Constant phase IF self-tracking receiver analysis and characterisation

A phase locked loop module architecture is implemented as a means for achieving a maximally combining constant phase IF self-tracking receiver. Here each antenna element in the receive array is connected to a PLL which automatically compensates for the phase associated with the angle of arrival of the signal at the array. Thus, the PLL outputs when summed represent IF signals which are automatically beam steered towards the incoming signal. For the purpose of demonstration we have constructed a 6-element array operating using commercially available components at 1GHz. IF self-tracking receive functionality at 300 MHz is demonstrated experimentally for the first time. Near perfect operation over a full 360° azimuth scan is achieved. In addition, a theoretical analysis of the effect that nonlinear mixing has on RMS phase jitter at the IF output of the PLL module is also presented. It is shown that the inclusion of nonlinear mixing products increases IF RMS beam steering phase errors to several degrees as compared to an ideal mixer analysis which predicts almost zero RMS phase perturbation.