Compact Dual-Band Differential Power Splitter With Common-Mode Suppression and Filtering Capability Based on Differential-Mode Composite Right/Left-Handed Transmission-Line Metamaterials

This letter presents a compact differential-mode (balanced) power splitter with filtering capability and dual-band functionality. This multifunctional device is based on differential-mode composite right/left-handed (DM-CRLH) transmission lines specifically designed to achieve the dual-band behavior and to suppress the common-mode noise over a broad frequency band. The DM-CRLH lines are implemented by means of pairs of CRLH lines with series connected interdigital capacitors and strip inductors in the series branches and mirrored step impedance resonators (SIRs) in the shunt branches. For the differential mode, the SIRs are described by parallel resonant tanks, and the resulting equivalent circuit model is the canonical circuit of a CRLH line, which can be used for designing the dual-band balanced splitter/filter. However, the SIRs are opened under common-mode operation, introducing transmission zeros for that mode. By tailoring the position of these transmission zeros, the common mode can be effectively rejected over a frequency band that covers the splitter operating frequencies. The fabricated dual-band balanced power splitter exhibits a measured matching level better than -11 dB, and measured insertion losses (power splitting) lower than 4.1 dB at the design frequencies ( f
₁
=1.8 GHz and f
₂
=2.4 GHz). The common-mode suppression at f
₁
and f
₂
is better than 30 dB.