Designing of a Small Wearable Conformal Phased Array Antenna for Wireless Communications

In this thesis, a unique design of a self-adapting conformal phased-array antenna system for wireless communications is presented. The antenna system is comprised of one microstrip antenna array and a sensor circuit. A 1x4 printed microstrip patch antenna array was designed on a flexible substrate with a resonant frequency of 2.47 GHz. However, the performance of the antenna starts to degrade as the curvature of the surface of the substrate changes. To recover the performance of the system, a flexible sensor circuitry was designed. This sensor circuitry uses analog phase shifters, a flexible resistor and operational-amplifier circuitry to compensate the phase of each array element of the antenna. The proposed analytical method for phase compensation has been first verified by designing an RF test platform consisting of a microstrip antenna array, commercially available analog phase shifters, analog voltage attenuators, 4-port power dividers and amplifiers. The platform can be operated through a LabVIEW GUI interface using a 12-bit digital-to-analog converter. This test board was used to design and calibrate the sensor circuitry by observing the behavior of the antenna array system on surfaces with different curvatures. In particular, this phased array antenna system was designed to be used on the surface of a spacesuit or any other flexible prototype. This work was supported in part by the Defense Miroelectronics Activity (DMEA), NASA ND EPSCoR and DARPA/MTO.DMEANASA NDEPSCoRDERPA/MT

Adaptive array antenna design for wireless communication systems

Adaptive array antennas use has been limited to non-commercial applications due to their high cost and hardware complexity. The implementation cost of adaptive array antennas can be kept to a minimum by using cost effective antennas, reducing the number of elements in the array and implementing efficient beamforming techniques. This thesis presents techniques for the design of adaptive array antennas which will enable their cost effective implementation in wireless communication systems. The techniques are investigated from three perspectives, namely, reconfigurable antenna design, wide scan array design and single-port beamforming technique. A novel single-feed polarisation reconfigurable antenna design is proposed in the first stage of this study. Different polarisation states, namely, linear polarisation (LP), left-hand circular polarisation (LHCP) and right-hand circular polarisation (RHCP), are achieved by perturbing the shape of the main radiating structure of the antenna. The proposed antenna exhibits good axial ratio (< 3 dB at 2.4 GHz) and has high radiation efficiency in both polarisation modes (91.5 % - LHCP and 86.9 % - RHCP). With a compact single feeding structure, the antenna is suitable for implementation in wireless communication devices. The second stage of the study presents the design procedure of wide scan adaptive array antennas with reduced number of elements. Adaptive array antennas with limited number of elements have limited scanning range, reduced angular scanning resolution and high sidelobe levels. To date, design synthesis of adaptive array antennas has been targeted on arrays with a large number of elements. This thesis presents a comprehensive analysis of adaptive array antennas with less than 10 elements. Different array configurations are analysed and various array design parameters such as number of elements, separation between elements and orientation of the elements are analysed in terms of their 3 dB scan range. The proposed array, the 3-faceted array, achieves a scanning range up to ±70°, which is higher than ±56° obtained from the Uniform Linear Array. The faceted arrays are then evaluated in the context of adaptive beamforming properties. It was shown that the 3-faceted array is suitable for adaptive array applications in wireless communication systems as it achieves the highest directivity compared to other faceted structures. The 3-faceted array is then synthesised for low sidelobe level. Phase correction together with amplitude tapering technique is applied to the 3-faceted array. The use of conventional and tuneable windowing techniques on the 3- faceted array is also analysed. The final stage of the study investigates beamforming techniques for the adaptive array antenna. In the first part, beamforming algorithms using different performance criteria, which include maximum signal-to noise-ratio (SINR), minimum (mean-square Error) MSE and power minimisation, are evaluated. In the second part, single-port beamforming techniques are explored. In previous single-port beamforming methods, the spatial information of the signals is not fully recovered and this limits the use of conventional adaptive beamforming algorithms. In this thesis, a novel signal estimation technique using pseudo-inverse function for single-port beamforming is proposed. The proposed polarisation reconfigurable antenna, the 3-faceted array antenna and the single-port beamforming technique achieve the required performance, which suggests the potential of adaptive array antennas to be deployed commercially, especially in wireless communication industry

Mutual Coupling Compensated Multiband Linear Antenna Arrays for Radio Frequency Energy Harvesting/Transmitting

RF energy transmitting is an approach to deliver charging energy wirelessly, while RF energy harvesting is an approach to re-charge battery by capturing ambient RF energy. A multiband system composed of mutual coupling compensated linear antenna arrays and output LC matched RF-DC rectifier is proposed for RF energy harvesting and transmitting. The designed system operates in standard communication bands such as GSM850, GSM900, GSM1800, GSM1900, WiFi, Bluetooth, and LTE since ample RF ambient signals are present and numerous IoT sensors operates in these frequency bands. The design starts from a highly efficient double-ring monopole antenna. The proposed antenna has both wideband and multiband features to cover the target operating frequencies. According to Friis transmission equation, the captured/radiated RF power is proportional to the antenna gain, thus antenna array composed of double-ring monopoles is investigated to increase antenna gain. In the proposed four-element antenna array, a four-way RF energy combiner with optimum power combining efficiency is implemented to connect four antennas. Triple-band radiation patterns are synthesized by by mutual coupling compensation structure. The proposed output LC matched RF-DC rectifier is connected to antenna array to convert RF power to DC energy. The rectifier sensitivity and power conversion efficiency is boosted with dual frequency tones. System measurement results state that not only the antenna gain but also the radiation pattern of antenna array affects the total captured RF power. Antenna array is preferable to be installed at the transmitting side for RF energy transfer, while the single antenna is preferable to be installed at the receiving side for RF energy harvesting. If the receiving area is not limited, then the rectenna array composed of antenna arrays and RF-DC rectifiers can be applied for RF energy harvesting