A Compact Transmission-Line Metamaterial Antenna With Extended Bandwidth

A wideband and compact planar antenna is proposed using a doubly resonant transmission-line metamaterial (TL-MTM) structure. The antenna consists of two TL-MTM arms that resonate at different frequencies. Each arm comprises a microstrip transmission-line loaded with five spiral inductors and is well matched to 50 Omega through an embedded series meandered line. Each arm is designed to work as a single antenna at its own resonant frequency, determined by the loading spiral inductance, where a zero insertion phase occurs. A wideband antenna matching is enabled when these two resonances suitably merge together. A fabricated prototype has dimensions of lambda
_o
/4 times lambda
_o
/7 times lambda
_o
/29, yielding a vertical linear electric field polarization, and provides a 100-MHz bandwidth (-10 dB) with a measured radiation efficiency of 65.8% at 3.30 GHz.