Abstract

With the goal of producing larger working regions of uniform irradiance and phase in microwave anechoic chambers, we have built a disassemblable, tapered chamber in which to study the effects of (a) source size and (b) source position. Recognizing that the long walls of tapered anechoic chambers are partially reflecting mirrors, we have developed an elementary theory for optical design of chambers, and made computations that agree with microwave experiments. To design wider plateaus of irradiance in the working region, we have used computer programs for the interference patterns produced by the primary source and the multiple-image virtual sources.

© 1972 Optical Society of America

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References

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  1. C. L. Andrews and C. R. Carpenter, J. Opt. Soc. Am. 60, 741A (1970).
  2. C. R. Carpenter and C. L. Andrews, J. Opt. Soc. Am. 60, 742A (1970).
  3. A. Golab and C. L. Andrews, Am. J. Phys. 39, 121 (1971).
    [Crossref]
  4. C. R. Carpenter, Am. J. Phys. 39, 120 (1971).
    [Crossref]
  5. Available from Emerson and Cuming, Inc., Microwave Products Division, Canton, Mass., as Eccosorb SPY and from B. F. Goodrich, Sponge Products, Shelton, Conn., as type VHP.
  6. Available from B. F. Goodrich as type HV-4 and from Emerson and Cuming as a thinner Flexible Foam Absorber as a type AN series.
  7. S. Galagan, Microwaves 9, 44 (1970).
  8. W. H. Emerson and H. B. Sefton, Proc. IEEE 53, 1079 (1965).
    [Crossref]
  9. Available from Emerson and Cumings, Inc.
  10. Paul Drude, The Theory of Optics, translated by C. R. Mann and R. A. Millikan (Dover, New York, 1959).
  11. V. M. Kulkarni, Am. J. Phys. 28, 317 (1960).
    [Crossref]
  12. Chung-Heng Liu, Am. J. Phys. 30, 380 (1962).
    [Crossref]
  13. Because of the angular dependence of the horn field pattern, and because images farther from the source represent rays that have encountered the absorbing material more times and at smaller angles of incidence, image intensity decreases with distance of the image from the source. Images are neglected if their intensities fall below preset tolerances.

1971 (2)

A. Golab and C. L. Andrews, Am. J. Phys. 39, 121 (1971).
[Crossref]

C. R. Carpenter, Am. J. Phys. 39, 120 (1971).
[Crossref]

1970 (3)

S. Galagan, Microwaves 9, 44 (1970).

C. L. Andrews and C. R. Carpenter, J. Opt. Soc. Am. 60, 741A (1970).

C. R. Carpenter and C. L. Andrews, J. Opt. Soc. Am. 60, 742A (1970).

1965 (1)

W. H. Emerson and H. B. Sefton, Proc. IEEE 53, 1079 (1965).
[Crossref]

1962 (1)

Chung-Heng Liu, Am. J. Phys. 30, 380 (1962).
[Crossref]

1960 (1)

V. M. Kulkarni, Am. J. Phys. 28, 317 (1960).
[Crossref]

Andrews, C. L.

A. Golab and C. L. Andrews, Am. J. Phys. 39, 121 (1971).
[Crossref]

C. L. Andrews and C. R. Carpenter, J. Opt. Soc. Am. 60, 741A (1970).

C. R. Carpenter and C. L. Andrews, J. Opt. Soc. Am. 60, 742A (1970).

Carpenter, C. R.

C. R. Carpenter, Am. J. Phys. 39, 120 (1971).
[Crossref]

C. L. Andrews and C. R. Carpenter, J. Opt. Soc. Am. 60, 741A (1970).

C. R. Carpenter and C. L. Andrews, J. Opt. Soc. Am. 60, 742A (1970).

Drude, Paul

Paul Drude, The Theory of Optics, translated by C. R. Mann and R. A. Millikan (Dover, New York, 1959).

Emerson, W. H.

W. H. Emerson and H. B. Sefton, Proc. IEEE 53, 1079 (1965).
[Crossref]

Galagan, S.

S. Galagan, Microwaves 9, 44 (1970).

Golab, A.

A. Golab and C. L. Andrews, Am. J. Phys. 39, 121 (1971).
[Crossref]

Kulkarni, V. M.

V. M. Kulkarni, Am. J. Phys. 28, 317 (1960).
[Crossref]

Liu, Chung-Heng

Chung-Heng Liu, Am. J. Phys. 30, 380 (1962).
[Crossref]

Sefton, H. B.

W. H. Emerson and H. B. Sefton, Proc. IEEE 53, 1079 (1965).
[Crossref]

Am. J. Phys. (4)

A. Golab and C. L. Andrews, Am. J. Phys. 39, 121 (1971).
[Crossref]

C. R. Carpenter, Am. J. Phys. 39, 120 (1971).
[Crossref]

V. M. Kulkarni, Am. J. Phys. 28, 317 (1960).
[Crossref]

Chung-Heng Liu, Am. J. Phys. 30, 380 (1962).
[Crossref]

J. Opt. Soc. Am. (2)

C. L. Andrews and C. R. Carpenter, J. Opt. Soc. Am. 60, 741A (1970).

C. R. Carpenter and C. L. Andrews, J. Opt. Soc. Am. 60, 742A (1970).

Microwaves (1)

S. Galagan, Microwaves 9, 44 (1970).

Proc. IEEE (1)

W. H. Emerson and H. B. Sefton, Proc. IEEE 53, 1079 (1965).
[Crossref]

Other (5)

Available from Emerson and Cumings, Inc.

Paul Drude, The Theory of Optics, translated by C. R. Mann and R. A. Millikan (Dover, New York, 1959).

Available from Emerson and Cuming, Inc., Microwave Products Division, Canton, Mass., as Eccosorb SPY and from B. F. Goodrich, Sponge Products, Shelton, Conn., as type VHP.

Available from B. F. Goodrich as type HV-4 and from Emerson and Cuming as a thinner Flexible Foam Absorber as a type AN series.

Because of the angular dependence of the horn field pattern, and because images farther from the source represent rays that have encountered the absorbing material more times and at smaller angles of incidence, image intensity decreases with distance of the image from the source. Images are neglected if their intensities fall below preset tolerances.

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Figures (7)

Fig. 1
Fig. 1

Experimental tapered chamber with motor-driven optical bench for scanning the irradiance across the chamber, string supports S for cardboard c, which supports the diode-detector D.D. A twisted lead T.L. extends from the detector to the lock-in ac amplifier and recorder. The optical bench O.B. is symbolic of the precision adjustments for positioning X band waveguide W.G. at the input end.

Fig. 2
Fig. 2

Scans parallel to the electric field, when the small horn was inserted along the axis of the chamber a distance of (a) 4 cm, (b) 3.0 cm, and (c) 3.2 cm. Positions of the source differing by a few tenths of a wavelength produce gross changes of the pattern of irradiance.

Fig. 3
Fig. 3

Scans parallel to the electric field when (a) the horn was centered on the axis of the chamber, (b) displaced to the left by a quarter wavelength, (c) displaced to the right by a quarter wavelength.

Fig. 4
Fig. 4

Scans perpendicular to the electric field for two optimum plateaus; (a) the large horn placed on the axis one-quarter wavelength outside the throat, (b) the small horn placed on the axis 0.6 wavelengths outside the throat, and (c) straight-edge diffraction pattern in the plane of the screen using the plateau of case (b).

Fig. 5
Fig. 5

Diagram to show the positions of the images formed by the partially reflecting walls when the source is on the axis in a 30°-tapered chamber. Two ray paths are shown from source S to an arbitrary scan point P. The first ray encounters the chamber surfaces once on its journey to point P, whereas the second ray encounters the chamber surfaces twice.

Fig. 6
Fig. 6

Diagram to show the positions of the images formed by the partially reflecting walls of the chamber when the source is off axis in a 30°-tapered chamber.

Fig. 7
Fig. 7

Sequence of computer-generated irradiance distributions along the scan line parallel to the E field for the source positioned progressively further from the apex of the chamber. For the transition from curve (a) to curve (e) the source was moved through a total distance of approximately 1 2 wavelength. Superimposed on curve (c) is our best experimental curve for this direction of scan [Fig. 3(c)].

Equations (1)

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U T ϕ T = ( λ / R 0 ) e i k R 0 + j = 1 n D j [ A U j ( λ / R U j ) e i k R U j + A L j ( λ / R L j ) e i k R L j ] ,