A novel variable-distance antenna test range and high spatial resolution corroboration of the inverse square law for 433.5 MHz radiation

Abstract: A novel, low-budget, open-air, slant-geometry antenna test range for UHF radiation is presented. It was designed primarily to facilitate variation of the distance between emitter and receiver antennas, but has also the potential for adaptation to simultaneous variation of distance and receiver antenna orientation. In support of the validity of the range the inverse square law for 433.5 MHz radiation between two naked half-wave dipole antennas was tested with high spatial resolution from close to the far field limit outward to 46 wavelengths. The ratio of sine-amplitude input voltages to the receiver antenna at two distances between the antennas diminished in proportion to the corresponding inverse distance ratio to the power 0.9970 +/- 0.0051 (R^2 = 0.992). This value is indistinguishable from the theoretical value of 1 and confirms the proportionality of the electric field strength to the inverse distance from the radiation source. Given the known proportionality of irradiance to the square of the electric field strength, the result corroborates the inverse square law for irradiance at the lowest frequency for which thus far data have been published.