Coupled Phase-Locked Loop Arrays for beam steering
Some of the limitations of Coupled Oscillator Arrays, mainly intrinsic small locking bandwidth, amplitude fluctuations and limited agreement between unit cells and models, can be overcome with the use of Coupled Phase-Locked Loop Arrays, which with appropriate models are more predictable than COAs and offers larger locking range and amplitude-independent phase relationships. The two offer similar advantages, such as phase-shifterless beam scanning and modulation abilities, as well as analogous challenges, for example the modeling and consequent design of unit cell and coupling schemes at microwave frequencies. The discrete and continuum modeling of CPLLAs is presented. The phase dynamics shows a diffusion type behavior, where the locking propagates away from the detuning points. The ability of beam scanning is then showed as the steady state solution of edge detuning. Additionally, the length of the coupling line together with the sign of the IF loop gain is proved to be an important factor in the transient and the steady-state phase distribution along the array. These theoretical results are experimentally verified through the design of a 2.45 GHz CPLLA and its characterization. Being governed by strongly nonlinear behaviors, still a lot needs to be understood about these synchronized arrays: the aim of these paper is to show that, together with some limitations, they also present interesting properties that future research may exploit.
