This communication proposes the wideband circularly polarized (CP) phased array antenna system for wide axial ratio scanning. For mobile satellite communication, the low-profile CP antenna with a wide axial ratio scanning region in wide frequency bandwidth is necessary, but the antenna with the required axial ratio performance is rarely reported. In this communication, the proposed CP phased array antenna system with an axial ratio control scheme has a wide axial ratio scanning region in the wide frequency bandwidth. In the proposed axial ratio control scheme, the amplitude and phase of the received signals are controlled to compensate for the difference between dual polarizations. The proposed antenna system is designed at 5.8 GHz and has a fractional frequency bandwidth of 20%. In a simulation, the axial ratio is under 1 dB at the elevation scanning region from −60° to 60° at every 360° azimuth angle in the operating frequency bandwidth. For validation, the $1\times 8$ CP phased array antenna system was implemented. The measured axial ratio is under 2 dB at the elevation scanning region from −57° to 57° in the operating frequency bandwidth.

In this paper, a transparent antenna made with a new structure of ITO/Ag/ITO is proposed. Overcoming the physical limitations of transparency and conductivity is an important problem with transparent materials. By studying and comparing previously reported transprent materials, a transparent electrode with thin film Ag inserted between two layers of ITO instead of a single layer is selected for a highly efficient transparent antenna. This electrode has low sheet resistance (3.1 Ω/sq) relative to its high transparency (88 % at 550 nm), which is a factor that can increase the efficiency of the antenna. In general, it is difficult to measure sheet resistance (SR) using a 4-point DC probe for very thin films (thickness of transparent material is less than the skin-depth). Therefore, a form of reverse engineering that can estimate DC sheet resistance using RF SR was presented and verified. As a result, it was possible to predict and design the performance of the transparent antenna with the new material structure. The selected transparent material is applied to design the wideband transparent antenna and the design process for wideband performance is covered in the paper. The proposed antenna with ITO/Ag/ITO was implemented for verification. The peak efficiency of the fabricated antenna was 66 %, and the measured bandwidth was 123 % (from 2.5 GHz to 10.6 GHz), which is the best performance than previously reported transparent antennas.

This communication presents a shorted trapezoidal substrate integrated waveguide (SIW) antenna with a quasi-hemispherical pattern composed of a 64-element (8 $\times $ 8) 2-D planar phased array. The proposed low-profile SIW antenna is analyzed in terms of resonating mode and magnetic current and is simulated. The proposed antenna is composed of a trapezoidal patch and shorting vias. The upper side of the trapezoid is the shorting wall, and the middle of the bottom side provides shorting with a via. The resonance produced by the structure causes the magnetic currents to have three different directions. Hence, the single element has a quasi-hemispherical beam pattern on a large ground. The 64-element (8 $\times $ 8) 2-D planar phased array was implemented and measured. Because the constituent elements have a quasi-hemispherical pattern, the phased array antenna has a wide scanning range in all azimuth directions. The measured scanning range with 5 dB gain fluctuation in the $\phi = 0^\circ $ plane, $\phi = 45^\circ $ plane, and $\phi = 90^\circ $ plane are 170°, 143°, and 168°, respectively.

Herein, a robust constant false alarm rate (CFAR) detector with ordered statistic of sub-reference cells (OSS-CFAR) is proposed in multiple target situations. This detector can improve background level estimation and reduce computational complexity using sub-reference cells. The detection performance of the OSS-CFAR detector and of conventional CFAR detectors in multiple target situations are investigated and compared using computer simulations and experimental data with sea clutter. The simulations and experimental results show that the OSS-CFAR detector achieves robust detection performance with low computational complexity, whereas conventional CFAR detectors suffer performance degradation in multiple target situations. At the clutter edge, the OSS-CFAR detector with appropriate parameters achieves an acceptable false alarm rate compared to conventional CFAR detectors.

This paper presents a curved-retrodirective beamforming system for improving microwave power transmission efficiency in the Fresnel region. Since microwave power transmission in the far-field region has very low efficiency, studies on the Fresnel region are being actively conducted. In these studies, a retrodirective beamforming (RDB) technique is popular. The RDB system with a sub-array structure was a realistic structure that reduced system complexity. However, the transmission efficiency is lowered because the beamwidth of the transmitter antenna element is narrow. To solve this problem, this paper proposes a curved-retrodirective beamforming system that can focus the microwave power on the receiver. The proposed system uses the peak gain of the transmitter antenna element by using tilted beams to improve transmission efficiency. The system design method that can maximize the transmission efficiency is also presented depending on the given conditions such as transmission distance, characteristics of the transmitter and receiver antenna. The simulation showed a reduction in power leakage compared to the conventional system. The fabrication and measurement validated the efficiency improvement of the proposed system for IoT devices in the Fresnel region.

This paper presents a gain enhanced wide azimuth beam automotive antenna using half-mode substrate integrated waveguide (HMSIW) cavity for automotive applications. The antenna is separated into two HMSIW cavities by electrical via walls. The two HMSIW cavities are excited through differential feeding, including a 180 $^{\circ }$ delay line in the center of the antenna. The antenna was operated in $TM_{11}$ mode and investigated using aperture theory based on the cavity model. The antenna size is small enough to mount in the rear-view mirror, which has a long rectangular shape. For comparison, the proposed antenna and a conventional 1 × 2 microstrip square patch antenna array were fabricated to the same dimensions. Then, these antennas were tested to provide validation. The tested results were consistent with the simulation results. The tested results show that the antenna, with the overall dimensions of 70 mm × 35 mm × 1.52 mm (1.38 $\lambda _{0}$ × 0.69 $\lambda _{0}$ × 0.03 $\lambda _{0}$ ), operates at 5.9 GHz. The gain of the antenna is 9.49 dB, and the azimuth beam width is 74.0 $^{\circ }$ . The proposed antenna has a wider azimuth beam width (74.0 $^{\circ }$ ) than a conventional 1 × 2 square patch array antenna (42.0 $^{\circ }$ ) with similar gain and size.