Composite Right-/Left-Handed Bandpass Filters With Enhanced Out-of-Band Rejection Using Slow Wave Metamaterial Structure

A compact and easy-to-fabricate metamaterial by virtue of multilayer slow wave structure is introduced to effectively enhance the out-of-band rejection of composite right-/left-handed (CRLH) bandpass filters (BPFs). An equivalent circuit model of this multilayer slow wave metamaterial structure is derived and discussed. Four BPFs are designed and fabricated using 3-D glass integrated passive device (IPD) technology. The first two BPFs consist only of novel CRLH resonator unit cells, and the last two BPFs are composed of multilayer slow wave metamaterial structures introduced with the same parameters as the first two BPFs. The electromagnetic field in the BPFs is redistributed due to the presence of this metamaterial structure, which can significantly improve the filter attenuation capability at high-frequency spurious. Through simulations and measurements, the two BPFs incorporating multilayer slow wave metamaterial structures enhance the out-of-band attenuation capability at the high-frequency end by nearly 3 and nearly 18 times compared to the first two BPFs.