Software defined noise radar on the basis of FPGA based SPOS board

Software Defined Radar concept supposes to leave for a computer or Digital Signal Processor (DSP) as much “work” as possible. In particular it implies no application of frequency down conversion which in particular, eliminates negative influence of phase noise and frequency instability of local oscillator to be used in conventional radar. In Noise Radar this supposes sampling of both reference and radar returns with the help of analog-to-digital converters (ADC). Nowadays rather fast ADCs with sampling rate up to 3GSamples/second are readily available. This makes feasible implementation of software defined radar not only in HF frequencies, but also in P-band and L-band. One of the challenges of real time signal processing in software defined radar would be a high sampling rate and huge data flow to be processed. In spite of availability of rather efficient DSPs a reduction of sampling rate without loss of radar information is always needed in software defined noise radar implementation. A thinkable approach to overcoming Software Defined Radar design challenges consists in performing with analog circuits not only amplification and radiation/reception of electromagnetic signals, but also primary coherent processing of radar returns in analog way at a carrier frequency. One of the well developed approaches that may be used here is LFM and stepped frequency techniques. They exploit an analog cross-correlation of the radar returns, which enables application of rather slow ADCs and low data flow rate. However elaboration of similar approach to design of wideband Noise Radar in straightforward fashion is rather problematic and requires application of more sophisticated technique. One possible solution consists in application of fast Arbitrary Waveform Generators (AWG) capable of storing not only sounding signal, but also its delayed copies. For real time operation it will require either usage of multichannel AWG (having as many channels as many samples are- - required for cross-correlation function) or two channels AWG for implementation of time-delay waveform with shorter realizations. The latter case may be named as Stepped Delay Noise Radar. A significant constrain in implementing such a radar is related to limited number of range bins and integration time because of finite size of the onboard memory.