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.