Design of a tracking correlation receiver with feedback for radio astronomical interferometry

Abstract

A tracking correlation receiver being developed as part of a flux-density measurement programme for 12·5 MHz radio sources will employ three type-one negative feedback loops. An amplitude insensitive phase loop will control an internal phase shifter to track radio sources through an interferometer aerial pattern. Simultaneously, this loop will keep the inputs to an amplitude multiplier in phase or antiphase. Relative phase read-out will provide for detection of possible phase scintillation.An amplitude loop will use the integrated output from an amplitude multiplier to control a variable reference noise source whose output is added directly to the aerial inputs. This loop will keep the time-averaged multiplier output nulled, such that the output level setting of the controlled reference source is, at all times, indicative of the signal power received by the aerials.A third loop will control an independent noise source whose output is added to one receiver channel. This loop will provide an output of the total noise power received and will keep the operating points of all receiver elements equal in the two channels. The proposed receiver combines principles developed by the authors with those of several other workers. The overall receiver scheme is expected to provide exceptional accuracy and stability, independent of channel gain, phase, and bandwidth. Frequent recalibration will be unnecessary. This paper describes the operation of the proposed receiver scheme and provides test results and data regarding an analogue simulation study of the multiple feedback loop schemes to be used in the receiver.