High-Isolation Resistorless Tunable Filtering Power Divider

This paper presents a novel architecture for a resistorless tunable filtering RF power divider with good isolation. The design is based on coupled dual-mode cavity resonators. At the even mode excitation, the primary resonance mode is coupled through the evanescent resonators, delivering the filtering response. The divided outputs are symmetrically coupled from the second resonator. During the odd excitation, the secondary mode emerges. The coupling in the presented power divider, however, is designed to prohibit the propagation of the secondary mode through the filter. Thus, the energy from the odd excitation is dissipated in the secondary mode resonance. As a result, the design requires no resistors. The presented power divider is designed, fabricated and measured. The varactor-tunable filtering power divider covers the frequency range of 2.15–2.45 GHz. The out-of-band isolation remains better than 13 dB. The 30-dB isolation bandwidth varies between 3.6%–5.2%.