Acoustically driven integrated microstrip antennas and electromagnetic radiation from piezoelectric devices
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For a receiver system to be considered integrated, the antenna and electronics need to be fabricated on a single semiconductor wafer. To avoid EMI problems, the circuitry must somehow be shielded from the environment where the antenna resides. The required shielding may be accomplished by separating the antenna on one side of the wafer from the electronics on the other side with a conducting ground plane. Energy may be acoustically coupled from the antenna to the circuitry through the ground plane via thin film piezoelectric transducers on either side of the wafer. The radiating side of the wafer would then consist of a microstrip antenna and a piezoelectric transducer. Unfortunately, integrated circuit processing constraints place severe limitations on the performance of the microstrip antenna. For the frequency range of interest (1GHz to 2GHz) the thickness of the aluminum metalization may be less than a skin depth, and the conductor losses for the antenna would increase. The thickness of the microstrip antenna substrate can have a strong effect on the radiation efficiency of the antenna, and using standard integrated circuit film deposition techniques it is difficult to produce a thick layer of dielectric material. In this work, the electromagnetic radiation characteristics of the integrated antenna system are studied. Like the microstrip antenna, the piezoelectric transducer is also a resonant device, however, it is acoustically resonant and the radiated electromagnetic fields from the transducer need to be characterized. The radiation spectrum for bulk acoustic wave resonators in the vicinity of acoustic resonance is investigated for general and electrically small devices. The theoretical radiation spectrums are experimentally verified for rf-frequency quartz and lithium niobate devices. The effect of thin metalizations on microstrip antenna performance is modeled and experimentally verified, and the use of superconductors is considered. Radiation efficiency versus substrate thickness calculations are performed in order to determine a minimum substrate thickness for a specified efficiency level. A system analysis is then performed in order to predict the characteristics of the acoustically driven integrated microstrip antenna system.