Variable capacitor for RF power applications

A radio-frequency (RF) power variable capacitor, capable of operating at at least 50 W, comprising at least two electrodes separated by a dielectric, wherein the capacitance of the capacitor is variable by varying a voltage, denoted by Vc, applied across the at least two electrodes, and wherein:

• the dielectric comprises a high dielectric constant-low dielectric constant (HDK-NDK) composite ceramic;
• the HDK component forms at least 80% by weight, of the material of the dielectric and comprises an active matrix wherein the active matrix comprises a HDK ferroelectric ceramic material, chosen from barium titanate, strontium titanate, barium-strontium titanate, calcium titanate and barium zirconate titanate;
• the NDK component less than 20% by weight, of the dielectric and comprises an acoustic resonance reduction agent (ARRA), wherein the ARRA comprises a metal oxide ceramic which is stable at 1200° C., and wherein the ARRA is distributed throughout the active matrix;
• and
• the active matrix material has a mean grain size between 1.5 μm and 5 μm.