Low-Profile Wideband Single-layer Monopolar Antenna with High-Selectivity and Stable Radiation Patterns

This letter proposes a novel wideband, single-layer monopolar antenna with high selectivity and enhanced pattern stability across the operating band. Building upon a conventional circular patch antenna, the rejection levels of the upper and lower sidebands are carefully analyzed, designed, and optimized to achieve the desired performance. To further improve performance, a shorting-via-loaded ring is incorporated, effectively broadening the bandwidth while maintaining stable realized gain and consistent radiation patterns. Considering the trade-off between gain and stopband rejection, an appropriate substrate is selected to enhance upper-sideband rejection and ensure pattern stability. Additionally, an outer ring structure is introduced and precisely adjusted to enhance the roll-off characteristics of the lower band. The results indicate that the antenna achieves a simulated and measured -10 dB fractional bandwidth (FBW) of 31.2% (4.09 - 5.60 GHz) and 31.8% (4.04 - 5.57 GHz), respectively. It exhibits stable radiation patterns with an average gain of 6.17 dBi at an elevation angle of θ = 30°. The antenna also demonstrates sideband rejection levels exceeding 20 dB in the lower band and 19.5 dB in the upper band. With its single-layer structure, high selectivity, and stable pattern characteristics, the proposed design presents a promising solution for wireless applications.