An extremely broadband circularly polarized (CP) antenna is presented. The proposed antenna consists of a crossed bowtie dipole loaded with four unequal parasitic cross-slots, four parasitic bowtie patches, and four parasitic rectangular strips. The cross-slots can generate a CP mode due to the sequential phases of the crossed bowtie dipole. The parasitic bowtie patches are gap-coupled with two arms of the crossed bowtie dipole, and they are sequentially rotated along diagonals to generate an additional CP mode. The parasitic strips also generate one CP mode due to the sequentially rotated configuration parallel to the crossed bowtie dipole. By properly combing with two CP modes of the crossed bowtie dipole, broadband CP operation is achieved. The experimental and simulated results are in agreement, and the measured results show that the proposed antenna exhibits a very wide impedance bandwidth of 93.1% (2.21-6.06 GHz) and an excellent axial ratio (AR) bandwidth of 90.9% (2.2-6.4 GHz). In addition, the proposed antenna produces a right-hand circular polarization (RHCP) with a peak gain of 8.6 dBi.

The wearable ultra-wideband antenna that is appropriate for body area networks is designed and implemented in this article. Stepped circular radiation patches, microstrip feeders, and trapezoidal floors make up the majority of the antenna. Good bending qualities have been attained by using liquid crystal polymer, a flexible material, as a dielectric substrate. An antenna measuring 30 mm × 35 mm × 0.1 mm was designed with two C-shaped slots etched on it to achieve notch function in the 3.20–4.10 GHz and 5.19–5.98 GHz frequency bands. Its working frequency range was 1.96–11.61 GHz, and its specific absorption rate for the human body was less than 2 W/kg. The test findings demonstrate that ultra-wideband body area network systems can be implemented using the antenna impedance and radiation characteristics.

A circularly polarized (CP) and frequency reconfigurable microstrip antenna with loading inductive is presented in this paper. The designed antenna is comprised of a radiating patch, four short-circuited grounded metal posts, and four coupling branches. Each coupling branch has an end that is coupled to the shorted ground post and is also connected to the parasitic branches by means of a group of PIN diodes. By controlling the state of the PIN diodes connected to each parasitic branch, the working resonant frequency of the antenna can be changed. In order to further understand the mechanisms of operation of the antenna, the equivalent circuit model was built, and the circuit model of the antenna was analyzed, and this analysis was used for the development of the frequency reconfigurable microstrip patch antenna. Furthermore, the parameters of specific equivalent circuits can be solved by the three lengths of branch. Meanwhile, the calculated results derived from the given resonant frequency formula for the antenna are in good agreement with the simulation results of the antenna. Simulated results for the input impedance of the antenna are also in good agreement with the calculated values for the equivalent circuit. Finally, the antenna is fabricated and measured, and the measured results show that the antenna can not only achieve frequency reconfiguration at 1.14 GHz, 1.21 GHz, and 1.39 GHz but also accord well with the simulation value, while maintaining a compact size.

Electromagnetic wave sensing technologies, such as radar and large-scale antenna systems, usually involve complex radio frequency (RF) transceiver chains and sophisticated data processing, leading to high system complexity and latency. While reconfigurable metasurfaces provide a simplified architecture for sensing tasks, they frequently require additional algorithms or integrated sensors, reintroducing computational overhead and hardware demands. To address these limitations, an active amplifier-based sensing metasurface is proposed with a simpler architecture. An active amplifier-based sensing metasurface consists of a metantenna and a power amplifier (PA), enabling it not only to enhance detection wave energy but also to directly demodulate object-scattered waves through measurable variations in the amplifier’s DC current. This approach eliminates the need for conventional RF receiving chains and extensive sensor networks. The proposed method significantly reduces both hardware complexity and processing latency while simplifying baseband algorithm and platform requirements, presenting a streamlined and efficient alternative for object detection and environmental sensing.