A quad-band printed quadrifilar helix antenna (QB-PQHA) with ultra-wide half-power beamwidths (HPBW) and 3dB axial ratio beamwidths (ARBW) for satellite communication applications on the movable platform is proposed in this paper. To operate simultaneously at four frequencies and achieve wide bandwidths, the QB-PQHA features two dual-band printed quadrifilar helix antennas (DB-PQHAs) which are placed coaxially. The inner DB-PQHA is directly fed by the feed network at the bottom via the probes, while the outer DB-PQHA is coupling fed by the branches of the inner DB-PQHA. With optimal spacing between the inner and outer DB-PQHA, the coupling between the radiating branches of the inner and outer DB-PQHA not only enhances the antenna's impedance matching, but also increases the HPBWs and 3dB ARBWs. This QB-PQHA has been manufactured and measured, both the measured bandwidths and beamwidths are outstanding and in good agreement with the simulations. The measured four impedance bandwidths are 1.93-2.07 GHz, 2.16-2.4 GHz, 2.44-2.58 GHz and 2.63-2.70 GHz. The HPBWs at their respective center frequencies exceed 148°, 152°, 158°, and 200°, while the 3 dB ARBWs exceed 144°, 166°, 164°, and 178°, respectively. This novel QB-PQHA is the first to achieve both ultra-wide 3 dB ARBWs, HPBWs and exceptional bandwidth at all four frequencies. These outstanding features provide significant advantages for satellite communication terminals on fast-moving platforms, such as ships and vehicles.

A dual-band gyrotron traveling wave amplifier (Gyro-TWT) can reduce the size, cost, and weight of a transmitter in dual-band radar and communication systems. In this paper, a dual-mode input coupler for K/Ka dual-band gyrotron traveling wave amplifier (Gyro-TWT) is designed. This structure is composed of two different types of input couplers, one is the coaxial input coupler for the Ka-band ${\mathrm{TE}}_{2,1}$ Gyro-TWT and the other is a Y-type input coupler for the K-band ${\mathrm{TE}}_{1,1}$Gyro-TWT. For reducing the backward wave of the${ \mathrm{TE}}_{2,1}$ mode reflecting into the Y-type input coupler to influence the operating bandwidth, a Bragg reflector with a strong mode selective characteristic is inserted between these two couplers, which can make the reflection coefficient of the ${\mathrm{TE}}_{2,1}$ mode better than −1 dB and the phase matched in the whole bandwidth, and the transmission coefficient of the ${\mathrm{TE}}_{1,1}$ mode can reach better than −1 dB. Based on the simulation results, the −1 dB bandwidth of the Ka-band ${\mathrm{TE}}_{1,0}^{⬜}$-${\mathrm{TE}}_{2,1}^{◯}$ mode input coupler reaches 3.32 GHz and the −1 dB bandwidth of K-band ${\mathrm{TE}}_{1,0}^{⬜}$-${\mathrm{TE}}_{1,1}^{◯}$ mode input coupler reaches 3.15 GHz. The designed dual-mode input coupler has the advantages of broad bandwidth and low loss and can be well used in dual-band Gyro-TWTs.

A dual-band printed quadrifilar helix antenna (PQHA) with ultra-wide beam width for S-band satellite communication is proposed in this paper. The antenna is characterized by its ultra-wide half-power beam width and wide 3dB axial ratio width, which is achieved with a simple structure that is easy to design and fabricate. The simulation results demonstrate that the impedance bandwidth is 85 MHz and 78 MHz, respectively, each of which exceeds twice the bandwidth requirement of both frequency bands (uplink:1995±15 MHz, downlink: 2185 ± 15 MHz) in the satellite communication. The 3 dB beam widths at the center frequency of the two bands of the antenna are 194.0° and 194.4°, respectively, and the gain of both frequency bands on the upper sphere is greater than 0.47dBi. Additionally the axial ratio width (lower than 3 dB ) reaches 170.6° and 176.2°, which can meet the requirements of satellite communication in the case of a large elevation angle.

This paper presents a novel wide-beam antenna array for automotive radars. The antenna is designed based on microstrip lines and patches, combined with a proximity-coupled feeding method, achieving high radiation efficiency and a low quality factor. Measured results show that the antenna bandwidth is from 74.4-79.57 GHz, and the short-range detection angle is greater than 126.18 °. Moreover, the low-profile characteristic of the antenna allows it to be easily integrated with radio frequency (RF) chips. Its maximum gain is 14.26 dB, and the gain fluctuation within the impedance bandwidth is only 1.79 dB. Based on this antenna, a automotive forward-looking radar antenna array capable of simultaneous detection in medium and long ranges is designed. Measured results show that the long-range gain of the designed antenna array exceeds 20.62 dB, and the gain fluctuation within the operating frequency band is less than 1.2 dB. The measured results are in good agreement with the simulation results.

As wireless systems evolve toward multiband, multifunctional convergence and high-throughput services, the demand for ultra-wideband circularly polarized (CP) antennas for multi-standard terrestrial–satellite terminals continues to grow; however, because of the dispersive nature of the three-quarter-ring phase shifter, the relative bandwidth achievable with conventional crossed-dipole antennas rarely exceeds 100%. This paper presents a compact left-hand circularly polarized (LHCP) crossed-dipole antenna that combines a cavity-backed ground, ground-slot perturbations, and parasitic patches to simultaneously broaden the impedance and axial-ratio bandwidths. The fabricated prototype achieves an impedance bandwidth (IMBW) of 0.71–3.89 GHz (138%) and a 3 dB axial-ratio bandwidth (ARBW) of 0.98–3.27 GHz (108%), while maintaining gains above 3.5 dBic across most of the frequency range. The good agreement validates the multi-technique co-design and shows that the compact architecture (0.302 λ × 0.302 λ × 0.129 λ) breaks classical crossed-dipole limits. The antenna provides a scalable building block for wideband conformal arrays in next-generation integrated GNSS–SatCom systems.