Implementations of ACJ Technique in Different Four-Port Filter Networks

This chapter proposes the use of asynchronously coupled-resonator junctions (ACJ) in the design of a multi-input multi-output (MIMO) filtering network and a masthead combiner (MHC). By employing the resonator junctions, miniaturised circuits are achieved without using any transmission-line-based impedance matching circuits. The main challenge in the designs is the control and implementation of the external couplings at the common ports of this all-resonator-based MIMO filtering network and MHC. Both devices are four ports-based with the MIMO filtering network operating at 1.8, 2.1, and 2.6 GHz, while the MHC operates at the two channels of 1.8 and 2.1 GHz. The demonstrated designs achieved fractional bandwidths of 1.764 GHz to 1.836 GHz, 2.058 GHz to 2.142 GHz, and 2.548 GHz to 2.652 GHz, respectively. Good agreements have been achieved between the measurements of the prototype devices and the simulations.