是德科技矢量网络分析的基本原理 应用指南
引言
(S ) DC-110 GHz 通信系统中的测量要求 ( ) ( 1) Sin 360º * f * t Input DUT A t o A * Sin 360º * f (t t o ) A phase shift = t o * 360º * f f 1 Output Linear behavior input and output frequencies are the same (no additional frequencies created) output frequency only undergoes magnitude and phase change f 1 Nonlinear behavior output frequency may undergo frequency shift (e.g. with mixers) additional frequencies created (harmonics, intermodulation) f 1 1. 3
(DUT) ( 2) 3 ( 3) F(t) = sin wt + 1 /3 sin 3wt + 1 /5 sin 5wt Linear network Magnitude 2. F(t) = sin wt + 1 /3 sin 3wt + 1 /5 sin 5wt Linear network Magnitude 0º 180º 360º 3. 4
Nonlinear networks Saturation, crossover, intermodulation, and other nonlinear effects can cause signal distortion 4. ( 4) LC 矢量测量的重要性 (CAE) ( ) 5
入射功率和反射功率的基本概念 ( ) ( )( 5) ( ) ( ) Lightwave analogy Reflected Transmitted 5. 史密斯圆图 (R+jX G+jB) ( ) 6
0 ( 6) 50 Ω 75 Ω +jx Polar plane 90 o 1.0 0 +R ±180º.8.6.4.2 0 o jx Rectilinear impedance plane Smith chart maps rectilinear impedance plane onto polar plane 0 Z = Zo L = 0 Z L= 0 (short) = 1180º 90º Constant X Constant R Z L= (open) = 10º Smith chart 6. 功率传送条件 R s R L R L = R S ( 7) R s = 0.6 + j 0.3 R s = 0.6 - j 0.3 ( ) 7
( 8) R S Load power (normalized) 1.2 1 0.8 0.6 0.4 0.2 R L For complex impedances, maximum power transfer occurs when Z L = Z S * (conjugate match) Zs = R + jx 0 0 1 2 3 4 5 6 7 8 9 10 R L / R S Maximum power is transferred when R L = R S Z L = Zs * = R jx 7. Zs = Zo Zo = characteristic impedance of transmission line Zo V inc V refl = 0 (all the incident power is absorbed in the load) For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission line 8. Z 0 8
( ) ( 9) ; 108 ( ) 180 0 0 2 25 Ω 1/3 180 0 2:1 / VSWR ( ) VSWR ( VSWR) Zs = Zo V inc V refl In phase (0º) for open Out of phase (180º) for short For reflection, a transmission line terminated in a short or open reflects all power back to source 9., 9
网络分析的名词术语 R A B ( 10) ; (DUT) ( ) ( ) A/R B/R R Reflected A Reflection Transmitted B Transmission Reflected = A R Transmitted = B R SWR S-parameters S11, S22 Reflection coefficient, Return loss Impedance, admittance R+jX, G+jB Gain/loss S-parameters S21, S12 Transmission coefficient T, Group delay Insertion phase 10. G 11G ρ Z o V refi = 0 ρ = 0 Z L ρ 0 ρ = 1 ρ 0~1 10
Reflection coefficient No reflection (Z L = Zo) = V reflected V incident = r F Return loss = 20 log( ), = Emax Emin = Z - L Z O Z L + Z O Voltage standing wave ratio VSWR = Emax Emin = 1 + r 1 r Full reflection (Z L = open, short) 0 1 db RL 0 db 1 VSWR 11. (db) db ( ) 0 db ( ) (VSRW)VSRW ρ (1 + ρ)/(1 - ρ)vswr 1 ( ) ( ) ( 12) V DUT V Transmitted Transmission coefficient = T V Transmitted = = V Insertion loss (db) = 20 Log V Trans V Inc = 20 log Gain (db) = 20 Log V Trans V Inc = 20 log 12. 11
( ) (13 ) Use electrical delay to remove linear portion of phase response Phase 45º/div RF filter response Low resolution Linear electrical length added (Electrical delay function) + yields Deviation from linear phase High resolution Phase 1º/div 13. 测量群时延 ( 14) ( ) tg Group delay t o Group delay Average delay Phase Group delay (tg) = d = 1 360 o * d d f Deviation from constant group delay indicates distortion Average delay indicates transit time f in radians in radians/sec in degrees f in Hz ( = 2 ) 14. 12
- ( 15) Phase Phase dφ d f dφ d f Group delay Group delay f Same peak-to-peak phase ripple can result in different group delay f 15.? 网络的表征 ( ) HY Z S ( 16) S S S CAE HY Z S S 4 S S S S 21 1 2 ( S 11 ) 13
H,Y, and Z parameters Hard to measure total voltage and current at device ports at high frequencies Active devices may oscillate or self-destruct with shorts or opens S-parameters Relate to familiar measurements S (gain, loss, reflection coefficient, etc.) 21 Transmitted a 1 Relatively easy to measure S 11 Reflected DUT S 22 Can cascade S-parameters of multiple Port 1 Port 2 b Reflected devices to predict system performance 1 a 2 Transmitted S 12 Analytically convenient b 1 = S 11 a CAD programs 1 + S 12 a 2 b 2 = S 21 a 1 + S 22 a 2 Flow-graph analysis Can compute H, Y, or Z parameters from S-parameters if desired b2 16. HY Z ( S?) Forward S 21 b Transmitted 2 a 1 S 11 Z 0 b Reflected DUT Load 1 a 2 = 0 Reflected S 11 = S 21 = Transmitted = b 1 a 1 a 2 = 0 = b 2 a 1 a 2 = 0 Reflected S 22 = S 12 = Transmitted = b a 2 2 1 = b a 2 a = 0 1 a = 0 1 Z 0 Load a 1 = 0 b 1 DUT Transmitted S 12 b 2 S 22 Reflected a 2 Reverse 17. S S S 11 S 21 ( ) S S 22 S 12 ( 17) 14
Related Literature Exploring the Architectures of Network Analyzers, Application Note 1287-2, Literature number 5965-7708E Applying Error Correction to Network Analyzer Measurements, Application Note 1287-3, Literature number 5965-7709E Network Analyzer Measurements: Filter and Amplifier Examples, Application Note 1287-4, Literature number 5965-7710E 15
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