| Summary: | 碩士 === 國立中央大學 === 電機工程學系 === 105 === The operating frequency of an antenna can be made reconfigurable by incorporating tuning elements. In this thesis, microstrip patch antennas are loaded with variable capacitors (varactors) to acquire frequency tunability. We design and fabricate two kinds of frequency-reconfigurable microstrip patch antennas, both of which use ferroelectric varactors with barium strontium titinate (BSTO) as the dielectric material for the capacitive loading. One of the microstrip patch antennas uses benzocyclobutene (BCB) as its dielectric whereas the other patch antenna uses high-resistivity silicon substrate.
The operating frequency of the frequency-reconfigurable patch antenna with BCB as its dielectric is set at around 15 GHz. The ferroelectric capacitors and the patch are connected using the BCB stacked via process developed by our lab. Measurement results show that, when the bias voltage of the varactor is tuned from 0 V to 25 V, the operating frequency of the antenna varies from 13.8 GHz to 14.3 GHz, which translates into a 3.5% frequency tuning range (FTR).
The operating frequency of the microstrip patch antenna with high-resistivity silicon as its dielectric is also designed to be around 15 GHz. The ferroelectric varactors are connected to the ground plane on the backside of the silicon substrate by through substrate vias (TSVs). Measurement results of this antenna show that the operating frequency is fixed at 9.7 GHz. No frequency tunability is observed. We find that the reason why the antenna is not tunable is because the annealing temperature for the BSTO thin film is too low for this sample. As for the large frequency shift, it is due to a mistake in layout. The layout mistake results in an unexpected silicon-nitride capacitor with a large capacitance, which becomes part of the capacitive loading.
In this thesis, we successfully realize a frequency-reconfigurable microstrip patch antenna with BCB as its dielectric and with ferroelectric varactors as its capacitive loading. On the other hand, we successfully fabricate a capacitively loaded microstrip patch antenna using the TSV process we develop. Though the measured operating frequency has deviated from the designed value and cannot be tuned, we have discovered the reasons that result in these problems. We believe that the expected performance can be obtained after these issues are resolved.
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