SiC Varactor Based Tunable Filters with Enhanced Linearity

The wide bandgap material silicon carbide(SiC) has been used to implement a varactor which provides high Q, high voltage capability, and low losses when employed to realize tunable filters for high power signals in the VHF band. The variable capacitance diode can reach reverse bias levels of -120 Volts. These varactors have been used in a three pole filter at VHF frequencies and have shown < 3 dB loss with bandwidth of less than ~10% in the ISO MHz range. The devices have been designed and fabricated in a manner to facilitate employing the varactors as back-to-back pairs. Measurements of the three pole filters demonstrate that this arrangement results in a substantial improvement in input intercept point (IIP3) power levels.