GB2265223A

GB2265223A - Phase discriminator with spatial sampling

Info

Publication number: GB2265223A
Application number: GB9020077A
Authority: GB
Inventors: Jean-Luc Montardy; Eric Chamouard; Daniel Jahan
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1990-09-14
Filing date: 1990-09-14
Publication date: 1993-09-22
Also published as: DE4031447A1; GB9020077D0; DE4031447C2

Description

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- I - 2265223 Phase discriminator with spatial sampling I0 The present invention relates to a device for measuring the phase shift existing between two signals with the same frequency, in particular in the microwave range. It relates more particularly to a phase discriminator operating from a spatial sampling of a standing-wave pattern envelope generated by the signals whose phase shift is to be measured in a transmission line they travel in opposite directions.

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In this kind of phase discriminator which requires neither any coupler nor any 90 -phase shifter, difficult to implement for wideband operation, it is known to perform the phase shift measurement by measuring the distance separating the midpoint of the transmission line from the closest maximum of the standing-wave pattern and by computing the ratio of this distance to that separating two consecutive maximums of the standing- wave pattern. This measurement is inaccurate for it is difficult to locate with high accuracy the position of the maximums of the standing-wave pattern which is sampled from a limited number of points.

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A purpose of the present invention is accordingly to perform an accurate measurement of the phase shift between two signals with the same frequency that is simple to implement over a very wide range of frequencies.

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According to the present invention there is provided a phase discriminator with spatial sampling, comprising:

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- a transmission line travlled in opposite directions by two signals with the same frequency whose phase shift is to be measured, said signal generating in the transmission line a standing-wave pattern; - detectors distributed along said transmission line and sampling the amplitude of the envelope of the standing-wave pattern established within the transmission line; and - a spatial-phase discriminator which is connected to the outputs of the detectors and which comprises at least: o first computing means for computing a weighted sum of the output signals from the detectors proportional to the sine of the phase shift angle to be measured; second computing means for computing a weighted sum of the output signals From the detectors proportional to the cosine of the phase shift angle to be measured; and a divider circuit computing the ratio of the output signals from said first and second computing means Advantageously, the phase discriminator with spatial sampling includes in addition an average-component eliminating circuit inserted at the output of the detectors.

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Other features and advantages of the invention will become apparent frbm the following detailed description of a preferred embodiment given as a non-limitative example with reference to the accompanying drawings, in which:

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- Figures 1 and 2 are schematics of phase discriminators with spatial sampling in Thich the present invention is embodied.

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H-l(x) = sign (x) Glxl and each includes a multiplier 56, G6 with two inputs connected to the output of the respective summing circuit 55, 65, one through a sign extracting circuit 57, 67, and the other through a square-root extracting circuit 58, 68 preceded by an absolute-value extracting circuit 59, 69.

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At the output of the multipliers 56, 66 of the counterdistortion circuits is connected a divider circuit 70 which performs the division of the signal From the multiplier 56, globally corresponding to the imaginary part Y and proportional to the sine of the phase shift angle, by the signal From the multiplier 65, globally corresponding to the real part X and proportional to the cosine of the phase shift angle. The quotient thus obtained is applied to an arctangent computing circuit 71 which can be, as previously, comprised of two analog-to-dgital converters addressing a digital memory containing a table defining the arctangent function, and that delivers the phase shift angle 4:

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As a variant, it is possible to imagine other types of distortions promoting the high amplitudes of the real and imaginary components of the points of the discrete Fourier trans- Form at the expense of the low amptitudes, for example a distortion of the kind:

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H(x)- = ex - 1, and the inverse distortion:

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}'1-l(x): ln(x + 1) where in = Napierian logarithm.

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These non-linear processings have the advantage of substantialty decreasing the systematic errors due, for example, to the effects of sampling, and to inccease the sensitivity through an incúease of the signal-to-noise catio.

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Claims

Claims .CLME:

I0 1. A phase discriminator wit% spatial sampling, comprising: - a transmission line traveled in opposite direction by two signals with the same frequency whose phase shift is to be measured; - detectors spaced along said transmission line and sampling the amplitude of the envelope of the standing-wave pattern. established within said transmission line; and - a spatial phase discriminator which is connected tc] the outputs of said detectors and which comprises at least:

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first computing means performing a weigthed summation of the output signals from said detectors proportional to the sine of said phase shift angle to be measured; second computing means performing a weighted summation of the output signals from said detectors proportional to the cosine of said phase shift angle to be measured; and a divider circuit computing the ratio of the output signals from said first and second computing means.

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2. A discriminator according to claim 1, comprising in addition an average-component eliminating circuit inserted at the output of said detectors.

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5. A discriminator according to claim I, wherein said first computing means comprise:

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- a first stage comprising a group of summing circuits providing weighted sums of said output signals from the detectors proportional to the imaginary components of the points of the I0 discrete Fourier transform constructed from the spatial samples of the envelope amplitude delivered by said detectors; and - a second stage constituted by a summing circuit (55) providing the sum of the output signals of said group of summing circuits and delivering sums proportional to the imaginary components of the points of said discrete Fourier transform, and wherein said second computing means comprises:

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- a first stage comprising a group of summing circuits providing weighted sums of the output signals from said detectors proportional to the real components of the points of said discrete ourier transform; and - a second stage constituted by a summing cirzuit providing the sum of the output signals from said group of summing ciccuit and delivering sums proportional t3 the real components of the points of said discrete Fourier transform.

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& discriminator according to claim 3, wherein said First and second computing means include distortion circuits individually inserted at the" outputs of said summing circuits of their first stage and performing a tansformation expanding the high-amplitude signals relative to the lowamplitude ones, and counter-distortion circuits individually inserted at the outputs of said summing circuits of their second stage and performing a transformaton inverse of that performed by said distortion circuits.

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5. A discriminator according to claim, wherein said distortion ciruits perform on the output signals from said summing circuits of the first stage of said first and second computing means a transformation defined by an inversible function H(x) such that:

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d CI) '3,I-.-. C i-r" ]" (-I- :3" < (::3 :3" CD X r" (3 (-I- ul x v ii x v x v I I 8. A phase discriminator with spatial sampling substantially as described hereinbefore with reference to the accompanying drawings and as illustrated in either Figure 1 or Figure 2 of those drawings.

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