Microstrip elliptic-function low-pass filters using distributed elements or slotted ground structure

This paper presents two microstrip elliptic-function low-pass filters, one using distributed elements and one using a slotted ground structure. The one using distributed elements consists of a microstrip line section in parallel with an interdigital capacitor; the other one using a slotted ground structure consists of a low-impedance microstrip line with a slotted ground structure cell under the center of the line. A transmission-line model and a full-wave simulation are used to calculate the inductance/capacitance values of the equivalent circuits. The design concept was validated through experiments showing good agreements with the full-wave simulated results.