Growing evanescent waves in continuous microstrip grids containing meandered lines

We demonstrate through a combination of circuit and full-wave simulations that a grid of continuous microstrip transmission lines without any lumped elements, is capable of growing evanescent waves. These continuous microstrip grids come in two flavors: a backward-wave transmission line (BWTL) grid and a forward-wave transmission line (FWTL) grid. It has already been demonstrated through ideal transmission-line simulations that a BWTL grid, sandwiched between two FWTL grids, supports growing evanescent waves. However, the size of the FWTL unit cell is larger than that of the BWTL unit cell; this results in a physical mismatch at the boundary between the two grids. To this end, we show that by meandering the microstrip lines of the FWTL unit cell its size can be matched to that of the BWTL unit cell. Using this approach, we design a physically realizable microstrip implementation of the two grids and show, through a combination of full-wave and circuit simulations, that a 3-region FWTL/BWTL/FWTL setup can support growing evanescent waves.