*Corresponding author. Tel +6689 555 2266 Email address: elecpnt@rmutl.ac.th; hs5qab@hotmail.com doi: 10.14456/kkuenj.2016.115 KKU ENGINEERING JOURNAL 2016;43(S2):303-306 Research Article KKU Engineering Journal https://www.tci-thaijo.org/index.php/kkuenj/index Hybrid of scattering matrix method and wave iterative algorithm for waveguide cascaded irises Pinit Nuangpirom* 1) and Somsak Akatimagool 2) 1) Faculty of Engineering, Rajamangala University of Technology Lanna, Chiang Mai, Thailand. 2) Faculty of Technical Education, King Mongkut's University of Technology North Bangkok, Thailand. Received April 2016 Accepted June 2016 Abstract In this paper, the application of the wave scattering matrix method of two domains using wave iterative algorithm is presented in order to obtain the incident wave, reflected wave and transmitted wave parameters of the waveguide iris. Traditionally, the conversion of the wave scattering matrix to the frequency response and electromagnetics characterization has been used in order to perform the cascaded connection in waveguide filters. The numerical results of waveguide bandpass filter using the wave scattering parameters integrated with wave iterative procedures, were reported as efficient examples. Keywords: Scattering matric method, Wave iterative algorithm, Waveguide cascaded irises 1. Introduction Modern analysis of microwave circuits with the help of powerful simulation tool makes to precision analysis. In the design and analysis of microwave components is being used by numerical method, such as the finite Differential Time Domain (FDTD) [1], Method of Moments (MOM) [2]. Most high frequency two port networks are characterized in terms of scattering parameters, which have been arranged in matrix forms and related transmitted and reflected waves in the input and output ports [3]. Likewise, The modeling of microwave systems formed by subsystems usually characterized by mono modal scattering matrix. On the other hand, the characterization of microwave systems or components formed by networks connected in usable cascaded connection of two-port scattering matrix in order to obtain the overall scattering parameters. Especially, one of the classic problems in waveguide iris filter is a design and analysis of an optimum equalizer to match an arbitrary multilayer load (cascaded irises) to generators with complex internal impedance of two port network [4]. In this paper, we present a novel numerical technique for the efficient cascaded connection of N multimodal two-port scattering matrix. The proposed methods based on wave iterative algorithm apply to analyze waveguide filter. 2. The modal scattering matrix of length of waveguide Considering the 2-port network as shown in Figure 1, where Vn is the amplitude of the voltage wave on port n, and In is the amplitude of the current wave on port n. The modal Scattering matrix, or S matrix, is defined in relation to these incidents (an) and reflected waves (bn) as [5]. Linear 2-Port Network 0 R 0 R s1 V s2 V 1 V 1 I 2 I 2 V 1 a 1 b 2 a 2 b Figure 1 Two port network with scattering waves 1 11 12 1 2 21 22 2 b S S a b S S a                 (1) A specific element of the S matrix can be determined as i ij j b S a  (2) In equation (2) says that Sij is the transmission coefficient from port j to port i, Sii is the reflection coefficient seen looking into port I when all other ports are terminated in matched loads. Therefore, the form of the scattering matrix of a length of waveguide for a propagation mode is often taken as [6]. l l 0 e e 0         (3) Where  is the propagation constant of the mode above cutoff frequency.