Low pass filter design and manufacture with coaxial lines

In this study, a low-pass filter is designed by using a coaxial transmission line. Microwave and 3D electromagnetic simulators were used in the filter design. The design was started by establishing an 11th Order Chebyshev Low-Pass Filter prototype giving 0.05 dB ripple. Based on this prototype, a filter circuit consisting of capacitors and inductors as lumped elements was designed. The low and high impedances to be selected for the stepped impedance method, which is the basis of the transition to coaxial transmission lines, have been decided and the most suitable impedances for manufacturing was determined. Using these impedances, the filter circuit designed with stepped impedance lines was transformed into the filter circuit where coaxial transmission lines will be used. The designed filter has been manufactured . The basic properties of the produced filter were characterized using RF measuring devices and compared with the properties of the designed filter. It has been shown that the frequency responses of the designed filter and the produced filter are very close to each other. In this article, the design and manufacture of a low-pass filter with a cutoff frequency of 6 GHz, which will be transmitted using coaxial transmission lines, is discussed. It is foreseen that the pass loss of the filter should be as low as possible in the passband. While the return loss is expected to be kept below 20 dB, a sharp suppression of 50 dB at 9 GHz in the stop band is targeted. Coaxial transmission lines in the low-pass filter circuit consist of interconnected conductors with an insulating material between them. While the insulating material is selected as air in the high impedance sections of the transmission lines, it is PTFE (Polytetrafluoroethylene) in the low impedance sections, that is, the Teflon material with an insulating constant of 2.1.