Millimeter‐wave bandpass filter on LCP using CSRR‐loaded triangular‐shape quarter‐mode substrate integrated waveguide

A millimeter‐wave two‐pole bandpass filter (BPF) with an asymmetrical frequency response is realized on a flexible liquid crystal polymer substrate for wearable/conformal wireless applications. The design uses the triangular‐shape quarter‐mode substrate integrated waveguide (QMSIW) cavity loaded with a complementary split‐ring resonator. The compact cavity shows a resonant mode below the quasi‐TE 1,0,0.5 mode of an original QMSIW cavity, which indicates a further size reduction. In addition, its low quality factor (Q) is useful for BPFs with broad fractional bandwidth (FBW). A surface micromachined two‐pole Chebyshev BPF is realized for operation at 35 GHz with a 20 dB return loss FBW of 8% and an insertion loss of 1.7 dB. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1782–1784, 2015