Omnidirectional Monopole Antenna with Embedded SIR as Reflectionless Band-Notched Structure for UWB Applications

In this paper, an omnidirectional monopole antenna with a reflectionless band-notched structure for ultra-wideband (UWB) applications is proposed. The reflectionless band-notched structure is an absorptive bandstop filter (ABSF) composed of two stepped impedance resonators (SIR) and a 500 Ω resistor. The input signal components at notched band are absorbed by the resistor instead of being reflected, generating the reflectionless band-notched characteristic. Simulation results show that the reflection coefficient of the proposed antenna is below −10 dB from 3.1 to 10.6 GHz, and the realized gain at
$+z$
-direction drops to −25 dBi at 5.8 GHz. Besides, this antenna features a good omnidirectional radiation pattern in its operating band. The proposed antenna could be used in the UWB system to inhibit the WLAN interference at 5.8 GHz.