13 th International Conference on DEVELOPMENT AND APPLICATION SYSTEMS, Suceava, Romania, May 19-21, 2016 978-1-5090-1993-9/16/$31.00 ©2016 IEEE Insertion loss measurement of a lowpass microwave filter manufactured on FR4 laminate Aurel Chirap, Valentin Popa Department of Computers, Electronics and Automatics Stefan cel Mare University of Suceava Suceava, Romania aurel@eed.usv.ro; valentin@eed.usv.ro Abstract — In this paper a microstrip low-pass filter modeling and designed for UTMS-2100 band is presented. The full wave EM simulated and measured results are compared and a good agreement has been achieved for this low-pass filter fabricated prototypes. The measured insertion loss is 28.6 times higher for the FR4 laminate as for the reference laminate. Keywords — microstrip filters; microwave filters; loss measurement; insertion loss, dielectric losses, dielectric substrates; FR-4; RO4003C. I. INTRODUCTION Most often, filters are used for selection or suppression of specific frequency bands. Furthermore, they are utilized for adapting impedances between the functional blocks of high- frequency systems. The passive components with lumped parameters (capacitors, inductors) are frequently used in designing filters. Passive filters with lumped parameters elements operate well up to several hundred MHz frequencies, but above this level, the performance of the filter varies significantly. Is it possible to use passive circuit elements with distributed parameters, in which case the performances of the device are dependent on the characteristics of the laminate used, in special of the substrate losses [1],[2],[3]. The present study aims at estimating the losses caused by the substrate electric properties, in particular, loss angle tangent. For this objective achievement we are proposing a working method based on following steps: 1. Modeling a microstrip technology filter allowing the pass of the UTMS-2100 frequency band. 2. Simulation and designing of two prototype filters; the first one, used as a reference and realized on a laminate (producer certified), as RO4003C[4]; the second one, realized on an ordinary laminate, as FR4 [5], used for comparing. 3. Measurements for both prototypes and results evaluation. II. FILTER MODELING The circuit elements with distributed parameters can be produced on plane structures using short-circuited line stubs or open-circuited transmission line stubs, that are characterized by Z 0 impedance and electrical length. Two successive conversions described in [2] are necessary for prototype filter elements transformation into circuit elements with distributed parameters. The first one, Richard’s conversion, allows the replacement of the lumped parameters inductors and capacitors with short-circuited or open-circuited transmission line stubs, with length l=λ/8, where λ is the line wavelength at the cut-off frequency, ω c . Fig. 1. Equivalent circuits a Kuroda identity. Thereby, an inductor can be replaced with an short-circuit transmission line stub, characterized by L impedance, while a capacitor can be replaced with a open-circuit transmission line stub, characterized by 1/C impedance (Fig. 1). However, from a practical point of view, it is difficult to design short-circuit transmission line stub but is possible to transform them in open circuit line stubs. This is possible through application of the Kuroda identity (Fig. 1), which allows conversion a short- circuit stub into open-circuit stub by adding a line segment, called unit element, with length l=λ/8 and impedance z=1 at both ends of the line stub. This unit element does not affect the filter functionality and n depends on impedances rate: n 2 =1+z2/z1. The proposed low-pass filter prototype is a 3rd order Chebyschev filter, with a cut-off frequency f C =2.2 GHz (Fig. 2). The g constants for element values (L and C) determining 231