Ryle's participation in the prize was for aperture synthesis interferometry while Hewish's was for the discovery of pulsars. From [0]:
> The Nobel Prize in Physics 1974 was awarded jointly to Sir Martin Ryle and Antony Hewish "for their pioneering research in radio astrophysics: Ryle for his observations and inventions, in particular of the aperture synthesis technique, and Hewish for his decisive role in the discovery of pulsars."
Aperture synthesis is useful for achieving higher angular resolutions than would otherwise be possible. But pulsars are unresolved and so angular resolution isn't as important for their study (the localization of pulsars can be done very precisely from the modeling of the arrival times of individual pulses). Collecting area (overall sensitivity of the telescope) is the driving consideration for pulsar science.