Abstract: In order to measure the amplitude and the phase of the reflection coefficient of a structure (S) such as a radar protection radome, particularly following a repair, a measuring device is proposed, whereof a portable part (10) makes it possible to transform the microwave measuring and reference signals into low frequency signals. These low frequency signals are then transferred by flexible cables (16, 17) to a calculating part (12, 14) without it being possible to create phase distortions by twisting of the cable. The signals are transformed by giving the portable part, in addition to the main microwave generator (18), a second microwave generator (32), whose frequency (f.sub.2) differs from that (f.sub.1) of the main generator by a given low frequency (f.sub.0). Microwave mixers (38, 42) use the radiation emitted by the second generator (32) in order to give the measuring signal and the reference signal, initially at the frequency (f.sub.1), the low frequency (f.sub.0).