Multiband Design Techniques for Passive Planar Microwave Circuits: A Review

Currently, the wireless communication industry is experiencing rapid advances in the smooth migration and upgrading of technology. Because of this, communication systems operating in multiple frequency bands are of interest, and multiband circuits play an important role in the design of compact and low-cost multiband communication systems. A multiband multimode communication system based on software-defined radio (SDR) is shown inFigure 1. In this communication system, the multiband capability is primarily achieved by the hardware, (i.e., using multiband microwave circuits)[1]. Passive microwave circuits are essential to the design of any communication system; for example, quadrature branch line couplers (BLCs) are used in array beamforming circuit designs[2], while Wilkinson power dividers (WPDs)[3], baluns[4], and out-of-phase power dividers[5]play a vital role in designing balanced/unbalanced circuits.