Array_agg containing distinct structs

I'm attempting to create an array with distinct struct as values for a column, something like so

select array_agg(distinct struct(field_a, field_b)) as c FROM tables ...

is that possible?

#standardSQL
SELECT ARRAY_AGG(STRUCT(field_a, field_b)) c 
FROM (
  SELECT DISTINCT field_a, field_b
  FROM `project.dataset.table`
)