| dc.description.abstract | Incorporating tuning elements into a narrowband antennas makes its operating frequency become tunable, thus increases its effective bandwidth. In this thesis, a microstrip patch antenna is loaded with ferroelectric varactors to achieve frequency agility.
In this thesis, a Ku-band tunable microstrip patch antenna is designed. The patch antenna is loaded at its two radiating slots with 8 ferroelectric varactors. The varactors are equally spaced. The design procedure is described. Simulation results show that, when the capacitance of the ferroelectric varactors changes from 0.25 pF to 0.1 pF, the operating frequency of the patch antenna would vary from 14.5 GHz to 18 GHz, corresponding to a 21.9% frequency tuning range. Within the frequency tuning range, the maximum antenna gain is −2.38 dBi. The patch antenna employs a direct microstrip feed. For measurement, we design two types of transition – probing and connectorized. Both transition types exhibit similar simulation results, except that the maximum antenna gain of the connectorized type is slightly lower, which is −2.76 dBi.
The proposed tunable microstrip patch antenna is fabricated using a fabrication process developed by our lab. Measurement results show that, under 0-V bias, the operating frequency of the antenna is shifted down to 12.5 GHz from the originally expected 14.5 GHz. The reason for the frequency shift is because the increase of parasitic capacitance due to the over-etching when making the through silicon vias. Besides, it is found that the operating frequency cannot be adjusted by the bias voltage of the varactors. Unfortunately, we have not found the reason that leads to this failure. In the future, to successfully fabricate the proposed tunable antenna, the stability of the etching processes and the yield must be improved.
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