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 |
Design Considerations
The Taylor distribution is the standard for radar arrays because it provides a specified first sidelobe level with the minimum possible beamwidth broadening. The design parameter n̄ (n-bar) controls how many sidelobes near the main beam are held at the specified level before transitioning to a lower envelope. Higher n̄ provides sidelobes closer to the main beam at the specified level but increases the beamwidth slightly.
Performance Trade-offs
In digital beamforming systems, the amplitude taper is applied digitally by multiplying each element's signal by the appropriate weight. This allows real-time taper optimization: use uniform weights for maximum gain during search, and switch to Taylor weights for low-sidelobe tracking. No hardware changes are needed; only the digital weight vector changes.
- 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
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Practical Implementation
When evaluating the effect of amplitude taper across a phased array on beamwidth and sidelobe level?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
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.