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FEED: Feed characteristics

FEED: Feed characteristics
Name	Format	Units	Measure	Comments
Columns
Keys
ANTENNA_ID	Int			Antenna id
ARRAY_ID	Int			Array id
FEED_ID	Int			Feed id
INTERVAL	Double	s		Interval
SPECTRAL_WINDOW_ID	Int			Spectral Window id
TIME	Double	s	EPOCH	Midpoint of validity range of parameters
Data description
NUM_RECEPTORS	Int			# receptors on this feed
Data
BEAM_ID	Int			Beam model
BEAM_OFFSET	Double(2, NUM_RECEPTORS)	rad	DIRECTION	Beam position offset (on sky but in antenna reference frame).
PHASED_FEED_ID	Int			Phased feed
POLARIZATION_TYPE	String (NUM_RECEPTORS)			Type of polarization to which a given RECEPTOR responds. Probably R, L or X, Y.
POL_RESPONSE	Complex (NUM_RECEPTORS, NUM_RECEPTORS)			D-matrix i.e. leakage between two receptors
POSITION	Double(3)	m	POSITION	Position of feed relative to feed reference position for this antenna
RECEPTOR_ANGLE	Double (NUM_RECEPTORS)	rad		The reference angle for polarization. Converts into Parallactic angle in the Sky domain.

Notes:

FEED

A FEED is e.g. a single horn. A FEED can have one or two RECEPTORs that respond to different polarization states. Feeds are numbered from 0 on each separate antenna and for each SPECTRAL_WINDOW_ID. So FEED_ID should be non-zero only in the case of feed-arrays, i.e., multiple simultaneous beams on the sky at the same frequency and polarization.

SPECTRAL_WINDOW_ID

A value of -1 indicates the row is valid for all spectral windows.

BEAM_ID

Points to an optional BEAM subtable with parameters (or image) for the primary beam for this antenna with this feed. No format specified yet for the BEAM table.