A Frequency- and Pattern-Reconfigurable Center-Shorted Microstrip Antenna

A frequency- and pattern-reconfigurable antenna based on a center-shorted microstrip patch is presented. The novel design utilizes two resonance modes of a microstrip antenna with shorting vias at the patch center. To set up the antenna tuning mechanism, two groups of varactors with a measured tuning range of [0.149, 1.304] pF are placed at two opposite sides of the antenna, followed by open-circuited loading stubs. For a particular bias voltage configuration, the structure operates as a dual-band antenna with broadside radiation at the upper resonance frequency and monopole-like radiation at the lower band. By varying the dc bias voltage, both resonance frequencies can be changed simultaneously. Based on the proposed concept, a demonstration antenna has been designed so that the two types of aforementioned patterns can be reconfigured across a continuous fractional frequency range of more than 20%. Experimental results are provided, which validate the proposed concept and design procedure.