Wide bandwidth measurements and Calibration

Agenda Wide bandwidth measurement definitions The need for wide bandwidth measurements Types of wide bandwidth measurements Accurate measurements and system calibration Extended calibration Multi-instrument calibration Equipment alternatives for making wide BW measurements Conclusion

Wide Bandwidth Definitions Wide bandwidth means different things to different industries Communications Industry -Cellular Communications (Channel spacing to 20 MHz) -WiMax (to 28 MHz) -4 Carrier WCDMA (to 40 MHz) -6 Carrier WiMax (to 60 MHz) -Ultra wideband (~500 MHz) Aerospace Defense -Narrow band radar (100 MHz, 10 ns pulse) -JTRS sig hopping over 255 MHz -Satellite 200 MHz BW -Chirp and coded radar (>1 GHz)

Broadband signal measurement issues Two general methods of measuring broad band signals: 1. Swept tuned receiver using a sweeping LO and relatively narrow resolution bandwidths. (i.e. sweep across the broadband signal) 2. High speed digitization in the time domain, then performing a Fast Fourier Transform (FFT) (i.e. digitize fast enough to capture the highest frequency component in the band)

Swept tuned measurements of broadband signals RF In IF out BPF Detectors Display processor Swept LO With narrow band measurements some information can be gained, such as amplitude and frequency range occupied by signal. Information contained within the signal will be lost because of the reduced BW.

Digitization and FFT of broadband signals RF In IF out WBF ADC Display processor Fixed or step tuned All information is captured using a fast digitizer. An FFT is then performed to view signal in the frequency domain

Types of WB measurements There are basically two types of wide BW measurements: 1. Signal amplitude and lobe width for very narrow pulse radar measured in the pulse mode. 2. Phase and amplitude are needed for complete evaluation such as Chirp Radar 200 MHz linear chirp

Instrument and System Calibration Calibration Q Amplitude error Amplitude Flatness Phase linearity Measured signal θ Ideal Signal Phase linearity error Minimum Error Vector Magnitude The goal is to measure the EVM of the DUT not the EVM introduced by the measuring system EVM I

Types of calibration to be presented Different levels of calibration available: Built-in (Internal) calibration available on PSA, X series Extended calibration at a specific center frequency and over the information BW (uses 89601A SW) Wideband extended calibration on multiinstrument systems (89601A, PSA and Scope)

Wide Band Block Diagram of the PSA option 122 Third Converter WB Analog IF WB Digital IF UPHB* HB 3 rd LO Calibrator FPGA Low Band 1 st LO 2 nd LO 3 rd LO NB IF *Un-preselected High Band

Amplitude and phase characterized comb covering the entire 80 MHz information BW Signal used to calibrate IF path

Three loops of calibration Outer Loop IF cal Third Converter WB Analog IF WB Digital IF UPHB HB 1 st LO 2 nd LO Low Band 3 rd LO Calibrator FPGA ADC cal Inner Loop IF cal 3 rd LO NB IF

Extended Calibration: The next step in system calibration Amplitude and phase calibration and correction at a single frequency (300 MHz) PSA internal calibration (80 MHz) Amplitude and phase calibration and correction at a selected frequency Extended Calibration in 89601A (80 MHz) Amplitude and phase calibration and correction at selected frequency and for multiple instruments Extended Calibration for multiple instruments in 89601A (250 MHz)

Extended Calibration for PSA while using µwave preselector (example) PSA user may want to place µwave preselection in the signal path to reduce unwanted signals which may cause overload or images Calibration is required each time the preselector is tuned because of the hysteresis and slight changes in band pass shape. For broad µwave frequency steps the preselector must thermally stabilized before calibration. For other external devices (amps, filters etc) perform an external cal once.

Extended Calibration Process Sources Supported: MXG, ESG and PSG

EVM and Spectrum display without correcting for µwave preselector ~10% EVM

EVM and Spectrum display with µwave preselector correction ~0.6% EVM

Comparison of corrections With µwave preselector correction Without µwave preselector correction

Measurement system with added devices (amps, filters etc) Added Devices PSA opt 122 plus 89601 VSA SW RF IF Digital correction filter Meas. Plane ADC Analysis Source controlled by VSA SW Calibration: measure system to determine the frequency response Correction: apply inverse response with a digital filter Note: The source generates a comb with known amplitude and phase relationships

Calibration of multi-instrument systems 250 MHz to 300 MHz VSA measurement bandwidth 40dB-50dB dynamic range All of the power of the 89601 VSA to 50 GHz Powerful Calibration Wizard to ensure phase and magnitude flatness over the full band Works with PSA as downconverter Guided calibration procedure & documented calibration performance Nominal specifications available anticipate 2% to 3% better residual EVM Infiniium Digital Oscilloscope 89601A VSA Software + Cal Wizard PSA 321.4 MHz IF output to digitizer PSA Spectrum Analyzer + Opt. 123

Simplified Block Diagram for System Calibration RF out Calibration source PSG, ESG, MXG 10 MHz in 89601A and Calibration SW on PC 10 MHz in L A N 10 MHz out E4440A Series PSA or N8201A down converter Digitizer (Infiniium Scope) DUT signal RF input 321.4 MHz out Chan 1 input

Results of using multi-instrument extended cal Satellite Downlink Band (18 GHz) EVM = 2.4 % for 210 MSym/sec QPSK, 300 MHz BW

Summary of different levels of calibration Type of Calibration Requirements Benefits Comment Internal Included in instrument Calibrates internal IF path to 80MHz Available on PSA Extended 89601A software, PSA, Source Include external devices (preselector, amp, filter) in cal @ desired center freq PSA Opt. 235 App Note 1443 Wideband Extended 89601A software, PSA, Scope, Source Full wideband path calibration @ desired center freq Available Summer 2008

Equipment alternatives for measuring wide BW signals (Amplitude measurements*) E4440A PSA Series Spectrum Analyzers To 10 MHz information BW E4440A PSA Series Spectrum Analyzers Option 122 To 80 MHz information BW Internal correction capability *With specific comms options phase is measured

Equipment alternatives for measuring wide BW signals (Phase and amplitude) 89601A software connected to the PSA over LAN or USB Extended correction capability The digitized signal (amplitude and phase) from the PSA is analyzed by the 89601A software Information BW up to 80 MHz

Equipment alternatives for measuring wide BW signals (Phase and amplitude) Cont d N9020A MXA spectrum analyzer with 89601A VSA software built-in 25 MHz Information bandwidth

Equipment alternatives for measuring wide BW signals (Phase and amplitude) Cont d PSA, Infiniium Scope and 89601A VSA software Multi-instrument wideband extended calibration capability 250 MHz information bandwidth using PSA as down converter Available Summer 2008

Equipment alternatives for measuring wide BW signals (Phase and amplitude) Cont d DSO 90000A Infiniium Scope with 89601 VSA SW 13 GHz Information Bandwidth, 89601A VSA SW installed in built-in PC

Conclusion Three different levels of calibration have been presented: Built-in calibration available on PSA, X series (Created by: Jay Wardle, David Rasmussen, Dave Nunnaly, Joe Tarantino, Bob Matreci) Extended calibration at a specific center frequency and over the information BW (using 89601A SW) (Created by: David Rasmussen, Bob Cutler) Wideband extended calibration on multi-instrument systems (89601A, PSA and Scope) (Created by: Bob Matreci, David Rasmussen, Eric Spotted-Elk)