A Low-Loss Fully Board-Integrated Low-Pass Filter Using Suspended Integrated Strip-Line Technology

This paper presents a low-loss fully board-integrated low-pass filter (LPF) using suspended integrated strip-line (SISL) technology. A multilayer board stack-up, with internally buried hollow cavities, is used to create the suspended strip-line. By transitioning from the top copper ground-backed coplanar waveguide trace to an internal strip-line and vice versa, a more traditional industry-standard utilization of the top copper can be realized with this SISL implementation. Based on the proposed design, an 11th-order generalized Chebyshev LPF, with a cutoff frequency of 18 GHz, has been designed and fabricated using standard printed circuit board fabrication processes. Compensated measured results show less than 1 dB of attenuation over the dc-18-GHz passband and greater than 30 dB of stopband attenuation up to 26 GHz. The proposed SISL technology LPF has advantages of low loss, compact size, and low cost, which are crucial to meet unprecedented reductions in size, weight, power, and cost (SWaP-C) of future systems.