directivity

System object: phased.ShortDipoleAntennaElement
Namespace: phased

Directivity of short-dipole antenna element

Syntax

D = directivity(H,FREQ,ANGLE)


Description

D = directivity(H,FREQ,ANGLE) returns the Directivity (dBi) of a short-dipole antenna element, H, at frequencies specified by FREQ and in direction angles specified by ANGLE.

Input Arguments

H — Short-dipole antenna element

System object™

Short-dipole antenna element specified as a phased.ShortDipoleAntennaElement System object.

Example: H = phased.ShortDipoleAntennaElement;

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 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

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

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

Directivity of Short-Dipole Antenna Element

Compute the directivity of a z-directed short-dipole antenna element as a function of elevation.

Create the crossed-dipole antenna element System object™.

myAnt = phased.ShortDipoleAntennaElement;
myAnt.AxisDirection = 'Z';
myAnt.FrequencyRange = [0,10e9];

Select the desired angles of interest to be at constant azimuth angle at zero degrees. Set the elevation angles to center around boresight (zero degrees azimuth and zero degrees elevation). Set the frequency to 1 GHz.

elev = [-30:30];
azm = zeros(size(elev));
ang = [azm;elev];
freq = 1e9;

Plot the directivity along the constant azimuth cut.

d = directivity(myAnt,freq,ang);
plot(elev,d)
xlabel('Elevation (deg)');
ylabel('Directivity (dBi)');

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

$$D=4\pi \frac{U_{\text{rad}}\left(\theta ,\phi \right)}{P_{\text{total}}}$$

where U_rad(θ,φ) is the radiant intensity of a transmitter in the direction (θ,φ) and P_total 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.