Design of Stubs in a Comb-Line Leaky-Wave Antenna for Minimizing Gain Variation at Broadside

In this work, the effect of a two-section stub for minimizing gain variation near broadside frequency in a comb-line leaky-wave antenna (LWA) is investigated. Mathematical design conditions for stubs are derived based on the matched input impedance requirement of the unit cell. Based on the derived conditions, two different stubs (Case-I and Case-II) are designed and placed in the middle of the host transmission line (50 Ω delay line) to make comb-line unit cells (UC#1, and UC#2). The open stopband (OSB) suppression is investigated by analyzing the input impedance and the leakage constant of the unit cells. Next, the variation in the gain of the LWAs (LWA#1, and LWA#2) with the proposed stubs is compared with a comb-line LWA with the conventional radiating stub (CRS). The gain variation in LWA#1 is only 0.7 dB as compared to the 2.5 dB gain variation for LWA using CRSs. Moreover, the gain is improved by 2 dB near the broadside for LWA#2 as compared to LWA using CRS. In the entire analysis, the broadside frequency is chosen near 10 GHz.