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 basis vectors specified at each pixel, 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 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, center of the channel, 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: “az_za”, “orthoslant_zenith”, “healpix”. “az_za” is a uniformly gridded azimuth, zenith angle coordinate system, where az runs from East to North in radians. It has axes [azimuth, zen_angle]. “orthoslant_zenith” is a orthoslant projection at zenith where y points North, x point East. It has axes [zenorth_x, zenorth_y]. “healpix” is a HEALPix map with zenith at the north pole and az, za coordinate axes (for the basis_vector_array) where az runs from East to North. It has axes [hpx_inds].

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”.

Ncomponents_vec

Number of basis vectors components specified at each pixel, options are 2 or 3. Only required for E-field beams.

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, Ncomponents_vec, Npixels), otherwise it is (Naxes_vec, Ncomponents_vec, 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. Keys should be 8 character or less strings if writing to beam fits files. Use the special key “comment” for long multi-line string comments.

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”.

freq_interp_kind

String indicating frequency interpolation kind. See scipy.interpolate.interp1d for details. Default is linear.

gain_array

Required if antenna_type = “phased_array”. Array of element gains, units: dB, shape: (Nelements)

interpolation_function

String indicating interpolation function. Must be set to use the interp_* methods. Allowed values are : “az_za_simple”, “healpix_simple”.

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). Uses the same convention as UVData: pseudo-stokes 1:4 (pI, pQ, pU, pV); 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_impedance

Reference impedance of the beam model. The radiated E-farfield or the realised gain depend on the impedance of the port used to excite the simulation. This is the reference impedance (Z0) of the simulation. units: Ohms

s_parameters

S parameters of receiving chain, shape (4, Nspws, Nfreqs), ordering: s11, s12, s21, s22. see https://en.wikipedia.org/wiki/Scattering_parameters#Two-Port_S-Parameters

x_orientation

Orientation of the physical dipole corresponding to what is labelled as the x polarization. Options are “east” (indicating east/west orientation) and “north” (indicating north/south orientation)

last updated: 2021-10-21