Which statement about convex sequential arrays is false?

Which statement about convex sequential arrays is false?

• A. The active elements are larger than in a phased array.
• B. Each crystal is about 1 wavelength in width.
• C. Some but not all crystals are fired simultaneously to create a single beam.
• D. Beams transmitted from a convex array are parallel.

Answer: (D)

Convex sequential arrays produce a fan-shaped beam because the curved (convex) aperture bends the wavefronts as they are emitted and the firing happens in steps across the aperture. Since only a portion of the elements fire at a time and the aperture is curved, the resulting beam is spread into a sector rather than remaining as a set of parallel rays. That makes the statement about beams being parallel incorrect. The other statements align with how this type of array is typically designed and used: the active region tends to be larger than in a phased array, since you’re using fewer, wider elements to form the beam; each crystal is commonly about a wavelength wide to balance resolution and to avoid grating lobes; and you fire some but not all elements simultaneously, in groups, to create a single scanned beam.

Convex sequential arrays produce a fan-shaped beam because the curved (convex) aperture bends the wavefronts as they are emitted and the firing happens in steps across the aperture. Since only a portion of the elements fire at a time and the aperture is curved, the resulting beam is spread into a sector rather than remaining as a set of parallel rays. That makes the statement about beams being parallel incorrect.

The other statements align with how this type of array is typically designed and used: the active region tends to be larger than in a phased array, since you’re using fewer, wider elements to form the beam; each crystal is commonly about a wavelength wide to balance resolution and to avoid grating lobes; and you fire some but not all elements simultaneously, in groups, to create a single scanned beam.