We have developed an original concept of a quasi-optical mixer based on a superconducting bolometer for heterodyne detection in the terahertz domain. The detector is a membrane based hot electron bolometer (HEB) and the superconducting material is niobium nitride (NbN) on a dielectric membrane of Si3N4/SiO2, 1.4 microns thick. The membrane is obtained by etching of the silicon substrate. A mirror is used to focus the THz signal and a planar antenna couples the radiation to the HEB. Two mixers blocks have been developed during this thesis: one in the on-axis configuration and another one with an off-axis mirror. Planar antennas spiral and double slot were designed to run on the silicon nitride membrane at frequencies of 0.6 and 1.4 THz. A FTS characterization performed with a double slot antenna at 0.6 THz showed a very good match between the resonance frequency measured and the simulated one. A RF bandwidth of 40% of the center frequency was measured. The first measures of sensitivity with the off-axis mixer block yielded encouraging results with a receiver noise temperature of 1300 K at 0.6 THz. The intermediate frequency bandwidth was measured at 750 MHz. Future works are the increase of the RF frequency beyond the THz, improving the receiver sensitivity and the development of a matrix of HEB. The concept of membrane based HEB could be an interesting solution for THz imaging.
