Broadband VHF radiometry with a notch-filtered antenna exhibiting a large impedance mismatch

VHF radiometry is employed in radio astronomy, ionospheric riometry, and in the measurement of signals and noise in communications applications. Accurate techniques for broadband VHF radiometry are well-known, however these techniques assume well-matched broadband antennas and/or receivers having real-valued input impedance over the bandwidth of interest. In this paper we demonstrate through theory and measurement the efficacy of accurate VHF radiometry over a large fractional bandwidth using a thin (thus, narrowband) dipole connected to a receiver whose first stage consists of notch filters that contribute significant and variable reactance throughout the passband. This technique facilitates the use of small antennas combined with aggressive notch filtering, resulting in compact systems that may be used in high-interference environments.