Antenna Array
Understanding Antenna Arrays
Antenna arrays provide capabilities impossible with single antennas: electronic beam steering, adaptive nulling of interference, multiple simultaneous beams, and reconfigurable radiation patterns. The array factor (determined by element positions and excitation) multiplied by the element pattern gives the total array radiation pattern.
Array Types
- Linear array: Elements in a line. Produces a fan beam (narrow in one plane, broad in the other).
- Planar array: Elements in a 2D grid. Produces a pencil beam (narrow in both planes). Can scan in two dimensions.
- Conformal array: Elements on a curved surface (aircraft fuselage, missile body). Maintains aerodynamic profile.
Array Parameters
- Number of elements (N): Gain increases as 10log(N) above element gain.
- Element spacing (d): Typically lambda/2. Wider spacing causes grating lobes.
- Amplitude taper: Non-uniform excitation reduces sidelobes at the cost of gain and beamwidth.
G_array = G_element + 10 log10(N) (uniform excitation)
Linear array beamwidth:
theta = 0.886 lambda / (N d cos(theta_s))
Grating lobe condition:
d > lambda / (1 + sin(theta_max))
For 60-degree scan: d < 0.536 lambda
16-element array with 7 dBi patches:
G = 7 + 10log(16) = 7 + 12 = 19 dBi
Frequently Asked Questions
What is an antenna array?
An antenna array combines multiple antenna elements with controlled amplitude and phase to shape the radiation pattern. Arrays enable beam steering, null steering, sidelobe control, and higher gain than a single element.
Why use an array instead of a larger single antenna?
Arrays enable electronic beam steering (no mechanical movement), adaptive pattern control, multiple simultaneous beams, and reconfigurable patterns. A phased array can switch beam direction in microseconds, while a mechanical dish takes seconds.
What determines the maximum scan angle?
Element spacing limits the scan angle before grating lobes appear. For grating-lobe-free scanning to theta_max, element spacing must be less than lambda/(1+sin(theta_max)). Half-wavelength spacing allows scanning to about 60 degrees off broadside.