feedTab.html

Table 1:

FEED: Feed characteristics

FEED: Feed charactersitics


Name	Format	Units	Measure	Comments

Columns

Key
ANTENNA_ID	Int			Antenna id
FEED_NUM	Int			Feed number
SPECTRAL_WINDOW_ID	Int			Spectral window id.
TIME	Double	s	EPOCH	Integration midpoint
INTERVAL	Double	s		Time interval

Data description
NUM_RECEPTORS				# receptors on this feed

Data
RECEIVER_ID	Int(NUM_RECEPTORS)			Receiver id.
BEAM_ID	Int(NUM_RECEPTORS )			Beam model
BEAM_OFFSET	Double(2, NUM_RECEPTORS)	rad	DIRECTION	Beam position offset (on sky but in antenna reference frame).
(FOCUS_REFERENCE)	Double(3,NUM_RECEPTORS)	m		Focus reference position
(ILLUM_OFFSET)	Float	m		Illumination offset
(ILLUM_OFFSET_PA)	Float	rad		Illumination offset position angle
( PHASE_FEED_ID)	Int			Phased feed
POLARIZATION_TYPE	String(NUM_RECEPTORS)			Type of polarization to which a given RECEPTOR responds
POL_RESPONSE	Complex (NUM_RECEPTORS, NUM_RECEPTORS)			Feed polarization response
POSITION	Double(3)		POSITION	Correlation function
RECEPTOR_ANGLE	Double (NUM_RECEPTORS)	rad		The reference angle for polarization

Notes: A feed is a collecting element on an antenna, such as a single horn, that shares joint physical properties and makes sense to calibrate as a single entity. It is an abstraction of a generic antenna feed and is considered to have one or more RECEPTORs that respond to different polarization states. A FEED may have a time-variable beam and polarization response. FEEDS are numbered from 0 on each separate antenna and for each SPECTRAL_WINDOW_ID. Consequently, FEED_NUM should be non-zero only in the case of feed arrays, i.e. multiple, simultaneous beam on the sky at the same frequency and polarization.

ANTENNA_ID: Antenna number, as indexed from ANTENNAn in MAIN
FEED_ID: Feed number, as indexed from FEEDn in the MAIN .
SPECTRAL_WINDOW_ID: Spectral window identifier. A value of -1 indicates the row is valid for all spectral windows. If a specific spectral window has its own feed characteristics these have to be defined separately using a value > 0, to override the global specifications for that specific window.
TIME: Mid point of time interval for which the feed parameters in the row are valid. The same reference used fir the TIME column in the MAIN must be used.
INTERVAL: Time interval.
NUM_RECEPTORS: Number of receptors on this feed. See POLARIZATION_TYPE for further information.
RECEIVER_ID: Receiver identifier(s) for each receptor. NB in MS2 RECEIVER_IDis in the SPECTRAL_WINDOW table.
BEAM_ID: Beam identifier. Points to an optional BEAM sub-table defining the antenna beam and the polarizetion response for this FEED. A value of -1 indicates that no associated beam response is defined.
BEAM_OFFSET: Beam position offset, as defined on the sky but in the antenna reference frame.
FOCUS_REFERENCE: Focus reference position. Mandatory for ALMA. Notice that receptor independent part in the focus position is specified in the FOCUS sub-table.
ILLUM_OFFSET: Illumination offset
ILLUM_OFFSET_PA: Illumination offset position angle
PHASE_FEED_ID
POLARIZATION_TYPE: Polarization type to which each receptor responds (e.g. “R”, “L”, “X”, “Y”). This is the receptor polarization type as recorded in the final correlated data (eg “RR); i.e. as measured after all polarization combiners.
POL_RESPONSE: Polarization response at the center of the beam for this feed. Expressed in a linearly polarized basis using the IEEE convention.
POSITION: Offset of the feed relative to the feed reference position for this antenna (see ANTENNA sub-table).
RECEPTOR_ANGLE: Polarization reference angle. Converts into parallactic angle in the sky domain.