Low-Profile Top-Hat Monopole Yagi Antenna for End-Fire Radiation

A top-hat monopole Yagi antenna is presented to produce an end-fire radiation beam. The antenna has an extremely low profile and wide operating bandwidth. It consists of a folded top-hat monopole as the driven element and four short-circuited top-hat monopoles as parasitic elements. A broad bandwidth can be achieved by adjusting the different resonances introduced by the driven and parasitic elements. A prototype operating at the UHF band (f₀ = 550 MHz) is fabricated and tested. Measured results show that a fractional bandwidth (|S₁₁| <; -10 dB) of 20.5% is obtained while the antenna height is only λ₀/28 at the center frequency.