Design of Wideband Combined Annular Slot-Monopole Antenna

The magnetic current in an annular slot is used to enhance the impedance bandwidth of a monopole and preserve consistent radiation patterns from K-band through V-band. The equivalent circuit models of monopole, annular slot, and their combination are derived to aid the RF system analysis with this antenna, herein referred to as a combined annular slot-monopole antenna. The proposed antenna is designed using full-wave and circuit simulations and the theory is experimentally validated. The measured VSWR is below 2 from 17.9 to 50 GHz. A consistent far-field characterized with monopole-like E-plane pattern, flat gain around 5.5±1 dBi, and good omnidirectionality (<;2.5 dB) is preserved over the bandwidth. To further reduce in-band mismatch losses, a concentric ring atop the monopole is introduced and VSWR below 1.5 is achieved from 18.5 to 47.4 GHz.