directivity
System object: phased.OmnidirectionalMicrophoneElement
Namespace: phased
Directivity of omnidirectional microphone element
Syntax
D = directivity(H,FREQ,ANGLE)
Description
D = directivity(
returns
the Directivity (dBi) of an omnidirectional
microphone element, H
,FREQ
,ANGLE
)H
, at frequencies specified
by FREQ
and in direction angles specified by ANGLE
.
Input Arguments
H
— Omnidirectional Microphone Element
System object™
Omnidirectional microphone element specified as a phased.OmnidirectionalMicrophoneElement
System object.
Example: H = phased.OmnidirectionalMicrophoneElement
FREQ
— Frequency for computing directivity and patterns
positive scalar | 1-by-L real-valued row vector
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 theFrequencyRange
orFrequencyVector
property of the element. Otherwise, the element produces no response and the directivity is returned as–Inf
. Most elements use theFrequencyRange
property except forphased.CustomAntennaElement
andphased.CustomMicrophoneElement
, which use theFrequencyVector
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
ANGLE
— Angles for computing directivity
1-by-M real-valued row vector | 2-by-M real-valued matrix
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
D
— Directivity
M-by-L matrix
Examples
Directivity of Omnidirectional Microphone Element
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
Directivity (dBi)
Directivity describes the directionality of the radiation pattern of a sensor element or array of sensor elements.
Higher directivity is desired when you want to transmit more radiation in a specific direction. Directivity is the ratio of the transmitted radiant intensity in a specified direction to the radiant intensity transmitted by an isotropic radiator with the same total transmitted power
where Urad(θ,φ) is the radiant intensity of a transmitter in the direction (θ,φ) and Ptotal is the total power transmitted by an isotropic radiator. For a receiving element or array, directivity measures the sensitivity toward radiation arriving from a specific direction. The principle of reciprocity shows that the directivity of an element or array used for reception equals the directivity of the same element or array used for transmission. When converted to decibels, the directivity is denoted as dBi. For information on directivity, read the notes on Element Directivity and Array Directivity.
See Also
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