An active subharmonic retrodirective array using dual polarized microstrip antennas

Retrodirective antenna arrays, when illuminated by an interrogator signal, transmit a signal back towards the interrogator in the same direction as the incoming signal, without any prior knowledge of the source direction. With a retrodirective array the system efficiently transmits a signal without any digital signal processing.

This thesis focuses on the design of an active subharmonic retrodirective array. It involves the design of novel dual polarized coplanar waveguide fed microstrip antenna. Aperture coupling is used for the microwave power to couple to the radiating patch. A common ground plane between the feeds and patch supports the apertures. Orthogonal coplanar waveguide feeds have been used to obtain dual polarization. Also, a part of the thesis deals with the single balanced active subharmonic mixer design. To have a conversion gain, useful in link gain, FETs have been used as the mixing devices. Subharmonic mixer structures are employed when fundamental LO injection is not feasible due to oscillator frequency limitations. A subharmonic mixer is pumped at half the LO frequency, and the RF signal is mixed with the second harmonic of the LO frequency.

Full-wave analyses were performed in the commercial software package Ansoft Ensemble. Subharmonic mixer was realized in Serenade SV. The antenna and mixer models were implemented in hardware as well using a T-Tech milling machine. Results were measured on a network analyzer to show simulation validity.