Conformal Array
Why Curved Apertures Need Per-Element Steering
A flat phased array enjoys a simple geometry: every element shares the same boresight, so the steering phase is just a linear ramp across the aperture and the far-field pattern follows the familiar array factor. The moment those elements are bent onto a curved skin, that symmetry disappears. Each element now has its own surface normal, so its individual pattern peaks in a different direction, and its phase center sits at a different distance from any common reference plane. The beamformer must compensate for both effects at once, computing a unique steering phase for every element from its 3D position vector and then adding a correction for the rotated element pattern and the local polarization basis.
This is why conformal arrays are almost always built with digital or hybrid beamforming and fully calibrated transmit-receive modules behind each element. A passive corporate feed with fixed phase shifters cannot track the curvature-dependent corrections needed as the beam scans, especially when active sub-arrays are switched on and off to follow the illuminated patch of the surface. The payoff is structural: antennas disappear into the wing leading edge, the nose cone, or the cylindrical mast of a ship, removing protruding radomes and their aerodynamic and radar-cross-section penalties.
The penalty is in realized gain and scan range. On a cylinder, only the elements whose normals point roughly toward the target contribute usefully; elements past about 60 degrees off the beam direction are shadowed by the body itself. The effective aperture is therefore the projected area of the illuminated patch, not the full element count, which translates to several dB of scan loss compared with a planar array of identical size.
Conformal Steering and Scan-Loss Equations
φn = −k (rn · u0) + Δφpol,n
Geodesic element spacing (cylinder of radius R):
dgeo = R × Δφ ≈ λ/2 (to suppress grating lobes)
Single-element scan contribution:
Gn(θ) ≈ G0 × cosq(θ − θn,normal), q ≈ 1 to 1.5
Quasi-planar curvature limit:
δsag < λ/16 → linear taper valid; δsag > λ/8 → full 3D correction required
Where k = 2π/λ, rn = element position vector, u0 = unit beam direction, Δφpol,n = polarization-alignment correction, δsag = element height deviation from the best-fit plane.
Conformal Surface Geometry Comparison
| Host Surface | Elements Useful per Beam | Pattern Control | Scan Coverage | Typical Platform |
|---|---|---|---|---|
| Full cylinder | 30 to 50% | Good (360° azimuth) | Omnidirectional | Ship mast, base station |
| Cylinder sector | 60 to 90% | Very good | Wide azimuth, limited elevation | Tower, vehicle |
| Faceted (planar facets) | ~25% per face | Per-face planar | Hemispheric (multi-face) | Fighter aircraft skin |
| Cone / ogive | ~30% | Forward-biased | Narrow, axial | Missile seeker nose |
| Body of revolution | ~50% | Axially symmetric | Wide azimuth | Satellite / UAV fuselage |
Frequently Asked Questions
How does element phase correction differ between a conformal array and a planar array?
A planar array uses one linear phase ramp because every element shares a boresight. A conformal array must compute a full 3D steering phase, φn = −k(rn · u0), from each element's position vector, then add a correction for its rotated pattern and local polarization. That demands stored per-element steering vectors, which is why these arrays rely on digital or hybrid beamforming with calibrated per-element transmit-receive modules rather than a single aperture taper.
Why do conformal arrays suffer scan loss and how is it estimated?
Only elements whose normals point near the beam direction contribute; far-side elements roll off as cos(θ − θnormal) and those beyond ~60° are shadowed by the body. The usable aperture is the projected illuminated patch, so on a full cylinder roughly 30 to 50% of elements are effective at any angle, costing 3 to 5 dB of realized gain versus a flat panel of equal element count. Designers over-populate the surface or switch active sub-arrays as the beam scans.
What surface curvature is acceptable before a conformal array needs full 3D calibration?
If the maximum element height deviation from a best-fit plane stays under about λ/16, the surface is quasi-planar and a linear taper with small fixed offsets works. Past λ/8 the per-element path error exceeds 45° of phase, raising sidelobes and pointing error, so full geometric compensation is mandatory. At Ka-band (~30 GHz, λ = 10 mm) that λ/8 limit is only 1.25 mm of sag, which makes millimeter-wave conformal integration far stricter than at L-band.