Beamformers and elements

EveryBeam is designed such that it can handle an arbitrary number of nested beamformers within each station. The smallest entity in the EveryBeam nomenclature is the Element. Beamformers as well as the element inherit from the Antenna base class.

For efficiency reasons, certain telescopes (in conjunction with their response models) have dedicated implementations for the beamformer. This includes for example the BeamFormerIdenticalAntennas, BeamFormerLofarLBA, BeamFormerLofarHBA classes.

class Antenna

Abstract class describing an antenna, and computing the corresponding Response() and ArrayFactor(). Element and BeamFormer classes - and childs thereof - inherit from this class.

Subclassed by BeamFormer, BeamFormerLofar, Element

Public Functions

inline Antenna(): Construct a new Antenna object.

inline Antenna(const CoordinateSystem &coordinate_system)

Construct a new Antenna object, given a coordinate system.

Parameters:: coordinate_system –

inline virtual ~Antenna()

Antenna(const CoordinateSystem &coordinate_system, const vector3r_t &phase_reference_position)

Construct a new Antenna object, given a coordinate system and a phase reference position.

Parameters:

coordinate_system – Coordinate system
phase_reference_position – Phase reference position (ITRF, m)

Antenna(const vector3r_t &phase_reference_position)

Construct a new Antenna object.

Parameters:: phase_reference_position – Phase reference position (ITRF, m)

virtual std::shared_ptr<Antenna> Clone() const = 0

Makes a copy of this Antenna object.

The method is virtual, so that copies can be created from a pointer to the base (Antenna) class. The original remains unchanged, therefore the method is const. The method has no implementation in the Antenna class, because Antenna is abstract, so no copy can be instantiated.

This method is used by the ExtractAntenna method of the BeamFormer class to create a copy of one of the Antennas it contains.

void Transform(const CoordinateSystem &coordinate_system)

Transform internal coordinate systems and positions.

This method is used by BeamFormer::ExtractAntenna to lift an antenna out of the beamformer.

The transformation is needed because the coordinate system of an antenna in a beamformer is expressed in terms of the coordinate system of the beamformer. To turn an embedded antenna into a stand-alone antenna, the coordinate system of the beamformer needs to be applied to the coordinate system of the antenna

Parameters:: coordinate_system – to apply in the transformation

inline virtual void Response(aocommon::MC2x2 *result, const ElementResponse &element_response, double time, const std::span<const double> &freqs, const vector3r_t &direction, const Options &options = {}) const

Compute the Antenna Response.

Parameters:

time – Time, modified Julian date, UTC, in seconds (MJD(UTC), s).
freq – Frequency of the plane wave (Hz).
direction – Direction of arrival (ITRF, m).
options –

inline virtual void ArrayFactor(aocommon::MC2x2Diag *result, double time, const std::span<const double> &freqs, const vector3r_t &direction, const Options &options) const

Compute the array factor of the antenna.

Parameters:

time – Time, modified Julian date, UTC, in seconds (MJD(UTC), s).
freq – Frequency of the plane wave (Hz).
direction – Direction of arrival (ITRF, m).
options –

Public Members

CoordinateSystem coordinate_system_

vector3r_t phase_reference_position_

bool enabled_[2]

Public Static Attributes

static constexpr CoordinateSystem IdentityCoordinateSystem = {CoordinateSystem::zero_origin, CoordinateSystem::identity_axes}

struct CoordinateSystem

Station coordinate system.

A right handed, cartesian, local coordinate system with coordinate axes p, q, and r is associated with each antenna field.

The r-axis is orthogonal to the antenna field, and points towards the local pseudo zenith.

The q-axis is the northern bisector of the X and Y dipoles, i.e. it is the reference direction from which the orientation of the dual dipole antennae is determined. The q-axis points towards the North at the core. At remote sites it is defined as the intersection of the antenna field plane and a plane parallel to the meridian plane at the core. This ensures the reference directions at all sites are similar.

The p-axis is orthogonal to both other axes, and points towards the East at the core.

The axes and origin of the anntena field coordinate system are expressed as vectors in the geocentric, cartesian, ITRF coordinate system, in meters.