Active integrated antennas (AIAs) with one or more active devices and circuits within the radiating element have been garnering quite a bit of attention. They promise to deliver advantages like compact size, low cost, and adaptability to phased-array-antenna systems. Recently, an AIA element was successfully fabricated on a high-dielectric-constant ({? r} = 10.2) microwave laminate that is 0.635 mm thick. The development hails from Carl H. Mueller, Carol L. Kory, and Kevin M. Lambert from QinetQ's Mission Solutions Group (www.qinetiq.com) together with Richard Q. Lee, Robert R. Romanofsky, and Fe'lix A. Miranda from the NASA-Glenn Research Center's Antenna, Microwave, and Optical System Branch. They were joined in this effort by Frederick W. Van Keuls from the Ohio Aerospace Institute.
That antenna consists of a transmissionfeedback oscillator loaded with a microstrip antenna. The oscillator antenna comprises a very-low-noise, high-frequency field-effect transistor (HF FET) from NEC (www.nec.com). The FET is integrated into the center of a segmented patch antenna that was designed for X-band at 8.5 GHz. At 5 x 6 mm2, the antenna is smaller than most X-band AIAseven though it also was fabricated using microwave laminate and surface-mount active and passive devices.
The researchers set out to improve the phase noise of AIAs fabricated on high ? r substrates while achieving high radiated power levels and good radiation efficiency. See "Small-Size X-Band Active Integrated Antenna with Feedback Loop," IEEE Transactions on Antennas and Propagation, May 2008, p. 1236.