CRAC Class B (2025) — Questions 631–640

Initially both horizontal dipoles → matching polarization → good. Changing one to vertical creates cross-polarization (horizontal vs vertical), which loses roughly 20+ dB, so communication deteriorates (A).

Initially cross-polarized (one H, one V) → poor. After both become vertical → matching polarization → improves (A).

Initially cross-polarized → poor. After both become horizontal → matching polarization → improves (A).

Initially opposite circular polarizations (LHCP vs RHCP) → near- complete rejection, very poor. After both become LHCP → matched → improves (A).

Same as U0476: initially mismatched opposite circular polarizations → poor; both RHCP → matched → improves (A).

A linear polarization (horizontal or vertical) can be decomposed into equal left- and right-hand circular components. Thus a circularly polarized antenna receiving a linear signal (or vice versa) always captures half the power (−3 dB) regardless of the linear orientation. Changing station B from a horizontal to a vertical linear dipole still yields the same −3 dB, so the effect is unchanged (A).

A linear polarization (the dipole) contains equal LHCP and RHCP parts, so a circularly polarized antenna — whether LHCP or RHCP — captures the same half-power regardless of its sense. Switching A from LHCP to RHCP while its partner is a linear dipole yields an unchanged result (A).

Initially B is a linear dipole, which contains both circular components, so it couples to A's LHCP at −3 dB. After B becomes RHCP, it is opposite to A's LHCP → near-total rejection → much worse (A).

Initially B is a linear dipole → −3 dB capture by A's LHCP. After B becomes LHCP matching A, the link is fully matched → improves (A).

Initially opposite circular polarizations → near-total rejection (very poor). After both become horizontal dipoles (matched linear polarization) → big improvement (A).