Solving the broadside radiation issue in periodic leaky-wave antennas

Based on a generic equivalent circuit model, the radiation degradation at broadside of fully symmetrical LWAs is reviewed. Breaking the symmetry overcomes this degradation and allows to control solely the broadside radiation direction, where the backward and forward (off-broadside) radiation directions remain unaffected. With the degree of asymmetry in the unit cell, the broadside radiation efficiency is then adjusted so to match to the off-broadside radiation efficiency, a procedure referred to as equalization. This paper first summarizes the underlying theory. Next, it provides practical hints on how to implement this asymmetry in the unit cell by demonstrating the equalization in several LWA types including a combline LWA (double-stub loaded transmission line). The broadside issue in this combline LWA is finally resolved by realizing unit cell asymmetry in terms of slightly different stub lengths.