Abstract: In this paper, a wideband and highly-integrated tiled active phased array antenna (APAA) with 256 elements in Ka band is introduced. By using the low temperature co-fired ceramic (LTCC) process and three-dimension stacking technology, the high-density integrations of antenna, T/ R module, integrated network, and power supply module are realized within the antenna aperture. The height of the entire APAA is sharply decreased and only about 15mm. In detail, the -10 dB impedance bandwidth of the patch antenna is largely broaden to about 17. 1% by means of digging substrate cavity and structural optimization; the miniaturization and lightweight design of T/ R modules are realized using the highdensity three-dimension stacking technology; The metal holes and ball grid array under the module help conduct its heat to the cold plate effectively, and the simulated temperature rise of the entire APAA is only about 30 ℃. The measured results show that the tiled APAA can partially achieve a scanning range of ±30° without grating lobes. The sidelobe level is lower than -12. 9 dB. In summary, this proposed tiled APAA has advantages of wide bandwidth, high integration and scalability in two dimensions, and has high engineering application value.