Compact Balanced-to-Balanced Diplexer Based on Split-Ring Resonators Balanced Bandpass Filters

A compact balanced-to-balanced diplexer composed of two balanced bandpass filters is proposed in this letter. The balanced filters are implemented using compact edge-coupled square split-ring resonators. The design methodology is based on the standard coupled-resonators filter synthesis procedure.

First, each filter is independently designed. Then, they are connected to a common differential input port in order to achieve the desired diplexing operation, with the pertinent adjustments to take into account the loading effect of the second filter. Magnetic coupling inherently prevents common-mode transmission.

An illustrative prototype example is provided with simulations and measurements to demonstrate the benefits of the proposed topology.



The interest in balanced/differential circuits has considerably increased along the last couple of decades. In comparison with single-ended signals, differential signals offer enhanced electrical performance in terms of signal-tonoise ratio, noise immunity, crosstalk, and electromagnetic interference (EMI). In recent years, with the requirement for multi-band services, differential diplexers have attracted the interest of the microwave community. A well designed balanced-to-balanced diplexer must simultaneously provide good differential-mode (DM) performance, strong commonmode (CM) rejection, and high isolation between the output ports. Several strategies have been proposed to achieve all those goals.

Authors: Armando Fernández-Prieto  (Member IEEE), Aintzane Lujambio, Ferran Martín, (Fellow IEEE), Jesús Martel (Senior Member IEEE), Francisco Medina , (Fellow IEEE), and Rafael R. Boix, (Member IEEE).