This study proposes a design of a low-profile cylindrical antenna array with plus/minus 45 degree dual polarization. The proposed antenna array produces an omnidirectional radiation pattern in azimuth plane to cover all directions. The proposed compact cylindrical array consists of 20×4 dual polarized 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, a rotational symmetry of radiation patterns in the horizontal plane was demonstrated 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 was 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 proposed array design overcomes many challenges associated with wide-band MIMO systems, covering the entire sub-6 GHz band, while providing wide 360 degree coverage in azimuth, with a potential for multibeam applications.

Online calibration is desired in antenna arrays of ultrawide bandwidth. This study proposes a time domain calibration method based on the simultaneous perturbation algorithm. Two objective functions were established: power of the received signal at array output; or combination of power and correlation coefficient between the signal at array output and a target signal. For both criteria, the convergence settings require only two measurements at each iteration. One advantage of the method is that the entire signal operation for calibration is performed in the time domain. This is achieved by resolving the effects of distortion on time delay of each channel, which accounts for both amplitude and phase distortions at different frequencies. Therefore, the proposed method significantly increased the calibration efficiency for ultra-wideband antenna arrays. Since time delay coefficients for calibration associated with array elements were determined independently due to characteristic of the simultaneous perturbation, estimation accuracy of the method is tangential to the number of elements in the array, and is mainly dependent on the convergence conditions. This gives the method an additional distinct advantage for calibrating large-scale antenna arrays with ultrawide bandwidth. An estimation accuracy of 99% on time delay adjustments has been achieved and demonstrated.

The limitations of conventional sensors have made array antennas increasingly crucial for gathering information and communication applications in intelligent transportation and communication systems. Compact cylindrical arrays are particularly favored for their ability to achieve azimuth angle scanning. However, the substantial mutual coupling effect between the elements on curved surfaces and its implication for these arrays remain unclear, which is a key factor to consider when such arrays are used for multibeam applications. This study investigates the effect of mutual coupling in a dual-slant-polarized cylindrical array. The results showed that mutual coupling is predominantly observed among the closely located elements, and it is essential for achieving an ultra-wide bandwidth. The study also analyzes the impact of mutual coupling on the scan impedance and radiation characteristics for multibeam applications and reveals that these arrays exhibit robust multibeam capability, hence having great potential for use in sensing and communication applications.

Achieving reliable initial alignment of liquid crystal (LC) molecules on copper surface of microwave materials remains a key challenge, primarily due to a more significant surface roughness of radio frequency (RF) materials compared to smoother substrates traditionally used in optical devices, where LCs were initially tailored for. To address this problem, we studied two principle LC alignment strategies: (i) direct alignment of the LC layer on microwave device substrates via a polyimide (PI) coating, and (ii) integration of a conventional LC cell incorporating two glass substrates to provide well controlled surface anchoring. Both approaches are implemented in two distinct phase shifter designs and evaluated through full wave simulations and experimental measurements at the X- and Ku-bands respectively. The results demonstrated that the LC cell with glass substrates supports thinner LC layer, which is pivotal for obtaining a more rapid response. Devices based on the LC cell configuration exhibit a 35$\%$ improvement in response time, attributed to enhanced molecular orientation and reduced fringing field effects. However, the inclusion of extra glass substrates will degrade the phase shift range. The analytic study indicated that incooperation of glass layers reduced the differential phase shift ($\Delta \phi$) by 50$\%$ under the same LC thickness. These findings highlighted the advantages of glass substrate LC cells in enabling low loss, compact, and fast response phase shifters, making them well suited for reconfigurable antenna arrays and beamforming systems in next generation wireless communication networks.

The limitations of conventional sensors have made phased array antennas increasingly crucial for gathering information and communication applications in intelligent transportation systems. Compact cylindrical arrays, in particular, are favored for their ability to achieve azimuth angle scan. However, the substantial mutual coupling effect between elements on curved surfaces and its implication in these arrays remains unclear, which is a crucial factor to consider when such arrays are used for multibeam applications. This study investigated the effect of mutual coupling in a dual-slant-polarized cylindrical array. The results showed that mutual coupling is essential for achieving an ultra-wide bandwidth. Mutual coupling is predominantly observed among elements that are closely positioned. The study also analyzes the impact of mutual coupling on scan impedance and radiation characteristics for multibeam applications and reveals that these arrays exhibit robust multibeam capability, hence having great potential for use in intelligent transportation systems.