What is the effect of amplitude taper across a phased array on beamwidth and sidelobe level?
Amplitude Weighting
The amplitude distribution across an array (or aperture) controls the sidelobe structure through the Fourier transform relationship between the aperture field and the radiation pattern. Uniform distribution has the narrowest mainlobe (best resolution) but the highest sidelobes. Any smooth taper that reduces the edge illumination relative to the center will reduce sidelobes.
| 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 |
Frequently Asked Questions
How much gain do I lose with tapering?
Taylor -25 dB: 0.4 dB gain loss. Taylor -30 dB: 0.8 dB gain loss. Taylor -40 dB: 1.5 dB gain loss. Hamming: 1.3 dB gain loss. The gain loss is the taper efficiency: the ratio of the tapered gain to the uniform gain for the same aperture.
How do I implement the taper in a passive array?
Unequal power dividers in the corporate feed network distribute different power levels to different elements. The power divider ratios are designed to match the desired amplitude taper. This is fixed at fabrication and cannot be changed. Active arrays with variable-gain amplifiers can implement dynamic amplitude tapers.
What about 2D tapers?
For planar arrays, the 2D taper is typically the product of two 1D tapers: w(x,y) = wx(x) × wy(y). This separable taper is simple to implement but does not provide optimal performance for circular apertures. Circularly symmetric tapers (Taylor circular distribution) are used for circular apertures to achieve rotationally symmetric sidelobe patterns.