Primary beam
Definition: The angular sensitivity pattern of one antenna and feed on the sky.
Why it matters here: It is needed to answer At fixed frequency, double dish diameter. What happens to FWHM and collecting area if aperture efficiency remains fixed? Explain the different powers. and to interpret For a filled circular aperture, beamwidth scales as wavelength divided by diameter; longer wavelengths broaden a single-dish beam.
Relationships: Use it with Effective area and Aperture efficiency; the lecture model is \(\theta_{\rm FWHM}\simeq1.02\frac{\lambda}{D},\qquad A_{\rm eff}=\eta_a\frac{\pi D^2}{4}\).
Boundary or common confusion: The 1.02 coefficient is an approximate FWHM for a tapered aperture, not the Airy first-null coefficient; quote which beam definition is used.
Aperture efficiency
Definition: The fraction of a dish's geometric area that contributes to effective collecting area.
Why it matters here: It is needed to answer At fixed frequency, double dish diameter. What happens to FWHM and collecting area if aperture efficiency remains fixed? Explain the different powers. and to interpret For a filled circular aperture, beamwidth scales as wavelength divided by diameter; longer wavelengths broaden a single-dish beam.
Relationships: Use it with Primary beam and Feed illumination; the lecture model is \(\theta_{\rm FWHM}\simeq1.02\frac{\lambda}{D},\qquad A_{\rm eff}=\eta_a\frac{\pi D^2}{4}\).
Boundary or common confusion: The 1.02 coefficient is an approximate FWHM for a tapered aperture, not the Airy first-null coefficient; quote which beam definition is used.
Feed illumination
Definition: The amplitude and phase pattern with which a feed couples radiation to the reflector aperture.
Why it matters here: It is needed to answer At fixed frequency, double dish diameter. What happens to FWHM and collecting area if aperture efficiency remains fixed? Explain the different powers. and to interpret For a filled circular aperture, beamwidth scales as wavelength divided by diameter; longer wavelengths broaden a single-dish beam.
Relationships: Use it with Aperture efficiency and System temperature; the lecture model is \(\theta_{\rm FWHM}\simeq1.02\frac{\lambda}{D},\qquad A_{\rm eff}=\eta_a\frac{\pi D^2}{4}\).
Boundary or common confusion: The 1.02 coefficient is an approximate FWHM for a tapered aperture, not the Airy first-null coefficient; quote which beam definition is used.
System temperature
Definition: The equivalent noise temperature combining receiver, sky, atmosphere, and spillover contributions.
Why it matters here: It is needed to answer At fixed frequency, double dish diameter. What happens to FWHM and collecting area if aperture efficiency remains fixed? Explain the different powers. and to interpret For a filled circular aperture, beamwidth scales as wavelength divided by diameter; longer wavelengths broaden a single-dish beam.
Relationships: Use it with Feed illumination and Effective area; the lecture model is \(\theta_{\rm FWHM}\simeq1.02\frac{\lambda}{D},\qquad A_{\rm eff}=\eta_a\frac{\pi D^2}{4}\).
Boundary or common confusion: The 1.02 coefficient is an approximate FWHM for a tapered aperture, not the Airy first-null coefficient; quote which beam definition is used.
Effective area
Definition: The collecting area that converts incident flux density into received power after aperture losses.
Why it matters here: It is needed to answer At fixed frequency, double dish diameter. What happens to FWHM and collecting area if aperture efficiency remains fixed? Explain the different powers. and to interpret For a filled circular aperture, beamwidth scales as wavelength divided by diameter; longer wavelengths broaden a single-dish beam.
Relationships: Use it with System temperature and Primary beam; the lecture model is \(\theta_{\rm FWHM}\simeq1.02\frac{\lambda}{D},\qquad A_{\rm eff}=\eta_a\frac{\pi D^2}{4}\).
Boundary or common confusion: The 1.02 coefficient is an approximate FWHM for a tapered aperture, not the Airy first-null coefficient; quote which beam definition is used.