A Miniature Planar Dual-Band Bandpass Filter using Modified Stepped Impedance Resonator (SIR) with Defected Ground Structure

A planar dual-band bandpass filter (BPF) is proposed which consists of a stepped impedance resonator (SIR) with loading stub. Loading stubs is used to provide additional parameters to move resonant frequency of filter with compact size compared to simple SIR structure can. Desired bandwidth of filter achieved by adjusting resonating frequencies, through varying characteristic impedance, Stub length of SIR and size of loading stubs. SIR with parallel feed structure enhances stopband performance by cross coupling. Resonating stub provide an addition frequency band to make filter as dual band. Rectangle-slot broad-defected ground structure (BDGS) is employed to enhance the attenuation performance in the stopband. Filter covers two frequency band 4.949-5.320 GHz and 8.006-8.237GHz with relevant resonant frequencies are 5.136GHz and 8.112GHz respective return losses are 38.10dB and 26.88dB and insertion losses are 0.385dB and 0.064dB. Aeronautical radio navigation (5-5.15GHz), Satellite communication and mobile communication (8.025-8.215 GHz) are some applications of frequency bands. Filter cover unlicensed national information infrastructure (UNII) radio band (5.15-5.25 GHz), so it can be used in WLAN/Wi-Fi etc. applications. The filter size is 12 x 15 mm(2). All above features makes filter attractive for wireless communication applications. Filter designed and simulated using commercial software CST Microwave Studio 2013.