Compact inkjet printed bandstop filters using defected microstrip structure on flexible substrate

This paper presents a compact inkjet printed microstrip Bandstop Filters (BSF) on Flexible Substrate. To achieve a compact size, the defected microstrip structure (DMS) structure was employed. A 0.05 mm thick kapton polymide substrate with a dielectric constant of 3.4 suitable for inkjet printing was used. Simulated results show a narrowband response with good stopband attenuation of -39 dB, excellent passband return loss of -0.14 dB and inter-band return loss greater than -35 dB up to 10 GHz. Whilst sustaining its outstanding performance, miniaturisation is also achieved as the presented BSF occupies the least normalised area (0.267 λ_g × 0.002 λ_g) when compared to other published filters. A spurline DMS is also simulated and presented, and exhibits improved stopband attenuation up to -45 dB, compact size and excellent passband return loss of -0.09 dB at resonant frequency of 3.425 GHz. These types of filters are very useful for wireless systems such as the WLAN, WiMax and 4G.