A 4-Element Balanced Retrodirective Array for Direct Conversion Transmitter

A phase conjugated array capable of sending two individually modulated signals towards the direction of an interrogator is proposed. Each of the array elements is a dual-fed patch with one input port connected to a 90° phase shifting element and a resistive field effect transistor (FET) mixer and the other port just the mixer alone, making the array a balanced structure. A 4-element working prototype was designed at the center frequency of 5.8 GHz. A linearly polarized retrodirectivity has been experimentally confirmed by measuring bi-static radiation patterns with the interrogating signal coming at 0°, +30°, +60°, -15°, and -45°. A 8.6-dB peak power variation of re-radiation within ±60° normal to plane of the array has been shown in the measured mono-static radiation patterns. To test the ability of direct conversion, an active integrated direct conversion receiver employing the same array has been designed to receive and demodulate the response signals from the phase conjugated array. A 5 MHz square and 8 MHz sinusoidal waves as two base-band signals were carried through the phase conjugated array and successfully recovered by the direct conversion receiver.