IQ reflected power canceller for an FMCW radar

[摘要] ENGLISH ABSTRACT: Large close range environmental reflections or poor isolation between the transmitand receive paths of an FMCW radar can overload the receiver. The In phaseand Quadrature phase (IQ) Reflected Power Canceller (RPC) provides a solution tothe problem by cancelling any close range reflections. In this study a procedure tooptimise the design of an RPC is developed and the performance limits of a practicalRPC is investigated in depth.There are four focus areas in the evaluation and design of the IQ Reflected PowerCanceller. First, an analysis was performed on a theoretical IQ Reflected Power Canceller,which provided insight into how the system functioned and made it possibleto identify practical application issues that would arise during the design.The next focus area was the IQ Reflected Power Canceller's dynamic range.Equations, based on the power and noise characteristics of each component in thecanceller, were derived. From these equations, a system, with an optimised dynamicrange, could be developed.Next, the IQ Reflected Power Canceller's feedback loop stability was investigated.The canceller is an active negative feedback control system but, in order to obtainthe negative feedback, the feedback signal has to be phase shifted by 180 degrees tothe phase of the input signal. An analysis of the canceller's RF phase contributionresulted in an equation that can be used to manage the nett RF phase in the feedbackloop.The evaluation model of the IQ Reflected Power Canceller produced favourableresults. The tests performed on the system included measuring the level of cancellationthat can be achieved, whether the dynamic range corresponds to the predictedvalues and the amount of RF phase error that can be introduced in the feedbackpath while maintaining a stable system.The IQ Reflected Power Canceller was found to perform well in the evaluation.It provided a cancellation of more than 45 dB for close range reflections and thecanceller remained stable across a wide range of RF centre frequencies (1 GHz).This means that the FMCW radar's frequency modulation bandwidth will not belimited because of the IQ Reflected Power Canceller. The evaluation clearly showedthat the modulator in the feedback loop is the critical element that determines thedynamic range of the radar with an RPC.

[发布机构] Stellenbosch University