A microstrip folded compact wideband band‐pass filter with wide upper stopband

A miniaturized wideband band‐pass filter with a 3‐dB fractional bandwidth of 109.3% (1.53 GHz to 5.22 GHz), high out‐of‐band attenuation greater than 25 dB, and wide upper stopband up to 14 GHz is proposed. The design consists of a dual‐composite right/left handed resonator, embedded open‐circuited stub, and a pair of quarter‐wavelength short‐circuited stubs. These elements are coupled in the near distance to form a miniature filter with a compact occupied area of 0.21 λg× 0.19 λg (≈ 0.013 cm2). The optimized filter has multi‐transmission poles in the passband, substantially improving the return loss and insertion loss characteristics. The behavior of the passband and stopband is verified against the results of a lumped element model and matrix analysis with a full‐wave moment‐based analysis and actual measurements. The results of this verification and a comparison with the performance of filters in other references indicate that the proposed filter is very efficient and applicable to compact microwave systems.