A circuit to generate a sweep frequency signal that includes a reference frequency source to generate a reference frequency signal, a first frequency combination circuit coupled to the reference frequency source, and operative to generate a sweep frequency signal in a first frequency band based on the reference frequency signal, a second frequency combination circuit coupled to the reference frequency source, and operative to generate a sweep frequency signal in a second frequency band different from the first frequency band based on the reference frequency signal, a multiple-level switch coupled to outputs of the first frequency combination circuit and the second frequency combination circuit, and a control circuit controlling the first and second frequency combination circuits and the multiple-level switch to output the sweep frequency signal in the first frequency band and the sweep frequency signal in the second frequency band at an output of the multiple-level switch alternately.