A Low-Loss Ultrawideband 3-dB Coupler Using Hybrid Integrated Suspended Line (HISL) With Multiple Inner Boards

This letter presents the hybrid integrated suspended line (HISL) platform with multiple inner boards. By employing cutting-out dielectric and multiple-inner board technology, low loss and modal phase velocity balance can be achieved simultaneously. The utilization of HISL platforms helps enhance the mechanical strength of the entire structure. The loss and the modal phase velocity of the structure and the influence of various physical dimensions on the odd- and even-mode impedance are analyzed. Based on the proposed HISL platform with multiple inner boards, a low-loss ultrawideband 2–18-GHz 3-dB coupler utilizing nonuniform technology is designed. The proposed coupler exhibits low measured insertion loss, achieving better than 0.3 dB at the center frequency. Additionally, both measured isolation and return loss are better than 15 dB.