A frequency multiplier, comprising: a first stepped-impedance transmission line configured to receive a first signal of a first differential signal at an input end; a second stepped-impedance transmission line configured to receive a second signal of the first differential signal at an input end, wherein the first stepped-impedance transmission line and the second stepped-impedance transmission line superpose the first signal of the first differential signal on the second signal of the first differential signal to obtain a first frequency multiplied signal at a first output end, a frequency of the first frequency multiplied signal is 2*N times a frequency of the first differential signal, and N is an integer greater than or equal to 1; a first inverse stepped-impedance transmission line configured to be inversely ground-coupled with the first stepped-impedance transmission line and grounded at an end near the first output end of the first stepped-impedance transmission line; a second inverse stepped-impedance transmission line configured to be inversely ground-coupled with the second stepped-impedance transmission line and grounded at an end near the first output end of the second stepped-impedance transmission line, wherein the first stepped-impedance transmission line and the first inverse stepped-impedance transmission line are placed in parallel, and wherein the second stepped-impedance transmission line and the second inverse stepped-impedance transmission line are placed in parallel, so that when a signal is transmitted in the first stepped-impedance transmission line and the second stepped-impedance transmission line, a corresponding resonance signal is generated in the first inverse stepped-impedance transmission line and the second inverse stepped-impedance transmission line; and wherein another end of the first inverse stepped-impedance transmission line and another end of the second inverse stepped-impedance transmission line superpose signals to output a second frequency multiplied signal at a second output end, a frequency of the second frequency multiplied signal is 2*N times the frequency of the first differential signal, wherein a phase difference between the first frequency multiplied signal and the second frequency multiplied signal is equal to 180 degrees, or, wherein a phase difference between the first frequency multiplied signal and the second frequency multiplied signal is equal to 90 degrees. a first stepped-impedance transmission line configured to receive a first signal of a first differential signal at an input end; a second stepped-impedance transmission line configured to receive a second signal of the first differential signal at an input end, wherein the first stepped-impedance transmission line and the second stepped-impedance transmission line superpose the first signal of the first differential signal on the second signal of the first differential signal to obtain a first frequency multiplied signal at a first output end, a frequency of the first frequency multiplied signal is 2*N times a frequency of the first differential signal, and N is an integer greater than or equal to 1; a first inverse stepped-impedance transmission line configured to be inversely ground-coupled with the first stepped-impedance transmission line and grounded at an end near the first output end of the first stepped-impedance transmission line; a second inverse stepped-impedance transmission line configured to be inversely ground-coupled with the second stepped-impedance transmission line and grounded at an end near the first output end of the second stepped-impedance transmission line, wherein the first stepped-impedance transmission line and the first inverse stepped-impedance transmission line are placed in parallel, and wherein the second stepped-impedance transmission line and the second inverse stepped-impedance transmission line are placed in parallel, so that when a signal is transmitted in the first stepped-impedance transmission line and the second stepped-impedance transmission line, a corresponding resonance signal is generated in the first inverse stepped-impedance transmission line and the second inverse stepped-impedance transmission line; and wherein another end of the first inverse stepped-impedance transmission line and another end of the second inverse stepped-impedance transmission line superpose signals to output a second frequency multiplied signal at a second output end, a frequency of the second frequency multiplied signal is 2*N times the frequency of the first differential signal, wherein a phase difference between the first frequency multiplied signal and the second frequency multiplied signal is equal to 180 degrees, or, wherein a phase difference between the first frequency multiplied signal and the second frequency multiplied signal is equal to 90 degrees.