How is the cylinder radius and element spacing chosen for a cylindrical array?

Element spacing around the circumference and along the axis is kept at or below half a wavelength, near 0.5 lambda, to suppress grating lobes over the intended scan range, identical to the rule for a planar array. The cylinder radius is then set by the number of elements per ring: radius r = N times d divided by 2 pi, where N is elements per ring and d is the arc spacing. A larger radius flattens the active sector so it behaves more like a planar aperture and tightens the beam, but it increases size, weight, and the number of elements. At 10 GHz with 0.5 lambda spacing of 15 mm and 48 elements per ring, the radius is about 115 mm.

Antenna Technology

Cylindrical Array

Q: How does a cylindrical array achieve 360-degree coverage without scan loss?

A cylindrical array activates a commutating sector of elements, typically a 90 to 120 degree arc of the circumference, and steers the beam by rotating which elements are excited. Because a new sector with the same physical aperture always faces the target azimuth, the effective aperture, beamwidth, and gain stay essentially constant as the beam sweeps the full 360 degrees. This avoids the cosine scan loss of a planar array, where gain falls off as the beam steers away from boresight and drops by roughly 3 dB near 60 degrees. The trade-off is that only the active sector contributes, so a cylindrical array uses a larger total element count and more switching hardware than a single planar face covering the same instantaneous sector.

Q: What is the difference between a cylindrical array and a circular ring array?

A circular ring array places elements on a single circle in one plane and controls only the azimuth pattern. A cylindrical array stacks multiple such rings vertically along the cylinder axis, so the rings set azimuth scanning and 360-degree coverage while the columns along the axis set elevation beamwidth and elevation steering. A cylinder of N rings by M columns therefore gives independent two-dimensional control: the ring spacing and radius govern azimuth, and the column spacing governs elevation grating-lobe-free scan range. A pure ring array is essentially the single-ring degenerate case of a cylindrical array.

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Wrapping radiating elements around the curved wall of a cylinder produces a conformal antenna that scans the full 360° in azimuth without the aperture shrinkage that limits a flat phased array. Only the sector of elements facing the target is excited at any instant, and the beam is moved by commutating that active sector around the circumference while applying the appropriate beam steering phases. Because an identical physical aperture always faces the look direction, beamwidth and gain stay nearly constant at every azimuth, eliminating the cosine scan loss of planar faces. Stacking multiple rings along the cylinder axis adds independent elevation control, and the array can be analyzed by decomposing the geometry into per-ring and per-column array factor contributions. Cylindrical arrays are favored for shipboard and ground radar, IFF, and base-station systems that demand uniform all-around coverage.

Category: Antenna Technology

Azimuth Coverage: Full 360°

Element Spacing: ≤ 0.5λ

Geometry and Commutating-Sector Scanning

A cylindrical array distributes radiators on the lateral surface of a circular cylinder, normally as N elements per ring around the circumference and M rings stacked along the vertical axis. The defining advantage over a flat aperture is rotational symmetry: every azimuth direction sees a geometrically identical curved surface, so the antenna behaves the same whether the beam points north, east, or any angle between. This is what gives the structure its scan-invariant pattern and makes it the natural choice when a system must search and track over the entire horizon from a single fixed structure.

Beam pointing is accomplished by selecting an active sector, typically a 90° to 120° arc of the circumference, and applying both an amplitude taper and a phase distribution that compensate for the curvature of the elements relative to the desired wavefront. The curved geometry means elements in the active sector sit at different radial projections toward the target, so each requires a phase term proportional to its angular offset from the sector center. As the commanded azimuth advances, the controller rotates which elements are switched on, a process called commutation, while the same per-element phase recipe slides around the ring. The instantaneous aperture, and therefore the gain near 35 dBi for a large cylinder, stays constant across all 360°.

The penalty for this uniformity is hardware count. Only the active arc radiates at any moment, so a cylinder needs far more elements, phase shifters, and switching networks than a planar array covering the same instantaneous field of view. Designers balance the active-sector width against efficiency: a wider sector raises gain and narrows the beam but increases mutual coupling and the dynamic range demanded of the beamformer, while a narrower sector wastes fewer active channels but produces a broader, lower-gain beam.

Governing Relations for Ring and Cylinder Geometry

Cylinder radius from elements per ring:
r = N × d / (2π) (d = arc spacing ≤ 0.5λ)

Element azimuth position (ring of N elements):
φ_n = 2πn / N, n = 0, 1, …, N−1

Ring array factor toward (θ, φ):
AF(θ,φ) = ∑ I_n · e^{j[k·r·sinθ·cos(φ−φ_n) + β_n]}

Steering phase for direction φ₀:
β_n = −k · r · sinθ₀ · cos(φ₀ − φ_n)

Where k = 2π/λ, r = cylinder radius, I_n = element excitation amplitude, β_n = applied phase. Example: 48 elements/ring at 10 GHz with d = 15 mm (0.5λ) → r ≈ 115 mm.

Cylindrical Array vs. Other Array Geometries

Geometry	Azimuth Coverage	Scan Loss	Elevation Control	Relative Element Count	Typical Use
Cylindrical array	Full 360°	Negligible (active sector)	Yes (multiple rings)	High	Shipboard radar, IFF, base stations
Circular ring array	Full 360°	Negligible	None (single ring)	Medium	Direction finding, beacons
Planar phased array	±60° per face	~3 dB at 60° (cos law)	Yes	Low to medium	Sector radar, SATCOM
Conformal (curved) array	Surface dependent	Geometry dependent	Yes	Medium to high	Aircraft skin, missile seekers
Spherical / geodesic dome	Full hemisphere	Negligible	Yes	Very high	Multi-target wide-FOV radar

Common Questions

Frequently Asked Questions

How does a cylindrical array achieve 360-degree coverage without scan loss?

It excites a commutating sector, typically a 90° to 120° arc, and steers by rotating which elements are on. A new sector with the same physical aperture always faces the target, so beamwidth and gain stay nearly constant across all 360°. This avoids the cosine scan loss of a planar face, which loses about 3 dB near 60°. The cost is a higher total element count and more switching hardware, since only the active arc radiates at any instant.

What is the difference between a cylindrical array and a circular ring array?

A ring array places elements on one circle in a single plane and controls only azimuth. A cylindrical array stacks several such rings along the axis, so the rings handle azimuth and 360° coverage while the columns set elevation beamwidth and elevation steering. An N-ring by M-column cylinder gives independent two-dimensional control; a ring array is just the single-ring case.

How is the cylinder radius and element spacing chosen?

Arc and axial spacing are kept at or below 0.5λ to suppress grating lobes, the same rule as a planar array. The radius follows from elements per ring: r = N × d / (2π). A larger radius flattens the active sector toward planar behavior and tightens the beam but adds size and elements. At 10 GHz with d = 15 mm and 48 elements per ring, r is about 115 mm.

Related Terms

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