PhD defence - Ahmed Abdellatif

Thursday, July 16, 2015 10:00 am - 10:00 am EDT (GMT -04:00)


Ahmed Abdellatif


High Performance Integrated Beam-Steering Techniques for Millimeter-Wave Systems


Safieddin Safavi-Naeini


Recently, the research and development of low cost and highly efficient millimeter-wave (mmWave) devices with beam-steering antenna systems have been significantly advanced to address the ever-increasing demand for future wireless ultra-broadband applications. These applications include, but are not limited to, automotive anti-collision surveillance radar, smart navigation systems, improved wireless tracking, satellite communication, imaging, 5G wireless communication, and 60GHz multigigabit wireless personal and local area network (WPAN/WLAN). In general, beam-steering capability significantly relaxes the overall system power budget and minimizes the interference. In communication applications, it enhances the link robustness through multi-path mitigation and increases the channel and the aggregated channel throughput by exploiting the spatial dimension. In imaging/radar systems, beam-steering is essential for achieving the required resolution (angle-of-arrival). More details about other beam-steering advantages and beam-steering related specs are explored in this work through applying a simple channel model based on ray-tracing to some practical wireless mmWave applications to extract the antenna system requirements and quantitatively illustrate the usefulness of the presented beam-steerable systems.

Despite the advantages it provides, the realization of these (electronic) beam-steerable mmWave antenna systems is quite challenging. In general, the mmWave components' design, integration, fabrication and testing processes are far more complex than their lower frequency counterparts. This can be attributed to the significant losses and parasitics experienced at mmWave frequencies, as well as the lack of reliable design models. Integrated (on-chip) mmWave radios which includes the antenna system have been widely studied and presented as a practical implementation; however the performance (low antenna gain, high phase noise, etc…) and the cost (die size is huge) are still major issues for these systems. In addition to the significant power consumption and other thermal issues. Hybrid integration tackles those issues by combining a die (or multiple dies) that is efficiently (area-wise) populated with active components (analog/digital blocks) and high performance off-chip passives (antenna, feed, passive phase shifters and resonators); however, this integration has to be carefully designed to ensure minimum mismatch which if it has been ignored can significantly deteriorate the whole performance. In addition, there is a high cost associated with the implementation of high performance components (advanced/non-standard types of fabrication process technologies, complex integration and packaging techniques, etc..); therefore the hybrid integration should be efficiently done and implemented in the minimal cost. This calls for a multi-disciplinary approach which involves electromagnetic theory, integrated circuits, silicon micro-fabrication, parasitics modeling and MEMS.

The proposed study is introducing high performance all-Silicon (high resistivity Silicon) beam-steering mmWave antenna system along with its integration into active components with special consideration to the fabrication cost. Electronic beam-steering can be implemented through beam-switching configurations (fast but coarse) or phase array configurations (highly desirable in large arrays). Novel low cost, highly efficient (91%) and compact switched-beam antenna has been proposed for the 77GHz automotive radar application. The design optimization along with the fabrication and measurement details have been discussed. For phased array applications, various all-Silicon antenna designs have been proposed and discussed in this study among them is the novel pixelated antenna which represents a new approach for designing a compact single-mask antenna for mmWave/sub-THz applications. We have developed a method using Genetic Algorithm to optimize the shape of the antenna in a given allocated space for certain performance metrics. This can be also used to explore the practical performance bounds for dielectric based antennas. The other important component in phased array system is the phase shifter. Low-cost, compact and easily integrated phase shifters with low insertion loss and low power consumption are highly desirable. In addition, minimal insertion loss variation for the full range of phase shift over a wide frequency band is a crucial requirement. This as well as some other non-idealities in the phase shifter affects the overall system performance and can result in significant beam distortion while steering. Therefore, we carefully studied those effects taking into consideration system level requirements and presented a novel phase shifter with optimal characteristics for mmWave phased array applications.

The proposed phase shifting structure is also based on high resistivity Silicon dielectric image guide which is easily integrable with the other antennas we presented. The proposed structure changes the phase shift of the propagating mode by varying the image guide propagation constant using a high dielectric constant (40-170) slab of Barium Lanthanide Tetratitanates (BLT). This leads to a compact phase shifter design. It also makes the field concentrated in the air gap which minimizes the losses. Different types of the proposed phase shifter has been developed and tested including electrically controlled versions. Finally, we presented new techniques for low cost and efficient integration for the proposed high quality mmWave passives with active components. Detailed explanation, experimental results and comparisons with different integration and packaging technologies are also presented.