Network Analyzer Basics

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## Network Analyzer Basics

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**Network Analyzer Basics**Network Analyzer Basics**Network Analysis is NOT.…**Network Analyzer Basics**What Types of Devices are Tested?**High Duplexers Diplexers Filters Couplers Bridges Splitters, dividers Combiners Isolators Circulators Attenuators Adapters Opens, shorts, loads Delay lines Cables Transmission lines Waveguide Resonators Dielectrics R, L, C's RFICs MMICs T/R modules Transceivers Receivers Tuners Converters VCAs Amplifiers VCOs VTFs Oscillators Modulators VCAtten’s Transistors Integration Antennas Switches Multiplexers Mixers Samplers Multipliers Diodes Low Device type Active Passive Network Analyzer Basics**Device Test Measurement Model**84000 RFIC test Complex Full call sequence Ded. Testers BER EVM ACP Regrowth Constell. Eye Pulsed S-parm. Pulse profiling VSA Harm. Dist. LO stability Image Rej. Intermodulation Distortion SA NF VNA Gain/Flat. Phase/GD Isolation Rtn Ls/VSWR Impedance S-parameters Compr'n AM-PM TG/SA Response tool SNA NF Mtr. NF Imped. An. LCR/Z Param. An. I-V Measurement plane Absol. Power Power Mtr. Simple Det/Scope Gain/Flatness DC CW Swept Swept Noise 2-tone Multi- Complex Pulsed- Protocol freq power tone modulation RF Stimulus type Simple Complex Network Analyzer Basics**Lightwave Analogy to RF Energy**Incident Transmitted Reflected Lightwave DUT RF Network Analyzer Basics**Why Do We Need to Test Components?**• Verify specifications of “building blocks” for more complex RF systems • Ensure distortionless transmission of communications signals • linear:constant amplitude, linear phase / constant group delay • nonlinear: harmonics, intermodulation, compression, AM-to-PM conversion • Ensure good match when absorbing power (e.g., an antenna) Network Analyzer Basics**S21**S11 S22 S12 Mag Time High-frequency transistor model Base Collector Error Measured Emitter Actual The Need for Both Magnitude and Phase 1. Complete characterization of linear networks 2. Complex impedance needed to design matching circuits 4. Time-domain characterization 3. Complex values needed for device modeling 5. Vector-error correction Network Analyzer Basics**Transmission Line Basics**- + I Low frequencies • wavelengths >> wire length • current (I) travels down wires easily for efficient power transmission • measured voltage and current not dependent on position along wire High frequencies • wavelength » or << length of transmission medium • need transmission lines for efficient power transmission • matching to characteristic impedance (Zo) is very important for low reflection and maximum power transfer • measured envelope voltage dependent on position along line Network Analyzer Basics**1.5**attenuation is lowest at 77 ohms 1.4 1.3 1.2 50 ohm standard 1.1 normalized values 1.0 0.9 0.8 power handling capacity peaks at 30 ohms 0.7 0.6 0.5 10 20 30 40 50 60 70 80 90 100 characteristic impedance for coaxial airlines (ohms) Transmission line Zo • Zo determines relationship between voltage and current waves • Zo is a function of physical dimensions and r • Zo is usually a real impedance (e.g. 50 or 75 ohms) Network Analyzer Basics**RS**RL 1.2 1 0.8 Load Power (normalized) 0.6 0.4 0.2 0 0 1 2 3 4 5 6 7 8 9 10 Power Transfer Efficiency For complex impedances, maximum power transfer occurs when ZL = ZS* (conjugate match) RL / RS Maximum power is transferred when RL = RS Network Analyzer Basics**V**inc Transmission Line Terminated with Zo Zo = characteristic impedance of transmission line Zs = Zo Zo Vrefl = 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 Network Analyzer Basics**V**inc Transmission Line Terminated with Short, Open Zs = Zo In-phase (0o) for open, out-of-phase (180o) for short Vrefl For reflection, a transmission line terminated in a short or open reflects all power back to source Network Analyzer Basics**V**inc Transmission Line Terminated with 25 W Zs = Zo ZL = 25 W Vrefl Standing wave pattern does not go to zero as with short or open Network Analyzer Basics**A**Reflected = R Incident High-Frequency Device Characterization Incident Transmitted R B Reflected A TRANSMISSION REFLECTION B Transmitted = R Incident Group Return SWR Gain / Loss Delay Loss Insertion S-Parameters Impedance, Admittance S-Parameters S11, S22 Phase Reflection Transmission S21, S12 Coefficient R+jX, G+jB Coefficient G, r T,t Network Analyzer Basics**Reflection Coefficient**G - r V Z Z = = F = reflected O L V Z Z + incident r O L G Return loss = -20 log(r), = Emax Emin 1 + r Emax VSWR = = 1 - r Emin r RL VSWR Reflection Parameters Voltage Standing Wave Ratio Full reflection (ZL = open, short) No reflection (ZL = Zo) 1 0 ¥dB 0 dB ¥ 1 Network Analyzer Basics**+jX**o 90 0 +R o + o 180 0 ¥ - 0 -jX Rectilinear impedance plane o -90 (open) Z = (short) L Z = 0 L G O 0 = 1 G O 1 ±180 = Smith Chart Review . Polar plane 1.0 .8 .6 .4 ¥ ® .2 Constant X Z = Zo Constant R L G Smith Chart maps rectilinear impedance plane onto polar plane = 0 Smith chart Network Analyzer Basics**V**Transmitted V Transmitted V Incident V Trans V Inc V Trans V Inc Transmission Parameters V Incident DUT T = tÐf Transmission Coefficient = = = - 20 log t Insertion Loss (dB) = - 20 Log Gain (dB) = 20 Log = 20 log t Network Analyzer Basics**A * Sin 360o * f (t - to)**A Time t o Sin 360o * f * t A phase shift = to * 360o * f f Time Frequency 1 Time f 1 Frequency f 1 Linear Versus Nonlinear Behavior Linear behavior: • input and output frequencies are the same (no additional frequencies created) • output frequency only undergoes magnitude and phase change DUT Input Output Nonlinear behavior: • output frequency may undergo frequency shift (e.g. with mixers) • additional frequencies created (harmonics, intermodulation) Frequency Network Analyzer Basics**Criteria for Distortionless Transmission**Linear Networks Constant amplitude over bandwidth of interest Linear phase over bandwidth of interest Frequency Magnitude Phase Frequency Network Analyzer Basics**Magnitude Variation with Frequency**F(t) = sin wt + 1/3 sin 3wt + 1/5 sin 5wt Time Time Linear Network Magnitude Frequency Frequency Frequency Network Analyzer Basics**Phase Variation with Frequency**F(t) = sin wt + 1 /3 sin 3wt + 1 /5 sin 5wt Linear Network Time Time Magnitude Frequency 0 ° Frequency Frequency -180 ° -360 ° Network Analyzer Basics**o**o Phase 45 /Div Phase 1 /Div Deviation from Linear Phase Use electrical delay to remove linear portion of phase response Linear electrical length added Deviation from linear phase RF filter response (Electrical delay function) + yields Frequency Frequency Frequency Low resolution High resolution Network Analyzer Basics**t**g = Group Delay (t ) g d f -d f -1 = * d w o d f 360 f in radians w in radians/sec f in degrees f in Hertz (w = 2 p f) Group Delay w Group delay ripple Frequency Dw f t o Average delay Phase Df Frequency • group-delay ripple indicates phase distortion • average delay indicates electrical length of DUT • aperture of measurement is very important Network Analyzer Basics**Phase**Phase f f -d f -d f d w d w Group Delay Group Delay f f Why Measure Group Delay? Same p-p phase ripple can result in different group delay Network Analyzer Basics**V1**h11 = I1 (requires short circuit) V2=0 V1 h12 = V2 (requires open circuit) I1=0 Characterizing Unknown Devices Using parameters (H, Y, Z, S) to characterize devices: • gives linear behavioral model of our device • measure parameters (e.g. voltage and current) versus frequency under various source and load conditions (e.g. short and open circuits) • compute device parameters from measured data • predict circuit performance under any source and load conditions H-parameters V1 = h11I1 + h12V2 I2 = h21I1 + h22V2 Y-parameters I1 = y11V1 + y12V2 I2 = y21V1 + y22V2 Z-parameters V1 = z11I1 + z12I2 V2 = z21I1 + z22I2 Network Analyzer Basics**S**21 Incident Transmitted S 11 DUT Reflected S 22 Port 2 Port 1 Reflected Incident S Transmitted 12 a 1 b 2 b 1 a 2 a a b S = S + 1 2 1 11 12 a a b = S S + 2 2 21 1 22 Why Use S-Parameters? • relatively easy to obtain at high frequencies • measure voltage traveling waves with a vector network analyzer • don't need shorts/opens which can cause active devices to oscillate or self-destruct • relate to familiar measurements (gain, loss, reflection coefficient ...) • can cascade S-parameters of multiple devices to predict system performance • can compute H, Y, or Z parameters from S-parameters if desired • can easily import and use S-parameter files in our electronic-simulation tools Network Analyzer Basics**Z**0 Load b Reflected 1 S = = 11 a a Incident 0 = b 1 2 Reflected 2 S = = b 22 a a Transmitted Incident 0 = 2 S 1 2 = = 21 a a 0 = b Incident 2 Transmitted 1 S 1 = = 12 a a 0 = Incident 1 2 S Z 22 0 Reflected Load Measuring S-Parameters b S 2 Incident Transmitted 21 a 1 S 11 Forward DUT Reflected b a 0 = 1 2 a b 0 = 1 2 Reverse DUT a 2 S b Transmitted Incident 12 1 Network Analyzer Basics**Equating S-Parameters 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 Network Analyzer Basics**Time**Time Frequency Frequency Criteria for Distortionless TransmissionNonlinear Networks • Saturation, crossover, intermodulation, and other nonlinear effects can cause signal distortion • Effect on system depends on amount and type of distortion and system architecture Network Analyzer Basics**RL 0 dBm ATTEN 10 dB 10 dB / DIV**8563A SPECTRUM ANALYZER 9 kHz - 26.5 GHz LPF DUT CENTER 20.00000 MHz SPAN 10.00 kHz RB 30 Hz VB 30 Hz ST 20 sec LPF Measuring Nonlinear Behavior Most common measurements: • using a network analyzer and power sweeps • gain compression • AM to PM conversion • using a spectrum analyzer + source(s) • harmonics, particularly second and third • intermodulation products resulting from two or more RF carriers Network Analyzer Basics**8563A**SPECTRUM ANALYZER 9 kHz - 26.5 GHz Amplitude Ratio Amplitude Network analyzers: • measure components, devices, circuits, sub-assemblies • contain source and receiver • display ratioed amplitude and phase(frequency or power sweeps) • offer advanced error correction Spectrum analyzers: • measure signal amplitude characteristicscarrier level, sidebands, harmonics...) • can demodulate (& measure) complex signals • are receivers only (single channel) • can be used for scalar component test (nophase) with tracking gen. or ext. source(s) Frequency Frequency What is the Difference Between Network and Spectrum Analyzers? . Measures unknown signals Measures known signal Network Analyzer Basics**Incident**Transmitted DUT Reflected SOURCE SIGNAL SEPARATION INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLAY Generalized Network Analyzer Block Diagram Network Analyzer Basics**Source**• Supplies stimulus for system • Swept frequency or power • Traditionally NAs used separate source • Most Agilent analyzers sold today have integrated, synthesized sources Network Analyzer Basics**Incident**Transmitted DUT Reflected SOURCE SIGNAL SEPARATION INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLAY Signal Separation • measure incident signal for reference • separate incident and reflected signals splitter bridge Detector directional coupler Test Port Network Analyzer Basics**Directivity**Directivity is a measure of how well a coupler can separate signals moving in opposite directions (undesired leakage signal) (desired reflected signal) Test port Directional Coupler Network Analyzer Basics**Device**Directivity Interaction of Directivity with the DUT (Without Error Correction) 0 Data Max DUT RL = 40 dB Add in-phase Directivity 30 Device Return Loss 60 Frequency Device Data Min Data = Vector Sum Directivity Add out-of-phase (cancellation) Network Analyzer Basics**Incident**Transmitted DUT Reflected SOURCE SIGNAL SEPARATION Diode INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR PROCESSOR / DISPLAY DC RF AC RF ± IF = F LO ADC / DSP IF Filter F RF LO Detector Types Scalar broadband (no phase information) Tuned Receiver Vector (magnitude and phase) Network Analyzer Basics**Broadband Diode Detection**• Easy to make broadband • Inexpensive compared to tuned receiver • Good for measuring frequency-translating devices • Improve dynamic range by increasing power • Medium sensitivity / dynamic range 10 MHz 26.5 GHz Network Analyzer Basics**ADC / DSP**Narrowband Detection - Tuned Receiver • 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 26.5 GHz 10 MHz Network Analyzer Basics**0 dB**-50 dB -100 dB Comparison of Receiver Techniques Broadband (diode) detection Narrowband (tuned-receiver) detection 0 dB -50 dB -100 dB -60 dBm Sensitivity < -100 dBm Sensitivity • higher noise floor • false responses • high dynamic range • harmonic immunity Dynamic range = maximum receiver power - receiver noise floor Network Analyzer Basics**-**+ phase error magn error Dynamic Range and Accuracy Dynamic range is very important for measurement accuracy! Network Analyzer Basics**Transmission/Reflection Test Set**S-Parameter Test Set Source Source Source Transfer switch Transfer switch R1 R A R B B B A A R2 Port 2 Port 1 Port 2 Port 1 Port 1 Port 2 Fwd Fwd Rev DUT DUT • RF always comes out port 1 • port 2 is always receiver • response, one-port cal available • RF comes out port 1 or port 2 • forward and reverse measurements • two-port calibration possible T/R Versus S-Parameter Test Sets Network Analyzer Basics**Incident**Transmitted DUT Reflected SOURCE SIGNAL SEPARATION INCIDENT (R) REFLECTED (A) TRANSMITTED (B) RECEIVER / DETECTOR 50 MH-20GHz NETWORK ANYZER ACTIVE CHANNEL ENTRY PROCESSOR / DISPLAY RESPONSE R CHANNEL INSTRUMENT STATE STIMULUS L T S R HP-IB STATUS PORT 1 PORT 2 Processor / Display • markers • limit lines • pass/fail indicators • linear/log formats • grid/polar/Smith charts Network Analyzer Basics**log MAG**10 dB/ REF 0 dB CH1 21 S REF 0 dB CH1 S log MAG 5 dB/ 11 Cor Stopband rejection 69.1 dB STOP 400.000 000 MHz START .300 000 MHz Cor 1 m1: 4.000 000 GHz -0.16 dB m2-ref: 2.145 234 GHz 0.00 dB 2 ref SPAN 50.000 MHz CENTER 200.000 MHz log MAG 1 dB/ REF 0 dB S CH1 21 Cor 1 2 x2 START 2 000.000 MHz STOP 6 000.000 MHz Frequency Sweep - Filter Test Return loss Insertion loss Network Analyzer Basics**Power Sweeps - Compression**Saturated output power Output Power (dBm) Compression region Linear region (slope = small-signal gain) Input Power (dBm) Network Analyzer Basics**1**START -10 dBm CW 902.7 MHz STOP 15 dBm Power Sweep - Gain Compression CH1 S21 1og MAG 1 dB/ REF 32 dB 30.991 dB 12.3 dBm 1 dB compression: input power resulting in 1 dB drop in gain 0 Network Analyzer Basics