Beamwidth, Half-Power Beamwidth, Field of View

The amount of sky covered by a radio telescope is typically referred to as its field of view (FoV).

Key Terms:

• Field of View (FoV): This is the angular area of the sky that the telescope can observe at one time. It depends primarily on the wavelength of observation and the size or configuration of the antenna.
  • For a dish antenna, FoV is approximately:

FoV≈λD radians\text{FoV} \approx \frac{\lambda}{D} \text{ radians}

where λ\lambda is the wavelength and DD is the diameter of the dish.

• Beamwidth (or Half-Power Beamwidth – HPBW): This is a more specific term often used interchangeably with FoV in single-dish systems. It refers to the angular width of the main lobe of the antenna radiation pattern at half its maximum power. For example, a typical 3-meter dish at 1420 MHz has a beamwidth of around 5–6 degrees.
• Survey Speed / Sky Coverage Rate: In wide-field surveys, especially with interferometer arrays or phased arrays, the total amount of sky a telescope can map over time is also important. This is often measured in square degrees per hour or similar units.