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Title: Design of printed array antennas for wireless communications
Author: Li, Wenting
Awarding Body: University of Kent
Current Institution: University of Kent
Date of Award: 2018
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Compared to parabolic reflector antennas, printed array antennas have compact size, light weight and low cost. Many printed array antennas have been reported in the literature, but there are lots of challenges remaining. For example, how to achieve polarization-reconfigurable circularly polarized (CP) array antennas? How to reduce the thickness of folded reflectarray CP antennas? How to increase the bandwidth of reflectarray antennas? How to achieve multi-beam radiation? To tackle these challenges, several novel designs of printed array antennas are proposed in this dissertation. First, a novel design of a polarization-reconfigurable CP antenna is proposed. It is the first time an electronically polarization-reconfigurable CP antenna with a single-substrate polarizer is reported. The antenna consists of a slot antenna and an electronically polarization-reconfigurable polarizer (EPRP), which could convert the linearly polarized (LP) waves from the slot antenna to CP waves. The polarization of the antenna could be electronically switched to left-hand circular polarization (LHCP) or right-hand circular polarization (RHCP) by changing the states of the positive-intrinsic-negative (PIN) diodes that are loaded on the polarizer. There are several features of applying an EPRP in this design. 1) The DC circuit of PIN diodes is completely isolated from the RF signals. 2) The PIN diodes are not mounted on the RF feed network. 3) In this antenna, 32 PIN diodes are mounted on the EPRP. The average current of each PIN diode is quite small. Therefore, the antenna can radiate more power without damaging the diodes. 4) The gain of antennas is improved as the aperture of the slot antenna is enlarged by the EPRP. Then, a novel folded CP reflectarray with a significantly-reduced antenna thickness is designed. The antenna consists of a CP feed antenna, a reflecting surface and a circular polarization selective surface (CPSS). The CPSS is transparent for RHCP waves and reflects LHCP waves. By applying the CPSS as the polarization grid for CP waves, the thickness of the CP reflectarray antenna is reduced significantly. It is the first time that the CPSS is applied as the polarization grid in a folded CP reflectarray antenna. To overcome the problem of narrow bandwidth of reflectarrays, one ultra-wide-band tightly coupled dipole reflectarray (TCDR) antenna is proposed. This is the first report of a reflectarray using the concept of tightly coupled elements, and the reflectarray antenna is shown to achieve much wider working bandwidth compared with all the reflectarray antennas that are reported in the previous literature. The reflectarray consist of a wide-band feed antenna and a wide-band reflecting surface. The proposed antenna combines the features of tightly coupled arrays and those of reflectarrays. As a result, the TCDR antenna has an ultra-wide bandwidth, and a much simpler feed network compared with tightly coupled arrays and other ultra-wide-band direct radiation array. A novel method to mini-mize the phase errors of the wideband reflectarray is also proposed. In its operating frequency band, the TCDR antenna has stable main beams and reasonable side lobe levels (SLL). A new method of improving the polarization purity of the TCDR antenna is also proposed. Based on the method, two reflectarray antennas are designed and simulated. The simulated results show that the proposed method could reduce the cross-polarization of the TCDR antenna significantly. Finally, a novel method of designing a Nolen matrix is proposed, and the derivation of the method is given as well. The method is more concise compared with that reported in the previous literature. Based on this method, a multi-beam antenna fed by a 5×5 Nolen matrix network is proposed. The multi-beam antenna is simulated, fabricated and measured. The simulated and measured results prove the effectiveness of the proposed method of designing a Nolen matrix. In this thesis, in order to accurately evaluate the performance of the proposed antennas, full-wave electromagnetic simulations are carried out by using commercial tools such as High Frequency Structure Simulator and Computer Simulation Technology Microwave Studio. Prototypes of the antenna designs are fabricated and measured. The simulated and measured results agree well.
Supervisor: Gao, Steven Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available