Low-pass Elliptic Filters Using Mixed Microstrip-CPW Technologies

Stepped-impedance low-pass elliptic fllters are presented in this paper which make use of patterning of both sides of the microstrip substrate. Microstrip and coplanar waveguide components as well as their interactions are used jointly to synthesize the required fllter elements. Relatively compact implementations with good electrical performance are obtained in this way. Conventional stepped-impedance low pass fllters (SI-LPF) consist of a cascading of electrically short high and low impedance sections to approximate the corresponding ladder LC lumped circuit prototype (1). However, this kind of fllter inherently presents two problems. One of them is the degradation of the stop band rejection level because of the frequency-distributed behavior of the flnite section lines. The second problem comes from the limits imposed by the microstrip technology to achieve very narrow strip widths and, consequently, high impedance section lines.