Wide-band phase-metering frequency transducers with fixed frequency heterodynes

Conclusions

It has already been pointed out [3] that the PMFTs with a repeated sequential transformation of frequency in ISSs and restoration of the heterodyne frequency contain a minimum number of transducers (two WBFSs) and provide, only for the condition that Ω<ω, an adequately small error due to an incomplete suppression of the image frequencies (∥Δ∥≤δ₁δ₂) in the WBFSs.

Over a wider frequency range (ω≷Ω), i.e., at any frequency with the exception ofω=Ω, the PMFTs operate with the same small errors due to an incomplete suppression of the WBFS image frequencies (∥Δ∥≤δ₁δ₂), provided that the ISS contains two WBFSs and an SM, or three WBFSs, and that the reference-signal shaping channel consists of a frequency doubler and k₁=k₂=1.

Certain PMFTs which contain an FST at one of the heterodyne outputs [5] (k₂>k₁=1) have even a. wider band. Thus, the PMFTs corresponding to combinations of their component transducers shown in the lines 2, 5, 8, and 11 of Table 1 operate, for any relationship of the frequenciesω ₁Ω and k₂Ω, with adequately small errors due to an incomplete supression of the image frequency (∥Δ∥≤δ₁δ₂) in the WBFSs.

The above error, with the remaining conditions being the same, is minimal (∥Δ∥≤δ¹δ²δ³) in the PMFTs which consist of three WBFSs and have transducer combinations shown in the lines 1 and 3 of Table 1.

Bearing in mind that WBFSs can now be made with an image frequency suppression factor of the order of 5·10⁻³, the error under consideration of such PMFTs can be of the order of 10⁻⁷ rad or 5·10⁻⁵ degrees, i.e., it can be small as compared with other modern phase-metering devices' error components (due to coupling between channels, presence of higher signal harmonic components, etc).