Agilent ENA Series 2, 3 and 4 Port RF Network Analyzers

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1 gilent EN Series 2, 3 and 4 Port RF Network nalyzers 蔡明汎 gilent EO Project Manager (07) ming-fan_tsai@agilent.com OTS: EN 1 genda What measurements do we make? Network nalyzer Hardware Error Model and Calibration EN 2

2 Lightwave nalogy to RF Energy Lightwave (R) () RF/uwave (B) EN 3 Reflection Coefficient No reflection (ZL = Zo) Γ Return loss = -20 log(ρ), Reflection Parameters = V reflected V incident = ρ Φ ρ = Emax Emin Γ = Z L Z O Z L + Z O Voltage Standing Wave Ratio VSWR = Emax Emin = 1 + ρ 1 - ρ Full reflection (ZL = open, short) 0 ρ 1 db RL 0 db 1 VSWR EN 4

3 . Smith Chart Review +jx Polar plane 90 o R o o -jx Rectilinear impedance plane 0-90 o Smith Chart maps rectilinear impedance plane onto polar plane Z = Zo L Γ = 0 (short) Z L= Z L= 0 Γ = 1 ±180 O Constant X Constant R Γ = 1 0 O (open) Smith chart EN 5 Transmission Parameters V V Transmission Coefficient = Τ = V V = τ φ Insertion Loss (db) = - 20 Log V Trans V Inc = - 20 log τ Gain (db) = 20 Log V Trans V Inc = 20 log τ EN 6

4 Group Delay Frequency ω ω t g Group delay ripple Phase φ t o φ verage delay Group Delay (t ) g = d φ d ω = 1 d φ 360 o * d f φ ω φ in radians in radians/sec in degrees f in Hertz (ω = 2 π f) Frequency group-delay ripple indicates phase distortion average delay indicates electrical length of aperture of measurement is very important EN 7 Why Measure Group Delay? Phase Phase d φ d ω f d φ d ω f Group Delay Group Delay f Same p-p phase ripple can result in different group delay f EN 8

5 Measuring S-ParametersS S 21 Forward b 1 a 1 b 2 Z 0 S 11 a 2 = 0 Load S 11 = S 21 = = b 1 a 1 a 2 = 0 = b 2 a 1 a 2 = 0 S 22 = S 12 = = b 2 a 2 a 1 = 0 = b 1 a 2 a 1 = 0 Z 0 Load a 1 = 0 b 1 S 12 S 22 b 2 a 2 Reverse EN 9 Equating S-Parameters S with Common Measurement Terms S11 = forward reflection coefficient (input match) S22 = reverse reflection coefficient (output match) S21 = forward transmission coefficient (gain or loss) S12 = reverse transmission coefficient (isolation) Remember, S-parameters are inherently complex, linear quantities -- however, we often express them in a log - magnitude format EN 10

6 High-Frequency Device Characterization (R) () REFLECTION (B) TRNSMISSION = R = B R VSWR (SWR) Return Loss (LOG) Gain / Loss S-Parameters (LOG) Group Delay (Delay) S 11, S 22 Reflection Impedance S-Parameters (Smith) Insertion Phase S 21, S Transmission 12 (Phase) Coefficient (Linear or Polar) R+jX, Coefficient G+jB Γ, ρ (Linear) EN Τ,τ 11 genda What measurements do we make? Network nalyzer Hardware Error Model and Calibration EN 12

7 Generalized Network nalyzer Block Diagram SOURCE SIGNL SEPRTION INCIDENT (R) REFLECTED () TRNSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLY EN 13 Source Supplies stimulus for system Swept frequency or power Traditionally Ns used separate source Most gilent analyzers sold today have integrated, synthesized sources SOURCE INCIDENT (R) SIGNL SEPRTION REFLECTED TRNSMITTED () (B) RECEIVER / DETECTOR PROCESSOR / DISPLY EN 14

8 Signal Separation SOURCE measure incident signal for reference separate incident and reflected signals INCIDENT (R) SIGNL SEPRTION REFLECTED TRNSMITTED () (B) RECEIVER / DETECTOR PROCESSOR / DISPLY directional coupler splitter EN 15 Transmission/Reflection Measurement Configuration Power Splitter Transmission -6 db -6 db Receiver Display Directional Coupler (or Bridge) -6 db Receiver Display Reflection -6 db EN 16

9 Narrowband Detection Tuned Receiver SOURCE RF IF filter IF=F LO -F RF DC / DSP INCIDENT (R) SIGNL SEPRTION REFLECTED TRNSMITTED () (B) RECEIVER / DETECTOR PROCESSOR / DISPLY LO Best sensitivity / dynamic range Provides harmonic / spurious signal rejection Improve dynamic range by increasing power, decreasing IF bandwidth, or averaging Trade off noise floor and measurement speed 10 MHz 26.5 GHz EN 17 Processor / Display SOURCE SIGNL SEPRTION INCIDENT (R) REFLECTED () TRNSMITTED (B) Frequency base RECEIVER / DETECTOR PROCESSOR / DISPLY markers limit lines pass/fail indicators linear/log formats grid/polar/smith charts Order base EN 18

10 genda What measurements do we make? Network nalyzer Hardware Error Model and Calibration EN 19 Measurement Error Modeling CL RE-CL Systematic errors due to imperfections in the analyzer and test setup assumed to be time invariant (predictable) Random errors vary with time in random fashion (unpredictable) main contributors: instrument noise, switch and connector repeatability Drift errors due to system performance changing after a calibration has been done primarily caused by temperature variation Measured Data Errors: SYSTEMTIC RNDOM DRIFT Unknown Device EN 20

11 Systematic Error Modeling Imperfect network analyzer viewed as an ideal network analyzer plus an imperfect connecting network Imperfect Network nalyzer System Ideal Network nalyzer Imperfect Connecting Network EN 21 Systematic Errors Reflection: One-Port R Directivity Termination Frequency response reflection tracking (/R) Source Mismatch ssumes good termination at port two if testing two-port devices EN 22

12 Reflection: One-Port Model RF in Ideal RF in Error dapter 1 E D E RT = Directivity = Reflection tracking S11 E D E S S11 E S = Source Match S11 M = Measured S11 M S11 M S11 = ctual E RT S11M = ED + ERT S ES S11 To solve for error terms, we measure 3 standards to generate 3 equations and 3 unknowns. EN 23 Measurement Calibration(1/3) Step 1 -- "Perfect" Load E D Directivity S 11 =0 R S11M = ED + ERT S ES S11 LOD S11M = ED + ERT ES 0 = E D EN 24

13 Measurement Calibration(2/3) STEP 2 - SHORT S11 M S11 = = -1 Reflection Tracking/Source Match S11M = ED + ERT ES (-1) EN 25 Measurement Calibration(3/3) STEP 3 - OPEN S11 M S11 =1 0 0 = 1 Reflection Tracking/Source Match S11M = ED + ERT ES (1) EN 26

14 Systematic Measurement Errors Two Port Measurement R Directivity Crosstalk B Frequency response reflection tracking (/R) transmission tracking (B/R) Source Mismatch Load Mismatch Six forward and six reverse error terms yields 12 error terms for two-port devices EN 27 Two-Port Error Correction Forward model Port 1 EX Port 2 a 1 Reverse model Port 1 Port 2 S21 ERT' b 2 a 1 ES S21 ETT b 2 b 1 EL' S11 S22 ES' ED' a 2 b 1 ED S11 S22 EL a 2 ETT' S12 ERT S12 EX' E D E S ERT = fwd directivity = fwd source match = fwd reflection tracking E D' = rev directivity E S' = rev source match ERT' = rev reflection tracking E L E TT E X = fwd load match = fwd transmission tracking = fwd isolation EL' = rev load match ETT' = rev transmission tracking E X' = rev isolation Each actual S-parameter is a function of all four measured S-parameters nalyzer must make forward and reverse sweep to update any one S-parameter Luckily, you don't need to know these equations to use network analyzers!!! EN 28

15 Errors and Calibration Standards UNCORRECTED RESPONSE 1-PORT FULL 2-PORT thru SHORT OPEN SHORT OPEN SHORT OPEN Convenient Generally not accurate No errors removed Easy to perform Use when highest accuracy is not required Removes frequency response error ENHNCED-RESPONSE Combines response and 1-port Corrects source match for transmission measurements LOD For reflection measurements Need good termination for high accuracy with two-port devices Removes these errors: Directivity Source match Reflection tracking LOD thru LOD Highest accuracy Removes these errors: Directivity Source, load match Reflection tracking Transmission tracking Crosstalk EN 29