Compact two pole metamaterial bandpass filter using inverted IDC, meander line and rectangular stub for WiMAX application

Abstract

This paper represents a via-less compact metamaterial (MTM) bandpass filter. The proposed filter is configured with a symmetrical shunt meander line and rectangular stub on both side of the inverted interdigital capacitor and makes pi-type equivalent circuit diagram. Inverted interdigital capacitor generates a series left handed capacitance and current flowing through it forms right handed inductance. Left handed inductance generated by meander line and right handed capacitance produced by parasitic effect of fingers of IDC and ground plane. The rectangular stub works as a virtual ground and form large capacitance connected with meander line. Two poles are generated due to two meander line and two rectangular stub and it is shown by its electric field distribution. Two transmission zeros are produced one before the passband and other after the passband and its position is controlled by meander line length. The MTM properties of designed filter is verified by dispersion diagram. The designed filter delivers excellent scattering parameters with measured insertion loss of 0.70 dB and return loss greater than 25 dB with 3 dB fractional bandwidth 50.4% at centre frequency 3.01 GHz. The frequency band from 1.95 GHz to 2.62 GHz comes under left handed region due to negative slope and from 2.62 GHz to 3.9 GHz comes under right handed region due to positive slope. The electrical size of the suggested filter is 0.13λ g × 0.24λ g , where λ g is the guided wavelength at ZOR frequency of 2.62 GHz. The designed structure has been fabricated and experimentally validated. The designed filter offers measured group delay variation between 0.5 ns to 0.75 ns within the passband. It is suitable for WLAN (2.4–2.48 GHz) and WiMAX (2.5–2.69 GHz, 3.3–3.69 GHz) applications.