DE8304409U1 - Broadband microwave radiator - Google Patents

Description

SIEMENS AKTIENGESELLSCHAFT Our symbols Berlin and Munich VPA

83 P 1 O 8 O DE

Broadband microwave ovens

The invention relates to a broadband microwave radiator (Primary radiator) for two polarizations to illuminate a rotationally symmetrical table parabolic reflector.

Through the "Pocket Book of High Frequency Technology" by Meinke, H.; Gundiach, F.W., 2nd edition, 1962, page 599 is ~ s For example, known, the open end of a waveguide expanded directly or funnel-shaped for radiation to use conducted microwaves in free space. An open waveguide end, however, has a high one Reflection with a strong frequency response, especially when approaching the waveguide cutoff frequency of the waveguide to be emitted Wave. Therefore, in the known horn antenna, the waveguide cross-section is continuously expanded and thereby the Reduced reflection. However, this also has the consequence that the main lobe of the radiation is significantly narrower and there is also stronger shadowing due to the enlarged horn aperture.

The main problem lies with an open, abrupt waveguide end in it, at the transition point from the open waveguide end In den'frei Raum the strongly frequency-dependent wave resistance jump existing here over a broad band adapt. While namely the wave resistance of free space

Z = V = 377 JPL

⁰ ι C ₀

is frequency-independent, the square hollow conductor has the for the adaptation decisive line impedance

February 16, 1983 / Klu 1 Kdg

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V ^ KHIO /

The surge in wave resistance is

¹ - s - K ¹ O m _z ^{Z =} ^ / A ₀ \ 2 ' V ^ KHIO /

10

The restricted range of uniqueness of the square _{waveguide often forces operating frequencies just above the H 10} limit frequency, with the above wave resistance jump increasing sharply.

The invention is based on the object of a simply constructed, very broadband microwave radiator create the two mutually perpendicular linear polarizations, each with a separate antenna output high mutual decoupling and small reflection and its open, abrupt waveguide end broadband is matched as well as possible.

This object is achieved according to the invention with a waveguide with a square or round cross section, its a floor area facing away from the parabolic reflector a metal plate is completed and to which, offset from one another in the direction of the waveguide axis and in Circumferential direction arranged at an angle of 90 ° to each other, two preferably designed as coaxial lines Leads are connected and on its inner wall near the opening (aperture), in the circumferential direction, respectively offset by 90 ° and opposite one another, cylinder made of dielectric material with small losses in pairs in the direction of the waveguide

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axis are arranged one behind the other.

Advantageous refinements and developments of the subject of the application are specified in the subclaims. 5

The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing.

Show it:

1 shows an antenna arrangement with a microwave radiator and a rotationally symmetrical parabolic reflector and

Fig. 2 is a microwave radiator in Einzelciarstel development.

In Fig. 1 is an antenna arrangement with a microwave radiator 1 (primary radiator) and a rotationally symmetrical parabolic reflector illuminated by this a flat apex plate 15 shown in the middle. The primary radiator is held by a support 13, which reaches through an opening 14 of the parabolic reflector 12. In the exemplary embodiment, the microwave radiator 1 is designed as a waveguide with a square cross-section, which is shown in Fig. 2 in detail.

The waveguide in the microwave radiator is closed with a metal plate 2 on the floor surface facing away from the parabolic reflector. The two perpendicular HQ polarizations are coupled in and out of each other with a coaxial line 3, 5, which, offset from one another in the direction of the waveguide axis, penetrate two adjacent side walls in the middle of the hollow conductor side and their extended inner conductor 4, 6 as a coaxial probe 0.3a protrudes deep into the waveguide, a is the inside length of the square base of the waveguide. The coaxial probe 4 close to the opening excites the vertically polarized H ₁₀ -WeHe with its vertical E field. Also generated

83 P 1 O 8 O DE I.

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this probe generates a longitudinal electric field, which is squared i \

Waveguide results in an E ^ interference field. The length |

L _{En of} the square waveguide section from the confluence I

of the probe 3 close to the opening up to the aperture is so |

dimensioned that its aperiodic E .. damping according to,

the requirement is sufficiently large, in particular ^{on:; :}

the critical upper band limit ^ _ο κ (Χ _ο κ) of the condition '-f.

suffices: i:

where ^ KFIi = ^a ~ f? i ^st

Special transformers with inductances L and capacitances C are housed in the coaxial arms, the length of which is approximately half the inner side length a. A short circuit is arranged at a distance of about a / 2 behind the two coaxial probes 4, 6. For the probe 4 close to the opening, this is formed by a vertical transverse plate 7 which is approximately 0.25 a wide and which practically does not interfere with the coaxial probe remote from the opening. The short circuit for the coaxial probe 6 remote from the opening is the metal plate 2, which terminates the square conductor at the rear. The distance between this metal plate 2 and the rear edge of the transverse plate 7 must be smaller than "A ^ ob ^ ² _{at the highest operating frequency f Qb} · ^When

% / Z resonance of this space, which is closed on both sides, occurs a strong break in the decoupling between the two polarizations, and the reflection at the coaxial accesses increases like a resonance.

To the coaxial feed lines compared to that in Fig. 1 To further shorten the sketched course, it is expedient to use one of the two coaxial couplings, preferably the one remote from the opening, immediately before the confluence

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angled into the waveguide by 90 ° and if necessary equal to pivot in the direction of the inclined support 13, which holds the microwave heater in his position. This enables straight, rigid coaxial feed lines to be used with the lowest possible attenuation and reflection.

For broadband adaptation of the heavily frequency-dependent Wave resistance jump at the transition point from the open Waveguide ends in the free space are in the area of the

^ O aperture parallel capacitances provided, preferably by ^ _H / 8 in front of 6 ^ r aperture in the Oaudrathohlleiter, where> ^ _{H is assigned to} a mean frequency of the frequency band. These capacities are divided into two partial capacities and consist of cylinders made of dielectric

^ Material with small losses, which on the four inner walls lie opposite one another in the middle of the inside of the waveguide and are arranged offset from one another in the direction of the waveguide axis. In the illustrated microwave radiator according to FIG. 2, the cylinders 8, 8 'are mounted on the underside, the cylinders 9, 9' on the top, the cylinders 10, 10 'on the left-hand side and the cylinders 11, 11' on the right-hand side . The distance between two partial capacities or the cylinders realizing them is chosen so that it is approximately _Hob / 4 at the upper band limit. So here both partial capacities almost cancel each other out. In contrast, at the much lower frequency f at the lower band limit and with the same geometric spacing of the partial capacitances as above, their electrical spacing is l / Λ ^ much

smaller than at the higher frequency f _b , whereby not only the frequency difference of f. according to f is decisive, but rather the significantly larger wavelength difference in the waveguide. Both partial capacitances therefore almost add up at the lower frequency f,

°° and the resulting capacity acts locally in the Middle between the partial capacities, the amount de ^ resulting Capacity decreases in the desired manner from the

»T ■

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lower frequency limit f after the upper frequency limit f _Qb sharply. Frequency response, amount and location of the resulting capacitance can be influenced in a defined manner via the distance, size and position of the individual capacities. 5

It is very important that the partial capacities are not used as metal cylinders are realized on the waveguide wall. Such "cylinders are only effective for that polarization capacitive, the E field of which is parallel to the cylinder axis.

In contrast, they have an inductive effect for the polarization perpendicular thereto, ie the effective waveguide width for this polarization is narrowed compared to the clear waveguide width. Thus, the associated Η ,,, - limit frequency in the square hollow conductor increases and moves closer to the lower band limit f _u>, which makes the adjustment very difficult here. Such difficulties are avoided in that the eight cylinders behind the aperture are made of dielectric material with low losses. The dielectric cylinders act capacitively for both polarizations. With a targeted correction of the dielectric cylinders close to the opening, the dielectric interference of a cover can also be compensated, which is preferably arranged approximately in the plane of the aperture for the weatherproof closure of the radiator. The excitation of interfering wave types απ the dielectric cylinders is suppressed in that each individual capacitance is designed symmetrically, that is to say is formed from two halves on the two opposite waveguide walls.

The double capacitance for adapting the surge in wave impedance at the transition point from the open waveguide end to the free space can also be attached to the waveguide axis. In this case, the cylinder of metal or dielectric could then be ^r tehen.

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The above explanations also apply to the round hollow conductor, but preferably to the square hollow conductor, because this has the theoretical uniqueness of the relative width ~ f2 * compared to only 1.3 for round hollow conductors.

The inventive measures for adapting the wave resistance jump at the transition point from the open Waveguide ends in the free space are a matter of course Can also be used for waveguides whose aperture, deviating from the exactly abrupt end, has a funnel-shaped attachment, for example.

11 claims

2 figures

Claims (11)

- 8 - VPA63 P 1 O 8 O OE claims 1. Broadband microwave radiator (primary radiator) for two polarizations to illuminate a rotationally symmetrical parabolic reflector, characterized by a waveguide (1) of square or round cross-section, one of which is the bottom surface facing away from the parabolic reflector (12) is closed with a metal plate (2) and on which, offset from one another in the direction of the waveguide axis and arranged in the circumferential direction at an angle of 90 to one another , two feed lines (3, 5), preferably designed as coaxial lines, are connected, and cylinders (8-8 \ 9 -9 ¹ , 10-10 ', 11-11') made of dielectric material with small losses are arranged in pairs in the direction of the waveguide axis one behind the other. 2. microwave radiator according to claim 1, characterized in that the distance between two in the direction of the Höh 1leiterl £ ngsachse one behind the other arranged dielectric cylinder (8-8 ', 9-9', 10-10 ', 11-11') is chosen so that it is on the upper band limit approximated ,,. / 4 is (Λ ,, u MOD ³ Hob is the waveguide wavelength of the wave to be transmitted highest frequency). 3. Microwave radiator according to claim 1 or 2 with a waveguide of square cross-section, characterized in that the feed lines (3, 5) are each connected in the middle of two adjacent side walls and the dielectric cylinders (8-8 ¹ , 9-9 ', 10 -10 ', 11-1Γ) - 9 - VPA 83 P t 08 0 DE in the middle of the four side walls and on opposite sides Inner walls are arranged symmetrically to one another. 4. microwave radiator according to claim 1, characterized in that the double capacity is an alternative to the eight cylinders (8 to 11 ') of two arranged on the waveguide axis and against one another in the direction of the longitudinal axis of the waveguide offset, dielectric or metallic discs is formed. 5. Microwave radiator according to claim 3 or 4, d a d u rc h indicates that that when the supply lines (3, 5) are designed as coaxial lines, their inner conductors (4, 6) are lengthened and approximately o, 3a protrude deep into the waveguide (1) (a is the inside length of the square green area of the waveguide ). 6. A microwave radiator according to claim 5, characterized in that the elongated inner conductor (4) (coaxial probe) of the coaxial line (3) close to the opening _{is arranged at such a distance (Lc n} ) from the aperture that the aperiodic E ₁ . -Interference field in this height 1 conductor section at the upper band limit (3 _ο κ) the following relationship is sufficient: > _ ^{22t L} En η / 1 - (üili—) ² [Np] ^a apE11 -j [If SL. ^y KE11 ^Ob with ^ - _KE11 = a 7. microwave radiator according to claim 6, characterized in that dai3 at a distance of about half an inner side length (a / 2) of the waveguide behind the Koaxia 1 probes (4,6) each one - ίο - VPA 83 P 1 08 0 OE Short circuit is appropriate. 8. microwave radiator according to claim 7, characterized, that the short circuit for the coaxial probe (4) close to the opening is formed by a perpendicularly arranged transverse plate (7) which is about a quarter of the inside surface of the Waveguide is wide. to 9. microwave radiator according to claim 7, characterized, that the short circuit for the coaxial probe (6) remote from the opening is formed by the metal plate (2) which closes off the waveguide (1) on one side. 10. Microwave radiator according to one of claims 7 to 9, characterized, da3 the distance between the metal plate (2) and the rear edge of the transverse plate (7) for the highest operating frequency f _{Qb is} less than half the waveguide wavelength T ^ _Ho κ of the highest frequency wave to be transmitted. 11. Microwave radiator according to one of claims 5 to 10, characterized in that special transformation elements are arranged in the coaxial line sections (3, 5) with a length of approximately half the inner side length (a / 2) of the waveguide.