Microstrip patch antennas of a proposed type would be tunable over broad wavelength ranges. These antennas would be attractive for use in a variety of microwave communication systems in which there are requirements for transmission and/or reception at multiple, widely separated frequencies.
efforts have been somewhat successful, but have yielded tuning ranges of 20 percent and smaller — much smaller than needed in typical practical cases.
Like prior microstrip patch antennas (both tunable and non-tunable), the proposed antennas would have instantaneous bandwidths of about 1 percent of their nominal or resonance frequencies. However, these would be tunable over much broader frequency ranges — as much as several octaves, depending on specific designs. They could be fabricated relatively simply and inexpensively by use of conventional photolithography, and without need for integration with solid-state electronic or piezoelectric control devices.
An antenna as proposed (see figure) would include a microstrip patch radiating element on a thin ferroelectric film on a semiconductor substrate with a ground-plane conductor on the underside of the substrate. The ferroelectric film could be, for example, SrTiO3 with a thickness of the order of 1 or 2 µm.
To enable operation at multiple desired frequencies, the antenna would be designed to resonate in a fundamental TM01 mode that lies at an odd common denominator of the desired frequencies. (In an odd mode, the antenna would radiate strongly in a direction perpendicular to the antenna plane, while an even mode would place a null of the radiation pattern in the perpendicular direction.)
A simple cavity mathematical model yields the following equation for the resonance frequency of the m,n mode:
fmn = (c/2Πer1/2)[(m/w)2+(n/l)2]1/2,
where m and n are integers, c is the speed of light in vacuum, er is the effective relative permittivity of the combination of the ferroelectric film and dielectric substrate, and w and l are the width and length of the patch, respectively. In practice, resonance frequencies tend to be somewhat lower than predicted by this simple formula, because of fringing fields.
This work was done by Robert R. Romanofsky of Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Computers/Electronics category. Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Commercial Technology Office, Attn: Steve Fedor, Mail Stop 4—8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-16792.