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This paper proposes a low-profile wideband circularly polarized (CP) antenna using solar cell patches as radiation elements and a sequentially rotated feeding network for CubeSat applications. To realize a wide axial ratio (AR) bandwidth with a compact size, a sequentially rotated feeding network was designed by modifying a quadrature hybrid coupler and a rat-race coupler that has a small change in phase difference even when the frequency changes. A wideband CP patch array antenna was designed by combining a Cshaped slot-coupled solar cell patch in conjunction with a novel feeding network. The overall size of the proposed CP CubeSat antenna is 100 × 100 × 7.2 mm 3 (0.83 λo × 0.83 λo × 0.06 λo at 2.5 GHz). Solar cells occupy 79% of the antenna area, enabling efficient energy harvesting. The -10 dB impedance bandwidth is 1.98-3.0 GHz, which is a fractional bandwidth of approximately 41.0%. The 3-dB AR and 3-dB gain bandwidths are 1.98-3.0 GHz (41.0%) and 1.82-2.98 GHz (46.6%), respectively. The proposed CP solar patch array antenna demonstrates a constant radiation pattern within the -10 dB impedance bandwidth. The proposed CubeSat antenna is suitable for use in an Internet of Space Things (IoST) autonomous communication system.INDEX TERMS circularly polarized antenna, CubeSat antenna, hybrid coupler, Internet of Space Things, S-band antenna, sequentially rotated antenna, solar cell integrated antenna.

This paper investigated the characteristics of series-fed angled dipole antennas as the number of dipoles increased from one to two, four, and eight. A parallel strip line printed on both sides of the substrate was used to connect angled printed dipoles of the same size in a series with equal spacing. As expected, although the gain increased as the number of dipoles increased, the impedance and gain bandwidths decreased. In addition, as the number of dipoles increased, the half-power beamwidth (HPBW) differences between the xz- and yzplanes decreased and the radiation pattern of the xz-plane became more symmetric. Antennas with one, two, four, and eight-dipole elements in a series were designed, and their peak gains were 5.0 dBi, 7.2 dBi, 9.4 dBi, and 10.4 dBi, respectively. The differences between the xz- and yz-plane HPBWs of the four antennas were 160.4°, 41.7°, 14.2°, and 5.3°, respectively. As the number of dipoles in the antenna increased, the differences between the HPBWs in the xz- and yz-planes decreased.

A compact and low-profile photovoltaic (PV) cell with a built-in antenna is proposed for Internet of Things (IoT) applications. The proposed design exploits the gallium arsenide (GaAs)-based PV cell for antenna operation; for this purpose, a hexagonal slot with a trapezoidal perturbation is cut from the active area and bottom contact of the PV cell for resonance. The bottom contact of the PV cell is also used as the ground plane for the antenna. An AC blocking circuit is designed to prevent the flow of RF current toward the PV cell, and a chip inductor is used as an RF choke in the circuit. Thus, a single device simultaneously functions as a PV cell and an antenna. The GaAs PV cell shows a power conversion efficiency (PCE) of 13.25% without antireflection coating, with an open-circuit voltage (Voc), a shortcircuit current density (Jsc), and a fill factor (FF) of 0.963 V, 21.00 mA/cm 2 , and 65.52%, respectively. Furthermore, the optical transparency of the proposed PV-cell antenna is greater than 90%. The complete structure occupies an overall volume of 31.4 mm × 33 mm × 0.639 mm (0.25λo × 0.26λo × 0.0052λo at 2.45 GHz), and the antenna operates in the range of 2.14 to 2.94 GHz, with a gain of 2.8 dBi at 2.45 GHz.INDEX TERMS Compact antenna, integrated antenna, IoT devices, photovoltaic (PV) cell, slot antenna.