directivity

System object: phased.IsotropicHydrophone
Package: phased

Directivity of isotropic hydrophone

Syntax

D = directivity(hydrophone,FREQ,ANGLE)

Description

D = directivity(hydrophone,FREQ,ANGLE) returns the Directivity of the isotropic hydrophone, hydrophone, at frequencies specified by FREQ and in direction angles specified by ANGLE.

Input Arguments

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Isotropic hydrophone, specified as a phased.IsotropicHydrophone System object.

Example: phased.IsotropicHydrophone

Frequencies for computing directivity and patterns, specified as a positive scalar or 1-by-L real-valued row vector. Frequency units are in hertz.

  • For an antenna, microphone, or sonar hydrophone or projector element, FREQ must lie within the range of values specified by the FrequencyRange or FrequencyVector property of the element. Otherwise, the element produces no response and the directivity is returned as –Inf. Most elements use the FrequencyRange property except for phased.CustomAntennaElement and phased.CustomMicrophoneElement, which use the FrequencyVector property.

  • For an array of elements, FREQ must lie within the frequency range of the elements that make up the array. Otherwise, the array produces no response and the directivity is returned as –Inf.

Example: [1e8 2e6]

Data Types: double

Angles for computing directivity, specified as a 1-by-M real-valued row vector or a 2-by-M real-valued matrix, where M is the number of angular directions. Angle units are in degrees. If ANGLE is a 2-by-M matrix, then each column specifies a direction in azimuth and elevation, [az;el]. The azimuth angle must lie between –180° and 180°. The elevation angle must lie between –90° and 90°.

If ANGLE is a 1-by-M vector, then each entry represents an azimuth angle, with the elevation angle assumed to be zero.

The azimuth angle is the angle between the x-axis and the projection of the direction vector onto the xy plane. This angle is positive when measured from the x-axis toward the y-axis. The elevation angle is the angle between the direction vector and xy plane. This angle is positive when measured towards the z-axis. See Azimuth and Elevation Angles.

Example: [45 60; 0 10]

Data Types: double

Output Arguments

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Directivity, returned as an M-by-L matrix. Each row corresponds to one of the M angles specified by ANGLE. Each column corresponds to one of the L frequency values specified in FREQ. Directivity units are in dBi where dBi is defined as the gain of an element relative to an isotropic radiator.

Examples

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Compute the directivity of an isotropic hydrophone in different directions. Assume the signal frequency is 3 kHz. First, set up the hydrophone parameters.

fc = 3e3;
hydrophone = phased.IsotropicHydrophone('FrequencyRange',[1,10]*1e3, ...
    'VoltageSensitivity',[-100,-90,-100]);
patternElevation(hydrophone,fc,45)

First, select the angles of interest to be constant elevation angle at zero degrees. The five azimuth angles are centered around boresight (zero degrees azimuth and zero degrees elevation).

ang = [-20,-10,0,10,20; 0,0,0,0,0];

Compute the directivity along the constant elevation cut.

d = directivity(hydrophone,fc,ang)
d = 5×1

     0
     0
     0
     0
     0

The directivity of an isotropic hydrophone is zero in every direction.

More About

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Introduced in R2017a