A Multistate Frequency Reconfigurable Monopole Antenna Using Fluidic Channels

A reconfigurable microstrip monopole antenna that uses three closely spaced substrate milled channels filled with either air or dielectric fluid is presented. Based on the number of channels filled with fluid, four states-namely states 0, 1, 2, and 3-of operation are selected. Introduction of fluid (distilled water) in the channel modifies the effective permittivity of the dielectric medium and perturbs the E-field distribution in vicinity to the antenna arm. The position and size of channels are optimized to maximize the shift in operating frequency and $S_{11}<; $$-$10 dB impedance bandwidth through full-wave electromagnetic (HFSS) simulations. A prototype of the antenna is fabricated and measured, exhibiting frequency shifts of 12.0%, 17.9%, and 23.7% with impedance bandwidth of 32.0%, 30.1%, and 29.9% in states 1, 2, and 3 of the antenna, respectively. The reference state, i.e., state 0, offers 34.7% impedance bandwidth. The measured peak gains achieved are 2.4, 1.6, 1.2, and 0.3 dBi for states 0, 1, 2, and 3, respectively. In all the states of operation, the radiation pattern remains stable and omnidirectional.