Still, i don't understand why this wasn't dealt with prior to giving the go ahead and
i would have thought others that use that band (sat downlinks, weather radars etc) would be complaining as well
WX radar is much higher power (75km/40nm+ range) so the received pulses are also higher power and therefore above the O/P power of the 5G masts at the range that a plane would be from them. Sat Downlinks AE's are generally placed on the top of the aircraft and that shields them somewhat for almost all stages of flying just due to the height the aircraft are flown at. Neither systems are considered safety critical during a landing phase so I can see why there's little issue with them so far.
Rad Alt's on the other-hand are uniquely at risk due to their low power TX/RX (only 2km/1nm range) which puts the power levels of returned pulses much closer to the levels output by 5G masts, after propagation due to distance, plus they're downward facing as well so they aren't shielded by the airframe and finally they are considered to be safety critical during the landing phase.
I think, it depends on what you are trying to achieve with the Radar (for example measuring speed). But yes some of them do rely on the doppler effect.
Yeap, however with the Radar Altimeter it's just a time based calculation rather than Doppler Shift which gives the distance. Generally a "sync pulse" within the TX section starts a timer when a pulse is sent out and the processing section stops the timer when a return is detected by the RX aerial, then it's just basic maths - Speed of light X time taken - divided by 2.