A Technique to improve the dynamic range and linearity of a near-field imager based on the modulated scatterer approach

This paper describes a technique to improve the linear dynamic range of a near-field (NF) imager based on the modulated scatterer technique (MST). The potential of achieving a better dynamic range at the receiver is investigated by eliminating the carrier on which no information is transmitted. This enables us to increase the amplification gain to obtain better signal-to-noise ratio (SNR) and more importantly, expand the imager´s dynamic range. The carrier at the receiving port is minimized by combining the received signal with a 180deg out-of-phase canceller whose magnitude and phase are adjusted adaptively. We first examined the canceller performance, which leads to a reduction of about 60 dB in the magnitude of the carrier, and then its impact on the operation of the NF imager. Significant improvements of NF images were obtained, both in terms of dynamic range and linearity.