An Enhanced Skirt Characteristics Triple-Mode Filter

This paper presents a compact microstrip triple-mode filter with enhanced skirt characteristics. The presented triple-mode filter configuration supports three transmission poles and three transmission zeros within the nearby pass-band. Two of transmission zeros are generated by a triple-mode resonator itself, and the third one is generated by small cross-couplings between the I/O ports. Each resonance condition and the transmission zero generation conditions are analyzed using an equivalent circuit. The bandpass filter is designed for a 2.4 GHz WLAN. The filter was fabricated with a relative dielectic constant of 3.5 and a thickness of 0.76 mm. The fabricated filter has a small size (7.9 mmx7.2 mm, i.e., 0.107 lambda(g) x0.098 lambda(g), where lambda(g) is guided wavelength at a center frequency) and shows high performing skirt characteristics.