We present the design of a mm-wave phased array antenna enabled by photonic beam steering. The mm-wave signal is generated by InP uni-traveling-carrier (UTC) photodiodes within the photonic integrated chip (PIC). The antenna array consists of four sub-arrays, each comprising two stacked patch elements. The bottom patch is shorted to create a compact element, enabling a half-wavelength spacing in the scanning plane. This configuration results in a relatively wide scanning range of +/-30° without significant sidelobe levels. The complexity of this structure lies in the heterogeneous integration of the InP chip with the antenna array and biasing network, all printed on a low-loss substrate with low relative permittivity. The proposed array exhibits a simulated peak directivity of 16 dBi and an impedance and -3 dB gain bandwidth ranging from 43.8 GHz to 58.8 GHz.