A Single-Layer SIW Slots Array Monopulse Antenna Excited by a Dual-Mode Resonator

The conventional monopulse comparator, which commonly consists of a power divider, a standard 3dB-coupler and a 90-degree phase shifter, occupies a significantly large area of the antenna aperture. This results in a low efficiency. In order to improve the antenna's aperture efficiency and keep a planar single-layer structure simultaneously, a substrate integrated waveguide (SIW) slots array monopulse antenna excited only by a square dual-mode (TE120 and TE210) SIW resonator is proposed, fabricated and measured in this communication. The sum and difference beams are obtained when the feeding cavity operates at two high-order modes, respectively. The needless of complex feeding network reduces the antenna's structure complexity and improves its aperture efficiency. The aperture efficiency of the antenna can reach 42%. Besides, the sum and difference ports have good isolation due to the orthogonality between the two modes. The proposed antenna obtains a 100 MHz impedance bandwidth, determined by the reflection coefficient less than -10 dB. The measured gain of the sum pattern is 11.9 dBi at 10 GHz, while the null depth of the difference pattern is lower than -27 dB.