A novel technique for the elimination of the open stopband in one-dimensional periodic printed leaky-wave antennas is presented. A quarter-wave transformer, or alternatively a matching stub, is introduced into the unit cell of the antenna, which forces the Bloch-wave impedance of the structure to remain real and non-zero at broadside. The effectiveness of the proposed technique is first demonstrated on a printed periodic microstrip leaky-wave antenna consisting of a single radiating stub per unit cell, which exhibits a significant stopband at broadside. The technique is then also applied to a structure consisting of two radiating stubs per unit cell, which is capable of mitigating, but not eliminating, the open stopband. In both cases the open stopband at broadside is completely suppressed.
Paulotto, S., Baccarelli, P., Frezza, F., Jackson, D.R. (2009). A Novel Technique for Open-Stopband Suppression in 1-D Periodic Printed Leaky-Wave Antennas. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, 57(7), 1894-1906 [10.1109/tap.2009.2019900].