The invention provides frequency multiplier circuitry which may be used in the output section of high power microwave systems to efficiently provide higher output frequencies. Generally, one multiplier stage may be utilized to double the frequency of the input signal with several stages being cascaded to achieve even higher frequencies. The varactor diodes utilized in circuits of the invention are preferably constructed primarily of silicon carbide, which has many advantages when compared with current varactors constructed of GaAs or silicon. Some presently preferred embodiments utilize a four terminal varactor bridge instead of a single varactor diode. The invention also teaches several significant techniques for improving the bandwidth of the circuitry, thus allowing variation of the frequency of the input signal without significantly attenuating the output signal.