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Title: Compact antennas and array for ultra-wideband communications and radars
Author: Zhu , Fuguo
Awarding Body: University of Kent
Current Institution: University of Kent
Date of Award: 2013
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The allocation of the frequency spectrum from 3.1 to 10.6 GHz by the Federal Communications Commission (FCC) has attract~d much interest in various Ultra- . I wideband (UWB) applications including short-range, high-data-rate communication and high-resolution imaging radar/sensor due to its large bandwidth. This has increased the demands on the UWB systems and subsequently to stimulate the research activities in various UWB antenna designs. Challenges of the UWB antenna design include the wide impedance bandwidth, radiation stability, low profile, compact size, and low cost for portable consumer electronics applications. Moreover, dual-polarized UWB antennas are more attractive compared to single-polarized , antennas, as the channel capacity is significantly enhanced due to the polarization diversity technique. The performance of imaginglradar systems can also be improved by employing dual-polarized UWB antennas, since more information about the target can be obtained using a fully polarimetric system. To mitigate interferences with coexisting wireless systems operating over 3.3-3.6 GHz, 5.15-5.35 GHz, or 5.725-5.825 GHz bands, this work presents the design, development and measurement of printed band-notched antennas for UWB short-range indoor con1munications. These include UWB antennas with a single wide notched band, a single narrow notche? band, dual notched bands, and triple notched bands. Good band-notched performance is ach.ieved by using a high permittivity and low dielectric loss subsh'ate, and . inserting quarter-wavelength band-notched elements within the feed line. These antennas can achieve high gain suppression over 10 dB in each notched frequency band. In addition, they occupy a compact size of 28 mm by 28.5 mm due to the use.r0f a high permittivity substrate. For the purpose of alleviating the requirement on space for band-notched elements, a printed asymmetrical UWB antenna with .multiple notched bands is also designed, fabricated and measured. Only one single band-notChed element is required to notch each frequency due to its symmetry. This work also presents the design of two types of dual-polarized UWB patch antennas. One is a cavity-backed capacitively c01:lp~ed patch antenna which consists of a square patch and four capacitively coupled feeds to enhance the impedance bandwidth. Each feed 1 ----- - ----- is formed by a vertical isosceles trapezoidal patch and a horizontal isosceles triangular patch. The four feeds are connected to the microstrip lines that are printed on thy bottom layer of the grounded FR4 substrate. Two tapered baluns are util,ized to excite the antelma to achieve high isolation between the POlts and reduce the cross-polarization levels. In order to increase the antenna gain and reduce the backward radiation, a compaCt surface mounted cavity is integrated with the antenna. The antenna prototype has achieved an impedance bandwidth of 112% at (lS111 :::; -10 dB) whereas the coupling between the two ports is below -28 dB across the operating frequency range. The measured _ ~ntenna gain varies from 3.91 to 10.2 dBi for Port 1 and from 3.38to 9.21 dBi for POlt 2, with a 3-dB gain bandwidth of 107%. The second design is a slot-loaded patch antenna which consists of a square ring patch and four inclined triangular-shaped patches. The vertices of the triangular patches are connected to the micro strip lines which are printed on the bottom layer of the grounded FR4 substrate. The antenna prototype can provide two orthgonal polarizations with an impedance bandwidth (IS111 :::; -10 dB) of 113% and isolation of over 28 dB across the whole operating frequency band. The measured antenna gain varies from 2.09 to 7.66 dBi for Port 1 and from 0.02 to 6.77 dBi fcir Port 2 with a 3-dB gain bandwidth of 96%. Finally, a cOlnpact connected eight-e~ement UWB antenna array integrated with a wideband eight-way power divider is designed, fabricated and tested.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available