Multifunctional Reconfigurable Millimeter Wave Loop Antenna Array for 5G and B5G Applications

Antennas serve as pivotal components within communication systems, facilitating the transmission and reception of signals through electromagnetic radiation. Traditional antenna designs prioritize optimization for fixed frequencies, radiation patterns, and polarisations. In contrast, contemporary electronic and wireless communication technologies demand antennas that are both compact and multifunctional, capable of adapting to dynamic operating scenarios. Reconfigurable antennas (RAs) emerge as a compelling alternative, offering dynamic adaptability to varying conditions and thereby enhancing system functionality and operational flexibility. The distinctive advantage of reconfigurability positions an RA as the equivalent of several non-reconfigurable antennas, resulting in compactness, cost reduction, and simplified system integration.
This research focuses on the development of compact and low-profile RAs through streamlined control mechanisms. The objective is to achieve multiple reconfigurability functionality while maintaining uniform performance across all states. The proposed reconfigurable antenna concepts aim to circumvent complex feeding structures and biasing arrangements, ultimately enhancing antenna performance. The thesis presents a comprehensive exploration of novel antenna designs, each addressing specific challenges and requirements within the realm of wireless communication. The research contributes five distinct advancements to antenna technology, spanning various frequency bands and applications.
Initially, a cost-effective circular polarisation open-loop antenna is designed at 6 GHz. An in-depth analysis of parameters such as size, shape, substrate thickness, and loop gap size yield valuable insights, enabling tailored optimization for specific applications. To expand the CP bandwidth, the design incorporates concentric parasitic open-loop antennas. This is followed by designing a similar loop antenna that is customized to operate at 27.5 GHz. Subsequently, the millimetre-wave loop has been utilised to design a phased array featuring 4-elements. The precise control of the main beam steering has been achieved through the implementation of a corporate feed network and four-phase shifters employing transmission line time delay techniques. Experimental findings confirm the configuration's ability to facilitate left-hand circular polarisation (LHCP) radiation over a scanning angle of 50°, explicitly ranging from -25° to +25°. This accomplishment aligns with the stringent criteria for maintaining a radiation pattern with an axial ratio (AR) of less than 3 dB across a broad frequency spectrum. Additionally, the design achieves a peak gain of approximately 11 dBic in combination of a total efficiency surpassing 85% throughout the CP bandwidth. Besides, the proposed design offers the advantages of compact size and low cost.
Leveraging coplanar stripline (CPS) structure and photonic bandgap (PBG), a singly fed reconfigurable circular loop antenna is proposed for millimetre-wave communication systems. This antenna's distinctive feature lies in its capacity to adjust polarisation and bandwidth characteristics owing to the strategic integration of two PIN diodes. These diodes are engineered to function in various modes, allowing for three distinct polarisation states and accommodating two distinct bandwidths. A meticulous alignment of these PIN diodes enables a single DC bias network to be used as a highly effective RF choke, which simplifies the design and reduces the associated losses. The simple and totally planar configuration offers a choice of RHCP or LHCP radiation at 28 GHz. This is accompanied by impedance matching and axial ratio bandwidths of 12.9% and 8%, respectively, over the same frequency range with a gain of 7.5 dBic. Moreover, when the PIN diodes are unbiased, the antenna offers linear polarisation (LP) over two narrow bandwidths at 27 GHz and 29 GHz, featuring a maximum gain of 7.2 dBic. Therefore, the proposed configuration offers three operating modes: wide-band RHCP, wide-band-LHCP, and dual LP narrow-bands.
In pursuit of this objective, a 4-element multifunctional reconfigurability array antenna is designed to operate at 27.5 GHz. By controlling the PIN diodes biasing and using only two CPS lines, an innovative multifunctional reconfigurable array effortlessly generates a scanning beam at angles spanning up to ±25° across three distinct polarisations, RHCP, LHCP, and LP. Furthermore, the system achieves a reconfigurable frequency interface between circular and linear polarisations. This comprehensive study showcases a commendable array gain of approximately 10 dBic, coupled with a remarkable radiation efficiency surpassing 74%. This represents the first attempt to design a millimetre-wave multifunctional reconfigurable array. Furthermore, the proposed array offers simplicity and outperforms published counterparts that operate at lower frequencies.
Finally, a comprehensive assessment of the performance of on-chip CP circular loop antennas that have been designed and fabricated to operate in the Q/V frequency band. The study utilizes Gallium Arsenide (GaAs) and Silicon Carbide (4H-SiC) semiconductor wafer substrates. The measured results highlight the achievement of impedance matching at 40 GHz and 44 GHz for the 4H-SiC and GaAs substrates, respectively. Moreover, the outcomes confirm the generation of a left-hand circularly polarized wave in the case of the 4H-SiC substrate. As a result, a 4-element circularly polarised loop array antenna has been fabricated for operation at 40 GHz, employing the 4H-SiC wafer as a low-loss substrate. The results underscore the antenna's remarkable performance, exemplified by a broadside gain of approximately 9.7 dBic. Additionally, the proposed design showcases an impressive radiation efficiency of 92% emphasizing its efficacy and suitability for prospective applications.