# 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”
**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: “peak” and “solid_angle”. Peak normalized means each frequency is separately normalized such that the peak is 1 and the beam is dimensionless. Solid angle normalized means the peak normalized beam is divided by the integral of the beam over the sphere, giving the beam 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, Naxes1, Naxes2)
**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”.
**s_parameters**- S parameters of receiving chain, shape (4, Nspws, Nfreqs), ordering: s11, s12, s21, s22. units ?
**system_temperature_array**- Array of system temperatures, shape (Nspws, Nfreqs), units K

last updated: 2017-07-26