Sidelobe Suppression for Leaky-Wave Antennas Using a Complementary Paired Configuration

In this letter, an effective method is proposed to suppress the overall sidelobes for period-modulated leaky-wave antennas (PM-LWAs). The radiation mechanism of the high sidelobes in PM-LWAs is thoroughly investigated by space harmonic (SH) analysis of the aperture field. It is found that the $n = 0$ SH in PM-LWAs occupies a larger proportion of power than that in periodic LWAs (P-LWAs), resulting in a higher sidelobe level (SLL) in PM-LWAs than that in P-LWAs. An SLL suppression method for PM-LWAs is proposed based on even SH cancellation, which is realized by aligning inversed period modulations in a pair of PM-LWAs. Exciting the PM-LWA pair with equal amplitudes and reversed phases, all radiations from the even SHs are cancelled out and hence the overall sidelobes including the first sidelobe and grating lobe are efficiently suppressed. Prototypes are designed, simulated, fabricated, and experimentally measured. Measured results agree well with simulations, which verify the theoretical predictions. The overall sidelobes are suppressed by more than 10 dB in almost the entire forward region. The radiation of n =-2 SH (grating lobe) and the first sidelobe is reduced by more than 20 and 3.4 dB, respectively.