PhD Oral Exam - Yazan Al-Alem, PhD Electrical and Computer Engineering
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.
The advent of the fifth generation of wireless communication, millimeter wave frequency is required, which mandates the use of high gain antennas for both transmitting and receiving front ends. The use of high gain antennas is very vital in order to compensate for the high path loss of the propagating signals at high millimeter wave frequency bands. There are vast methods to implement high gain antennas; many of those solutions are expensive and complicated in terms of its fabrication process. Here, we emphasize on 60 GHz high antennas based on the low cost planar printed circuit board technology. The proposed solutions are low-cost with high-performance metrics. The proposed antennas suit short range, low power applications, such as wireless personal area networks (WPAN). Nonetheless, the study provided for the proposed structures reveals new physical insights, and new methods for the design procedure, where the design procedure becomes very straightforward.
The first proposed structure utilizes the radiation losses in microstrip line discontinuities to implement an efficient high gain radiator at 60 GHz. The second proposed structure utilizes the diffracted fields from the edges of metal sheets as secondary radiating sources to boost the gain of the element. Also, an enlarged distance between the antenna elements can be achieved without generating grating lobes; this can be comprehended by visualizing each element as a subarray of radiating sources. Such a concept has a significant implication on the relaxation of the design of feeding networks. The single antenna element realized gain goes up to 11.5 dBi, the 10 dB return loss bandwidth covers the 60 GHz ISM band, and the radiation efficiency goes above 90%.
A ME dipole is usually designed by superimposing electric and magnetic current elements orthogonally on each other. A new design perspective is proposed. The proposed design procedure can transform the radiation characteristics of an electric or magnetic current element to ME dipole characteristics. The proposed procedure doesn’t require the orthogonal combination of the magnetic and electric current elements. Hence, the procedure possesses a significant advantage, where it avoids the need for a quarter free-space wavelength spacing between the current element and the metallic ground plane. In addition, the proposed design increases the antenna gain dramatically, where the proposed structure has a boresight gain of 11.5-dBi, and a relative bandwidth of 13% centered at 60 GHz. The antenna element has been employed in a planar antenna array to achieve a gain of 22 dBi.
A novel technique is proposed to enhance the gain of a DRA antenna over a wideband range of frequencies. The proposed antenna structure has a relative bandwidth of 27.5% in the 60 GHz band, and a peak realized gain of 12.5 dBi. The peak of the total antenna radiation efficiency is 96%. The proposed antenna is suitable for high data rate short-range personal area networks applications. Printed Electromagnetic Band Gap (EBG) technology is used to feed the antenna to eliminate any parasitic radiation from the feed line. The characterization of 60 GHz antennas is very challenging. The end launch connector used to feed the antenna at such frequency is relatively massive compared to the antenna dimensions, and that consequently affects the fidelity of the characterization of the antenna, especially if it is in the vicinity of the antenna. EBG surfaces have been used to resolve such characterization impairments. In a 5G network, the data is communicated at mm-Wave frequencies between various communicating entities. The communicated high-frequency signal is processed internally within the communicating entity itself. Thus, the data is communicated through electrical interconnects between several chips or between several sub-circuits within the chip. In such a way, those electrical interconnects between various sub-circuits within an IC, or between several adjacent ICs, play a vital role in defining the performance limits of any system. As the frequencies of operation have been into a gradual increase, the design of interconnects, whether within the IC environment
(Intra-chip) or between several adjacent ICs (Inter-chip), turn into a more challenging task. As the frequencies of operation increase, the proper interconnect guiding structure dimensions become infeasible to realize, or it might exhibit a high level of losses, and large intrinsic RC time delay.
Moreover, by the increase of the number of interconnects, the mutual coupling between the interconnect structures become more severe, not to mention the complexity, and associated cost of such design. The wireless interconnects concept (wireless intra-chip/inter-chip communication) emerged as a suggested remedy to the high frequency interconnect problem. We provide a study of several aspects of wireless inter-chip communication between adjacent ICs at mm-Wave frequencies. The symmetrical layers concept is introduced as a general approach to eliminate the destructive interference and redirect the wasted radiated energy to free space towards the receiving antenna. In addition, the use of hard/soft surfaces and EBG structures to focus the radiated energy towards the receiving antenna is studied thoroughly. The use of such concepts has tremendous advantages, in focusing the energy towards the receiving antenna and eliminating the spherical spreading losses introduced by the radiated spherical wave nature. The incorporation of the symmetrical layers with hard/soft surfaces led to novel compact, low-cost wireless inter-chip structures with enhanced link budget performance.