Antenna arrays have gained significant interest in millimetre‐wave communication systems as an enabling technology to achieve higher capacity and mitigate the high propagation loss. Such arrays with a large bandwidth need to be efficiently calibrated to maximise their performance. An antenna array calibration method based on a stochastic approximation algorithm and simultaneous perturbation has been developed and the procedures to implement it in both frequency and time domains have been presented. The approaches to define objective functions and establish gradient approximations to fulfill a successful convergence for acquiring calibration coefficients in both domains have been explored. In the time domain implementation, only a fraction of the measurement time was required to calibrate an antenna array of ultrawide bandwidth compared with other methods using a perturbation technique. The effectiveness of the proposed method has been validated via numerical experiments in both domains.

A flexible coplanar waveguide (CPW) design is presented suitable for feeding planar antenna with a balanced structure. Two features are provided by the flexible design, transition from balance on the antenna side to unbalance on the receiver side; transformation of characteristic input impedance of the antenna to the value of a standard load. It is essential for the CPW to be bended to fit the purposes hence the effect of bending of CPW on the transmission performance and method to feed planar antenna are investigated. The common mode propagation due to the inserted feedline is observed and the solution to eliminate the auxiliary common-mode effect in the structure is also discussed.

This study proposes a design of a low-profile ultra wide-band cylindrical antenna array with plus/minus 45-degree dual polarization. The proposed compact cylindrical antenna array produces an omnidirectional radiation pattern in the azimuth plane to cover all directions. It consists of 20 × 4 dualpolarized elements within a diameter of 131 mm and a height of 116 mm. The array elements are tightly coupled slant-polarized wideband dipole antennas, and hence, rotational symmetry of radiation patterns in the horizontal plane is achieved for the two orthogonal polarizations. Furthermore, a metasurface structure has been designed and placed over the interconnected array elements to achieve ultrawideband capabilities. The proposed array provides less than −10 dB reflection coefficient over a frequency band between 1.7 GHz and 5.9 GHz. The cross-polarization discrimination (XPD) is 15 dB at boresight in the azimuth plane. The electromagnetic characteristics of the cylindrical array and its corresponding planar array before bending have been evaluated and compared via simulations, and verified by measurements. The compact size, lightweight, and printable design of the proposed antenna array enable low-cost manufacturing and ease of installation. The proposed array design overcomes many challenges encountered in wide-band MIMO systems by covering the entire sub-6 GHz band while providing wide 360-degree coverage in the azimuth plane, hence, supporting multibeam applications.INDEX TERMS Cylindrical arrays, frequency selective surfaces, phased arrays, planar arrays, ultrawideband antennas.

Planar antenna arrays of a balanced structure are of great importance in many applications due to their features including low‐profile, wideband, and high polarisation purity. However, feeding such antennas adds great complexity in terms of manufacturing and reduces the performance due to production of common mode propagation. A method for feeding such antennas using coplanar waveguide on a thin substrate is proposed. Not only does it terminate the antenna of a balanced structure with a single‐ended feed but it also enables impedance transformation. The design was an attempt towards a completely printed front‐end that incorporates the antenna elements and their feeding circuits on bendable substrates. The electromagnetic performance has been validated with a dual polarised prototype and its prospect for ultrawideband arrays, e.g. 5G sub‐6 GHz or square kilometre array, was explored.

Radio-frequency identification (RFID) tags are widely used in the food supply chain where they can be used to hold identification data of tagged objects. They can also be used to provide information related to the quality and safety of the tagged object. This can be achieved by analyzing the RF signals emitted by the tag which couples with the tagged objects, and hence can be used to acquire useful information related to the safety and quality of that object. This paper investigates the correlation between the radiated signals from the tags and the quality characteristics of the tagged objects. It focuses on analyzing the mutual coupling between the tags in an array, in particular, of orthogonal polarization configuration, which shows that more information can be extracted by an array of tags compared to the use of a single RFID tag emitter.