Balanced Dual-Band Bandpass Filter With Intrinsic Common-Mode Suppression Using Coplanar Stripline and Asymmetrical Coplanar Stripline

In this letter, a balanced dual-band bandpass filter with intrinsic common-mode suppression is proposed based on coplanar stripline and asymmetrical coplanar stripline. The proposed balanced dual-band bandpass filter is composed of a four-mode resonator, where two pairs of resonant modes form two two-pole passbands with adjustable passband locations. The four-mode resonator consists of two coupled hybrid coplanar stripline and asymmetrical coplanar stripline open-loop resonators. Four resonant modes of the proposed resonator can be independently controlled by adjusting the parameters of coplanar stripline and asymmetrical coplanar stripline sections. To validate the proposed structure and design method, a balanced dual-band bandpass filter working at 1.8 and 2.4 GHz was designed, fabricated, and measured. The measured results are in good agreement with the simulated ones, thus strongly demonstrating the feasibility of achieving a balanced dual-band bandpass filter with common mode suppression.