Modern radars are developing from MSA (Mechanically Scanned Array) to AESA (Active Electronically Scanned Array) due to the development of semiconductors. AESA is functionally superior to MSA in terms of achieving multi-function through beam agility but AESA is heavier than MSA. Also, the antenna aperture size is limited according to its thickness because antenna is mounted on the pointed shape nose part of the fighter. The aperture size is directly related to the antenna performance such as EIRP, G/T which has major influence on the radar performance. In this paper, we describe the design and implementation of a light-weight and slim active phased array antenna system for fighter.