Even if a fan port existed, distributing an ISO containing Capcom’s intellectual property (character names, music, code) is copyright infringement. While emulation is legal, downloading a pre-made ISO of a game you do not own is not.
, consider:
Less common, but technically possible, are homebrew ports using the Mugen engine. These are community-made fighting games compiled into an Eboot file (PSP executable). These are often labeled "UPD" to signify the latest version of the homebrew build. These can feature actual SF4 characters and stages, but they are often buggy and suffer from significant slowdowns on original PSP hardware due to memory constraints. Street Fighter 4 Psp Iso UPD