A Wideband SMM Antenna with Gap and Dielectric Loadings

A wideband four-arm spiral mode microstrip (SMM) antenna, which is loaded by dielectric and gap, is introduced in this paper. This antenna, which operates at mode 0, uses a shallow back cavity to suppress back radiation. Gap-loading and dielectric-loading are used to decrease the voltage standing wave ratio (vswr) of the antenna. A capacitive gap is introduced by a metal ring strip around the spiral, and a nylon disk is attached to the supporting substrate to introduce dielectric-loading. Measured results show that vswr of the antenna is noticeably lowered by dielectric and gap-loading (fractional bandwidth of vswr <; 2.5 is larger than 77%). The measured radiation patterns agree well with the simulated results, and show relatively good symmetry.