Miniaturized CPW-fed slot loop antenna with frequency agility

A frequency-agile miniaturized slot loop antenna inductively fed by a CPW is proposed. To reduce the size of the slot loop, a shunt capacitor is placed at the location of virtual open, and the associated capacitance C_ter is chosen according to a simple resonator model. For a given perimeter of the slot loop, increasing C_ter 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, fabricated, and tested. Both the simulated and measured results show that the resonant frequency is continuously tunable between 1.2 GHz and 2 GHz as the bias voltage is adjusted from 2V to 10V. The prototype design occupies a very small area of 10×10 mm².