A stopband-improved and size-miniaturized low-pass filter based on substrate integrated coaxial lines and etched substrate-integrated half-coaxial lines

A novel etched substrate-integrated half-coaxial line (ESIHCL) is proposed and utilized to compose a shielded low-pass filter with high performance. In comparison with substrate integrated coaxial lines (SICLs), the characteristic impedance of the proposed structure is significantly enhanced and can be modified flexibly, making it highly suitable for implementing the inductive components of low-pass filters. Finally, a fifth-order Chebyshev low-pass filter with a ripple factor of 0.1 dB and a cut-off frequency of 0.85 GHz was designed by combining the high-impedance features of the new proposed ESIHCL and the low-impedance characteristics of the conventional SICL. The experimental results indicate that the designed low-pass filter achieves a minimum insertion loss of −0.2 dB and exhibits a wide 20 dB stopband from 1.197 to 18 GHz, which is employed in a compact size of only 0.0097 λg 2 . Moreover, its roll-off rate (ROR) reaches 53.628 GHz, demonstrating higher advantages in terms of filtering passband loss, stopband suppression, and size optimization. These characteristics make the filter highly suitable for modern RF systems, and are of great significance in reducing the size of RF systems in microwave regime.