Overall Conclusions and Possible Future Directions
Active integrated antennas have found numerous applications as phased arrays, retro-directive arrays, and spatial power combiners. Coupled-oscillator antenna arrays represent a very exciting subset of active integrated antennas both from an application point of view and from a research and analysis point of view, due to some very attractive properties, such as their ability to produce arbitrary phase shift distributions, as well as their capabilities of frequency conversion and frequency generation. In addition, they inherit the practical advantages of active integrated antennas, which are compact low-profile circuit implementations that are compatible with low-cost fabrication technologies (such as microstrip and coplanar waveguide), using single and multilayer printed circuit boards.
As we have seen, however, the design of coupled-oscillator antenna arrays is far from trivial due to their highly nonlinear nature, which results in a dynamical behavior that is difficult to simulate and predict accurately and, in effect, increases the difficulty of designing coupled-oscillator arrays demonstrating a robust performance. Nonetheless, the progress of nonlinear circuit simulation and optimization techniques and the increase in computational power of low-cost personal computers has made possible the accurate analysis of coupled-oscillator arrays with as many as a few tens of elements via combining sophisticated nonlinear ...