Principles of Modern Radar - Volume 2 1891121537

744 CHAPTER 17 Advanced Processing Methods for Passive Bistatic Radar SystemsFinally few conclusions are drawn in Section 17.7 on the potentialities and furtherprocessing requirements for the future passive radar sensors.17.1.2 Key PointsImportant concepts developed throughout the chapter are summarized as follows:• PBR exploits existing illuminators of opportunity which results in the exciting possibilityof low cost surveillance, covert operation, and reduced electromagnetic pollution.• PBR practical feasibility for surveillance purposes has been well established. Nevertheless,there are still many challenges to be solved involving both technology developmentand processing techniques.• A dedicated and separate receiver channel is required to collect the transmitted signal.This is subsequently used as the reference signal and is correlated with the surveillancesignal for target echo detection.• The evaluation of the bistatic 2D-CCF represents one of the most costly processingsteps in terms of computational burden due to the long coherent integration times. Forreal time operation, cost-effective solutions can be adopted based on both optimum andsub-optimum techniques.• Disturbance cancellation is a required step in the typical PBR processing scheme sinceit allows the removal of undesired contributions received on the surveillance channelalong with the moving target echo (i.e. direct signal from the transmitter and strongclutter/multipath echoes).• The reference signal is usually assumed to be a high-quality copy of the transmittedsignal. In practice, some transmitter-specific conditioning of the reference signal maybe performed to improve its quality and hence the PBR performance.• PBR operation inherently implies that the transmitted waveform is not within the controlof the radar designer. However, in specific cases, proper filters can be used to controlthe sidelobes of the resulting AF.• With the aim to increase the performance and the reliability of PBR systems, advancedmultichannel processing techniques can be applied. These might exploit parallel receiving/processingchannels that differ by frequency, polarization, time, and space.17.1.3 NotationThe following lists many of the variable names found within this chapter:s ref (t), s ref [n] = reference signal complex envelope in continuous and discrete timenotations;s surv (t), s surv [n] = surveillance signal complex envelope in continuous and discrete timenotations;χ(τ,f D ), χ[l,m] = 2− dimensional cross-correlation function (2D-CCF) in continuousand discrete time notations;τ = bistatic time difference of arrival (s);f D = bistatic Doppler (Hz);f s = sampling frequency (Hz);R B = relative bistatic range, i.e. the difference between the 2-waypath length and the transmitter-receiver baseline (m);