European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems IMPEDANCE TRANSFORMERS AND TAPERS Lecturers: March 2010 Lluís Pradell (pradell@tsc.upc.edu) Francesc Torres (xtorres@tsc.upc.edu) Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology The quarter-Wave Transformer* (i) A quarter-wave transformer can be used to match a real impedance ZL to Z0 Zin Z0 If Z1 0 4 Z12 Z in ZL At a different frequency Z in Z 0 in Z0 ZL Z in Z1 Z L jZ1t Z1 jZ L t The matching condition at fo is Z1 Z L Z 0 and the input reflection coefficient is Z in Z 0 Z L Z0 Z in Z 0 Z L Z 0 j 2t Z L Z 0 The mismatch can be computed from: 1 in 1 *Pozar 5.5 t tg tg 4Z L Z 0 Z L Z 0 2 cos2 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems The quarter-Wave Transformer (ii) If Return Loss is constrained to yield a maximum value m , the frequency that reaches the bound can be computed from: m cos m 2 Z LZ0 1 m 2 Z L Z0 Where for a TEM transmission line 0 vp 4 2f v p f v p f0 4 2 f0 And the bound frequency is related to the design frequency as: fm 2 m f 0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems The quarter-Wave Transformer (iii) Finally, the fractional bandwdith is given by m 2 f 0 f m 4 f 2 cos1 f0 1 m 2 2 Z LZ0 Z L Z0 BW 4,5 % Z L / Z0 10 Z L / Z0 4 Z L / Z0 2 BW 18,1 % m 0,05 l f 2 f0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Multisection transformer* (i) The theory of small reflections In the case of small reflections, the reflection coefficient can be approximated taking into account the partial (transient) reflection coefficients: L 0 0 L e 2 j Z1 Z 0 Z1 Z 0 Z L Z1 L Z L Z1 0 4 0 2 That is, in the case of small reflections the permanent reflection is dominated by the two first transient terms: transmission line discontinuity 0 and load L *Pozar 5.6 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Multisection transformer (ii) The theory of small reflections can be extended to a multisection transformer Z0 0 Z1 ZN Z2 1 2 ZL N 0 1 e2 j 2 e4 j ... N e2 jN ; i Zi 1 Zi Zi 1 Zi (i 0,1,..., N ) It is assumed that the impedances ZN increase or decrease monotically Symmetric 0 N , 1 N 1, 2 N 2 ,... The reflection coefficients can be grouped in pairs (ZN may not be symmetric) e jN 0 e jN e jN 1 e j ( N 2) e j ( N 2) ... European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Multisection transformer (iii) The reflection coefficient can be represented as a Fourier series 1 2e jN 0 cos N 1 cos( N 2) ... i cos( N 2i ) ... N / 2 2 for N even 2e jN 0 cos N 1 cos( N 2) ... i cos( N 2i ) ... ( N 1) / 2 cos for N odd Finite Fourier Series: periodic function (period: ) F Any desired reflection coefficient behaviour over frequency can be L synthesized by properly choosing the coefficients i and using enough sections: • Binomial (maximally flat) response • Chebychev (equal ripple) response L 0 2 Z L Z0 Z L Z0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Binomial multisection matching transformer (i) Binomial function A(1 e 2 j ) 2 Ae N N jN cos N The constant A is computed from the transformer response at f=0: A 2 N (0) 2 N A The transformer coefficients n N ( ) A C e Z L Z0 Z L Z0 are computed from the response expansion: N! C N n !n! N n n ACnN The transformer impedances Zn are then computed, starting from n=0, as: Z n 1 N N Z L 2 Cn ln ln Zn Z0 n 0 N n 2 jn European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Binomial multisection matching transformer (ii) European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Binomial multisection matching transformer (iii) Bandwidth of the binomial transformer The maximum reflection at the band edge is given by: m 2N A cosN m 1 m arccos m 2 A 1/ N arccos m L m Z L / Z0 2 1 N BW 71 % ( N 3) The fractional bandwitdh is then: 0.05 1 1/ N f 2( f 0 f m ) 4m 4 2 2 arccos m f0 f0 2 A 1 l f 2 f0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Chebyshev multisection matching transformer Chebyshev polynomial cos A e jN TN cos m Z L / Z0 2 Tn ( x) cos(n cos1 x), for x 1 Tn ( x) cosh(n cosh1 x), for x 1 BW 102 % ( N 3) A Z L Z0 Z L Z0 m 0,05 1 1 TN cos m cosh L m N 1 cosh 1 cos m 1 1 cos m 1 1 Z L Z0 cosh cosh 1 N m Z L Z 0 l f 2 f0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Chebyshev transformer design European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Chebyshev transformer design Application: Microstrip to rectangular wave-guide transition: both source and load impedances are real. Ridge guide section Microstrip line Steped ridge guide Ridge guide: five λ/4 sections: Chebychev design Rectangular guide European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems TRANSFORMER EXAMPLE (1): ADS SIMULATION Chebyshev transformer, N = 3, |M|=0.05 (ltotal = 3/4) 50 W 57,37 W 70,71 W 87,14 W 100 W Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology TRANSFORMER EXAMPLE (2): ADS SIMULATION CHEBYSCHEV N=3 mag(S(1,1)) 0.4 0.3 0.2 BW = 102 % 0.1 m 0,05 0.0 0 2 4 6 8 10 12 14 16 18 20 microstrip loss freq, GHz 0 0.0 -0.2 dB(S(1,2)) dB(S(1,1)) -10 -20 -30 -0.4 -0.6 -40 -0.8 -50 0 2 4 6 8 10 12 freq, GHz 14 16 18 20 0 2 4 6 8 10 12 freq, GHz 14 16 18 20 Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology Tapered lines (i) Taper: transmission line with smooth (progressive) varying impedance Z(z) The transient ΔΓ for a piece Δz of transmission line is given by: Z Z Z Z Z Z In the limit, when z dz Z 2Z 0: 1 d Z z 2Z This expression can be developed taking into account the following property: d Ln f z 1 d f z dz f ( z ) dz ZL Z z Z0 0 L z Z Z Z z z z 1 1 d Ln f z d f z dz 2 f ( z) 2 dz z European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Tapered lines (ii) 1 d Ln Z z d z dz 2 dz Taking into account the theory of small reflections, the input reflection coefficient is the sum of all differential contributions, each one with its associated delay: in dz e L 2 j z 0 L Z z Taper electrical length •Exponential taper •Triangular taper •Klopfenstein taper 1 L 2 jz d Ln Z z e dz 2 0 dz Fourier Transform d Ln Z z dz Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology Exponential Taper Z z Z0e z for 0 <z < L Z 0 Z 0 Z L Z L 1 ZL ln L Z0 d Ln Z z dz 1 L 2 j z in e dz 0 2 Fourier Transform L ( L ) ln Z L / Z 0 j L sin L e 2 L (sinc function) min L L max 2 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Triangular taper Z z Z0 4 z 2 z2 Z L 1 ln L L2 Z0 Z0e 2 z2 Z ln L L2 Z0 e ZL d ln 4 z Z L ln Z 0 L2 Z0 4 ZL dz L2 ( L z )ln Z0 0 z L/2 L/2 z L 0 z L/2 L/2 z L Z sin( L / 2) 1 L e j L ln L 2 Z0 L / 2 2 (squared sinc function) - lower side lobes - wider main lobe L European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Klopfenstein Taper L L e j L cos L 2 A2 cosh A ( L A) Based on Chebychev coefficients when n→∞. Equal ripple in passband passband : L A L Z L Z0 1 Z ln L Z L Z0 2 Z0 L m cosh A Shortest length for a specified |M| Lowest |M| for a specified taper length Z L / Z0 2 ltaper = L European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Example of linear taper: ridged wave-guide Microstrip to rectangular wave-guide transition SECTION C-C’ SECTION B-B’ SECTION A-A’ Rectangular guide Ridged guide Microstrip line European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Example of taper: finline wave guide Rectangular wave-guide to finline to transition Finline mixer configuration European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems TAPER EXAMPLE (1): ADS SIMULATION ADS taper model Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology TAPER EXAMPLE (2): ADS SIMULATION Aproximation to exponential taper using ADS : 10 sections of /10 50 W 57,44 W 53,59 W 100 W 93,30 W 61,56 W 87,05 W 65,97 W 81,22 W 70,71 W 75,79 W European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems TAPER EXAMPLE (3): ADS SIMULATION Aproximation to exponential taper using ADS : 10 sections of /10 50 W 53,59 W 57,44 W 61,56 W 70,71 W 75,79 W 81,22 W 87,05 W 100 W 65,97 W 93,30 W European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems TAPER EXAMPLE (4): ADS SIMULATION EXPONENTIAL / ADS TAPER 0 m1 m3 freq=7.170GHz freq=9.980GHz m1=-22.116 m3=-32.452 m1 dB(S(3,3)) dB(S(1,1)) -20 m3 -40 -60 -80 0 2 − 10 section approx. − ADS model 4 6 8 10 12 freq, GHz 14 16 18 20 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems TAPER EXAMPLE (5): ADS SIMULATION Exponential taper mag(S(3,3)) mag(S(1,1)) 0.4 0.3 0.2 ltaper = @ 10 GHz 0.1 m 0,05 0.0 0 2 4 − 10 section approximation − ADS model 6 8 10 12 freq, GHz 14 16 18 20 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems TAPER EXAMPLE (6): ADS SIMULATION 10 section taper: periodicity in frequency 0 m1 m1 freq=49.41GHz m1=-9.824 (li=/2) dB(S(3,3)) dB(S(1,1)) -20 -40 m2 -60 -80 0 m2 freq=9.980GHz m2=-65.843 (li=/10) 20 40 60 − ADS model freq, GHz − 10 section approximation is periodic. 80 100 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems MATCHING NETWORKS LEVY DESIGN Lecturers: Lluís Pradell (pradell@tsc.upc.edu) Francesc Torres (xtorres@tsc.upc.edu) European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems MATCHING NETWORKS Z0 Vs Pd1 PdL Matching Network (passive lossless) r1 f 2 PdL Pd 1 1 2 Gt 1 r1 1 PavS PavS M1 2 Minimize |r1 (f)| Maximize Gt(2) r f Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology CONVENTIONAL CHEBYSHEV FILTER (1) g3 g1 LC low-pass filter g n 1 Rn 1 g0 Conversion from Low-Pass to BandPass filter LS1 CS 1 LS 3 1 0 w 0 1 f f1 Relative bandwidth w 2 2 0 f0 ' gn g2 02 21 Center frequency CS 3 LsiCsi Z0 LP 2 RN 1 g N 1.Z 0 CP 2 LPN CPN 1 02 LpiC pi Lsi gi Z 0 w0 , Csi 1 w 02 Lsi 0 gi Z0 C pi gi , Lpi 1 wZ0 02C pi 0 gi w0 Z 0 Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology CONVENTIONAL CHEBYSHEV FILTER (2) Gt ( ' 2 ) 1 Gt ' 1 n2Tn2 ' 2 1 Pass-band ripple GtMAX ( T 0 ) 1 n GtMIN ( T 1) n 1 1 n2 ' 1 r 10log GtMAX GtMIN 10log 1 n2 dB Chebychev polynomials cos n cos 1 x , x 1 Tn x 1 cosh n cosh x , x 1 Gt ( 2 ) 1 1 1 n2 02 1. 2 1 0 2 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems CONVENTIONAL CHEBYSHEV FILTER (3) g0 1 g1 2 • sin( 2n Fix pass-band ripple and filter order “n” ) , x g i • g i 1 4 • sin( x sinh( a ) , 2i 1 2i 1 ) • sin( ) 2n 2n i x 2 sin 2 ( ) n (i 1, 2,...., n 1) g n g n 1 2 • sin( 2n ) x g0, g1,.., gn+1 are the low-pass LC filter coefficients: w1' 1 n 1 sinh( na ) Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology APPLICATION TO A MATCHING NETWORK Ce L'S 1 Le CS' 1 Transistor modeled with a dominant RLC behaviour in the pass-band to be matched RN 1 g N 1.Re Re Transistor Model LP 2 CP 2 2.sin . R e g .R 2n Ls1 1 e w.0 x.w.0 Ls1 Ls1 Le Ls1 , Le ' Cs1 CeCs1 ' ' Ce Cs1 given Cs1 , Ce ' ' LPN CPN Ls1Cs1 1 r n a x g1 Ls1 Le ? n 02 increase n (n constant) a, x decrease or increase n (n constant) a, x decrease Solution (?): The final design may be out of specifications: n too high (too many sections) or r too large European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK (1) SOLUTION: An additional parameter is introduced: Kn<1 Gt '2 Gt ( ' 2 ) Kn 1 n2Tn2 ' ( Kn 1) Kn Kn 1 n2 GtMAX ( T 0 ) K n n GtMIN ( T 1) n r 10log Kn 1 n2 GtMAX GtMIN 10log 1 n2 cos n cos 1 x , x 1 Tn x 1 cosh n cosh x , x 1 ' 1 dB Gt ( 2 ) Kn Kn 1 n2 02 1. 2 1 0 2 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK (2) SOLUTION: Additional design equations g0 1 Example: n = 2 2.sin 2n g1 x y 2i 1 2i 1 4.sin .sin 2n 2n gi gi 1 i i x 2 y 2 sin 2 2. x. y.cos n n 2.sin 2n g n g n 1 x y x sinh a y sinh b (new freedom degree) 1 n sinh na sinh 2 nb Kn 1 , ( K n 1) sinh 2 na g0 1 2.sin 4 g1 x y , (i 1, 2...., n 1) g2 1 2 · 2 g1 x y 2 1 2.sin 1 4 g3 · g2 x y x sinh a y sinh b (new freedom degree) 2 1 sinh 2a sinh 2 2b K2 1 , ( K 2 1) sinh 2 2a European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK (3) Design procedure a) Choose Cs1 or Ls1 taking into account the load to be matched If Ls1Cs1 If Ls1Cs1 1 02 1 02 LeCe LeCe 1 e2 1 e2 take Cs1 Ce Ls1 Le take Ls1 Le Cs1 Ce b) Choose network order (n) and compute g1 g1 Ls1 .w.0 Re or g1 w 0 .Cs1 .Re c) Compute x-y from the parameter g1 2.sin 2n x y g1 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK (4) d) Choose x, compute y, OPTIMAL DESIGN: minimize r r 1 Gt tgh na tgh nb cosh a cosh b 2 r 2 MAX 1 GtMIN 1 cosh nb Kn 1 n2 cosh na Example: usual case n=2: tgh 2a tgh 2b For n=2: cosh a cosh b max r MAX 0 b sinh a sinh b x y ct Optimum x C2 C22 2 x 2 C2 x y Select Ls1 (or Cs1) and n. Compute g1. and x-y. Then determine x, y and Kn, n: xyb a Kn n The matched bandwith can be increased from ~5% to ~20% with n=2, with moderate Return Loss requirements (~20 dB) European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE (1) Ce Le Re Matching Network Re 15, 2 W Le 0,52 nH f e 8,86 GHz C 0,62 pF e R 50 W f1 5,5 GHz f 0 6, 4226 GHz f 7,5 GHz 2 R European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE (2) f1 5,5 Ghz f 2 7,5 Ghz f 0 6, 4226 GHz 2 w 0,3114 6, 4226 CS Ce 0, 62 pF LS g1 ( fe f0 ) 1 0,99 nH 02CS w CS 0 Re 0,8195 2sin( ) 4 1, 7257 C2 x y g1 RLmin 17.75 dB C2 C22 2 x 1,978 a 1, 434 2 y 0, 2535 b 0, 2509 RLmin 17.75 dB K n 0,996 GtMAX 0, 015dB RLmin 23.98 dB 0,114 G 0, 071dB n tMIN g 2 0, 4903 C p 2,57 pF , L p 0, 239nH g3 1, 2928 R3 g3 Re 19, 65 W Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE (3): ADS SIMULATION A transformer is necessary since g3≠1 (R3≠50 Ω). This transformed must be eliminated from the design LEVY NETWORK (LUMPED COMPONENTS) 0 0.0 -0.1 -5 -0.2 dB(S(2,1)) dB(S(2,2)) dB(S(2,1)) European Master of Research on Information Technology -10 -15 -20 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 -25 -1.0 4 5 6 7 freq, GHz 8 9 4 5 6 7 freq, GHz 8 9 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems Norton Transformer equivalences STEPS:1) the capacitor C2 is pushed towards the load through the transformer 2) The transformer is eliminated using Norton equivalences Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology 0 0.2 -5 -0.0 dB(S(2,1)) dB(S(2,2)) dB(S(2,1)) LEVY NETWORK EXAMPLE (4): ADS SIMULATION -10 -15 -0.2 -0.4 -0.6 -20 -0.8 -25 -1.0 4 5 6 freq, GHz 7 8 9 4.5 5.0 5.5 6.0 6.5 7.0 freq, GHz 7.5 8.0 8.5 9.0 Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology SMALL SERIES INDUCTANCES AND PARALLEL CAPACITANCES IMPLEMENTED USING SHORT TRANSMISSION LINES L, C elements are then synthesized by means of short transmission lines: l L Z0h 2 f 0 L Z 0 h l f 0 L Z 0 h l 0 l C Z0l 2 f 0 C Y0l l f 0 C Y0l l 0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems SMALL SERIES INDUCTANCES AND PARALLEL CAPACITANCES IMPLEMENTED USING SHORT TRANSMISSION LINES: EXAMPLE LS 0,33 nH Z 0h 106 W L2 0,23 nH Z0h 73,85 W C2 1,02 pF Z 0l 15,26 W for l1 0 l2 for for 0 l3 1 50 1 50 1 0 10 Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE ADS SIMULATION (5): 0 0.2 -5 0.0 dB(S(2,1)) dB(S(2,1)) dB(S(1,1)) European Master of Research on Information Technology -10 -15 -20 -25 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -30 4 5 6 7 freq, GHz 8 9 5.0 5.5 6.0 6.5 freq, GHz 7.0 7.5 8.0 Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE: ADS SIMULATION (6): 0 0.0 -0.5 -5 dB(S(2,1)) dB(S(1,2)) dB(S(1,1)) European Master of Research on Information Technology -10 -1.0 -1.5 -2.0 -15 -2.5 4 5 6 7 freq, GHz 8 9 5.0 5.5 6.0 6.5 freq, GHz 7.0 7.5 8.0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE (7): ADS SIMULATION: optimization Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology LEVY NETWORK EXAMPLE (8): ADS SIMULATION: optimization 0 1.5 1.0 dB(S(2,1)) dB(S(2,1)) dB(S(1,1)) -5 -10 -15 0.5 0.0 -0.5 -20 -1.0 -25 4 5 6 7 freq, GHz 8 9 -1.5 4.5 5.0 5.5 6.0 6.5 freq, GHz 7.0 7.5 8.0 European Master of Research on Information Technology Design and Analysis of RF and Microwave Systems LEVY NETWORK EXAMPLE (9): ADS SIMULATION: optimization Design and Analysis of RF and Microwave Systems European Master of Research on Information Technology 0 -5 -10 -15 -20 -25 4 5 6 7 8 9 dB(levy3_amb_T_optim..S(2,1)) dB(S(2,1)) dB(levy3_amb_T_optim..S(2,1)) dB(levy3_amb_T_optim..S(1,1)) dB(S(2,1)) dB(S(1,1)) LEVY NETWORK EXAMPLE (10): ADS SIMULATION: optimization 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 4.5 freq, GHz 5.0 5.5 6.0 6.5 freq, GHz 7.0 7.5 8.0 8.5