Series-Fed Monopulse Microstrip Array Antenna With Stripline Quadrature Hybrid Comparator Network

Microstrip series-fed weighted arrays have widespread applications in millimeter wave (MMW) radar due to their low profile and light weight. Our study proposes a novel Ka-band compact monopulse radar antenna design with a highly directional 2D series-fed microstrip array antenna. The structure is composed of a symmetrical four quadrant radiation array and an innovative stripline monopulse comparator with two segments. Our novel design applies the stripline in the back-end which considerably reduces the antenna’s backward radiation. The shaped patterns in the E and H planes are achieved by tapering patch widths and adjusting the impedance transformer of each subarray. Four half power quadrature hybrids are combined to form 2D monopulse feeding in the back-end. Both parts adopt a simple symmetrical layout that simplifies the design process. The measured reflection coefficients of each port are lower than −10 dB across 34.5 GHz to 35.5 GHz working band meanwhile isolation between these ports are better than 25 dB. Furthermore, the first side lobe level (FSLL) in the sum beam, which is remarkably suppressed by Taylor synthesis design method, achieves about −24 dB both in E and H planes. The measured gain of the sum pattern achieves 25.3 dBi at 35 GHz center frequency, while the nulling depth of the difference patterns in both planes are lower than −30 dB.