A flowmeter measures a fluid velocity and/or direction of a moving multiphase fluid within a hydrocarbon well. The flowmeter includes a microwave front end module comprising transmit and receive antennas and a microwave circuit. The transmit antenna transmits electromagnetic signals towards the fluid at a high frequency ranging from 10 to 100 GHz. The flowmeter includes an analog electronics module converting an analog doppler signal successively into an amplified analog doppler signal and a digital doppler signal. The flowmeter includes a digital processing module comprising a Fast Fourier Transform algorithm for processing the digital doppler signal into a Doppler frequency spectrum. The Doppler spectrum contains information indicative of the fluid velocity and/or direction. A protective shell protects the modules from multiphase fluid. The protective shell comprises a first part positioned over the antennas and being transparent to electromagnetic signals, and a second part being opaque to electromagnetic signals.