In one aspect, the present invention provides a frequency multiplier. In some embodiments, the frequency multiplier includes: a first transistor and a second transistor, wherein a first terminal of the first transistor is connected to a third terminal of the second transistor through a first capacitor, and a first terminal of the second transistor is connected to a third terminal of the first transistor through a second capacitor. The frequency multiplier may also include a balun, wherein the third terminal of the first transistor is connected to a terminal of the balun, and the third terminal of the second transistor is connected to a different terminal of the balun.