- plate was in an filters. respectively. difficulties strates. trial In might have and odd-mode placed 0,025 (a) Filter4. order been in the effective dielectric constant vicinity measured of the erately well sured VSW7R for G = 5.35 two points data. to be defined Tables of the of g~ values parameter in the pairs and cp in between mea- cp has in of detailed de- the essen- below. We that were prototype given in first de- filter Table filter, that give gi, Chebyshev, [7]. The between resonator, resonators. a values [6], coupling II. having element hairpin hairpin the of responses is the a single defined set be [5]. normalized II may hairpin-line however, in the design for prototype types to existing for given available Table hairpin-line dual equations the and are adjacent been badly geometries. procedures equations other constituting mod- Conseis mode A the allow low-pass of al’ Butterworth, Hence, is auxiliary frequency the The of match, First order Type summarized those for 4 corresponded computed only sub- are modifying cutoff resulted response filter theoretically showed alumina and of attenuation passband with the procedures by is the the not veloped N For cut- jo. hybrid equations; design because cover does design and than surface-wave design approximate parameters a metal velocities design 2j”0. response modifications present possible encountered above corn pensated The avoid velocities, This medial to 5. (b) Filter Space of the than surface-wave is topologically filter. suitable designs. velopment tial for 2(a), approximate after filter Fig. interdigital utilized of PROCEDURES circuit in mode Equations equivalent shown to the in surface-wave less the with DESIGN Hairpin-Line-Filter filter, the fre- frequency the greater be accomplished 111. (b) of cutoff length center attenuation Suppression C can A. slightly stopband diswas surface-wave M I C media considerably is degraded. the are the a wave j ~ is the on alumina frequency quently, MI the The the mode (approximately) are filters, However, filters off M I C media. 1972 to a sur- in surface-wave resonators propagates MIC mentioned corresponds at j = 2j ~, where filter. mode (a) in mode NOVEMBER to be due briefly The excited hairpin propagates determined was filters. this dielectric. the were that of stripline quency THEORY AND TECHNIQUES, line and not Mathematically, asz indicatL~j ing that the the peak VSWR less) filter so that width (0.1-dB further well the small adjustment brought 5 showed 4. the was percent, the value factor which from resonator the the same The of 1.35 The vicinity of qualitative practice, would a have attenuation the and passband behavior for as that of the is chosen, results discrepancy for between M I C filters wide-band 1 An alternate method d:scriherl by Podell [4]. spurious would the was theory have and the appearance responses been in — ~L~iLjj ing nator, A the of sig- the forj = i+ 1 (1) ‘ are defined ;nit;al resonators method and different in (2). synthesized all a simple arbitrary having the is presented values Once design same later of cp for the will cp con- Cp value. for obtain- each reso- if desired. hairpin-line prototype filter The defined experi- parameters of hairpin However, lines. A serious Lij where factor sist be obtained 8. In couplings 10 loglo bandVSWR corresponded would Fig. cp=— (1 .36 or pursued. that specification. in However, specifications not 4.5 to tuned. frequencies was in the up filter within with responses filter optimally tuning contraction this VSWR not between ripple) using mental was measured reasonably nificant was assumed array in terms coupling filter will of based consist 2N+2 of its on of coupled inductance conditions, can an 2N+ N-order low-pass 2 parallel-coupled lines matrix be written is completely which, for the as stopband to use ‘(wiggly lines” as 1 The equation for cp was originally cp = — 20 loglo (Lij/v’L&y), which is more logical than (1). However, the computer software was mistaklngly written using (1), and all of the experimental and most of the theoretical data were compiled before the error was noticed. CRISTAL AND FRANKEL: MICROWAVE FILTERS TABLE AUXILIARY EQUATIONS iV order of low-pass low-pass prototype filter w’ low-pass prototype radian w prototype fractional cutoff band-edge ‘ 1–; EQUATIONS and i=~,2. LP.~l,=+l = LPP 2 frequencies p=z;–l of the microwave I i=l,2, the bandcenter; . . ..(N+l) fi=zi ; LP,P+L = kLPP \ i=l,2, . . ..N .— tan Ox; 1 — ti@l’gi_lgi G,= N LU = AU(l) 1 =– ... 1 LSI{bZ,SNqt = A1l(N+l) the lower and upper () 7 FILTERS P=2; + A1l@+z) 2(1 – k) tilter; f~ is 111 FOR HAIRPIN-LINE L=;, = . . . . N + 1); frequency; f I and f~ are filter O,=; (i = O, 1,2, of the microwave % DESIGN AzJiJ values where – DEFINITIONS filter; element ~=2f2–f1_f2–f, f2+j, TABLE 11 AND PARAMETER g; bandwidth 725 1 —, G, = fori=land N+l; fori=2,3, . . ..N. ‘ the convenient form c~j/c by the equation (4) @l’V’gi-l&Ti cp hairpin ~ = llyloP/101 k arbitrary which coupling where in decibels; e, positive controls dimensionless the immittance Fori=land parameter level in the filter N+l G, effective 1 . . ..N E @Er; EO pe rmittivity From A M(~) = hGi sin 01 sions the to ZAV-l the L = of propagation L,, l~j/(Z~~–l) 1,! selfith 2A In source terms Lij the o normalized malized medium; inductance per unit of the conductors; [ I o L,a L33 LM O L34 JZ44 L45 by inductance capacitance equations Table matrix matrix given II 1. Having from may Table be in Table obtained I I 1, the computed II, the nor- by the will = [L]-’ (3) at C~j/ (8-’ self;th YA lsast and jth capacitance per unit length of the vari- case here, the C . ..0 sparse ordinarily the that may have way begin to same cp of signifi- in compa may rin e- also increase. matrix is approxi- configurations checking of estimating deviate be is increased, will filter a and the when appreciably the from behavior. the equations of hairpin-line transformation and frequencies, is one expected consisting the capacitance planar-array previously, are bandwidth C matrix at microwave theoretically noted filter represent diagonal be small fiIters, of the the the even the entries generally as the terms responses may only narrow-band for used ipal (It subdiagonal will terms it is known value. However, that in Table resonators, allows we III give all of which present modification next of a the l/zA. ~ These The for Since simple conductors; dimen- from - However, lower However, designs Y~) ; or mutual physical as is the be dense. entries mately As C~j and t Other the nonprincipal where c~j generally system.) upper cance. filter [c] the . nonprinc formula med- . glected. auxiliary given the (,2) sen, impedance. c~i/q be determined . ..0 Lga nonphysical length 0 Lg2 the jth of the are the ; or mutual and in for may is sparse, L12 matrix velocity v lines matrix 1 where of charts. LIIL]2 normalized constant space. values coupled desig;n If matrix dielectric of free numerical of the ous = k[Gi2 + ~] inductance relative ium; = /JT ~ll(o A,,@J = <z less than interior. Fori=2,3, ‘4,,@) = 1 A,,(i) usually normalized parameters Cij may be converted into All other will be referred to as principal terms or principal entries will be referred to as nonm-inciBal. –, -–_,. entries. 726 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, NOVEMBER . .. 1972 0 0 II (a) . (b) . 3 0 L2N*2 Fig. 16. Matrix transformation filter responses that leaves invariant. TABLE NORMALIZED L-VALUES 2..2 (c) Fig. hairpin-line 17. Progressive steps in transforming a parallel-coupled-line filter into an interdigital filter. (a) Parallel-coupled line filter. (b) Intermediate wicket form for interdigital filter. (c) Final form for interdigital filter. IV FOR EXAMPLE HYBRID FILTER OF FIG. 12 ..0 0 Normalized L-Matrix ; : 5 6 7 8 1: 1.40641 1.40641 0.08874 L(I, I) 4 5 6 7 8 1.00000 1.31767 1.31767 1.35828 1.35828 1.35828 1.35828 1.31767 between hybrid filters two (a) ..,2 c1 , -C,2 222’% o L(I, 1+1) 0 0 Coupled-Line The under discussion forming Fig. ant, provided that the ROW 2N , a hairpin, and by able redundancy numerical parallel-coupled- A hairpin-line that Parallel- filters their of the responses are type invari- matrix remains constant. In %,,. ., filter Aii to fori=2,4,6, addition, physical ..0, (2N) realizability (5) The that and visualized, all realizable Aii inductance hairpin-line (5), whose effect is depicted .Lij values suitable satisfies rows appropriate Thus and wicket (b) Wicket resonators. even-numbered the (5). interdigital matrix. in determining hairpin a computer, is easily the added ~atisfies the transformation geometry that flexibility for on physically expression i+l, -% z and values to equivalent Lii — 2L<,i+1+L~+1, .331C:3 18. Capacitance matrices for equivalent filters. (a) Interdigital filter capacitance filter capacitance matrix, Note reveals !T (b) 0.00000 0.30031 Filters for 0 “. o— Hairpin-Line/Half-Wave theory %3’33 0 1 be designed. detailed I . -C23 1“ lines of Hybrid ‘22”22 %3 programmed B. Design 1’ [: hairpin-line/half-wave may CN+I, N., 0.30031 1.31767 1.00000 coupling “.. ‘1 L-Matrix I ’33 1 0.30031 0.08874 0.08303 0.08570 0.06571 0.08570 0.08303 1 “23 10 — 1.00000 1; Iine 1+1) 1.00000 1.40641 1.40641 1.35828 1.35828 1.35828 1.35828 Normalized which I -c, L(I, L (I, I) I have values not the in is the in Fig. 16. increment a way violating matrices easily on that (6) give corresponding filters. transformation re- Aii — Li,i+ly = i=2,4, . . ..(2N) (7’) quires Lii Li, The mutual pin – Li,i_l parameters inductance resonators. – in Liri~l (5) between Thus for all L >0, correspond line pairs it is evident that to the constituting there self- (6) and hair- is consider- is particularly no useful, capacitive) constituting transforms coupled-line coupling a hairpin the hairpin resonator. for in this exists case no inductive between lines resonator. resonator Repeated hto (and originally 1% other words, (7) a half-wave parallel- application of (7) per- CRISTAL AND FRANKEL : MICROWAVE M L11 * I LIZ LIZ L22 ’23 ’23 L33 0 o * the design of serve as an filter in Fig. IV. physical The would By L34 ~’L12 2 N L22 ‘2L23 o ‘2L23 2 N L33 ● o . . . . NL34 Fig. 19. Example of inductance hairpin-line/half-wave The example L-matrix for a hairpin-resonator is given in the upper of the filter half filter like transformation par- following original realization given This in leads A,, the = – for in shown ing the tween to any the responses identical. matrix at this (8) lower half Fig. At of Table IV configuration are 12. suitable of Fig. The use Exact of the preceding straightforward tables for Tables way the interdigital to below some digital tional may the needed The details the intermediate cally nected, The and reader is referred as the have point it Fig. at the process physical filter duals. 17(c) can and It form that known can proved that in Fig. optimum responses [8]. that in Fig. can be the in Fig. The back filter to the was are wicket The electrical in form applied the capacitance 17(c). (N+ 18(a) expanded matrix in A second of does not permit, Fig. 1)X (N+ 1) corresponding into the capacitance to an (2N+2) matrix (with formally filter the with transformations the particufilter inverted it transformation very sirlilar to obtain cle- the C- realized. [10], The tion of level changing must this at to Fig. be performed transfer &.@er;or 19. Note allowed i and is to that the rows and scale the The sections of rows the transforma- of the filter is transformation Paired and columns, trarls- columns fori=2,4, 1, is filter, capacitance-matrix pairs i + that within response. the on paired The is a special transformations points to conventional formations. useful transformation specific its as applied in is transformation capacitance-matrix effect illustrated that congruence to The only the input exceptions and in column filter of constant-—say, matrix interdigital X (2N+2) 1 (or output) flat can be 2N+2) F’ig. are . . ..2N. be intermixed. larly usej-ul when computer are when In the (9) would of the filter be carried Both modify by out for to modify terminations, the by rowa suitable the factor and the in any transformations programmed terminal. transforming order be multiplied This transformation 16 may may share would ill. ccmgruence of rule impedances. to change impedance The tion to this output or, equivalently, given maximally but proceed. Lij Transformations inductance row–columns of Ctj are available and to by to obtain physically of by C. Fig. to achieve an interdigital Tables how the Next, is then Indwztance-Matrix these represent that performed is then in distinction folding filter maybe 17(c). [3]. interdigital L-matrix which without be con- procedure [9]. hairpin-line 17(b). are physimay given folding Chebyshev Space the they to be hairpin-line/parallel-coupled-line impedarme design. uniquely shown yield Fig. mathematically of duality filter is well 18(a) verified if principle a hairpin-line shown the be converted the into considerations been filter half- in other L replaced parallel-coupled-line 16 are any matrix be replaced so be but were capacitance evident to resonators. The form the wickets form addi- 17(a) shown this for in Fig. potential, for Consequently, 17(b), Fig. same [9] of folding of the the interdigital has since wicket filter” D. itself will real, of inter- interdigital shown ends justification on The In are are satisfy filter y (6) with is perhaps 18(b) in Fig. matrix, the to satisf a half-wave hybrid sired. of filters 18(b) not be- Furthermore, interdigital need normalization), depicted lar summarize design [6], a design filters. to result filter in of hybrid we the filt&-s. grounded yielding original based filter concerning “wicket the close exact design concisely on interdigital since to the facts parallel-coupled-line Then, the method be conceptualized wave [8] of parallel-coupled-line present filters. application filters hairpin-line/half-wave order allows and row correspond- coupling a wicket. if the wicket each latter is no a~, in Fig. point would of the there constituting parameters then Cij with which of the wicket open-circuited transformation in Of course, this ob- 18(b), intermediate 18(b) The Fig. pair The conditions. 1(a). filters. filter line of Table Fig. in a wicket coupling this that matrix will 0.08874 to the ph ysical Using . for hairpin-line represents Designs C. “ 0 realized, results ● ● o The A,8 = NL34 J be an all-hairpin-line tained. o ● letting the NL12 . 0 O**. Lll “ 0 12 with (cp = 12 dB) 0 — . hybrid illustration. shown 0 L34 structures. of 12 dB o ● o allel-coupled-line ,.. . ● . mits 727 FILTERS input (or il~z. transformasequence are an interactive or particutime- 728 IEEE TRANSACTIONS IV. SUMMARY Approximate Iine and Iine theory hybrid filters have are based pling beyond On nearest other hood the hand, rules design that hybrid that practical design is the engineer to hairpin-line/haIf-wave haIf-wave and of several equivalent yields circuit nearly over value. The showed for curve satisfactory that for the designs using The ap- hairpin-line, or a systematic using (in in design Chebyshev from the paper. of very these with filters can be con- judged narrow this A number of trial The experimental constructed good there haps due was the coplanar be practicoupled using spurious and j. it was be 2) bv lengths 5- and tested. hybrid filters be in relatively theory after accounted for. the How- contraction connecting for stripline per- line filters of a surface-wave at center mode N$O, where frequency that reduced geometry mode of and pairs resonators. demonstrated using was bandwidth line substantially a hybrid to approximate passbands is the and judged data presence surface-wave and/or finite filters constructed factor experimental give can the MIC that between a dielectric by filler N two and How- responses methods: the re- tended is an even filter. spurious interrupts input also that of the these the path output to eliminate data quencies just above it had a cutoff frequency pin resonators dielectric. The in M IC filters. the a hybrid To effect 1) by of the ports, the date, fiIters still allowing the of the the and that only was prove hairin the excited way mode of over- is to utilize surface-wave path is interrupted. be- with this parallel-coupled- satisfactory a considerable mode the always practical the output fre- of the filters. a wavelength mode presat to when hairpin-line/half-wave may of the surface-wave surface-wave such input hybrid Iine that for per- propagated corresponding surface-wave allowing passband approximately geometry the found are coming design was principal pass- stopband because that con- in the after the degraded mode the Specifically, tween theory severely the filters well However, a surface-wave reducing hairpin-line approximate were of for moderately contraction. formances thereby 1972 mode. C compared in MIC degree media, of flexibility while to the engineer. The fully authors and wish skillfully described experimental air to thank E. fabricated in this paper all and Fernandes, of the recorded who care- experimental many of the data. to approxi- is near hairpin-line were additional hairpin the integer ever, with to the constituting vealed for contraction ever, to data agreement and were in strz+line bandwidth The stripline bandwidths with bandwidth filters to lines. 20-percent band MI NOVEMBER ACKNOWLEDGMENT Consequently, are ;n nominal bandwidth Interestingly, realizing cases), the however, equations bandwidths theory interface, surface-wave experimental structed ence THEORY AND TECHNIQUES, dielectric to the method, an “exact” approximate a universal presented for designs contraction, by 25 percent. cal limit likeli- self-consistent in bandwidth bandwidth approximate mately to quite any design filters theoretical equiripple compensated the line a diminished traction to rela- procedures. way. Analysis but the parallel-coupled-line, parallel-coupled simple beyond procedures. of Aldual preclude a set equa- and leads the The cou- leads design assumption procedure permits usual coupling and circuits and negligible. the assumption latter hairpin- inductive is than circuits the of achieving theory that neighbors former equivalent proximate The capacitive equivalent for at coupling parallel-coupled- to satisfy neighbors, complicated equations assumption of negligible simple the design presented. the difficult assumption nearest been on the more tively and gaps CONCLUSIONS hairpin-line/half-wave tions though AND ON MICROWAVE REFERENCES [1] J. T. Bolljahn and G. L. Matthaei, “A study of the phase and filter properties of arrays of parallel conductors between ground planes, ” Proc. IRE, vol. 50: pp. 299-311, Mar. 1962. [2] S. Frankel, “Equivalent cu-cuits for TEM structures with periodic terminations, “ in Proc. 1971 IEEE Region 6 Conf. (Sacramento, Calif., May 11–13), Paper 5B-3, 1971. [3] R. Sato and E. G. Cristal, “Simplified analysis of coupled transmission-line networks, ” IEEE Trans. Microwave Theory Tech., vol. MTT-18, pp. 122–131, Mar, 1970. [4] A. Podell, “A high directivity microstrip coupler technique,” in ~~7’E G-MTT 1970 Int. Syw@. Dig. (May 11-14), pp. 33-36, . ..-. “New design equations for a class of microwave [5] E. G. Cristal, filters, ” IEEE Trans. Microwave Theory Tech. (Corresp.), vol. MTT-19, pp. 486-490, May 1971. [6] G. L. Matthaei, L. Young, and E. M. T. Jones, Design of Microwave Filters, ImPedance-Matching Networks, and Coupling Structures. New York: McGraw-Hil}, 1964. Network Analyszs and Synthesis. New York: [7] L. Weinberg, McGraw-Hill, 1962. [8] R. J. Wenzel and M. C. Horton, “Exact design techniques for microwave filters, ” Bendix Research Lab., Southfield, Mich., Final Rep., Contract DA28-043-AMC-00399 (E), Feb. l-Apr. 30, 1965. [9] G. L. Matthaei, “Interdigital band-pass filters, ” IEEE Trans. Microwave Theory Tech. (1962 Symposium Issue), vol. MTT-10, pp. 479491, Nov. 1962. and practical applications of capaci[10] R. J. Wenzel, “Theoretical tance matrix transformations to TEM network design, ” IEEE Trans. Microwave Theory Tech. (1966 Symposium Issue), vol. 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