A Compact Microstrip Multi-Layer Lowpass Filter Using Triangle Slots Etched in the Ground Plane

In this paper we present a new concept for implementing cascaded lowpass filters and multi-layer LPF by employing Pi-arrowhead resonators as a defected ground structure (DGS) and as a resonator cell in the upper layer. The effect of the arrowhead area of a DGS on the performance of the conventional LPF is examined. The LPF is designed easily by extracting the equivalent circuit elements of a uniform arrowhead DGS slot and compensating for the capacitance of the transmission line (Boutejdar et al., 2005). The proposed multi-layer LPF is 50% shorter than the conventional LPF. Only two cells of the new structure are necessary to obtain better performance by suppressing ripples and enlarging stopband. The measured results show excellent agreement with simulated and equivalent circuit results