Experimental Determination of the Total Radiated Power of Automotive Antennas in the Installed State

Total radiated power is one of the crucial figures-of merit to characterize the performance of automotive antennas, similar to hand-held user terminals. The presence of a truncated region in nearfield measurement facilities can introduce errors in the data after nearfield-to-far-field transformation, resulting in inaccurate estimation of the total radiated power. To improve the situation, different extrapolation techniques are used in post-processing to reconstruct the data in the truncated region. Extrapolation is performed either in the spectral domain (modal filtering) or in the spatial domain (equivalence principle). Various measurements were conducted for an automotive antenna installed at different locations on a car in a facility with truncated measurement region. The data measured over the frequency range from 700 MHz to 6000 MHz were then extrapolated into the truncated region. The impact of post-processing was analyzed by comparing the reconstructed pattern in the truncated region with the pattern obtained from a facility with no truncation, and by calculating the total radiated power values. The results indicate that extrapolation techniques, in particular modal filtering, are capable of accurately extracting the total radiated power values, with a deviation of only 0.1..1.1 dB compared to the reference.