The essentials elements in processing a complaint alleging retaliation constituting unlawful discrimination
(1) he or she had engaged in protected activity,
(2) his or her employer was aware that he or she participated in such activity,
(3) he or she suffered an adverse employment action based upon his or her activity, and
(4) there is "a causal connection between the protected activity and the adverse [personnel] action" alleged to have suffered by the individual.