Abstract: A broadband terahertz fourth-harmonic mixer circuit, a mixer and a method wherein the broadband terahertz fourth-harmonic mixer circuit includes a radio frequency signal coupled transmission unit, nonlinear device, local oscillator filter, local oscillator signal coupled transmission unit and intermediate frequency filter unit which are sequentially connected; and further includes a radio frequency input port, local oscillator input port and intermediate frequency output port, where the radio frequency input port is connected to the radio frequency signal coupled transmission unit, the local oscillator input port is connected to the local oscillator signal coupled transmission unit, the intermediate frequency output port is connected to an output end of the intermediate frequency filter unit, and the local oscillator filter is of a two-level cascaded filter structure.

Abstract: A method and system for testing the conversion losses of terahertz mixers capable of eliminating the influence of radio frequency sources includes grouping a mixer to be tested and at least two reference mixers in pairs; in each group, inputting a signal of a preset frequency and a preset power at an intermediate frequency port of a first mixer, and after up-conversion, outputting same to a second mixer to be down-converted, so as to obtain an output power with the frequency same as the preset frequency, and obtain the relationship between a first output power and a first preset power and the losses of two mixers; according to the relationship between the loss of the mixer in each group and the power, obtaining the loss of the mixer to be tested.