The Wide Angle Side Lobes of Reflector Antennas

Ratnasiri, P. A.; Kouyoumjian, R. G.; Pathak, P. H.

doi:10.21236/ad0707105

Cited by 41 publications

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“…where E+ and H+ are the incident field components tangent to the edge, and p is the impedance of free space. The Kouyoumjian group has evaluated the axial caustic fields of a focused paraboloid using these edge currents [8]. In the symmetric case it is possible to integrate the edge currents analytically and express the ring current field in terms of Bessel functions 191.…”

Section: ~I K~x Q S I N B P~~~q P + S~s I N 8 P S I N Q P + (~Q + 2mentioning

confidence: 99%

Application of the geometrical theory of diffraction to Cassegrain subreflectors with laterally defocused feeds

Sørensen

Rusch

1975

IEEE Trans. Antennas Propagat.

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The geometrical theory of diffraction (GTD) as formulated by R. G. Kouyoumjian has been applied to predict the radiation characteristics of hyperboloidal subreflectors with laterally defocused feeds. In caustic or multicaustic directions the scattered fields are. determined AZIMUTH ANGLE Fig. 7. Smoothed theoretical and measured radiation patterns of pyramidal horn reflector antenna with blinders in 4, 6 , and 1 1 GHz bands. GTD prediction-. Measured- .

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Section: ~I K~x Q S I N B P~~~q P + S~s I N 8 P S I N Q P + (~Q + 2mentioning

confidence: 99%

Application of the geometrical theory of diffraction to Cassegrain subreflectors with laterally defocused feeds

Sørensen

Rusch

1975

IEEE Trans. Antennas Propagat.

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“…The Kouyoumjian group has used a combination of a single edge-diffracted GTD, equivalent ring-currents, and physical optics to compute the complete radiation pattern of a prime focus paraboloid [8], [9]. Results were also reported in [11 ] that compare the calculated and measured scattered H-plane patterns from a hyperboloid illuminated by a corrugated horn with its phase center at the hyperboloid's external focus [12].…”

Section: A Radiation From Prime-focus Paraboloidmentioning

confidence: 99%

The geometrical theory of diffraction for axially symmetric reflectors

Rusch

Sørensen

1975

IEEE Trans. Antennas Propagat.

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6 -eedge -%dge x5 = R T t rf: z COS +.(29) where the angles and unit vectors for both sets of feeds are defined in the sense indicated in Fig. 1 If a point-source feed is located on the axis of an axially symmetric reflector, then only two singly edge-diffracted rays are possible for a distant field point P(R,B,$), if 0 # 0,n (Fig. 1).These rays are "diffracted" from QE+, where the plane 4 intersects the edge on the same side of the Z axis as the field point, and from QE-, where the plane 4 + .n intersects the edge diametrically opposite Qs+ on the opposite side of the Z axis from the field point.The geometry of the edge-diffracted ray from QE-is shown in Fig. 2. (The surface is assumed to be convex.) The ray from the feed to QE-defmes e&. , and the corresponding extreme geometrically reflected ray, when extended back to the Z axis, defines e,,,,. These two angles may then be used t o define two intermediate angles used in the edge-diffraction notation of where E,, and EfS are the 8 and 4 components of the incident field, pedge is the distance from feed to Q E -, Zedge is the z CO-ordinate of QE-(Zedge < O), Dren is the reflector diameter, E D G E -D I F F R A C T E D R A Y / E X T R E M E G E O M E T R I C A L RAY Fig IEEE T R A N S A~O N S ON ANTENNAS AND PROPAGATION, MAY 1975-0,-is zero in the direction of the surface tangent, 0 = x/2 -6, but Dh-i s not. Slightly modified but principally the same diffraction coefficients for singly edge-diffracted rays may be derived for concave surfaces. The geometry of the ray difftacted from QE+ is shown in Fig. 3. The fields of this ray are given byThe transition functions F(kLa) remove the singularities at the shadow boundary (8 = a -e&.,) and at the reflection boun-where Dl' and DZr are the principal radii of curvature of the re5ected geometrical ray at QE+ and (Drefl/2)/sin e,,,, is the caustic distance evaluated in the direction of the reflection boundary.For the point source on the 2 axis illuminating the axially symmetric reflector, the resulting single edge-diffracted rays have a caustic at all points on the Z axis. Thus all ray path-lengths FQEP are the same if both F and P lie on the axis of symmetry.Ray optical solutions fail in the neighborhood of these caustics, as, for example, the sin 0 denominator in the square-root factor of (4) and (6) Furthermore, for this symmetric case 4' = 4 2 + a).The most commonly encountered feed function is that of a far-field, m = 1, spherical-wave source for which the tangential fields incident on the edge areThe easily computed ring current fields then become as follows. 8, corresponds to a caustic at in6nity form point 2, while e, corresponds to a caustic at infinity from point 1 . Thus, as 0 increases from 0, to e, , the additional roots 3 and 4 move from 2 to 1. In practice, for typical reflector geometries the range of values from to 0, is sufficiently small so that the entire range is covered by radiation from the equivalent ring sources to avoid unrealistically large predicted fields.An example of a multi- hyperbolo...

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“…Although paraboloidal and hyperbololdal reflectors are studied in detail, the other types of reflectors did not draw the attention which they merited. Any reflector as shown in ?ig.1 in the plane where the scattered fields are to be calculated may be described by r=Fo(l-e)/(l-ecosV (1) (4) where R=s+ jeiel denotes the distance from the phase center located at O' A reflector, which is specified by eqns. 1 and 2, may have the shapes shown in iig.2 as its eccentricity varies between plus and minus infinity; these shapes correspond to differenit cormbinations of (to'y)…”

Section: Introductionmentioning

confidence: 99%

Calculation of the Radiation Patterns of Axially Symmetric Reflectors

Yazgan

Safak

1980

10th European Microwave Conference, 1980

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Scattered fields from axially symmetric reflectors (paraboloid, ellipsoid, hyperboloid, spheroid and plane) are calculated by highfrequency asymptotic techniques. For this purpose, the scattered fields from an axially symmetric reflector are expressed in terms of the reflector eccentricity. By using appropriate eccentricity values, the scattered fields from a reflector of any eccentricity can be obtained in a unified form. With the help of this approach, the effect of eccentricity on the focusing property of reflectors is studied.

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The Wide Angle Side Lobes of Reflector Antennas

Cited by 41 publications

References 0 publications

Application of the geometrical theory of diffraction to Cassegrain subreflectors with laterally defocused feeds

Application of the geometrical theory of diffraction to Cassegrain subreflectors with laterally defocused feeds

The geometrical theory of diffraction for axially symmetric reflectors

Calculation of the Radiation Patterns of Axially Symmetric Reflectors

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