DE8507587U1 - Double band groove horn with dielectric balancing - Google Patents

Description

Siemens Aktiengesellschaft Our reference _ __ Berlin and Munich VPA &bgr;5 &Rgr; 11^9 DE

Double band groove horn with dielectric balancing

The invention relates to a horn antenna consisting of a transition part connected to a feed waveguide of circular cross-section and a horn whose funnel-shaped, widening inner wall is provided with grooves for two separate frequency bands.

Such groove horns are often used in the microwave range due to their favorable properties. With appropriate dimensioning, they have good adaptation in a wide frequency band and directional characteristics with high axial symmetry and low cross-polarization. To achieve these properties, the groove dimensions must be precisely dimensioned.

When dimensioning double-bald directional radio antennas, short grooved horn radiators are mainly used as exciters for the mirror system, since horns with large opening angles, i.e. > 30°, enable good diagram properties over a wide frequency range with a short overall length. In series antennas, it is important that no mechanically complicated structures of the grooves and the transition zone from the feed waveguide to the grooved part of the horn are required, since otherwise the horn would have to be assembled in a complex manner from several fitting parts. In particular, the optimization of the reflection factor in two frequency bands that are 1.7 apart to values below 3% is not guaranteed when designing the horns according to known dimensioning rules by simply varying the grooves and the transition shape in the metal body of the horn. In the case of dry air-protected antenna feed lines, the pressure

14 March 1985 / KIu 1 Kdg

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Sealing on the horn, usually a dielectric plate, should be included in the reflection adjustment, the compensation of which is difficult at high bandwidths.

The invention is based on the object of designing a horn antenna of the type described above in such a way 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 expands according to a B _Q -e ^{> x} curve (B _Q = feed waveguide diameter, x = longitudinal extension of the horn, K = coefficient with the value <£1, n = coefficient with a value 2<n <8), 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 is completely or partially filled with a dielectric of low dielectric constant (£ _r i < ¹ » ³ ) over a length of S _Q /8 to S _Q /3 (S _Q = length of the transition part), in such a way that a partial length of the dielectric of low dielectric constant is replaced by at least one thin disk of a material of higher dielectric constant (E _r 2–2.5 to 4.7) to fulfil the function of a reflection-optimized pressure seal.

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

The invention is explained in more detail below using an embodiment shown in the drawing.

Show it

Fig. 1 the horn antenna with transition part 1 and horn in a sectional partial view and

Fig. 2 the end area of the transition part filled with dielectrics.

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The horn antenna shown in Fig. 1 consists of a transition part 1 of length S _Q and a horn 2 (horn 1). 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 impedance of the fundamental wave H ₁₁ in the lower band on the waveguide diameter comes out of the very steep range near the cut-off frequency, but the E ₁₁ wave in the upper range is as far as possible not yet able to propagate. The transition part 1 expands at x=o, starting from the diameter of the feed waveguide to a diameter at which the condition fu/ >1.3 is fulfilled (f _u = lowest operating frequency, f = cut-off frequency of the H ₁₁ wave) according to a B _Q .e curve in such a way that the opening angle at the first groove corresponds to 0.5 - 0.2 times the continuous opening angle of the following horn. Here, B _Q is the feed waveguide diameter, x the length of the horn, K is a coefficient with the value ^.1 and η a coefficient with a value 2<η <8, for example 5. Instead of a continuous diameter

For the expansion, cylindrical tube sections with constant diameter jumps are expediently used in the transition section. This stabilizes the position of the dielectric body and simplifies the manufacture of the arrangement. The transition section 1 has a flat start, _with the stepping only beginning after about 2/3 of its length. The following horn 2 is constructed according to the known formulas and calculation programs for radiation optimization. With appropriate dimensioning, such a horn typically has reflection factors of rO0% in the lower band and r< 5% in the upper band.

The disturbance of the fundamental wave H ₁₁ in the lower band, which is generated at the horn bend and at the first grooves, is compensated in an axially extended area in the B _Q .e transition with a very weak hard foam dielectric 3 (£ _r1 <C 1.3) at the closest possible location in the transition. The dielectric 3 fills approximately the last quarter of the transition area.

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partly 1 in the direction of the horn 2 in whole or in part. Because of the large distance between the frequency bands and thus the waveguide wavelength ratio "A^gJ _below / ^H F 1 above * ^{it is} " ¹ ^IiCh to design the interference caused in the upper band by the axial distance of the boundary surfaces of the weak dielectric itself to compensate. This is fulfilled if the average electrically effective length of the dielectric 3 in the stepped transition part corresponds to the condition 'ÄnC. /2 for the upper operating frequency range. The mechanical length S of the continuous weak dielectric 3, ie the dielectric with a low dielectric constant, is approximately Sq/8 to S _Q /3, depending on the position of the frequency bands, the transition diameter and the dielectric constant £ _r1 , if Sq is the length of the transition 1.

In the embodiment shown, a partial length of the dielectric 3 with low dielectric constant S _r1 is covered by a thin disk 4 (foil) with

higher dielectric constant £" _r2 (£ _r2 ~2.5 to 4.7). As shown in Fig. 2, the dielectric 3 with low dielectric constant £ _r1 is removed in the end region, ie shortened by the length SS^, where S^ is the

remaining length of the dielectric 3. The thin disc 4 of the material with a high dielectric constant £ _r2 (thickness S ₀ -S^j) is applied to the reduced end area of the dielectric 3, which is considerably thinner than the removed layer of material. This measure hardly changes the compensation in the lower band if the replaced length with the dielectric constant £ _r1 electrically corresponds to the influence of the thin layer with the dielectric constant £ _r2 , since the phase amplitude change at the long wavelength remains small. In the upper band, this change has a stronger effect, so that different dielectric combinations that have almost the same effect in the lower band can be used for

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The thin layer with the dielectric constant 6 _p2 (e.g. in 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 £ _r2 =4.7) now also acts as a reflection-optimized pressure seal. The thin layer with the dielectric constant £ * can also be applied to both ends of the layer with the dielectric constant £ _r1 .

The dielectric body 3,4 is glued into the step transition. The change in the radiation pattern compared to the non-adjusted horn is small and can usually be ignored. This is a great advantage when dimensioning the grooved horn, since, for example, changes to the first grooves to improve the adjustment, especially in the upper band, have a strong effect on the radiation pattern. If an axial groove structure is selected when dimensioning the horn, the type of compensation makes it possible to build grooved horns without undercuts and complicated curves, so that production in one piece as a turned part is possible.

The horn antenna according to the invention with the specially designed |

The transition part thus serves advantageously |

for fine adjustment of the reflection factor in two separate \

frequency bands in grooved horns, which are arranged according to \

aspects of radiation pattern optimization . At the same time, the problem of reflection

the pressure seal is separated into two bands. \

\

4 sayings *)backward-turned \

2 figure ^grooves \

Claims (4)

&bull; ti j . 6 - VPA 85 P Î 1 4 9 EN ji sayings (\ 1. Horn antenna, consisting of a transition part connected to a feed waveguide of circular cross-section and a horn, the funnel-shaped widening inner wall of which is provided with grooves, for two separate frequency bands,
. characterized in that the transition part (1) widens according to a B _Q .e curve 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 (1) facing the horn (2) is provided with a length of Sq/8 to Sq/3 (S _Q = length of the transition part) Dielectric (3) low dielectric constant (<£ _r i ^ ¹ >3) is completely or partially filled, in such a way that the average electrically effective length of the dielectric (3) in the stepped transition part satisfies the condition ^. _H , j /2 above for the upper operating frequency range. 2. Arrangement according to claim 1,
characterized in 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 (£^^2.5 to 4.7) to fulfill the function of a reflection-optimized pressure seal. 3. Arrangement according to claim 2, characterized in that a thin disk (4) of higher dielectric constant is arranged on one or both sides of the dielectric (3) of lower dielectric constant. * 11 ·· ■·■·■ - 7 - VPA 85 &rgr; 11 4 9DE 4. Arrangement according to one of claims 1 to 3, characterized in that the inner contour of the transition part follows the course Kx ^n
B ₀ - ^e is divided into steps with constant small diameter jumps. ttl Il 11)1 ItII ·· till III· t ( « ·