Monostatic continuous-wave radar integrating a tunable wideband leakage canceler for indoor tagless localization

Abstract

Continuous-wave (CW) radars have been recently investigated in healthcare aiming at contactless health monitoring. However, a major problem in monostatic CW architectures is represented by the unwanted leakage produced by poor isolation between transmitter and receiver, which can drastically decrease the receiver's sensitivity reducing therefore the radar dynamic range. Although this situation can be easily controlled in case of narrowband CW radar by an appropriate passive microwave design, it becomes much more complicated in case of stepped-frequency CW and frequency-modulated CW architectures that present an ultra-wideband nature. In this paper, a monostatic CW radar integrating a tunable wideband leakage canceler aiming at indoor tagless localization is presented and discussed. The use of the feedforward canceler allows a strong reduction of the unwanted leakage over the whole radar bandwidth. Experimental results demonstrate the feasibility of this approach, showing an outstanding improvement of the radar dynamic range.

Quasi-Circulator Using an Asymmetric Coupler for Tx Leakage Cancellation

“…A quasi-circulator that uses an asymmetric branch-line coupler is proposed for obtaining the optimal design characteristics at the operating frequency, including high Tx-Rx isolation. The asymmetric coupler for a highly isolated circulator is designed using the proposed design equation in (16), wherein the product of the asymmetric ratio of the characteristic impedances of the transmission lines and the unmatched ratio in the unused port of the coupler should be 1. The isolation improvements (compared with the conventional circulators) of 9.07 dB at 2.45 GHz and 7.95 dB at 24.125 GHz are achieved through the implementation of the proposed planar quasi-circulators.…”

“…In the conventional circulator using the symmetric coupler, the parameters k and m of (16) are each designed to be 1. Although the conventional circulator theoretically satisfies (16), the leakage signals that cannot be ignored in the monostatic radar and the wireless communication systems remain in the actual implemented circulator. The transmission lines in the coupler must be precisely implemented with a quarter-wave length to obtain k as 1.…”

“…In addition, insertion losses at all ports increased when the Tx and Rx signals passed through those circulators. Previous studies to reduce the effect of the Tx leakage signals applied to a balanced topology for radar systems [4,[14][15][16]. In this topology, it is necessary for Tx leakage cancellation to generate multiphase Tx signals.…”

An improved self‐interference canceller for X‐band radar transceivers

“…In [13], RPC topology was used to achieve 30 dB isolation with 2.2% FBW at 9.1 GHz. In [14], the authors used two couplers, one for the receiver path and the other for a vector modulator to generate a leakage cancelation signal. To enhance the leakage cancelation level, some articles combined digital techniques to radiofrequency (RF) front-end cancelation [15][16][17].…”