Abstract: This paper proposes a design for an environmentally adaptive impedance matching hemispherical helical antenna. To ensure the antenna maintains excellent impedance matching in its operating frequency band despite environmental changes, an adaptive impedance matching network is developed. This network, based on power detection, dynamically adjusts the tunable matching network to accommodate impedance variations caused by environmental changes, thereby preserving optimal matching performance at the target operating frequency. The antenna employs a spiral structure, with metal wires embedded on a hemispherical substrate with a diameter of 9 cm and a wall thickness of 2.5 mm. Experimental results demonstrate that the antenna operates at 206 MHz in free space. When the antenna’s environment changes, its operating frequency shifts. By incorporating the adaptive matching network, measurements confirm that the antenna can maintain excellent impedance matching at 206 MHz across diverse environments, including air, soil, and water.