directivity
System object: phased.CustomMicrophoneElement
Namespace: phased
Directivity of custom microphone element
Syntax
D = directivity(H,FREQ,ANGLE)
Description
D = directivity(
returns
the Directivity (dBi) of a custom microphone
element, H
,FREQ
,ANGLE
)H
, at frequencies specified by FREQ
and
in direction angles specified by ANGLE
.
Input Arguments
H
— Custom microphone element
System object™
Custom microphone element specified as a phased.CustomMicrophoneElement
System object.
Example: H = phased.CustomMicrophoneElement;
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 Custom Microphone Element
Compute the directivity of a custom microphone element. Create a custom cardioid microphone, and plot the microphone's response at 700 Hz for elevations between -90 and +90 degrees.
Define the pattern for the custom microphone element. The System object's PolarPatternAngles
property has default value of [-180:180]
degrees.
myAnt = phased.CustomMicrophoneElement; myAnt.PolarPatternFrequencies = [500 1000]; myAnt.PolarPattern = mag2db([... 0.5+0.5*cosd(myAnt.PolarPatternAngles);... 0.6+0.4*cosd(myAnt.PolarPatternAngles)]);
Calculate the directivity as a function of elevation at zero degrees azimuth.
elev = [-90:5:90]; azm = zeros(size(elev)); ang = [azm;elev]; freq = 700; d = directivity(myAnt,freq,ang); plot(elev,d) xlabel('Elevation (deg)') ylabel('Directivity (dBi)')
The directivity is maximum at elevation.
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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