Triple-Band Reconfigurable Low-Profile Monopolar Antenna With Independent Tunability

This article proposes a reconfigurable low-profile monopolar antenna with triple-band independent tuning capability. The antenna is based on the concept of a center-fed patch with shortings to achieve omnidirectional radiation patterns. Instead of using vias, varactor-loaded stubs are utilized to create reconfigurable equivalent shorting points. The triple bands can be achieved by using three sets of stubs. This configuration results in three magnetic current loops that spatially overlap at different independently tunable frequencies. Measurement results show that the design obtains three independent tunable frequencies centered at 2.51, 3.56, and 4.62 GHz with -10 dB relative tuning ranges of 22.8%, 22.8%, and 16.7%, respectively. The antenna radiates omnidirectionally with vertical polarization in the three sweeping bands. The proposed concept can be extended to a larger number of bands by adding sets of stubs with considerations of coupling and impedance matching.