Measurement and modeling of a microwave active-patch phased array for wide-angle scanning

An active antenna consisting of an integrated oscillator with a passive radiator has been arrayed and beam-scanned using a new principle for phase shifting. The radiating elements consist of a transistor oscillator whose frequency is controlled by a rectangular microstrip patch antenna. Each oscillator is injection locked to an external source. The phase control of the radiated wave is achieved by varying the bias on the transistor. Individual element performance has been characterized for potential use as an array element and is comprehensively reported. Methods used to achieve configurations with full 360° phase control have been investigated utilizing novel configurations and cascaded oscillator pairs. Close to 360° of radiated phase control from each element has been achieved. Measured results on an experimental four-element S-band array indicate that beam scanning in excess of ±60° can be achieved. Mutual coupling effects on this new form of array are studied both experimentally and theoretically. A van der Pol (1934) model for the weak coupling that is occurring on the array is developed and used to qualitatively predict the phase offsetting on array elements. Reasonable agreement between theory and experiment is obtained and it is observed that good control of the coupling mechanism is essential to array performance within this new form of active integrated phase shifterless array