In this study, we present an ultra‐wideband full‐duplex system constituted of a wideband 4‐element Vivaldi array and wideband microstrip‐to‐slotline baluns. The proposed system is characterised by its simplicity, high directivity, and high self‐interference cancellation levels over a wide frequency bandwidth. The system is fabricated using basic printed‐circuit board (PCB) technology and can provide at least 50 dB of self‐interference cancellation over the bandwidth of operation, 4–40 GHz, with an average gain of 7.8 dBi. The system has a size of 8 cm × 8 cm × 9.4 cm and can be used as a high data rate link between two distant wireless nodes. To assess the merits of the proposed system and compare it to other published works, a new figure of merit (FoM_WFD) dedicated to wide‐band full‐duplex antenna topologies is introduced in this study.

This work aims at realizing an antenna with a stable radiation pattern for base station applications. A novel high‐efficiency shared‐aperture triple‐band dipole array antenna configuration is proposed in sub‐6 GHz microcell base stations in environments where bi‐directional radiation patterns are preferred. The radiators of the antenna are composed of double‐sided square dipole array structures and two novel long‐side monopoles. To verify the principle, the antenna with an overall size of 0.3λ ₀ × 0.33λ ₀ × 0.002λ ₀ (λ ₀ is the free‐space wavelength at 900 MHz) is fabricated and measured. The measurements confirm impedance bandwidths of 9.5% (840–924 MHz), 21.9% (3–3.74 GHz), and 12.2% (4.9–5.54 GHz), respectively. The second frequency band covers the 5G sub‐6 GHz NR frequency band n78, mainly used in China and some other countries, and the LTE 42/43 bands (3.4–3.6 GHz, 3.6–3.8 GHz). The first and the third bands are also suitable for GSM 900, 5 GHz WiFi and are potential candidates for future 5G developments. The boresight gain is greater than 1, 6, and 10 dBi in these bands, respectively. The measured results also demonstrate that the proposed configuration has stable radiation patterns across the three frequency bands.

In this work, the authors experimentally show Dirac Leaky Wave Antennas (DLWAs) at upper microwave frequencies. For the first time, DLWAs are implemented using simple Parallel plate waveguide (PPW) technology, while yielding desirable radiation features and continuous beam scanning through broadside, as well as extremely low profile, with significant ease of fabrication, making them well suited for Ku band applications such as satellite communication, radar and emerging fifth‐generation (5G). A planar Dirac photonic crystal in PPW is shown with a closed bandgap and linear dispersion around broadside. In this work, 1D and 2D PPDLWAs are designed that provide scannable fan and pencil beams, respectively, with a symmetric beamwidth. Phase and attenuation constants are controlled with unit cell dimensions to obtain a directive beam and scanning in a wide range of angles. For the 2D design, an appropriate wideband feeding network is designed that excites the antenna appropriately. The presented PPDLWAs operate with a peak gain of about 13 dB for the fan beam and 22 dB for the pencil beam, in the frequency range from 12 to 16 GHz.

This study presents a novel approach to design the single‐feed circularly polarized (CP) microstrip antenna by the periodic fractal parasitic structure (PFPS). By adding the PFPS along the radiated patch, a new independent orthogonal mode is generated. When the magnitudes of these two modes are the same and the time‐phase difference between them is 90°, the antenna can realise CP radiation. Parameter studies of the PFPS show how to design the CP microstrip antenna. The proposed CP microstrip antenna, designed for the satellite navigation system, has a 30 MHz 10‐dB impedance bandwidth and an 8 MHz 3‐dB axial ratio bandwidth in the centre frequency of 1.575 GHz. The advantage of this presented CP antenna is that these two modes for realising the CP radiation are independent of each other. This makes it more convenient to simplify the designing and debugging of the proposed CP antenna.

Design procedure of a novel transmission line low‐pass filter is presented. The filter has a flexible rejection response for a prescribed cut‐off frequency and an in‐band ripple factor. It is compact by using a Z‐shaped coupled‐line section, which is loaded with open‐circuited stubs. All of the transmission line elements are identical in electrical length, and the impedances can be calculated by solving certain specific equations according to prescribed in‐band specifications. The simulated results show that the circuit can generate low‐pass responses with third‐, fifth‐, and seventh‐order filtering functions. The filter order depends on the number and position of the loading stubs. For verification, two sample filters with cut‐off frequency of 0.5/0.3 GHz are fabricated using a three‐/five‐layer PCB process, which generate seventh‐order low‐pass filtering responses with good selectivity. The experimental results agree well with the predictions.