Design of a coplanar waveguide (CPW) bandpass filter with wide harmonic suppression

In this present work a conductor-backed coplanar waveguide (CB-CPW) bandpass filter (BPF) centered at 2.8 GHz is proposed which consists of symmetrical L-shaped resonator pairs, shorted stubs, and L-shaped defected slot line (DSL). The center frequency of the proposed BPF can be tuned from 2.1 GHz to 3.8 GHz by changing the lengths of the resonator pairs. The passband ripple and spurious harmonics of the BPF are suppressed by adjusting the shorted and open stub section. The sharpness of the BPF is improved by including DSL near the feed line that exhibits stopband near the upper cut-off frequency. Simulated and measured result exhibits a stop-band rejection lower than -16 dB till 20 GHz with passband insertion loss of 0.7 dB and return loss of 29.66 dB. The BPF has much reduced circuit area of 8 × 20.2 mm
²
compared to work stated below, also has the group delay of 0.17 ns which remains almost flat for entire passband, fractional bandwidth of 60.71%, 30 dB shape factor of 2.98, 3 dB bandwidth of 1.7 GHz and roll-off factor of 17.12 dB/GHz. It is implemented on the FR4 substrate with dielectric constant ε
_r
= 4.4, substrate height = 0.8 mm and thickness of the CB-CPW conductor 0.02 mm. The BPF show better performance, and hence can be used for practical purposes such as in low-cost WLAN and WiMax devices.