Adjustment of circular-polarization antennas

“RadioAstron”-A telescope with a size of 300 000 km: Main parameters and first observational results

“…In this case, there usually exists some common "equivalent optimal-focus center" or "equivalent phase center" near the middle of these positions, where it is possible to minimize phase aberrations and distortion of the antenna beam [50,53]. The phase errors in the aperture are the sum of these three types of errors associated with the dish, feed, and shift of the feed from the dish focus [54,55]. Therefore, it is not possible to uniquely establish the real origin of phase distortions in the antenna aperture based purely purely on the results of inflight tests, without additional data or hypotheses.…”

“…The phase distribution of the field ϕ(x) at a point 0 ≤ x ≤ R 0 in a dish aperture with radius R 0 can be written [54] ϕ(x) = Φ(x) − Φ 0 , where Φ(x) and Φ 0 are the initial field phases at the point x and at the center of the aperture. Φ(x) = Ψ(ψ) + k(ρ + t) and is determined by the phase of the feed beam Ψ(ψ) (0 ≤ ψ ≤ ψ 0 ; here, ψ is the angle from the dish focus between the points x = 0 and x ≤ R 0 ) and the lengths of the path ρ from the feed to the dish and the path t from the dish to the aperture (k is the wavenumber).…”

“…Therefore, Φ(x) is a function of the phase beam of the feed, the dish profile (with the deviation δ 3 of the surface from an ideal surface), and the shift of the feed phase center relative to the paraboloid focus (by δ 1 in the longitudinal and δ 2 in the transverse direction relative to the antenna axis). The deviations of these factors from their projected values give rise to a total deviation of the phase distribution at the dish aperture from the projected (in the ideal case, close to co-phased) value δϕ(x), and can be estimated with sufficient accuracy for our purposes as [54] δϕ(x) = 2δΨ(ψ) + k[±δ 1 (1 − cos ψ) − δ 2 sin ψ − 2δ 3 (1 + cos(ψ/2)].…”

RadioAstron -- a Telescope with a Size of 300 000 km: Main Parameters and First Observational Results

“…In this case, there usually exists some common "equivalent optimalfocus center" or "equivalent phase center" near the middle of these positions, where it is possible to minimize phase aberrations and distortion of the antenna beam [50,53]. The phase errors in the aperture are the sum of these three types of errors associated with the dish, feed, and shift of the feed from the dish focus [54,55]. Therefore, it is not possible to uniquely establish the real origin of phase distortions in the antenna aperture based purely purely on the results of inflight tests, without additional data or hypotheses.…”

“…Therefore, Φ(x) is a function of the phase beam of the feed, the dish profile (with the deviation δ 3 of the surface from an ideal surface), and the shift of the feed phase center relative to the paraboloid focus (by δ 1 in the longitudinal and δ 2 in the transverse direction relative to the antenna axis). The deviations of these factors from their projected values give rise to a total deviation of the phase distribution at the dish aperture from the projected (in the ideal case, close to co-phased) value δϕ(x), and can be estimated with sufficient accuracy for our purposes as [54] Here, in the general case, δΨ(ψ) contains random and systematic deviations of the feed phase beam. The term with δ 3 is associated with inaccuracy of the dish surface, the terms with δ 1 and δ 2 reflect a systematic "incursion" of the phase from the center of the aperture toward the edge due to the lack of coincidence between the dish focus and the feed centerof focus (with even and odd functions relative to the center of the aperture, respectively), and k = 2π/λ is the wavenumber.…”