How do I calculate the antenna pattern of a linear array of elements?
Linear Array Pattern
The array factor represents the spatial filtering effect of the element arrangement. For uniformly-spaced elements with equal amplitude, the array factor is a periodic function in angular space that creates a main beam and a series of sidelobes. The pattern repeats at angles where the path difference between adjacent elements is a multiple of wavelength (grating lobe condition).
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Frequently Asked Questions
What is a grating lobe?
A grating lobe is a secondary main beam that appears when the element spacing exceeds λ/(1+|sinθmax|). At broadside (θmax=0): grating lobe condition is d > λ. For ±60° scan: d > λ/1.87 = 0.535λ. Standard design rule: d ≤ λ/2 ensures no grating lobes for any scan angle up to ±90°.
How do I steer the beam?
Apply a linear phase progression across the elements: β = -kd sinθ₀, where θ₀ is the desired beam direction. For electronic steering: use phase shifters (discrete or continuous) at each element to set the required phase. The beam steers instantaneously (microseconds for electronic phase shifters).
Can I have different beamwidths in two planes?
Yes, using a planar (2D) array with different numbers of elements in each dimension: Nx elements in x-direction and Ny in y-direction. The beamwidths are independent: θx ≈ 0.886λ/(Nx·dx) and θy ≈ 0.886λ/(Ny·dy).