A Bisected Miniaturized ZOR Antenna With Increased Bandwidth and Radiation Efficiency

A compact planar, via-free, and bisected zeroth-order resonator (ZOR) antenna based on bisected interdigital capacitor-loaded transmission line (B-CL-TL), with improved bandwidth and higher radiation efficiency is proposed. Strong miniaturization and increase of bandwidth and efficiency are obtained by dissecting the initial design by half without incurring compromise. The antenna consists of two cascaded coplanar interdigital capacitors as series capacitors shorted to the ground plane at one end. A meander-line inductor is implemented for matching. A fabricated prototype has dimensions of 0.11λ₀×0.18λ₀×0.01λ₀ in total size, yielding an omnidirectional far-field pattern, and provides a 135-MHz bandwidth (6.1%) with a measured radiation efficiency of 76.8% at 2.21 GHz.