Sensitivity of an Electromagnetic Vector Sensor

High sensitivity and angular resolution radio astronomy at sub-10 MHz frequencies is only possible with a space-borne observatory due to Earth’s ionospheric cutoff frequency. Due to mass and volume constraints, sensing low frequencies on a small spacecraft necessitates an electrically small antenna with inherently low sensitivity compared to a resonant antenna. Interferometric constellations must trade off antenna sensitivity with the number of constellation elements. More complex antennas that offer significant performance advantages can potentially lower constellation sizes and make implementation more practical. The electromagnetic vector sensor antenna, composed of three dipole elements and three loop elements with a common phase center, is compact and efficient, but is new to astronomy applications and less well characterized than simpler antennas. We investigate the sensitivity of vector sensor antennas as a function of spatial direction and frequency, which are key metrics in the design and calibration of an astronomy antenna array. We start by determining the sensor’s response to correlated external and uncorrelated internal noise. We then determine the sensor’s system equivalent flux density (SEFD) based on optimal beamforming of the constituent loops and dipoles. We compare the SEFD with that of the more commonly-considered dipole and tripole antennas and show that a vector sensor exceeds their performance twofold. Finally, we demonstrate our method on a case study of the AERO-VISTA CubeSat mission which features a pair of deployable vector sensor antennas.