Side Lobe Level Calculator

This side lobe level calculator evaluates the broadside performance of a uniformly-spaced linear antenna array — sidelobe level (SLL), half-power beamwidth (HPBW), first null angle, directivity, and grating-lobe risk — for a chosen element count, spacing, and amplitude taper. It's the standard first pass for phased-array antenna design, from HAM Yagi/collinear stacks to radar and 5G massive-MIMO panels.

Enter Number of Elements (N), Element Spacing (d/λ), Amplitude Distribution / Taper Profile exactly in the units shown by this side lobe level. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.

• Number of Elements (N).
• Element Spacing (d/λ) — use λ.
• Amplitude Distribution / Taper Profile.

The results describe the calculated side lobe level values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.

The Side Lobe Level uses AF(θ) = sin(Nψ/2) / [N·sin(ψ/2)] where ψ = 2π(d/λ)sin(θ) | HPBW ≈ 50.8° / ((N-1)·d/λ) | D_0 ≈ N. Supply Number of Elements (N), Element Spacing (d/λ) (λ), Amplitude Distribution / Taper Profile in the displayed units, then use the calculated values as the first engineering target for this antenna arrays design or analysis.

Every linear array design balances three competing goals: narrow beamwidth (for angular resolution), low sidelobes (for interference rejection and reduced clutter/jamming susceptibility), and high directivity (for gain). Uniform excitation maximizes directivity but is stuck with a -13.26 dB first sidelobe that no amount of extra elements can improve — only tapering the amplitude across the array (feeding the edge elements less than the center elements) suppresses sidelobes further. This calculator's taper options show the classic trade-off curve: a cosine taper reaches about -23 dB SLL at a modest directivity cost, cosine-squared pushes to roughly -32 dB with more loss, and binomial tapering eliminates sidelobes entirely in the ideal case — at the price of the widest beamwidth and lowest directivity of the group. There's no free lunch here: every dB of sidelobe suppression is paid for with either wider beamwidth, reduced directivity, or both, and the underlying reason is that suppressing sidelobes means less of the array's edge current is retained (an effect sometimes described as "aperture efficiency loss").

Grating lobes are the practical failure mode to watch for in real array builds: once element spacing reaches or exceeds one wavelength, a second full-strength main beam appears in the array factor at a different angle, which is indistinguishable from the desired beam and destroys pattern predictability. This calculator flags that risk for the broadside (θ=0°) case, but the safe spacing threshold shrinks further the moment the array is electronically scanned off-broadside — a rule of thumb is d ≤ λ/(1+|sin θ_scan|), so an array meant to scan to wide angles needs tighter spacing than one built only for broadside operation. Also keep in mind the HPBW and directivity figures here use standard array-factor approximations valid for reasonably large N (roughly N ≥ 8–10); for very small arrays (2–4 elements) these approximations lose accuracy and a full array-factor evaluation across all θ gives a more trustworthy beamwidth than the closed-form estimate.