Abstract

The quadrant multiplier phototube developed for use as a navigational aid is described. The tube contains four independent and adjacent semitransparent photocathode quadrants in a common image plane. By means of a retarding field three of the four photocathode segments are biased off during a quarter cycle while emission from the fourth is collected by the electron multiplier. Operating sequentially the photocathode quadrants perform the function of four multiplier phototubes in an all-electronic nulling-type tracker. No rotating reticles or mechanical choppers are required in the optical system. Position information of the image is discussed in relation to the size of the image spot. The performance characteristics are given in terms of nulling precision and signal-to-noise ratio for stars of different visual magnitudes.

© 1964 Optical Society of America

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References

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  1. J. P. Causse, IRE Trans. Nucl. Sci. NS-7, 66 (1960).
    [Crossref]
  2. C. W. Allen, Astrophysical Quantities (Athlone Press, Univ. of London, 1955), p. 174.

1960 (1)

J. P. Causse, IRE Trans. Nucl. Sci. NS-7, 66 (1960).
[Crossref]

Allen, C. W.

C. W. Allen, Astrophysical Quantities (Athlone Press, Univ. of London, 1955), p. 174.

Causse, J. P.

J. P. Causse, IRE Trans. Nucl. Sci. NS-7, 66 (1960).
[Crossref]

IRE Trans. Nucl. Sci. (1)

J. P. Causse, IRE Trans. Nucl. Sci. NS-7, 66 (1960).
[Crossref]

Other (1)

C. W. Allen, Astrophysical Quantities (Athlone Press, Univ. of London, 1955), p. 174.

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Figures (7)

Fig. 1
Fig. 1

Cross section of the ASCOP quadrant multiplier phototube.

Fig. 2
Fig. 2

The front-end assembly of the quadrant multiplier phototube. Emission from photocathode segment 2 is collected; photocathode segments 1, 3, and 4 are biased “off”.

Fig. 3
Fig. 3

Output display for star image at null position. (a) Defocused star image shown at dead center of quadrant photocathode plane. (b) Corresponding display of anode current outputs of equal amplitudes indicating null position, I1 = I2 = I3 = I4.

Fig. 4
Fig. 4

Output display for star image slightly off-null position. (a) Defocused star image on photocathode plane, and (b) corresponding display of anode current output arising from each of the four quadrants; Ix = I1 + I2I3I4 and Iy = I1 + I4I2I3.

Fig. 5
Fig. 5

Geometric factor; the fraction of circular-image area impinging on quadrants 1 and 2 as a function of image distance from center. The restricted case is given for distance along the x axis at y = 0. The separation between quadrant sections, δ, is 0.00762 cm.

Fig. 6
Fig. 6

Collection efficiency as a function of distance from center along a line 45° to the x axis for various image sizes.

Fig. 7
Fig. 7

Nulling precision of the QMP as a functon of star image diameter. The left ordinate shows the displacement from center for the x-direction signal at unity signal-to-noise ratio. The right ordinate is angle of arc precision at a signal-to-noise ratio of unity for a total field of view of 1°. Bandwidth = 3 cps; lens aperture = 45 cm2: m is the star magnitude (visual).

Tables (2)

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Table I Signal Current Ix in Units of 10−10 A for an Image-Center Displacement of 25 μ from Null. m = Star Magnitude

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Table II Noise Current in Units of 10−10 A

Equations (6)

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I x = I 1 + I 2 I 3 I 4 ,
I y = I 1 + I 4 I 2 I 3 .
I 1 + I 2 = k 2.51 m S L G γ ,
G = [ 1 2 π a 2 + z ( a 2 z 2 ) 1 / 2 + a 2 sin 1 ( z / a ) δ x ( a + z ) ] ( π a 2 ) 1 ,
I x = 2 ( I 1 + I 2 ) ( d G d x ) x = 0 x ,
I x = 2 k 2.51 m S L G γ ( d G d x ) x = 0 x .

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