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How do I design a circularly polarized microstrip patch antenna using sequential rotation?

Q: Does sequential rotation work for a scanned array?

Yes, but the AR bandwidth decreases as the beam is scanned, because the element patterns (and their polarization properties) change with scan angle. At broadside: best AR performance. At 30-45 degrees scan: AR bandwidth decreases by approximately 30-50%. At 60 degrees scan: AR bandwidth is approximately 50-70% of the broadside value. For wide-scan CP arrays, each element should be individually designed for good CP (e.g., dual-feed patches) in addition to using sequential rotation.

Sequential rotation is a technique for achieving circular polarization (CP) from a microstrip patch antenna array by arranging multiple linearly polarized patch elements in a specific spatial rotation pattern and feeding them with progressive phase delays, so that the combined radiation from the array produces a circularly polarized wave. The design involves: using 4 identical linearly polarized rectangular patch elements arranged in a 2x2 sub-array, rotating each successive element by 90 degrees (element 1 at 0 degrees, element 2 rotated 90 degrees, element 3 rotated 180 degrees, element 4 rotated 270 degrees), feeding each element with a progressive 90-degree phase shift (element 1 at 0 degrees phase, element 2 at 90 degrees, element 3 at 180 degrees, element 4 at 270 degrees), and designing a feed network (corporate feed with Wilkinson dividers and 90-degree delay lines, or a Butler matrix for multi-beam applications). The sequential rotation technique offers key advantages over single-element CP designs (such as truncated corner or dual-feed patches): much wider axial ratio bandwidth (the sequential rotation cancels the axial ratio degradation of individual elements; typical AR bandwidth is 15-30% compared to 1-5% for a single truncated-corner patch), improved cross-polarization isolation (> 20 dB), and relaxed manufacturing tolerances (element imperfections are averaged out by the array).

Category: Antenna Fundamentals and Integration

Updated: April 2026

Product Tie-In: Antennas, Arrays, Feeds

Sequential Rotation CP Antenna Design

Sequential rotation is the standard technique for wideband CP in patch antenna arrays, used extensively in GPS receivers, satellite communication terminals, weather radar, and RFID reader antennas where circular polarization is required over a wide operating bandwidth.

Design Parameters

Element spacing: Typically 0.5-0.7 lambda between elements (standard array spacing for grating-lobe suppression). The rotation is applied to each element's physical orientation, not its position
Feed network: A 1-to-4 power divider with progressive 90-degree phase increments. The power divider must have equal amplitude (< 0.5 dB imbalance) and accurate phase (< 5 degrees error) for good axial ratio. Use Wilkinson dividers for equal split and delay lines for phase control
Polarization sense: Right-hand circular polarization (RHCP) uses 0, +90, +180, +270 degree progression. Left-hand (LHCP) uses 0, -90, -180, -270 degree (or equivalently, reverse the rotation direction)

Sequential Rotation CP Parameters

Sequential rotation phases: phi_n = (n-1) × 90° for n = 1, 2, 3, 4
Element rotation angles: theta_n = (n-1) × 90°
Axial ratio bandwidth: > 15% (vs < 5% for single CP element)
Array gain: G_array = G_element + 10 log(4) = G_element + 6 dB
Cross-polarization: > 20 dB (cancellation of LP components)

Common Questions

Frequently Asked Questions

Can I use sequential rotation with only 2 elements?

A 2-element sequential rotation (90-degree rotation and 90-degree phase) produces CP but with narrower axial ratio bandwidth than the 4-element version. The 4-element rotation provides better cancellation of axial ratio errors because each orthogonal error component is cancelled by two opposing elements. A 2-element rotation achieves approximately 10-15% AR bandwidth, while 4-element achieves 15-30%.

What axial ratio can I achieve?

A well-designed 4-element sequential rotation array achieves < 1 dB axial ratio (nearly perfect CP) at the center frequency, with AR < 3 dB over a 15-30% bandwidth. The axial ratio at broadside depends on: the feed network amplitude and phase accuracy (< 0.5 dB and < 5 degrees), the element similarity (all patches should have the same resonant frequency within < 0.5%), and the element spacing accuracy.

Does sequential rotation work for a scanned array?

Yes, but the AR bandwidth decreases as the beam is scanned, because the element patterns (and their polarization properties) change with scan angle. At broadside: best AR performance. At 30-45 degrees scan: AR bandwidth decreases by approximately 30-50%. At 60 degrees scan: AR bandwidth is approximately 50-70% of the broadside value. For wide-scan CP arrays, each element should be individually designed for good CP (e.g., dual-feed patches) in addition to using sequential rotation.

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