When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Recently, the ever-increasing demand for fifth-generation (5G) wireless applications has turned millimeter-wave (mm-wave) multi-beam array antenna into quite a promising research direction. Besides offering a remarkable bandwidth for high-speed wireless connectivity, the short wavelengths (1 to 10 mm) of mm-wave signals makes the size of the antenna array with beamforming network (BFN) compatible with a transceiver front-end. The high losses associated with mm-wave wireless links and systems considered the foremost challenge and may restrict the wireless communication range. Therefore, a wideband substrate integrated waveguide (SIW)-based antenna with high gain and beam scanning capabilities would be an effective solution for these challenges, as it can increase the coverage area of mm-wave wireless systems and mitigate the multipath interference to achieve a high signal to noise (S/N) ratio, and thereby fulfill the link budget requirements.
This thesis focuses on the analysis and design of single- and multi-beam mm-wave antenna arrays based on SIW technology to fulfill the growing demand for wideband high-gain planar antenna arrays with beam steering capability at V-band. A tapered slot antenna (TSA) and cavity-backed patch antenna are used as the main radiators in these systems to achieve high-gain and high efficiency over a wide range of operating frequencies. Accordingly, numerous design challenges and BFN-related issues have been addressed in this work.
Firstly, an antipodal Fermi tapered slot antenna (AFTSA) with sine-shaped corrugations is proposed to improve the antenna characteristics at V-band. The proposed antenna provides a flat measured gain of 20 dB with a return loss better than 22 dB. In addition, A broadband double-layer SIW-to-slotline transition is proposed to feed a planar linearly tapered slot antenna (PLTSA) covering the band 46-72 GHz. This new feeding technique, which addresses the bandwidth limits of regular microstrip-to-slotline transitions and avoids the bond wires and air bridges, is utilized to feed a 1x4 SIW-based PLTSA array.
Secondly, a new cavity-backed aperture-coupled patch antenna with overlapped 1-dB gain and impedance bandwidth of 43.4 % (56-87 GHz) for SWR < 2 and an average gain of 8.2 dBi is designed. A detailed operating principle is presented. Based on the proposed element, an SIW based 1x8 array is constructed, whose beam-shape is synthesized by amplitude tapering according to Taylor distribution to reduce the sidelobe level. Moreover, a four-layered 4x4 cavity-backed antenna array with a low-loss full-corporate SIW feed network is implemented for gain and aperture efficiency enhancement. The measured results exhibited a bandwidth of 38.4 % (55.2-81.4 GHz) for SWR < 2 and a gain of 20.5 dBi. A single-layer right-angle transition between SIW and air-filled WR15 waveguide along with an equivalent circuit model is introduced and used to measure the performance of both proposed linear and planar arrays.
Thirdly, two 1-D scanning multi-beam array designs based on SIW technology, at 60 GHz, have been presented. The first design is a compact multi-beam scanning 4x4 slot antenna array with broadside radiation. The BFN is implemented using a dual-layer 4x4 Butler matrix, where the 450 and 00 phase shifters are designed on a separate layer with different permittivity, resulting in a significant size reduction compared to a conventional single layer. A detailed theoretical analysis, principle of operation and the circuit-model of the proposed phase shifter have been discussed, showing less desperation characteristics compared to ordinary phase shifters. The measured results show an azimuthal coverage of 1210, with peak gains of 13.1dBi, 11.5 dBi, when port 1 and 2 are excited, respectively. The second design is a wideband high gain multi-beam tapered slot antenna array with end-fire radiation. An SIW Butler matrix with a modified hybrid crossover is used as a beamformer network. The fabricated prototype exhibits a field of view of 970 in the azimuthal plane, with measured gain ranges from 12.7 to 15.6 dBi over the band 56-66 GHz.
Lastly, a novel three-layered SIW-fed cavity-backed linearly polarized (LP) patch antenna element is presented, covering a bandwidth of 36.2 % (53-76.4 GHz) with a flat gain ranging from 7.6 to 8.2 dBi. A compact two-layered beam forming network is designed with a size reduction of 28 % compared to a standard one-layered BFN without affecting its scattering parameters. The results show that the impedance bandwidth is 31.1 % (51.5-70.5 GHz) for |S11|<-16 dB with an average insertion loss of 1.3 dB. The proposed antenna element and BFN are employed to form a compact 2x2 multibeam array at 60 GHz for 2-D scanning applications. The proposed array shows a bandwidth better than 27 % with a radiation gain of up to 12.4 dBi and radiation efficiency of 80%. The proposed multi-beam array features four tilted beams at 330 from a boresight direction with 450, 1350, 2250 and 3150 in azimuth directions, i.e., one beam in each quadrant.