This paper introduces a high-power, compact active integrated antenna with extended voltage tuning capability, featuring a nearly 1 GHz oscillation range in the X-band (8.35–9.21 GHz). This broad frequency range enhances the oscillator’s flexibility and adaptability for advanced applications in radar systems and wireless communication. The design integrates InGaAs HEMT technology using a feedback circuit. The self-oscillating antenna, manufactured on a RO4003C substrate with a height of 0.508 mm and dimensions of 0.23 × 0.27 ${{\lambda}}_0^2$, demonstrates impressive performance through small- and large-signal analyses. The obtained results are based on harmonic balance simulation using the auxiliary generator technique within the Advanced Design Systems (ADS) tool. Simulation results indicate power levels from 10.928 dBm to 8.062 dBm, while measured output power ranges from 10.90 dBm to 7.916 dBm, and Equivalent Isotropically Radiated Power (EIRP) values were between 12.68 dBm and 10.198 dBm in the interval 8.35–9.21 GHz. Phase noise measurements are −102.94 dBc/Hz at 1 MHz and −124.13 dBc/Hz at 10 MHz. The simulated and measured results are in good agreement, highlighting the robustness and reliability of the oscillator, as well as the effectiveness of the design, which is well suited for applications requiring high stability, precise frequency control, high output power, and efficient performance for microwave applications.