Wideband and Frequency‐Reconfigurable Loop Antenna for Sub‐6 GHz Applications

This paper presents a horizontally polarised, low‐profile loop antenna that operates in two distinct modes: a wideband (WB) and a frequency‐reconfigurable (FR) mode. The antenna is based on a circular segmented loop integrated with varactor diodes and a compact printed microstrip balun, whereas the frequency control is realised through the adjustment of the balun line width. In the WB mode, the antenna exhibits an exceptionally large impedance bandwidth, ranging from 2.9 to 3.9 GHz ( dB), with a maximum realised gain of 2.7 dBi. Over a substantial range of this bandwidth, the structure provides a very low back‐lobe level, making the antenna particularly suitable for beam‐switching applications. In the FR mode, the antenna keeps an omnidirectional radiation pattern, whereas its operating frequency can be continuously tuned from 1.95 to 2.45 GHz simply by adjusting the capacitance of the varactor diodes. The proposed design achieves high radiation efficiency—exceeding in the FR mode and in the WB mode. Owing to its compact profile, high efficiency, beam controllability and flexible tuning capability, the antenna is a promising candidate for portable and wireless communication systems below 6 GHz, including emerging 5G applications.