High performance single antenna quadrature radar front-end with Tx leakage canceller

Abstract

Microwave and millimeter-wave radars have garnered much attention in many applications, such as speed-detection sensors, collision-avoidance sensors, traffic control sensors, health-care sensors, and human motion detectors. For these applications, high performance, small size, and low cost are crucial for the radars. Continuous wave (CW) radars are based on very simple structures, allowing small size with low-cost solutions. In CW radar systems such as FMCW radars or Doppler radars, a high Tx-to-Rx isolation is required to improve sensitivity [4]. A system with two antennas is likely to have high Tx-to-Rx isolation; however, the system size is two times larger than a system with a single antenna. A system with a single antenna must be implemented with a circulator or a coupler following the antenna. As circulators, and especially couplers, show low isolation characteristics, especially at mm-wave frequencies, there are significant Tx leakages from the transmitter to receiver. A reflected power canceller (RPC) has been proposed in order to achieve good Tx-to-Rx isolation in a single antenna system. Recently, an RPC based on DSP was reported. This RPC shows good Tx-to-Rx isolation performance up to K-band frequencies. Another approach to reduce Tx leakage, termed balanced radar topology, was proposed. However, in this approach, when a signal is transmitted, half of the transmitting signal power is dissipated at the terminating resistor of the coupler. In addition, half of the received signal power is dissipated. Quadrature receivers can detect the speed and direction of a target and can also measure the displacement. Even human vital signals are detected very well with quadrature mixing. The receivers receive Doppler signals with much higher signal-to-noise ratios. The two quadrature radar topologies with Tx leakage canceller using Lange couplers are proposed. Linear polarized quadrature Doppler radar with Tx leakage canceller using Lange coupler is f...