In this paper, we propose a new wide-scan active direct integrated phased array antenna (AIPAA) for mm-Wave applications. The AIPAA’s unit-cell comprises three K-band miniaturized taper slot elements, a GaN high electron mobility transistor (HEMT) as a power amplifier (PA), a stabilizer, an input matching network, and biasing components. The tapered slot antenna element is reshaped so that its input impedance closely matches the optimal load impedance of the HEMT (Zopt=6+j38 Ω@22 GHz), which enhances the system efficiency. The peak AIPAA’s Power-Added Efficiency (PAE) is ≥ 56% with ≤ 9% variation over scan coverage (±50⁰) at 1.5dB power backoff from P1dB. The relative frequency bandwidth with PAE above 25% is between 9%-13% over the scan range. The proposed AIPAA demonstrates less than 0.9dB and 1dB scanloss over the scan coverage in terms of antenna array gain and PAs’ power gain (Gp), respectively. The peak PA-integrated array gain and EIRP @P1dB of 24dBi and 51dBm are achieved, respectively. The proposed AIPAA is 18 × 58 × 17 mm3 with a cell size of 9.2 × 6.5 × 1.8 mm3 (0:67 × 0:5 × 0:13 λ3). The measurements are in good agreement with electromagnetic and circuit co-simulation results.