Design of compact dual-band semi-lumped mixed bandpass filter

In this paper, a miniaturized 5 G microstrip lumped hybrid dual-band bandpass filter (BPF) with ideal transmission response, simple structure, and compact size is proposed and characterized. The conversions from lumped elements to microstrip lines are analyzed and demonstrated by utilizing the ideal theoretical circuit model and EM field model. The center frequency of 0.57 GHz and the second passband located at 1.29 GHz are implemented by the proposed dual-band BPF with 3 dB fractional bandwidths of 59.6% and 15.5%, respectively. Additionally, five transmission zeros are strategically positioned on both sides of the passband. The prototype filter with minimized circuit size on occupies 0.05 lambda g x 0.06 lambda g is fabricated and verified that minimum insertion losses in the passbands are separately 0.83 dB and 0.52 dB. Ideal agreement between the simulated and measured results confirms the reliability of the design approach.