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  • Publication
    Circularly Polarized Antennas for 5G Millimetre-Wave Communications
    (University College Dublin. School of Electrical and Electronic Engineering, 2022)
    The need of a higher data rate, lower latency, and cost efficiency led to the fifth-generation (5G) emerging as a new communication standard. This generation includes many unused frequencies with high available bandwidth channels that can provide higher capacities such as millimeter-wave (mm-wave) bands. One of the main challenges of working at high frequencies of this generation is path loss that needs to be addressed. To overcome this issue, a high gain antenna with a small size is required. Consequently, the first major question arises: how to effectively increase the gain and efficiency of the antenna at a high frequency with a small size. Importantly, it is vital to transport as much as data is possible without any sensitivity to the alignment of the transmitter or receiver antenna that can be satisfied by using circularly polarized (CP) radiating waves. Thus, the second research question emerges: how to provide high gain small size antenna with CP at high frequencies. To address the first two major research questions in this thesis we designed a miniature dual-band CP antenna that works at 28 GHz and 38 GHz with high gain. This antenna can be implemented in mobile devices, unmanned aerial vehicles (UAVs), and base stations (BSs) because of the small sizes of 11 × 14 × 0.508 mm3. For getting a deep insight into the structure and the design procedures of the dual-band antenna, characteristic mode analysis (CMA) is employed. Note that the CMA is not sensitive to the feeding position and the material in this analysis is not lossy. Therefore, after using CMA, the optimization is conducted in the full-wave simulation as the feeding is added to the structure, and the material is lossy. The single CP antenna covered the bands of 27-28.4 GHz and 34.7-40 GHz, with a maximum gain of 6.3 dBiC and 5.51 dBiC at 28 GHz and 38 GHz, respectively, whereas the radiation efficiency is 94% and 96% with the ARBW of 2.5% and 1.5%. A phased antenna array is then constructed to provide a higher gain for this designed dual-band antenna. In a phased antenna array we consider four designed single element antennas close to each other to create a 2 × 2 antenna array with high gain at 28 GHz and 38 GHz. For a 4 × 4 antenna array, an electromagnetic band-gap (EBG) is used to reduce the mutual coupling between elements in the array. The radiating signals will be sent to different users with circular polarization via electronic beamforming. The position of each antenna element is also optimized to provide the constructive radiating wave towards our desired directions. The array was able to steer the beam between -26.5 to 29.5 degrees for the lower band and -29.5 to 35.5 degrees for the higher band with the maximum gain of 12.8 dBiC and 11.5 dBiC, respectively. Another method to enhance the gain is implementing a lens structure in front of the radiating antenna. Here, a significant challenge is to maintain the CP of the incoming CP wave while the gain is increased. Therefore, the third research question is how to design a lens with the capability of enhancing the gain and keeping the CP when the lens is fed by a CP antenna source. Concerning the third major research question, in this thesis, we designed a CP lens structure. First, a multi-layer lens with a thickness of 2.03 mm was designed, and then a one-layer lens structure with a thickness of just 0.508 mm was made. The lens was located in front of different radiating antennas. These lens structures resulted in significant gain enhancement for various feeding antennas working at 28 GHz. The unit cell of the one-layer lens can provide a broad phase shift compared to the multi-layer counterpart. The proposed lens structures not only increased the gain of the incoming CP wave but also kept its polarization to overcome the issues of reflectivity, absorption, inclement weather, and mis