One illustrative dual mode frequency multiplier embodiment includes: a first and a second nonlinear element, a summation node, and a switchable phase shifter. The first and second nonlinear elements are driven by a differential signal to produce a first and a second branch signal each having even and odd harmonics, the even harmonics being in-phase and the odd harmonics being out of phase. The first and second branch signals combine at the summation node to form a combined signal. The switchable phase shifter couples the first nonlinear element to the summation node, providing the first branch signal with a phase shift switchable between 0 and 180° to suppress either the odd or the even harmonics from the combined signal.