Reasearch On Measurement And Generation Of Wideband Pulse Signal Based On Frequency-domain Approach

Due to the simultaneous temporal and spatial focusing characteristics,time-reversal of electromagnetic waves is a promising technique for many applications in wireless communications,radar detection and positioning,wireless power transmission and so on.Time-reversal of high-frequency electromagnetic signals relies on the measurement and generation of wideband high speed waveforms,which may be very expensive or even impractical to implement if performed directly in the time domain by using high-speed analog-to-digital and digital-to-analog converters.This paper proposes a hardware architecture for time-reversal of electromagnetic impulse signals based on frequency-domain approach.In this approach,electromagnetic waveforms are measured and generated with low cost by employing the spectral segmentation and stitching schemes.Specifically,the work accomplished includes the follows:(1)Design and implementation of the frequency-domain approach of waveform measurements.Based on the idea of spectrum segmentation and stitching,the spectrum of a wideband pulse signal is divided into several subbands.A heterodyne circuit architecture is adopted to down-convert the subband signals to baseband,which can be measured with low sampling rates directly,and then stitched to reconstruct the complete spectrum.The performance of the proposed approach with reduced sampling rate is studied experimentally.The experiment is designed to measure a pulse signal with 400 MHz bandwidth divided into four segments,each segment recorded with a sampling rate of250 MHz and stitched to reconstruct the original pulse waveform.The experimental results are as expected,which verifies the feasibility of the frequency-domain approach.In another experiment with increased number of frequency segments,the pulse signal is divided into eight subbands.The sampling rate can be lowered to 125 MHz for measuring the 400MHz-wide pulse signals.The correlation coefficients between the reconstructed signal and original signal are all greater than 0.99,which indicates that the above circuit scheme can achieve high measurement accuracy.(2)Design and implementation of the frequency-domain approach of waveform generation.Based on the idea of spectrum segmentation and spectrum stitching,the spectrum of the pulse signal to be constructed is divided into several subbands.The subband signals is first generated by low-speed digital-to-analog converters in the baseband,and then up-converted to high frequency band.The high-frequency band signals are superposed to obtain the required wideband pulse waveform.Firstly,a frequency domain synthesis scheme for wideband Dirichlet pulse signals is designed and implemented.The baseband Dirichlet pulse sequence with a time-domain pulse width of 27 ns and a frequency-domain bandwidth of 50 MHz can be up-converted and combined to obtain a pulse signal with a time-domain pulse width of about 3ns and a frequency-domain bandwidth of 450 MHz.The experiments constitute a preliminarily verification of the spectrum stitching technique.Secondly,a hardware circuit system is designed to generate arbitrary waveforms based on multi-channel orthogonal modulation and spectral stitching.Pulse signals with 500 MHz bandwidth are successfully generated by superimposing five baseband signals,each with a bandwidth of 100 MHz.(3)An experimental system of time-reversal of wideband pulse signals is constructed.Focal characteristic of the time-reversal system is modeled and analyzed,based on which an experimental system for time-reversal transmission of 400MHz-wide pulse signals is developed.The frequency-domain approach is employed for measurement of received signals and generation of the time-reversed waveforms,which verifies the effectiveness of the proposed approaches.