2026-10-18 Latest Published
By Mohammed Yaqoub Yousif
Faris Mohammed Ali
Nasr Alkhafaji
Rand Muwafaq Hadi
Bahaa Hamzah Alkhuwaildi
Progress In Electromagnetics Research B, Vol. 119, 1-18, 2026
Abstract
This paper presents a single-layer quasi-reflectionless filtering antenna (filtenna) operating at 3.5\,GHz for compact 5G mid-band radio-frequency (RF) front-ends. The structure simultaneously provides radiation, bandpass filtering, and absorption of out-of-band reflections. Unlike conventional reflective filtennas, rejected energy is dissipated in a chip resistor rather than returned toward the source, which is beneficial when the antenna port drives or is driven by nonlinear stages such as power amplifiers or low-noise amplifiers. Theoretical analysis, full-wave simulation, and measurement are used as a proof of concept. A T-slot microstrip patch, a two-pole U-shaped bandpass filter (BPF), and a one-pole absorptive stub are co-integrated on flame-retardant type 4 (FR4) (εr = 4.6, thickness 1.6 mm). At the design frequency, the absorptive stub behaves nearly as an open circuit, so in-band power is delivered to the radiator; outside the passband, out-of-band signals are routed into the absorptive path. Quasi-reflectionless matching with S11 < -10 dB is obtained across approximately 1–7 GHz, with a realized gain of about 1.99 dBi and filtering radiation characteristics. Measured results agree well with analytical and simulated predictions.
