Advancements in antenna arrays for frequencies beyond 100 GHz

Most of today's wireless applications use frequencies below 6 GHz. While this might be sufficient for now, and even if lower millimeter-wave (mm Wave) frequency bands between 20 GHz and 80 GHz are already being considered, at some point, the desired data rates will become so high that a shift to frequencies beyond 100 GHz is required. However, one reason lower frequencies are currently favored is the relative simplicity of implementing radio systems, at least compared to doing it at 100 GHz. This thesis aims to change that by giving solutions for easier implementation of 100-GHz radio systems.

This thesis covers three specific topics, all aiming at making advancements in antenna arrays for frequencies beyond 100 GHz: Utilizing parasitic elements for improving the performance of both sparse and dense arrays; what to consider when designing, manufacturing, and assembling the arrays; and combining the design processes of antennas and radio-frequency integrated circuits (RFICs) to realize a truly integrated system.

Parasitic elements are elements of the antenna array that are not driven themselves and rely on the other antenna elements to excite them. When designed correctly, parasitic elements improve the performance of the antenna array, and thus the relationship can be considered commensal. This thesis utilizes parasitic elements for shaping the embedded element patterns of the driven elements, both for mitigating grating lobes in sparse arrays by up to 8.4 dB and improving the beam-steering range of dense arrays to ±85°. This demonstrates the viability of using parasitic elements when, for example, manufacturing limitations or the size of RFICs force the array to be sparse.

Given that the wavelength decreases as frequency increases, being 3 mm at 100 GHz, the dimensions of antenna arrays decrease accordingly. Therefore, the array becomes more difficult to manufacture, and the mechanical tolerances during assembly become tighter. This is addressed by studying separately manufactured fully metallic antennas and misalignment-robust aperture-coupled transitions on printed circuit boards (PCBs). Using these methods, a low-loss and compact radio system with bandwidths of up to 40 GHz are demonstrated.

The third and final topic merges two very different design processes into one, creating antenna–IC co-design. Considering an RFIC during the design of an antenna array, and vice versa, allows the creation of an optimal interface between the two. Simultaneously, knowing how the components affect each other during their design reduces the likelihood of unexpected performance reductions when the full system is assembled. Therefore, an antenna–IC co-designed system can provide a more compact and more reliable system that performs better, compared to separately designed antennas and RFICs.

From 5 GHz to beyond 100 GHz, the arrays proposed in this thesis showcase various approaches for solving the key challenges in realizing antenna arrays at frequencies beyond 100 GHz. The use of parasitic elements is demonstrated with prototypes of arrays operating at 5 GHz and up to 40 GHz, but the methods are directly scalable to higher frequencies. Viability of metallic 3D-printed antenna arrays is displayed with three separate prototypes, covering the frequencies 27–110 GHz. Finally, an antenna–IC co-designed integrated receiver is presented for 60–81 GHz, confirming the functionality of the differential aperture-coupled transition and illustrating the benefits of the combined design process. The methods validated by these prototypes form a solid foundation for the future of antenna-array design at frequencies beyond 100 GHz.