Small ZOR antenna with high efficiency based on epsilon negative transmission line

A Zeroth-Order Resonator (ZOR) antenna is presented, which consists of one unit cell of epsilon negative transmission line (ENG-TL). The size of the proposed antenna is drastically reduced and occupies only 9.8 mm × 14.75 mm (0.058 λ₀ × 0.085 λ₀ at 1.75 GHz) owing to the zeroth-order resonance. The Q factor of the ZOR antenna is decreased by introducing a series capacitor to the shunt branch of unit cell and reducing the shunt capacitive effect of ENG-TL, thus a higher radiation efficiency is obtained with more compact antenna size. A prototype antenna is fabricated and measured. The measured results exhibit a bandwidth of 41 MHz and monopole-like radiation pattern, and the gain of 1.30 dB and efficiency up to 78% are achieved.