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.