Ultra-wideband (UWB) balanced bandpass filters with wide stop band and intrinsic common-mode rejection based on embedded capacitive electromagnetic bandgaps (EBG)

A microstrip differential-mode (balanced) bandpass filter covering the frequency spectrum assigned for ultra-wideband (UWB) communications (3.1 GHz-10.6 GHz) is presented. The main relevant characteristics of the proposed filter are: (i) the good stop band performance above the band of interest, with high selectivity, harmonic suppression and broad rejection bandwidth, achieved thanks to the embedded capacitive electromagnetic bandgap (EBG) structure; and (ii) the intrinsic (and efficient) common-mode noise rejection (covering the differential filter pass band), related to the controllable transmission zeros provided by the reactively loaded transmission lines present between the pair of differential lines. Additional advantages are low cost, easy fabrication (vias are not required and layout dimensions are not critical), backside isolation (defect ground structures are not present), and compact size (due to the slow-wave effect of the EBG). The combination of performance and size makes the approach very competitive.