RFI Suppression in Low Frequency UWB SAR Using the RLS Algorithm

Sammanfattning: Synthetic Aperture Radar (SAR) has many applications within ground image sensing and navigation. UltraWide Band(UWB) SAR operating at Ultra High Frequency /Very High Frequency(UHF/VHF) are usually a ffected by the Radio Frequency Interferences(RFI) from civilian communication bands which causes SIR(Signal to Interference Ratio) to go down. In response target detection is drastically aff ected in the system. Therefore, mitigation of the dominating energy from Narrow Band(NB) broadcast and mobile communication sources is highly required. Which eventually speaks out demand for suppression of these RFI's for e ective SAR operation with such co-existing sources of UWB. The accurate discrimination of target, from sources scattered around surrounding objects, is practical advantage of UWB SAR due to ne resolution in range and azimuth after pulse compression and SAR processing. But this advantage is weakened due to the RFI. Mitigating RFI is the main aim of this thesis. For this, we have applied an adaptive ltering technique using Adaptive Line Enhancement(ALE) implemented with the Recursive Least Square (RLS) algorithm. The capability of fast tracking time varying signal and noise statistics is better in RLS compared to other adaptive techniques like LMS, NLMS etc. Due to which it is preferred for suppressing the mobile communication signal which is mixed with the SAR signal, due to operating in the same frequency ranges. ALE uses delayed received signal to de-correlate the SAR signal in order to do interference suppression. Thus it is being used for separating the desired SAR pulses for image formation. The results show that RFI has been reduced strongly in simulation and acquired real data using ALE with RLS. RFI suppression done by using this method, is also analyzed by testing in real laboratory environment.