EP0197350A1 - Dual-band corrugated horn with a dielectric transition - Google Patents

Abstract

1. Dual-band horn radiator consisting of a transition section adjoining a feeder waveguide of circular cross-section and of a horn the inner wall of which, which widens in the form of a funnel, is provided with corrugations, for two separate frequency bands, characterized in that the transition section (1) widens in accordance with a Bo . e**Kxn curve, where Bo = feeder waveguide diameter, x = longitudinal dimension of the horn, K = coefficient having a value of mch< 1, n = coefficent having a value of 2 < n < 8, in such a manner that the aperture angle at the first corrugation of the horn corresponds to 0.5 +- 0.2 times the constant aperture angle of the horn and that the end region of the transition section (1) facing the horn (2), having the length So is wholly or partially filled over a length of So /8 to So /3 (So = length of transition section) by a dielectric (3) of a low dielectric constant (vepsiln r1 ) of less than 1.3, in such a manner that the mean electrically active length of the dielectric (3) in the stepped transition section satisfies the condition lambda H vepsiln 1 /2 for the upper operating frequency range, where lambda H vepsiln 1 is the wavelength of the upper operating frequency.

Description

The invention relates to a horn radiator consisting of a transition part adjoining a feed waveguide of circular cross-section and a horn, the funnel-shaped inner wall of which is provided with grooves, for two frequency bands lying apart.

Grooved horns of this type are frequently used in the microwave range because of their favorable properties. With suitable dimensioning in a broad frequency band, they have good adaptation as well as directional characteristics with high axial symmetry and low cross polarization. To achieve these properties, the groove dimensions must be dimensioned precisely.

When dimensioning double-directional radio antennas, short grooved horn radiators are mainly used as exciters for the mirror system, since horns with large opening angles, ie> 30 °, enable good diagram characteristics over a wide frequency range with a short overall length. In the case of series antennas, it is important that no mechanically complicated structures of the grooves and the transition zone from the feed waveguide to the groove part of the horn are required, since otherwise the horn has to be assembled in a complex manner from several fitting parts. In particular, the optimization of the reflection factor in two frequency bands separated by a factor of 1.7 to values below 3% is not guaranteed in the design of the horns according to known dimensioning rules by simply varying the grooves and the transition form in the metal body of the horn. In the case of antenna feed lines protected from dry air, the pressure is also Sealing on the horn usually involves incorporating a dielectric plate in the reflection adjustment, the compensation of which is difficult at high bandwidths.

The invention has for its object to design a horn of the type described above so that an optimization of the reflection in two different frequency bands is achieved in a simple manner.

This object is achieved according to the invention in such a way that the transition part follows a B _o · e ^{K · xII} curve (B _o = feed waveguide diameter, x = longitudinal extension of the horn, _K = coefficient with the value 1, n = coefficient with a value of 2 <n <8), expanded in such a way that the opening angle at the first groove of the horn corresponds to 0.5 ± 0.2 times the continuous opening angle of the horn and that the end region of the transition part facing the horn has a length of S / 8 to / 3 (S ₀ = length of the transition portion) with a dielectric of low dielectric constant (ε _r1 <1.3) is filled entirely or partially So _0, in such a way that a partial length of the dielectric of low dielectric constant is replaced by at least a thin disk of a material with a higher dielectric constant (ε _r2 ~ 2.5 to 4.7) to fulfill the function of a reflection-optimized pressure seal.

Advantageous refinements and developments of the subject matter of the invention are specified in the subclaims.

The invention is explained in more detail below on the basis of an exemplary embodiment shown in the drawing.

• Fig. 1 den Hornstrahler mit Übergangsteil und Horn in einer geschnittenen Teildarstellung und
• Fig. 2 den mit Dielektrikas gefüllten Endbereich des Obergangsteils.

Show it

• Fig. 1 the horn radiator with transition part and horn in a sectional partial view and
• 2 shows the end region of the transition part filled with dielectrics.

1 consists of a transition part 1 of length S ₀ and a horn 2 (groove part). The diameter of the transition part 1 in the connection area of the feed waveguide in FIG. 1 at the point x = o is dimensioned such that the dependence of the field wave resistance of the fundamental wave H ₁₁ in the lower band on the waveguide diameter comes out of the very steep area close to the cutoff frequency, the E ₁₁ -wave in the upper area, however, is not yet capable of spreading. The upper part 1 widens at x = o, starting from the diameter of the feed waveguide to a diameter at which the condition fu /> 1.3 is fulfilled (f = lowest operating frequency, f _c = cut-off frequency of the H ₁₁ wave) after a B _o .e ^K.xn curve in ^{such a} way that the opening angle for the first groove corresponds to 0.5 ± 0.2 times the continuous opening angle of the following horn. Here B _{o is} the feed waveguide diameter, x the length of the horn, K is a coefficient with the value 1 and n is a coefficient with a value 2 <n <8, for example 5. Instead of a constant diameter expansion, cylinder tube regions with constant jumps in diameter are expediently used in the transition part. This stabilizes the position of the dielectric body and simplifies the manufacture of the arrangement. The transition part 1 has a flat start, in which the gradation only begins after about 2/3 of its length. The following horn 2 is constructed in accordance with the known formulas and computer programs for radiation optimization. With appropriate dimensions, such a horn typically has reflection factors of r <10% in the lower band and r <5% in the upper band.

The disturbance of the fundamental wave H ₁₁ in the lower band generated at the horn kink and in the first grooves is in an axially extended area in the B _o .e ^Kxn transition with a very weak rigid foam ^dielectric 3 (ε r ₁ <1.3) at the next possible location in the Transition compensated. The dielectric 3 fills approximately the last quarter of the transition partly or completely in the direction of the horn 2. Because of the large spacing of the frequency bands and thus the ^waveguide _{wavelength ratio} τ _Hε1 below / τ _Hε1 above, it is possible to interpret the interference caused in the upper band by the axial spacing of the interfaces of the weak dielectric itself. This is fulfilled if the average electrically effective length of the dielectric 3 in the stepped transition part corresponds to the condition τ _Hε 1/2 for the upper operating frequency range. The mechanical length S of the through weak dielectric 3, that of the dielectric with a low dielectric constant, is in this case depending on the location of the frequency bands, the transition diameter and the dielectric constant ε _r1 about S _0/8 to S _0/3, if S _{o is} the length of the transition 1 is.

In the illustrated embodiment, a partial length of the dielectric 3 with a low dielectric constant εr _{1 is} replaced by a thin disk 4 (film) with a higher dielectric constant ε _r2 (ε _r2 ~ 2.5 to 4.7). 2, the dielectric 3 with a low dielectric constant ε _{r1 is} removed in the end region, ie shortened by the length S-So, where S6 is the remaining length of the dielectric 3. The thin disk 4 of the material of high dielectric constant ε r ₂ (thickness S _D -S _D ), which is considerably thinner than the removed material layer, is applied to the reduced end region of the dielectric 3. This measure hardly changes the compensation in the lower band if the replaced length with the dielectric constant ε _r1 corresponds electrically to the influence of the thin layer with the dielectric constant ε _r2 , since the phase amplitude change remains small at the large wavelength. This change has a stronger effect in the upper band, so that different dielectric combinations, which act almost identically in the lower band, for Residual adjustment in the upper band can be designed. The thin layer with the dielectric constant ε _r2 (eg a horn for 2.1 to 2.3 gigahertz and 3.4 to 3.6 gigahertz a 0.1 mm thick glass fiber epoxy film with ε _r2 = 4.7) now also acts as reflection-optimized pressure seal. The thin layer with the dielectric constant ε _r2 can also be applied to both ends of the layer with the dielectric constant ε _r1 .

The dielectric body 3, 4 is glued into the step transition. The change in the radiation diagram compared to the unbalanced horn is small and can usually be neglected. This is a great advantage when dimensioning the grooved horn, e.g. Changes in the first grooves to improve the adjustment, especially in the upper band, have a strong impact on the radiation diagram. If an axial groove structure is selected when dimensioning the horn, the type of compensation enables groove horns to be built without undercuts and complicated curves, so that production in one piece is possible as a turned part.

The horn radiator according to the invention with the specially designed transition part thus advantageously serves to fine-tune the reflection factor in two spaced-apart frequency bands in grooved horns, which are designed in accordance with the principles of radiation diagram optimization. At the same time, the problem of reflection of the pressure seal in two bands is also solved.

Claims (4)

1. Horn radiator, consisting of a transition part adjoining a circular waveguide feeder and a horn, the funnel-shaped inner wall of which is provided with grooves, for two frequency bands lying apart.
characterized, n
that the transition part (1) widens after a B _o .e ^KXII curve in such a manner that the opening angle of the first groove of the horn 0.5 ± 0.2 times the corresponding continuous opening angle of the horn and in that the said horn ( 2) facing the end region of the transition part (1) is / to _{SD 3} (S ₀ filled over a length of S ₀ 8 _/ = length of the transition portion) with a dielectric (3) of low dielectric constant (ε _r1 <1.3) completely or partially , in such a way that the average electrically effective length of the dielectric (3) in the stepped transition part of the condition τ _Hε1 / 2 above is sufficient for the upper operating frequency range. 2. Arrangement according to claim 1,
characterized ,
that a partial length of the dielectric (3) of low dielectric constant is replaced by at least one thin disk (4) of a material of higher dielectric constant (ε _r2 ~ -2.5 to 4.7), to fulfill the function of a reflection-optimized pressure seal. 3. Arrangement according to claim 2,
characterized,
that a thin disk (4) with a higher dielectric constant is arranged on one or both sides of the dielectric (3) with a low dielectric constant. 4. Arrangement according to one of claims 1 to 3,
characterized,
that the inner contour of the transition part after the course B _o .e ^{Kxn is divided} into steps with constant small ^jumps in diameter.

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