Dual-band lumped element decoupling network design for two-antenna systems

In this study we outline a design process for lumped element implementation of dual-band decoupling network for two coupled antennas. We justify by extensive numerical experimentation that the mutual admittance of the antennas can be transformed to purely imaginary values at two given frequencies simultaneously by very simple transmission line transformers at the antenna inputs. Our study shows that this conclusion is practically speaking independent on the antennas under consideration, and applies to many different frequency band pairs. The decoupling itself is carried out by appropriate lumped element resonators, the topology of which is selected according to the sign of the imaginary part of the mutual admittance at each band, to provide perfect reactive cancellation of the admittance at the center of each band. We propose practical optimization criteria for the decoupling network design that guarantee both a successful re-matching of the generally distorted impedance match, and a minimal influence of the matching network to the decoupling.