Compact Wideband Lowpass Filter Based on Inverted Cascading Stubs

Abstract

In thisstudy, a new compact wideband lowpass filter was introduced. The proposed filteris developed by cascading two shapes of ‘4’ open stubs back to back embedded ona microstrip line. This structure results in wide cutoff frequency andrejection band with improved scattering parameters.  The filter utilized operating bands up to 4 GHz.Many useful wireless communication bands were allocated within this band,global system for mobile communications (GSM) bands (1.8, 1.9 and 2.1 GHz) and2.4 GHz which is used for industrial, scientific and medical (ISM) band andwireless local area networks (WLANs) applications.The designed filter alsocovers the band 3.5 GHz widely used for worldwide interoperability formicrowave access (WiMAX) applications. The frequency response of the filtershows good stopband characteristic and provides -3 dB cutoff frequency at 3.85GHz. The return loss of the designed filter is -50.8 dB at 3GHz and theinsertion loss is less than -0.18 dB along the passband. The proposed filterhas been designed, analyzed, and optimized on a substrate with 10.8 dielectricconstant and thickness of 1.27 mm using full wave Electromagnetic Simulator.The proposed filter is a compact size and the final optimized dimension of thesimulated filter with the above features is only 20 mm ×15mm.