Design of CRLH-TL BPF with controllable attenuation poles

Compact and pole-controllable resonators and bandpass filter (BPF) using a composite right/left-handed transmission line (CRLH-TL) are designed in this study. The distributed constant line in the CRLH-TL has applied a tap-coupling technique, and one tap-coupled stub is loaded with the left-handed (LH) circuit. Attenuation poles are generated when the input susceptance of the stub diverges. In the tap-coupled CRLH-TL resonator, the attenuation pole is controlled at either the desired lower or higher region frequency than a resonant frequency by adjusting the circuit parameters. Also, the BPF constructed by the CRLH-TL resonators is designed based on a filter design theory, where the attenuation poles are located at lower and higher region frequencies than a negative-first-order frequency. The BPF with microstrip structure is fabricated using MEGTRON6 R-5775 (εr\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varepsilon _\text {r}$$\end{document}: 3.7, h: 0.63 mm, t: 18 μm), chip capacitors, and wire inductors. The simulated results show that the desired characteristics are approximately satisfied, i.e., we can design the CRLH-TL BPF which is controllable for the attenuation poles at both lower and higher region frequencies than a resonant frequency. The measured results are good agreement with the simulation. The negative-first-order frequency is generated at 2.00 GHz with 133 MHz bandwidth, i.e., the fractional bandwidth is 6.65 %. The resonator lengths in the BPF are shortened by 81.5 % and 75.0 % in comparison with a conventional half-wavelength (λ/2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda /2$$\end{document}) openstub, and the size of the fabricated BPF is 0.18 λg×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda _\text {g} \times$$\end{document} 0.17 λg\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda _\text {g}$$\end{document}. Therefore, a compact BPF with two controllable attenuation poles is realized by the tap-coupled CRLH-TL.