MMWave array antennas for 5G handsets

Mobile communication systems have advanced to 4G (fourth generation), with 5G comprising visions, concepts and designs for better performance. The key 5G feature is the use of antenna arrays on handsets at mmWave frequencies. The higher frequencies enable higher capacities, but their reduced Friis path-gain calls for a higher antenna gain, realized with arrays. This thesis investigates mmWave arrays for handsets, requiring: element designs suitable for arrays; array feeds; array theory and practice; and integrability of the antenna with the cellphone chassis. Designing at different radio frequencies calls for different technologies, but for low-cost manufacturing, printed circuit board technology is required. The bandwidth of most printed antennas, and certainly arrays, is small, typically having a maxiumum relative bandwidth of less than 10%. The current set of 5G frequency bands span from 24.25 GHz to 43.5 GHz, i.e., a relative bandwidth of 57%. This extremely wide band represents a design challenge for printed antennas, and particularly for arrays. New designs are presented for printed antenna elements – a low profile one, so necessarily narrowband, that is suitable for a single mmWave band, and a higher profile one that can cover the set of mmWave bands. One antenna prototype is developed using conventional dielectric sheet of Rogers RT/duroid 6002 which is well-established material for mmWave frequency applications. Another prototype uses liquid crystal polymer due to its promising properties for performance, manufacture, and integrability with electronics. The narrow-band element is a slot-on-cavity configuration, having a perturbed cavity shape with an extra slot to boost the bandwidth with no significant extra manufacturing cost. The wide-band element is a printed Yagi-like structure where the mechanism for its extreme bandwidth is a parallel connection of dipoles of different lengths. Designing arrays of these elements is also presented. The slot-on-cavity design allows a choice of array polarization, with H-plane arrays and E-plane arrays requiring different supporting ground-plane sizes, particularly important for mounting on handsets. The wide bandwidth for the Yagi-like elements motivates a new look at array design, where the choice of element spacing is a trade-off between the impact of mutual coupling and the presence of grating lobes. The result is a new approach for phased array design that yields a better scan range than previous approaches.