Compact CRLH Asymmetric-CPS Resonant Antenna With Frequency Agility

A compact, uniplanar composite right/left-handed transmission line (CRLH TL) resonant antenna with frequency agility is proposed based on the asymmetric coplanar strip (ACPS). First, it is shown that a capacitor as the termination for an unbalanced CRLH ACPS is needed for excitation of an anti-resonance within the frequency range between the zeroth-order series and shunt resonances. The design formula to estimate the value of the termination capacitance for a given resonant frequency is derived as well. By utilizing a varactor diode as the termination, the termination capacitance can be controlled by changing its bias voltage, and the resonance of the antenna can thus be tuned between the two zeroth-order resonant frequencies. For verification, a prototype antenna was fabricated and tested. It has a continuously tunable resonant frequency between 2.15 GHz and 2.8 GHz as the bias voltage is adjusted in between 4 V and 22 V. When tuned to resonate at different frequencies in between the two zeroth-order resonances, the antenna still exhibits similar slot-like radiation pattern and stable peak gain and radiation efficiency owing to the same resonant mechanism in the frequency range.