Periodic Leaky-Wave Antennas Based on Microstrip-Fed Slot Array With Different Profile Modulations for Suppressing Open Stopband and n = −2 Space Harmonic

This article proposes a periodic leaky-wave antenna that is based on a microstrip-fed periodically modulated transverse-slot array in the ground plane. The profile of the transverse-slot array is periodically modulated to introduce a fast space harmonic ($n = -1$) that generates a narrow beam scanning in the backward and the forward quadrants. Different profile modulations are studied for suppressing the open stopband and the$n = -2$space harmonic. If the slot profile is designed to have the impedance matched at the broadside frequency, the leaky-wave antenna has the open stopband suppressed and allows continuous scanning of the main beam through the broadside from the backward endfire to the forward direction. However, it cannot avoid the$n = -2$space harmonic, which causes another stopband that limits the scanning range in the forward quadrant. If the slot profile is modulated with a profile such that the aperture illumination excludes the$n = -2$space harmonic, the leaky-wave antenna avoids the stopband and grating lobe caused by the harmonic and thereby has the scanning range in the forward quadrant enlarged, but its open stopband cannot be suppressed simultaneously. Prototypes with the two profile modulations are fabricated and measured for validation.