Computer-Aided Design and Applications of Planar Branch-Line Coupler Circuits

Introduction

Computer-aided design (CAD) is an important software tool in today's engineering system design. Recently, many new high technology systems, such as new mobile phones, can be designed and modified in a short time by using CAD tool without actual building the phone prototype. Normally, the CAD is particularly used in designing electronic system, which is also called as electronic design automation (EDA). Recently, the EDA tool has an important role in the communication industry sector as well as research-based universities. Hence, in this new era, graduated engineers are required to have skills in engineering design. Thus, some universities are incorporating commercial electronic design automation (EDA) into their electrical and computer engineering curriculum (You et al., 2017).

During the 70s and early 80s, most engineering systems were developed based on analytical analysis or experimental testing due to less sophisticated computer technology during that time. Analytical analysis is the simplest and fastest method, yet less accurate in engineering design. On the other hand, the engineering design based on experimental work method is most reliable, nonetheless requires high cost and time consuming. Furthermore, during the 80s and early 90s, several numerical methods, such as Finite-Difference Time-Domain Method (FDTD), Method of Moments (MoM), Finite Element Method (FEM), and Boundary Element Method (BEM) was studied and started applied in engineering system design. After the end of the 90's until the date, many numerical-based commercial EDA simulators have already exist, such as Advanced Design System (ADS), Microwave office (AWR), IE3D, High Frequency Electromagnetic Field Simulation (HFSS), Computer Simulation Technology (CST), COMSOL Multiphysics, FEKO, and Sonnet. Hence, the risks of trial-and-error in the experiment design can be diminished as well as saving the cost and time.

This book chapter mainly focuses on analytical analysis for the branch-line coupler in which this method provides an explicit solution in the coupler design. Generally, the directional coupler is one of the fundamental components for Microwave Integrated Circuit (MIC); especially the equal power-split coupler is used for signal monitoring, power measurement, power division, and balanced-type components such as balanced mixers. In this chapter, several applications of the branch-line coupler are also described. The analytical and design formulations of the coupler are derived based on ABCD matrix, transmission line principle, and even-odd mode decomposition (Reed and Wheeler, 1956). Although the simple analytical analysis is not sufficiently implemented in complex coupler structure, it is capable of providing an initial design guideline for the coupler dimensions. The initial design of the coupler dimensions based on analytical analysis can be gradually modified and optimized to achieve the desired size or performance of the coupler using advance numerical simulation. Hence, the time used in coupler design can be reduced significantly.