This work presents a novel technique for adjusting the input impedance of a low noise amplifier (LNA) using current injection. The proposed technique can significantly improve the input return loss under varying antenna impedance and/or process variation, with minimal effect on the amplifier's nominal performance. The simulation results show approximately 6dB input return loss improvement over the designed frequency range. The proposed current injection method is verified through the design of a single-stage LNA in a 28nm TSMC bulk CMOS technology. The LNA uses a 900mV supply voltage and operates from 17.5GHz to 20.5GHz. Nominally, the LNA exhibits 1.25dB of noise figure, 12dB of power gain, and dissipates approximately 14mW of power. Within this work, the LNA maintains an input return loss below -10dB under process (3σ), voltage (+10%), temperature (-40°C), and antenna impedance (45Ω) variations, without requiring stringent nominal design specifications, tuning, or trimming.