A circularly polarised (CP) monopulse waveguide antenna array for Ka-band wireless communication is proposed. The antenna structure can be divided into six layers from top to bottom, including radiating layer, aperture layer, cavity layer, aperture layer, feeding layer and monopulse comparator. The upper radiating layer allows two transmission modes of the transverse electric (TE) wave and the transverse magnetic (TM) wave to pass through. The 90° phase difference can be obtained by adjusting the horizontal and vertical angles of the horn radiator, which realises the CP radiation pattern. Besides, the 0° or180° phase difference produced by the monopulse comparator enables the antenna to obtain a monopulse radiation mode. In order to obtain the low sidelobe characteristics, the coupling parameters of the coupling layer are weighted by the Taylor distribution. The overall size of the antenna is 194 × 25 × 31 mm³. The slot waveguide antenna is fabricated and measured to validate the proposed design. The measured results show that the monopulse system can achieve an impedance bandwidth of 3.7% (34.5–35.8 GHz) in the Ka-band at the centre frequency of 35 GHz. The sum-pattern maximum gain and radiation efficiency are 23.3 dBic and 75% at 35 GHz, and the gain of the whole bandwidth is >20 dBic. The axial ratio and the sidelobe level is less than 1.2 and −28 dB, respectively. The difference-pattern amplitude imbalance is <0.2 dB and the null-depth lower than −30 dB. Also, the isolation is better than 30 dB. Besides, the pure metal structure of waveguide has incomparable advantages in a harsh environment.

This study presents a single-layer via-less antenna array operating in circular polarisation for wide-band operation in C-band. The antenna comprises disc based elements arranged in a sequential rotation architecture. Each element is tuned to exhibit multiple resonances with good circular polarisation performance over a broadband of frequencies. A proper feeding network is then designed so that the resulting array is capable of a wide-band operation and enhanced gain, equalising the frequency response of the set of elements. Simulations are validated by fabricating and measuring a prototype realised on a commercial FR408 dielectric substrate. Notwithstanding a dimension of only , that is only at centre frequency, measured performance of the proposed array can be summarised in a gain better than 7 dB over an operation bandwidth of , which is an unmatched result, given the via-less single-layer technology and the specific available area.

The authors have proposed a dual-band reconfigurable Fabry–Pérot (F-P) cavity antenna with high gain and meanwhile small radar cross-sections (RCSs) in wideband. Different from the traditional F-P antennas, they used a dynamic metasurface reflective plane (DMRP) as the lower superstrate to realise reconfigurable functions and a digital coding metasurface as the upper superstrate to achieve wideband RCS reduction. To investigate the dual-band reconfigurability, a wideband rectangular waveguide is used to feed the F-P antenna. By varying the bias voltage applied to varactors embedded in the elements of DMRP, the reflection phase of DMRP is changed and the two operating frequencies can be tuned electronically. To realise RCS reduction, they adopted a meticulous arrangement of the coding elements on partially reflecting surface. The designed metasurface-assisted F-P antenna has good radiation performance with high gain, high aperture efficiency, and high radiation efficiency. In the experiments, a prototype was fabricated via printed circuit board technology, and measured results agree well with numerical simulations. The measured peak gain reaches 17.52 dBi and the maximum aperture efficiency is 56.97%. The two reconfigurable bandwidths cover 5.10–5.40 and 6.60–6.93 GHz, respectively; and 7 dB RCS reduction is achieved from 9.40 to 13.7 GHz for arbitrary polarisation

A novel basic antenna element for travelling-wave substrate integrated waveguide (SIW) arrays is proposed in this study. The antenna element is based on a transverse slot and newly complemented by a pair of vias used for matching and a phase shifter. By changing the geometries of the slot and the phase shifter, the amplitude and phase of a radiated wave can be controlled. The proposed approach extends the potential of transverse slots in SIW-based travelling-wave antenna arrays. To verify the capabilities of the antenna element, the authors demonstrate a six-element array with side-lobe suppression, intended for a 24 GHz radar system. The measured results show good agreement with simulations.

An innovative design of a right hand circularly polarised (RHCP) antenna at two different resonant frequencies that is GPS (global positioning system) L2 and L5 has been proposed in this study. The proposed design comprised the concept of slotted radiator excited with a coaxial probe. Two asymmetric spiral slots were incorporated in a rectangular radiator to realise size miniaturisation, the axial ratio bandwidth and beamwidth at L2 (1.22760 GHz) and L5 (1.17645 GHz) frequencies of GPS applications. The proposed design has accomplished an excellent axial ratio bandwidth and beamwidth at both GPS L2 and L5 bands. The size of the designed antenna has been , which makes it attractive for the consumer market. Measured and simulated results achieved that the antenna conquered RHCP radiation at two separate operating bands, i.e. GPS L2 and L5.