UVBeam Parameters

These are the standard attributes of UVBeam objects.

Under the hood they are actually properties based on UVParameter objects.

Required

These parameters are required to have a sensible UVBeam object and are required for most kinds of beam files.

Naxes_vec
Number of directions in vector_coordinate_system, options are 2 or 3 (or 1 if beam_type is “power”)
Nfreqs
Number of frequency channels
Nspws
Number of spectral windows (ie non-contiguous spectral chunks). More than one spectral window is not currently supported.
antenna_type
String indicating antenna type. Allowed values are “simple”, and “phased_array”
bandpass_array
Frequency dependence of the beam. Depending on the data_normalization, this may contain only the frequency dependence of the receiving chain (“physical” normalization) or all the frequency dependence (“peak” normalization).
beam_type
String indicating beam type. Allowed values are “efield”, and “power”.
data_array
Depending on beam type, either complex E-field values (“efield” beam type) or power values (“power” beam type) for beam model. units are linear normalized to either peak or solid angle as given by data_normalization. The shape depends on the beam_type and pixel_coordinate_system, if it is “healpix”, the shape is: (Naxes_vec, Nspws, Nfeeds or Npols, Nfreqs, Npixels), otherwise it is (Naxes_vec, Nspws, Nfeeds or Npols, Nfreqs, Naxes2, Naxes1)
data_normalization
Normalization standard of data_array, options are: “physical”, “peak” or “solid_angle”. Physical normalization means that the frequency dependence of the antenna sensitivity is included in the data_array while the frequency dependence of the receiving chain is included in the bandpass_array. Peak normalized means that for each frequency the data_arrayis separately normalized such that the peak is 1 (so the beam is dimensionless) and all direction-independent frequency dependence is moved to the bandpass_array (if the beam_type is “efield”, then peak normalized means that the absolute value of the peak is 1). Solid angle normalized means the peak normalized beam is divided by the integral of the beam over the sphere, so the beam has dimensions of 1/stradian.
feed_name
Name of physical feed (string)
feed_version
Version of physical feed (string)
freq_array
Array of frequencies, shape (Nspws, Nfreqs), units Hz
history
String of history, units English
model_name
Name of beam model (string)
model_version
Version of beam model (string)
pixel_coordinate_system
Pixel coordinate system, options are: healpix, az_za, sin_zenith
spw_array
Array of spectral window Numbers, shape (Nspws)
telescope_name
Name of telescope (string)

Optional

These parameters are defined by one or more file standard but are not always required. Some of them are required depending on the beam_type, antenna_type and pixel_coordinate_systems (as noted below).

Naxes1
Number of elements along the first pixel axis. Not required if pixel_coordinate_system is “healpix”.
Naxes2
Number of elements along the second pixel axis. Not required if pixel_coordinate_system is “healpix”.
Nelements
Required if antenna_type = “phased_array”. Number of elements in phased array
Nfeeds
Number of feeds. Not required if beam_type is “power”.
Npixels
Number of healpix pixels. Only required if pixel_coordinate_system is “healpix”.
Npols
Number of polarizations. Only required if beam_type is “power”.
axis1_array
Coordinates along first pixel axis. Not required if pixel_coordinate_system is “healpix”.
axis2_array
Coordinates along second pixel axis. Not required if pixel_coordinate_system is “healpix”.
basis_vector_array
Beam basis vector components – directions for which the electric field values are recorded in the pixel coordinate system. Not required if beam_type is “power”. The shape depends on the pixel_coordinate_system, if it is “healpix”, the shape is: (Naxes_vec, 2, Npixels), otherwise it is (Naxes_vec, 2, Naxes2, Naxes1)
coupling_matrix
Required if antenna_type = “phased_array”. Matrix of complex element couplings, units: dB, shape: (Nelements, Nelements, Nfeed, Nfeed, Nspws, Nfreqs)
delay_array
Required if antenna_type = “phased_array”. Array of element delays, units: seconds, shape: (Nelements)
element_coordinate_system
Required if antenna_type = “phased_array”. Element coordinate system, options are: N-E or x-y
element_location_array
Required if antenna_type = “phased_array”. Array of element locations in element coordinate system, shape: (2, Nelements)
extra_keywords
Any user supplied extra keywords, type=dict
feed_array
Array of feed orientations. shape (Nfeeds). options are: N/E or x/y or R/L. Not required if beam_type is “power”.
gain_array
Required if antenna_type = “phased_array”. Array of element gains, units: dB, shape: (Nelements)
loss_array
Array of antenna losses, shape (Nspws, Nfreqs), units dB?
mismatch_array
Array of antenna-amplifier mismatches, shape (Nspws, Nfreqs), units ?
nside
Healpix nside parameter. Only required if pixel_coordinate_system is “healpix”.
ordering
Healpix ordering parameter, allowed values are “ring” and “nested”. Only required if pixel_coordinate_system is “healpix”.
pixel_array
Healpix pixel numbers. Only required if pixel_coordinate_system is “healpix”.
polarization_array
Array of polarization integers, shape (Npols). AIPS Memo 117 says: stokes 1:4 (I,Q,U,V); circular -1:-4 (RR,LL,RL,LR); linear -5:-8 (XX,YY,XY,YX). Only required if beam_type is “power”.
receiver_temperature_array
Array of receiver temperatures, shape (Nspws, Nfreqs), units K
reference_input_impedance
Reference input impedance of receiving chain (sets the reference for the S parameters), units: Ohms
reference_output_impedance
Reference output impedance of receiving chain (sets the reference for the S parameters), units: Ohms
s_parameters
S parameters of receiving chain, shape (4, Nspws, Nfreqs), ordering: s11, s12, s21, s22. units ?

last updated: 2017-11-18