Design of frequency‐agile microstrip antennas with conical‐beam radiation

A microstrip antenna with frequency agility is described in this article.The antenna has a circular radiating patch and operates at its TM 01 mode to generate omnidirectional radiation across the azimuthal plane. To change the resonant frequency, a capacitor is introduced and connected to the antenna input port in series. With the increasing of capacitance, the resonant frequency is decreased while the resonant resistance and radiation characteristic nearly remain constant. Experimental results indicate that the design can provide a frequency tunable range of 22%; moreover, good impedance matching and stable radiation pattern are also obtained in the range.