Hi, Jiwei,
The demodulators should be selected based on your frequency range and signal dynamic range requirements. RF/IF demodulators are listed on the following web page:
RF Modulators | RF Demodulators | Analog Devices
But be careful because some modulators are mistakenly listed on the Demodulator Table also. All these demodulators can be used with active mixers through ac coupling. Some have single-ended 50-ohm inputs, while others may have 200-ohm input or differential inputs. Balun transformers can be used to interface between devices with different impedances, as well as between single-ended and differential products.
Benjamin