Pulsed RF Signals & Frequency Hoppers Using Real Time Spectrum Analysis

Transcription

1 Pused RF Signas & Frequency Hoppers Using Rea Time Spectrum Anaysis 1 James Berry Rohde & Schwarz Pused Rea Time and Anaysis Frequency Seminar Hopper Agenda Pused Signas & Frequency Hoppers Characteristics Traditiona Measurement Methods & Limitations Rea Time Spectrum Anaysis Definition Impementation in FSVR Frequency Mask Triggering Live Demonstration Q & A 2 James Berry Pused Signas What is a pused signa? An RF signa which is switched on / off periodicay Within the puse the carrier frequency might have additiona ampitude/frequency or phase moduation. Important parameters are the Puse width t and the puse repetition interva time T 3 James Berry 1

2 Pused Signas 4 James Berry Pused Signas What does the Spectrum Anayzer dispay? Due to the periodic switching the typica puse spectrum is a sin x / x function. Remember: Important parameters are: the Puse Width (t) the Puse Repetition Interva time (T). Question: Where do we see them in the spectrum? 5 James Berry Pused Signas 6 James Berry 2

3 Measurement in Frequency domain How much power does the SA show in frequency domain view? Remember: Important parameters are the Puse Width (t) and the Puse Repetition Interva time (T). Depending on the puse parameters we can cacuate the Puse desensitation factor. The ine spectrum is dispayed for RBW < Puse Repetion Frequency For the ine spectrum the eve is independant of the RBW The puse desensitation factor is ony dependant on puse parameters: 7 James Berry Measurement in Frequency domain How much power does the SA show in frequency domain view? The desensitation factor is the reduction of the eve measured within the puse bandwidth of the spectrum anayzer Marker reading + desensitation factor = Peak Power Exampe: Puse Repetition Interva (T): 1ms Puse Width (t): 100 us Desensitation factor = - 20 db Peak Power = dbm 8 James Berry Measurement in Frequency domain Why is the RBW setting so important on pused measurements? With a bandwidth wider than the spacing but sti smaer than the spacing of the first nu in the enveope (1 / puse width), we get an enveope spectrum. Changing the RBW wi ead to changes in the measured eve. The Puse desensitation factor is now depending on the puse parameters and the RBW. Reason: The bandwidth is wider than the spacing of the spectra ines. The measured ampitude depends on the number of ines within the bandwidth and the tota signa bandwidth. 9 James Berry 3

4 Measurement in Time Domain What information is avaiabe in time domain measurements? With a wide bandwidth receiver we are abe to characterize many important parameters about the puse shape of our signa. Time domain information is what todays radar designers are most interested in. 10 James Berry Measurement in Time Domain Why is the RBW setting so important on pused measurements? With the RBW too wide the ine or enveope spectrum changes to a time domain spectrum, we start to see the impuse response of the RBW fiter 11 James Berry Measurement in Time Domain Which measurements on pused signas are aready avaiabe? With the SA in time domain, the N db down marker gives a direct singe button measurement for Puse Width. The norma Peak Marker aows to measurement of Peak Power The deta markers aows to measure the parameters ike rise time, fa time, puse repetition interva, overshoot etc. 12 James Berry 4

5 Measurement in Time Domain What is the shortest puse for a given RBW setting on pused signas? With a wide RBW and VBW the spectrum anayzer is abe to track the enveope of the RF puse, we can see the impuse response of the puse The maximum RBW/VBW imits the SA capabiity to measure narrow puses Rue of Thumb for the shortest Puse you can measure: Puse width >= 2 / RBW For SA 10 MHz RBW: FSV/FSU: ~ 200 ns 13 James Berry Frequency Hopping Signas Simiar to Pused Signa Frequency changes periodicay 14 James Berry Agenda Pused Signas & Frequency Hoppers Rea Time Spectrum Anaysis Limitations of conventiona methods Definition Impementation in FSVR Triggering 15 James Berry 5

6 time time Swept Spectrum Anaysis Limitations Sweep speed heps, but RBW fiter must sette at every frequency point LO setting from end 1 st sweep to start of next Processing time between points Great uncertainty with pused / hopping signas 17 James Berry Swept Spectrum Anaysis Limitations frequency 18 James Berry Swept Spectrum Anaysis Limitations frequency 19 James Berry 6

7 time How Can I See Everything? Frequency, MHz 20 James Berry What is Rea-Time Definition of Oscioscope Users: Rea-Time Over-samping foowing Nyquist rue Non Rea-Time: Nyquist Rue is vioated: Samping rate is smaer than 2x highest signa frequency. Fase reconstructed (aias) waveform is dispayed!!! Non Rea-Time scopes use varying offsets... >10 sampes Aias Input Signa 21 James Berry What is Rea-Time With scope definition R&S Spectrum Anayzers are Rea-Time instruments aready: FFT Fiters in IQ (non-swept) mode There is aways oversamping in modern spectrum anayzers BUT In the word of spectrum anayzers and monitoring appications Rea-Time means: Do not ose any information! 22 James Berry 7

8 What is Rea-Time Rea-Time scopes fufi this requirement for a wide input bandwidth range, when Number of sampes < Capture Memory: e.g. R&S RTO : 8 ms for 2 GHz Modern spectrum/signa anayzers fufi this requirement for imited bandwidth (demoduation bandwidth), when Number of sampes < Capture Memory: R&S FSQ: 2 s for 120 MHz Seamess capturing no bind time Capture Buffer Post Processing 23 James Berry What is Rea-Time Spectrum anayzers and Rea-Time scopes fufi this requirement for: Number of sampes < Capture Memory R&S FSQ: 8 s Rea-Time recording for 28 MHz R&S RTO : 10 ms Rea-Time recording for 2 GHz After this data capturing and signa processing there is a bind time and information is ost before next data can be captured! 24 James Berry What Reay is Rea-Time A Rea-Time spectrum anayzer shows the spectrum without any oss of data: R&S FSVR No Bind Time! Time FFT FFT FFT FFT 25 James Berry 8

9 Concept of R&S FSVR Based on R&S FSV The Rea-Time spectrum anayzer R&S FSVR Based on the successfu signa and spectrum anayzer R&S FSV Fuy fedged spectrum anayzer Same RF front end as FSV => same RF performance as R&S FSV Same user interface A appication firmware options, avaiabe for R&S FSV Neary a hardware options of R&S FSV avaiabe for R&S FSVR Input frequency range up to 40 GHz 27 James Berry Concept of R&S FSVR Additiona Hardware The R&S FSVR is equipped with additiona Hardware: Rea-Time board (extension unit) YIG-fiter-bypass (FSVR13/FSVR30) Necessary to transfer and processing of a huge amounts of data Very short time avaiabe Mother board is PCI-express Frontend With YIG-Bypass AD Converter Standard anayzer backend RTSA,FPGA PCIe- Interface CPU or Rea-Time board 30 James Berry Rea-Time Appications Spectrum Seamess Capturing and dispay of spectrum up to 40 MHz Digita Signa Processing: AD Converter 16 bit 128 Msampes/s Digita Downconverter 50 Msampes/s 50 Msampes/s I Q 250,000 FFT/s Detector Max, Min, Average, Screen Update Rate 30/s Sampe 32 James Berry 9

10 Concept of R&S FSVR Additiona Hardware 33 James Berry What About Short Events? Samping is a time domain process Occurs over a set period of time MSPS Many events shorter than fu samping time How to capture accuratey? 36 James Berry What About Short Events? Samping is a time domain process Overap ensures capture 37 James Berry 10

11 What is Rea-Time Overap of FFTs FSVR 80% Overap FFT Effective exposure time = 20 ms 38 James Berry What About Short Events? Samping occurs over a set period of time Overap ensures capture Windowing reduces side obes 39 James Berry What About Short Events? Samping occurs over a set period of time Overap ensures capture Windowing reduces side obes 40 James Berry 11

12 Time Resoution of FFT Events Exampe of Frequency Hop Freq F1 -> 10 ms gap -> Freq F2 Gap < 20 ms exposure time Overap => previous FFT resuts hed over Components from F1 & F2 may appear briefy 41 James Berry Time Resoution of FFT Events 42 James Berry Rea-Time Appications Spectrogram Typica appications: Observation of frequency hopping signas R&D of communication appications Service and Maintenance Monitoring of frequency bands for Reguation bodies Miitary appications - (radio monitoring) Aerospace appications - (sateite monitoring) Frequency hopping of a Buetooth signa During frequency scan 43 James Berry 12

13 Rea-Time Appications Spectrogram 44 James Berry Triggering Same as avaiabe in swept spectrum Free Run Externa Power Video Frequency Mask 45 James Berry Rea-Time Appications Frequency Mask Trigger, FMT With the Frequency Mask Trigger (FMT) the instrument can trigger on a specia event in the frequency domain If any FFT component vioates the mask, a trigger event occurs AD Converter 16 bit 128 Msampes/s Digita Downconverter 50 Msampes/s I 50 Msampes/s Q 250,000 FFT/s Frequency Mask Trigger 46 James Berry 13

14 Rea-Time Appications Frequency Mask Trigger, FMT mask definition tabe (Persistence), Spectrum 48 James Berry Rea-Time Appications Frequency Mask Trigger, FMT, Auto-Set mask 49 James Berry Rea-Time Appications Frequency Mask Trigger, FMT Typica appications: Evauation of the spectrum of of signas, which are avaiabe ony once in a whie: Causing mafunction of base stations Eectromagnetic interference Radio signas Deeper Evauation of signas (moduation anaysis), which are difficut to capture by post processing of capture memory using interna measurement appications: Post Processing Trigger-Event 50 James Berry 14

15 Rea-Time Appications Persistence Spectrum Digita Persistence Spectrum (Persistence Spectrum) shows a spectra histogram or probabiity density function reveaing effects, which cannot be seen in norma spectrum anayzer mode Digita Signa Processing: AD Converter 16 bit 128 Msampes/s Digita Downconverter 50 Msampes/s 50 Msampes/s I Q 250,000 FFT/s Persistence Spectrum 51 James Berry Rea-Time Appications Persistence Spectrum Typica appications: Evauation of combined signas, where one signa is hidden by another one Setting effects Monitoring 52 James Berry Rea-Time Appications Screen Shots Pused signas Swept sources Airborne RADAR Pused signas Setting of VCO GSM Band 53 James Berry 15