MODIFIED RECTANGULAR PATCHES FOR SELF-OSCILLATING ACTIVE-ANTENNA APPLICATIONS

Two modifications to a rectangular-patch antenna, suitable for the int egration of active devices, are presented. In the first modification, the impedance inverter was placed in the rectangular opening formed by removing the central part of the patch. This modification allows opti mal matching of the active device by changing the position, width, and length of the impedance-line transformer. An oscillating antenna, usi ng this modified patch and a Gunn diode, showed a high EIRP, higher sp ectral purity, and substantially lower cross-polarization levels, in c omparison with the reference active antenna with an unmodified patch. Because of the higher overall Q, this modification is recommended for active-antenna applications with active devices that have a narrower n egative-resistance bandwidth. In the second modification, an active de vice (Gunn diode) was integrated directly into a rectangular opening i nside the patch, without the use of a line transformer. This reduced t he overall Q of the antenna, thus allowing wide-band frequency tuning by changing the bias voltage. A clear spectrum, with no spurious compo nents of the free-running oscillating antenna, was observed. Radiation patterns in the E and H planes were measured. Low levels of crosspola rization, as for the first modification, were obtained. Injection-lock ing properties were investigated throughout the tuning range. A relati vely wide locking range, with a good locking gain, was achieved. Such a miniaturized wide-band VCO antenna is applicable for integration in injection-locked active arrays, and spatial power combiners.