High precision phase shifting techniques

The report describes techniques for the continuous monitoring and control of phase and output power in active phased array modules. The output phase and power of the signal from the module are sensed by a simple six-port network using Schottky barrier detectors; the output voltage from these detectors is used in a control loop to provide correction signals to a phase shifter and attenuator. Two control schemes have been compared. One is a digital loop using a microprocessor and this achieves an overall control accuracy of 0.1dB and 1 deg, but has the disadvantage of complexity and of a response time in the order of hundreds of milliseconds. The second is completely analogue loop which has a response time of less than 100ns and can provide real-time phase correction during the output pulse from a module. Although the control accuracy is marginally worse with the analogue loop in these initial tests, it is expected that refinements in the continuation of this work will enable the same accuracy to be achieved in both digital and analogue loop techniques. The application of these techniques may be particularly important in future monolithic integrated circuit radar module design.