GET10B Radar Measurement Basics- Spectrum Analysis of Pulsed Signals. Copyright 2001 Agilent Technologies, Inc.

Transcription

1 GET10B Radar Measurement Basics- Spectrum Analysis of Pulsed Signals Copyright 2001 Agilent Technologies, Inc.

2 Agenda: Power Measurements Module #1: Introduction Module #2: Power Measurements Module #3: Time Domain Measurements Module #4: Noise Measurements Module #5: Evaluating I/Q Demodulator Errors Module #6: Pulsed Component Measurements Page 2

3 Demo: Power Meter Measurement See Demo Page 3

4 Hi.. I m John Wineman, and I ll be presenting the demonstrations for today s seminar. Page 4

5 we are going to measure CW and then pulsed power from the new PSG signal generator. Page 5

6 I ll set the center frequency of the generator to 20GHz and the output power to +10dBm. Page 6

7 We ll use a high quality microwave cable with a 10dB pad at the output to insure a good VSWR. Page 7

8 The first thing we must do to make a good measurement is to calibrate the power head. Page 8

9 The first step in calibration is to zero the power meter. This corrects for DC offsets in the meter. Page 9

10 Once the zero is complete, we need to run the power cal. Note the precision 50MHz source. Page 10

11 After the cal is complete, we must enter the frequency of the signal to be measured 20GHz. Page 11

12 Now that the meter has been zeroed and calibrated, we will connect the sensor to the PSG. Page 12

13 The CW power of the PSG is set to +10dBm, and through the 10dB pad, we measure -0.89dBm. Page 13

14 Now turn on a the pulse modulator with a 1usec PW and 10usec PRI and measure dBm. Page 14

15 .and so with a 1 sec pulse width and a 10 sec pulse repetition interval, we have a 10% duty cycle. The average power of this signal is dBm. Note that the pulsed power dropped from our CW power (which is also our peak power in this instance) = 10log(PW/PRI) = 10*log(1 sec/10 sec) = -10dB This agrees nicely with our measured results. Page 15

16 Q and A Agilent Restricted Page 16

17 Why Measure Power Spectrum? Unintentional radiation Wastes expensive peak power Increases vulnerability (creates a signature for the particular transmitter) Interferes with other electronic signals Inbandspurs A F } } Desired Radiation Out of Band Radiation Unintentional Radiation Page 17

18 Spectrum Analyzer Block Diagram RF Input Mixer IF IF Peak Detector LO Smoothing Sweep (Animation) Animation Page 18

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23 Q and A Agilent Restricted Page 23

24 VSA Block Diagram Page 24

25 Measuring Pulsed Power with a Spectrum Analyzer Pulsing RF Desensitizes Measurement Pulse Desensitization = 20 log (PW/PRI){ = 60dB Peak Pulse Power PRF Measured Power -30dBm Example Measured: P meas = -30 dbm PRI = 1 ms PW = 1 s (Animation) Line Spectrum 1 PW Calculated: = -60 db P peak = 30 dbm Animation Page 25

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35 Q and A Agilent Restricted Page 35

36 Power Power Pulse Parameters PRF=1/T T Peak Power Pulse Width t Time PRF=1/T Average Power Pavg = Ppk * t /T The frequency domain representation of a pulse. 2/t Frequency Page 36

37 How the Spectrum Changes With PRF Same PRF t PRF Same t PRF Same t Same PRF t Page 37

38 Measuring with a Spectrum Analyzer Advantages Wide frequency range Wide dynamic range Zero span (time domain) Relative power measurement Band Power Considerations Identification of narrowband vs. broadband signals Absolute amplitude accuracy Dealing with noise like measurements Page 38

39 Spectrum Measurements COHO BPF AMP RF BPF PREDRIVER PULSED POWER DUPLEXER AMP TRANSMITTER Antenna Transmitter/Exciter STALO PRF GENERATOR PULSE MODULATOR RECEIVER PROTECTION LNA ADC S/H LPF VIDEO AMP FREQUENCY AGILE L.O. Doppler and Range FFT Processor COHO LIMITER LPF 90 o o 0 SPLITTER 2nd IFA IF BPF 1st IFA IF BPF ADC S/H LPF VIDEO AMP 2nd L.O. Receiver/Signal Processor Page 39

40 Demo: Band Power Measurement Using a Spectrum Analyzer See Demo Page 40

41 We will now use the spectrum analyzer to take a closer look at our pulsed signal. Page 41

42 First, we will do a preset. This defaults to a reference level of 0dBm. Our peak signal level. Don t let the smoke out!! Page 42

43 Connect the PSG to the spectrum analyzer, set the CF to 20GHz and Span to 5MHz. Observe the -.79dBm CW signal near the ref level Page 43

44 Now turn on the pulse modulation. The power of the central line drops as 20*log(duty cycle). The marker now reads dBm. Page 44

45 Now integrate the power in the central three lobes using band power markers. The band power (average power) is dBm. Page 45

46 Q and A Agilent Restricted Page 46

47 Frequency Selective Time Domain Measurement Swept tuned spectrum analyzer in zero span Using a fast internal digitizer Look at the spectrum analyzer s detected video Vector signal analyzer Faster than a swept tuned analyzer Can make complex measurements (phase, group delay, etc) Page 47

48 Pulsed Power Measurements COHO BPF AMP RF BPF PREDRIVER PULSED POWER DUPLEXER AMP TRANSMITTER Antenna Transmitter/Exciter STALO PRF GENERATOR PULSE MODULATOR RECEIVER PROTECTION LNA ADC S/H LPF VIDEO AMP FREQUENCY AGILE L.O. Doppler and Range FFT Processor COHO LIMITER LPF 90 o o 0 SPLITTER 2nd IFA IF BPF 1st IFA IF BPF ADC S/H LPF VIDEO AMP 2nd L.O. Receiver/Signal Processor PM SA Page 48

49 Demo: Zero Span Pulse Measurements Using a Spectrum Analyzer See Demo Page 49

50 Now we will use the spectrum analyzer as a fixed tuned receiver and see the pulse power vs time. Page 50

51 Set the Span to 0Hz, RBW to 8MHz, and the Sweep time to 10 sec, and trigger externally. Page 51

52 Now we can use the marker to measure the peak power of our signal in an 8MHz bandwidth. The marker reads a peak pulse power of dBm. Page 52

53 Q and A Agilent Restricted Page 53

54 Thanks for Attending!