On the tuning range of a reconfigurable half-mode substrate-integrated cavity antenna

In this paper the theoretical maximum tuning range of a frequency-reconfigurable antenna based on a half-mode substrate-integrated cavity is investigated and discussed. The antenna, which has recently been proposed by the authors, demonstrated a measured frequency tuning range of about 42% based on the capacitance range offered by practically available varactors. In the present investigation, the capacitance range is assumed to be unlimited, i.e. varying from 0 to infinity; then the tuning range is analytically calculated for different structure dimensions. It is shown that theoretical upper limit for the tuning range of this antenna is about 80% when the loading stubs' length is equal to the half guided-wavelength at the maximum frequency of operation. This investigation provides guidelines on the stub sized to be used in the design of stub-loaded reconfigurable antennas to achieve a maximum continuous tuning range.