Embedded Split Ring Resonator Tunable Notch Band Filter in Microstrip Transmission Lines
Farhad Farzami, Seiran Khaledian, Alex C. Stutts, Besma Smida, Danilo Erricolo
Abstract
Novel design techniques for tunable and fixed frequency notch band filters are presented and validated with experiments. A notch band filter based on an Embedded Split Ring Resonator (ESRR) in a Microstrip Transmission Line (MTL) is presented. The physical dimensions of the ESRR determine the filter resonance frequency, which, when combined with a Varactor (Varactor Loaded ESRRs or VLESRRs), provides a continuously tunable resonance frequency. Tunable notch bands centered from 1.7 GHz to 4.8 GHz are obtained with resonators having an unprecedented electric length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.05~\lambda _{0}$ </tex-math></inline-formula> at the lowest frequency, corresponding to a physical length of 7 mm and a total occupied area of 8.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Two or more ESRRs are proposed to provide a deeper single notch band, a wider notch band, and/or multi notch bands. The proposed ESRRs are used jointly with a trapezoidal antenna to form 1) a notch band at 2.5 GHz; and, 2) dual notch bands at 2.5 GHz and 3.5 GHz. In addition, ESRRs are used in a Low Pass Filter (LPF) with cutoff frequency of 1 GHz to suppress undesired harmonic at 3.46 GHz and improve band rejection. The proposed MTL loaded by ESRRs, LPF and trapezoidal antenna are fabricated, measured and the results of simulations and measurements are in good agreement.