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directivity

System object: phased.OmnidirectionalMicrophoneElement
Package: phased

Directivity of omnidirectional microphone element

Syntax

D = directivity(H,FREQ,ANGLE)

Description

D = directivity(H,FREQ,ANGLE) returns the Directivity (dBi) of an omnidirectional microphone element, H, at frequencies specified by FREQ and in direction angles specified by ANGLE.

Input Arguments

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Omnidirectional microphone element specified as a phased.OmnidirectionalMicrophoneElement System object.

Example: H = phased.OmnidirectionalMicrophoneElement

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 omnidirectional microphone element for several different directions.

Create the omnidirectional microphone element system object.

myMic = phased.OmnidirectionalMicrophoneElement();

Select the angles of interest at constant elevation angle set equal to zero degrees. Select seven azimuth angles centered at boresight (zero degrees azimuth and zero degrees elevation). Finally, set the desired frequency to 1 kHz.

ang = [-30,-20,-10,0,10,20,30; 0,0,0,0,0,0,0];
freq = 1000;

Compute the directivity along the constant elevation cut.

d = directivity(myMic,freq,ang)
d = 7×1

     0
     0
     0
     0
     0
     0
     0

Next select the angles of interest to be at constant azimuth angle at zero degrees. All elevation angles are centered around boresight. The five elevation angles range from -20 to +20 degrees. Set the desired frequency to 1 GHz.

ang = [0,0,0,0,0; -20,-10,0,10,20];
freq = 1000;

Compute the directivity along the constant azimuth cut.

d = directivity(myMic,freq,ang)
d = 5×1

     0
     0
     0
     0
     0

For an omnidirectional microphone, the directivity is independent of direction.

More About

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