Frigates of the Comandante João Belo class were built in France in 1967-1969. For the most part they were identical to the French Commandant Riviere class.
These four ships were supposed to replace destroyers of Vouga class and avisos of Afonso de Albuquerque class.
In the 1980's several modernization projects were considered but none of them actually took place due to lack of funding. Here's one of the proposals:
In the early 1990's these ships participated in various NATO activities including the Gulf War. By that time they've received the Nixie decoy launchers:
Later in that decade the ships undergo an actual modernization and receive the new sonars SQS-510 as well as Mk.54 ASW torpedo launchers instead of the outdated KT-50. Also one of the aft guns and the ASW mortar are removed.
By 2004 this class gets decommissioned; two ships are sunk as artificial reefs, the other two are transferred to Uruguay.