UWB Antennas & Measurements. Gabriela Quintero MICS UWB Network Meeting 11/12/2007

Transcription

1 UWB Antennas & Measurements Gabriela Quintero MICS UWB Network Meeting 11/12/27

2 Outline UWB Antenna Analysis Frequency Domain Time Domain Measurement Techniques Peak and Average Power Measurements Spectrum Analyzer Settings Fourier Series Fourier Transform UWB Measurements

3 Outline UWB Antenna Analysis Frequency Domain Time Domain Measurement Techniques Peak and Average Power Measurements Spectrum Analyzer Settings Fourier Series Fourier Transform UWB Measurements

4 UWB Antennas Impulse radio UWB pulse ( GHz) MICS pulse (4 4.5 GHz) Time and frequency domain Analysis Still with basic antenna architectures Monopole Vivaldi

5 Time and Frequency Domain Two different softwares used to characterize the antennas Ansoft HFSS FD Frequency Sweep at all frequencies Parameters in FD (S11, Gain, E-field, etc.) CST Microwave Studio TD Select the pulse BW Parameters in FD (S11, Gain, etc.) E-field in TD

6 Frequency Domain Tx Rx Transfer Function - S 21 Relates the output voltage with the input jωr voltage c V ( ω) = H( ω) V ( ω) e r Can be derived from the Friis Transmission Equation t λ (, ) (, ) ˆ ˆ cdt cdr t r t θt φ 2 t r θr φr ρt ρr P ( )( ) r 2 2 = e e Γ Γ Pt 4π R D D And obtain V ( ) ( 2 1 ) r ω λ = ecdt S11 Et ( ω, θt, φt ) V ( ω) 4πR t

7 Frequency Domain Tx Rx HFSS Simulation S11 E-field Matlab Transfer Function Rx Pulse TD IFFT Rx Pulse PSD Pulse PSD

8 Monopole System Tx Rx -5 Return Loss S11 Simulated Measured 1.9 Normalized Magnitude Simulated Measured -5 Phase [radians] Magnitude [db] TF S HFSS NWA Frequency [GHz] Frequency [GHz] Frequency [GHz] 2 Power Spectral Density 1 Input Vs. Output pulse (normalized) Rx + Tx Pulse PSD Gaussian Pulse [db] Frequency [GHz] Input Simulated Measured Gaussian Pulse Time [ns] Input Simulated Measured Rx + Tx Pulse 2.8 MICS Pulse, [db] MICS Pulse Frequency [GHz] Time [ns]

9 Vivaldi System Tx Rx -5 Return Loss S11 Simulated Measured 1.9 Normalized Magnitude Simulated Measured -5 Phase [radians] Magnitude [db] TF S HFSS NWA Frequency [GHz] Frequency [GHz] Frequency [GHz] 2 Power Spectral Density 1 Input Vs. Output pulse (normalized) Rx + Tx Pulse PSD Gaussian Pulse, [db] Frequency [GHz] Input Simulated Measured Gaussian Pulse Time [ns] Input Simulated Measured Rx + Tx Pulse MICS Pulse, [db] MICS Pulse Frequency [GHz] Time [ns]

10 CST: Monopole Antenna E-plane H-plane 4.25 GHz 6.85 GHz

11 CST: Vivaldi Antenna E-plane H-plane 4.25 GHz 6.85 GHz

12 Time Domain Monopole Vivaldi 1 UWB Pulse 1 UWB Pulse.5 Input Pulse E-field at 8.5 Input Pulse E-field at MICS Pulse 1 MICS Pulse

13 Time Domain Fidelity Factor Measures the faithfulness with which a device reproduces the time shape of the input signal. f(t) = Input signal at antenna terminals r(t) = Radiated E-field in time domain The signals are normalized to have unit energy r( t) and f() t rˆ( t) = r( t) 2 dt 1/ 2 fˆ( t ) f() t = 1/2 2 dt

14 Time Domain The fidelity parameter, F, is determined by the peak of the cross-correlation function of the signals F = max fˆ ( t) rˆ ( t+ τ ) dt τ

15 Time Domain Input signal CST Simulation Fidelity Factor E-field (t,θ, φ)

16 Time Domain Monopole Fidelity Factor Vivaldi Fidelity Factor 3-3 UWB Pulse MICS Pulse 3-3 UWB Pulse MICS Pulse ±18 ±18

17 Outline UWB Antenna Analysis Frequency Domain Time Domain Measurement Techniques Peak and Average Power Measurements Spectrum Analyzer Settings Fourier Series Fourier Transform UWB Measurements

18 MEASUREMENTS Average Power Peak Power E = P avg P Pτ eff τ = T eff = P avg T

19 MEASUREMENTS

20 Spectrum Analyzer RBW VBW Scan Time

21 Spectrum Analyzer Line Spectrum Pulse Spectrum 1 B> or B>PRF T A pulse repetition rate equal to the resolution bandwidth is the demarcation line between a true Fourier-series spectrum, where each line is a response representing the energy contained in that harmonic, and a pulse or Fouriertransform response. Agilent Spectrum Analyzers Series. Application note 15-2 pp. 32

22 Line Spectrum

23 Line Spectrum All individual frequency components are resolved. Line spacing is 1kHZ = PRF Spacing of sidelobe minima is 1kHz = The amplitude of each line will not change when RBW is changed, as long as RBW<.3PRF 1 τ eff

24 Line Spectrum Pulse Desensitization Only valid for Fourier line spectrum. τ eff αl[ db] = 2log1 = 2log1 T Pavg [ db] = 1log 1( τ eff PRF) P peak ( τeff PRF )

25 Pulse Spectrum It s a combination of time and frequency display. The lines that form the envelope are pulse lines in time domain. Each line is displayed when a pulse occurs. Frequency domain display of the spectrum envelope. The amplitude of the envelope increase linearly as RBW increases. (As long as RBW <.2/ τ eff ).

26 Pulse Spectrum -3dBm CW carrier modulated by a pulse train with a PRF of 1Hz, τ eff = 1µs and RBW = 1kHz =.1/ τ eff

27 Pulse Spectrum In Figure 23, we lost the linear relationship between bandwidth and display amplitude RBW >.2/ τ eff. The resolution of the sidelobes is lost to a great extent. In Figure 24 RBW = 1/ τ eff, we get a display with an amplitude practically equal to the peak amplitude of the pulsed signal.

28 Pulse Spectrum Pulse desensitization correction factor α [ db] = 2log1( τ K RBW ) K p = B imp RBW K = for Agilnet ESA Series 856x or 859x eff

29 Average Power FCC Definition The average limit is 5 uv/m, as measured at 3 meters with a 1 MHz resolution bandwidth (RBW). Equivalent to an EIRP of dbm/mhz EIRP [dbm/mhz] FCC Indoor Spectral Mask Frequency [GHz]

30 Average Measurements If 1 khz > VBW >1 Hz Video averaging should be used in conjunction with peak hold. If NO dithering or PPM Line spectrum setting (VBW RBW) RBW <.3 PRF Average level = highest line in the emission line spectrum

31 Average Measurements If dithering or PPM True pulse spectrum settings A pulse desensitization correction factor would be added to the measurement to obtain a peak level. The average is calculated using the duty cycle factor in db P P avg peak ( τ PRF ) [ db] = 1log 1 eff

32 Peak Measurements pp. 174

33 Peak Measurements Peak level when measured over a bandwidth of 5 MHz 5MHz widest victim receiver that is likely to be encountered. Peak measurements based on a 5 MHz (resolution) bandwidth may not be feasible. The widest available RBW that can be employed for peak measurements is 3 MHz.

34 Peak Measurements

35 Peak Measurements Peak emission level of dbm/5 MHz = 58mV/m at 3 meters is adopted. Equivalent to: A peak EIRP of dbm/3 MHz Peak field strength of 3.46 mv/m at 3 meters with a 3 MHz RBW.

36 Rules of Thumb P avg No dithering or PPM P avg Dithering or PPM Peak Interference Power Line Spectrum RBW<.3PRF Pulse Spectrum PRF < RBW < τ eff 1 scan time[s/div] PRF[Hz]

37 QUESTIONS?