An antimagic field suppresses any spell or magical effect used within, brought into, or cast into the area, but does not dispel it. Time spent within an antimagic field counts against the suppressed spell's duration.
Summoned creatures of any type wink out if they enter an antimagic field. They reappear in the same spot once the field goes away. Time spent winked out counts normally against the duration of the conjuration that is maintaining the creature. If you cast antimagic field in an area occupied by a summoned creature that has spell resistance, you must make a caster level check (1d20 + caster level) against the creature's spell resistance to make it wink out. (The effects of instantaneous conjurations are not affected by an antimagic field because the conjuration itself is no longer in effect, only its result.)
The description covers what happens if a spell is cast into/within the area of Antimagic Field, and what happens if Antmagic Field is cast with a summoned creature within its radius. My question is does Antimagic Field have the same effect on an ongoing affect as a summoned creature? And if the ongoing affect is an AoE (like Entangle), is the entire spell suppressed, or just the 10' area?
Apply the antimagic only to its own area of effect.
Just think of it as a bubble where magic does not function, if it were to move around for example, you would have spells, magic items, spell-like abilities, and supernatural abilities turning on and off (depending on the magic of course).
In an Entangle spell, only the Antimagic Field area of effect would be suppressed.
Well put, thank you!