Compact Bandpass Filter in Empty Substrate Integrated Coaxial Line

This paper presents a new design for size reduction of empty substrate integrated coaxial lines (ESICLs). The size enhancement is obtained by using improved impedance inverter arrangements. Taking advantage of the multilayer nature of the ESICL, a compact version of the inverters have been developed. The performance of the proposed inverter has been experimentally validated with a working prototype in Ku-band. A fifth-order 0.01-dB ripple Chebyshev filter operating at 13 GHz has been manufactured and measured. The experimental results are in excellent agreement with simulated predictions, confirming thus the advantages of the new proposed compact inverter design. The total length of the filter structure can be reduced by 17.75 % if the compact impedance inverted is employed.