頻率可調之共振環形小天線設計

Abstract

在本論文中，吾人提出具頻率可調特性之環形槽孔及環形帶線微小化天線。從半波長共振環形槽孔天線出發，在天線之虛開路端，並聯電容元件，透過改變邊界條件之方式以達縮小天線尺寸之目標，而對應縮短之長度所需要的電容值，更可以透過簡單的共振模型得到初步估計，另一方面，當天線尺寸固定不變的條件下，增加此電容值將會使得天線之基本共振頻率下降。一系列不同電容值但相同結構之原型天線被設計作為驗證，更進一步的，以可變電容取代固定電容的位置，透過可變電容端電壓的調整，藉以實現不同的電容值。

Frequency-agile miniaturized slot and strip loop antennas are proposed in this dissertation. Begin from half-wavelength resonant slot loop antenna, a shunt capacitor is placed at the location of virtual-open end to miniaturize the antenna, and the associated capacitance Cter is chosen according to a simple resonator model. For a given perimeter of the slot loop, increasing Cter would lower its resonant frequency. The design concept is verified both numerically and experimentally through a series of prototype antennas loaded with chip capacitors of different values. Beyond that, frequency tunability is achieved by replacing the chip capacitor with a varactor diode, of which the capacitance can be controlled by tuning its bias voltage. For verification, a prototype antenna is designed and both simulated and measured results show that the resonant frequency is continuously tunable between 1.5 GHz and 2.5 GHz as the bias voltage is adjusted from 4V to 16V.