Miniaturized sharp band-pass filter based on complementary electric-LC resonator Yalda Torabi 1 • Golamreza Dadashzadeh 1 • Homayoon Oraizi 2 Received: 25 August 2015 / Accepted: 21 October 2015 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract In this paper, a novel application of comple- mentary electric-LC (CELC) resonator as a basic element to synthesize miniaturized sharp band-pass filters is intro- duced. The proposed metamaterial band-pass filter is a three-stage CELC-based device, where two shunt short- circuited stubs are employed in the input and output stages and a series gap is etched in the middle stage. By these means, a high-selectivity prototype band-pass filter with 2 % fractional bandwidth in S band is designed and fab- ricated. The out-of-band attenuation is better than 40 dB, and the upper and lower transition bands are also quite sharp due to the presence of two transmission zeros (nearly 60 and 30 dB fall in 0.2 GHz at lower and upper edges, respectively). Moreover, the filter is substantially minia- turized with a size of effective region of 1.3 cm 9 1 cm at 2.9 GHz, which is quite smaller relative to conventional designs with the same performance. The fabrication and measurement of the proposed filter configuration attest to its expected desirable features. Therefore, the application of CELC resonator is proposed for super-compact sharp band-pass filters. 1 Introduction Planar band-pass filters (BPFs) with miniaturized size, low insertion loss, and high passband selectivity are highly desirable in the next generation of wireless and satellite communication systems. During the last decade, metamaterial transmission lines with double-negative constitutive param- eters have attracted a great deal of interest from researchers to design various types of band-pass filters [1, 2]). Split-ring resonator (SRR) and complementary split-ring resonator (CSRR) as the main building blocks of metamaterial trans- mission lines have been extensively used to design such filters [2–4]. Lately, electric-LC (ELC) resonator and its comple- mentary counterpart (CELC), introduced in references [5] and [6], respectively, have been used to realize planar metamate- rial transmission lines [7, 8]. ELC and CELC resonators have been known as high-symmetric structures which exhibit exclusively electric and magnetic resonances by appropriate excitation, respectively [9]. Contrary to SRRs and CSRRs, some few studies have been conducted to utilize these res- onators as the main building blocks of band-pass filters, although they have great potentialities for such applications. In [10], a band-pass filter was obtained by loading CELC at the back of microstrip line and using C-shaped input and output feeds. However, the systematic design procedure of the filter is lacking, and it is difficult to obtain its equivalent circuit parameters due to the intricate proposed electrical circuit. In [11], we previously illustrated that by etching an array of CELC resonators, below the conductor strip in the ground plane of microstrip line, the effective permeability of structure becomes negative in a narrow band above the CELC reso- nance frequency. Moreover, we demonstrated that the pro- posed combination of the CELC resonators with short- circuited stubs in microstrip lines provides the possibility of realizing left-handed cells with the frequency response similar & Yalda Torabi y.torabi@shahed.ac.ir Golamreza Dadashzadeh gdadashzadeh@shahed.ac.ir Homayoon Oraizi H.oraizi@iust.ac.ir 1 Electrical and Electronic Engineering Department, Shahed University, Tehran, Iran 2 Department of Electrical Engineering, Iran University of Science and Technology, Tehran, Iran 123 Appl. Phys. A (2016)122:273 DOI 10.1007/s00339-016-9787-2