EP0154858A2 - Antenna - Google Patents

Abstract

The invention relates to a microwave antenna (1) which is fitted with flat metallic radiating elements (2, 3), arranged on a dielectric substrate (4), which substrate (4) is applied onto a metallic baseplate (5). The microwave antenna (1) has a simple structural design and a high level of efficiency. The radiating elements (2 and 3) are arranged so closely together that the coupling of the radiating elements (2 and 3) is produced by electromagnetic scatter fields. <IMAGE>

Description

The invention relates to a microwave antenna according to the preamble of claim 1.

From the publication "IEE PROC. Vol 127, Pt. H. No 4, August 1980, Improved_bandwidth of mierostrip antennas using parasitic elements, C. Wood. B. Sc, pages 231 to 234." a microwave antenna is known which has a plurality of flat radiating elements. The radiator elements are arranged on the surface of a dielectric substrate applied to a metallic base plate. The outer radiator elements are connected on one side to the metallic base plate via a short circuit. The antenna is fed in via a coaxial feed line, the inner conductor of which is connected to the central radiation element and the outer conductor is connected to the base plate. To achieve certain required half-value widths in the radiation characteristic, this antenna cannot be interconnected to form larger antenna groups without further feed lines. In addition, the creation of the short circuits is technically complex.

• - ohmsche und dielektrische Verluste im Speiseleitungsnetzwerk den Antennenwirkungsgrad verringern,
• - die unerwünschte Abstrahlung, insbesondere an Leitungsknicken und Verzweigungsstellen des Speisenetzwerkes ebenfalls den Antennenwirkungsgrad vermindert sowie die Strahlungscharakteristik durch Neben- und Kreuzpolarisations-Strahlung stört,_und
• - durch Strahlungskopplung zwischen dem Speiseleitungsnetzwerk und den-Strahlerelementen ebenfalls die Strahlungscharakteristik nachteilig beeinflußt wird.

From the publication "IEEE Transactions on Antennas and Propagation, Vol. AP-31, No. 1, January 1983, A Modular Approach for the design of microstrip array antennas, J. Ashkenazy, P. Perlmutter, and David Treves, Fellow IEEE, pages 190 to 193 ", another microwave antenna arrangement is known, the radiator elements of which are combined into a group radiator via a special feed line network These and similar known arrangements have the disadvantages that

• ohmic and dielectric losses in the feed line network reduce the antenna efficiency,
• - The unwanted radiation, especially at line bends and branching points of the feed network also reduces the antenna efficiency and interferes with the radiation characteristics due to secondary and cross-polarization radiation, _and
• - The radiation characteristic is also adversely affected by radiation coupling between the feed line network and the radiator elements.

The invention is therefore based on the object of providing an antenna using planar technology for the microwave range in which the required half-value widths in the radiation characteristic can be achieved with little design effort, while achieving a wide bandwidth, high efficiency, low secondary peaks and low cross polarization .

-This object is achieved according to the invention by the characterizing features of patent claim 1.

The radiator elements of the antenna arrangement are so narrow arranged adjacent that their coupling is done by electromagnetic stray fields. The invention thus differs fundamentally from the known microwave group antennas in that a special feed line network is omitted in the grouping of the radiator elements and the above-mentioned disadvantages are thus avoided.

Further inventive features are characterized in the subclaims.

• Figur 1: den schematischen Aufbau einer Mikrowellenantenne gemäß der Erfindung;
• Figur 2: einen Vertikalschnitt durch die in Figur 1 dargestellte Antenne,
• Figur 3: die Ankopplung einer Koaxialen Speiseleitung,
• Figur 4: die Ankopplung einer koaxialen Speiseleitung an zwei zentrale Strahlerelemente,
• Figur 5: die Ankopplung an eine Streifenleitung zwischen zwei Strahlerelementen,
• Figur 6: die Ankopplung einer Speiseleitung an eine mit einem zentralen Strahlerelement verbundene Streifenleitung,
• Figur 7: die Ankopplung der Speiseleitung an eine Schlitzleitung.
• Figur 8: ein Diagramm mit Meßdaten der Mikrowellenantenne.

The invention is explained in more detail below with reference to drawings; show it:

• Figure 1: the schematic structure of a microwave antenna according to the invention;
• FIG. 2: a vertical section through the antenna shown in FIG. 1,
• FIG. 3: the coupling of a coaxial feed line,
• FIG. 4: the coupling of a coaxial feed line to two central radiator elements,
• FIG. 5: the coupling to a strip line between two radiator elements,
• FIG. 6: the coupling of a feed line to a strip line connected to a central radiator element,
• Figure 7: the coupling of the feed line to a slot line.
• Figure 8: a diagram with measurement data of the microwave antenna.

αg ist die Leitungswellenlänge der Mikrostreifenleitung mit der Breite w auf dem Substrat mit der Dicke h und der Dielektrizitätszahl ε_τ. A ist die äquivalente Leitungslänge zur Berücksichtigung des Endeffektes dieser Leitung. In dem hier dargestellen Ausführungsbeispiel erfolgt die Verkopplung der Strahlerelemente 2 und 3 bzw. der durch sie gebildeten Resonatoren durch elektromagnetische Streufelder. Bei dieser Verkopplung der Resonatoren treten abhängig von der Anzahl der Strahlerelemente 2 und 3 und den Kopplungsabständen zusätzliche Schaltungskapazitäten auf, die durch eine weitere Verkürzung der Längen 1, der Strahlerelemente 2 und 3 bzw. der Resonatoren kompensiert werden können. Bei dem in Figur ] dargestellten Ausführungsbeispiel sind auf der Substratoberfläche insgesamt 15 Strahlerelemente 2 und 3 angeordnet. Die Strahlerelemente sind so positioniert, daß in X-Richtung jeweils drei Strahlerelemente hintereinander, eine Reihe bildend, positioniert sind. Sie weisen, in X-Richtung gesehen, jeweils einen senkrechten Abstand sx voneinander auf. In Y-Richtung gesehen sind fünf solcher Strahlerelemente ebenfalls hintereinander, eine Reihe bildend, angeordnet. Der senkrechte Abstand zwischen zwei aufeinanderfolgenden Strahlerelementen ist, in Y-Richtung gesehen, immer gleich groß und mit sy bezeichnet. Das in der Mitte der Mikrowellenantenne 1 angeordnete Strahlerelement 2 besitzt in X-Richtung zu den benachbarten Strahlerelementen 3 hin einen etwas kleiner bemessenen Abstand sx₁, da seine Länge 1 geringfügig größer ist als die der Strahlerelemente 3. Die Abstände sx,sxi und s^y weisen Werte auf, die im Bereich zwischen 0,1 bis 1 multipliziert mit der Dicke h des Substrates 4 liegen. Durch diese Maßnahmen wird erreicht, daß zwischen allen Strahlerelementen 2 und 3 eine Verkopplung durch elektromagnetische Streufelder erzielt werden kann. Bei dem hier dargestellten Ausführungsbeispiel treten abhängig von der Anzahl der Strahlerelemente 2 und 3 und den Kopplungsabständen, insbesondere den Abständen sx,sx₁ und sy zwischen den Strahlerelementen 2 und 3 in X- und Y-Richtung zusätzliche Sehaltungskapazitäten auf, die durch eine weitere Verkürzung der Gesamtlänge 1 der Strahlerelemente kompensiert werden können. Durch den engen Abstand zwischen den Strahlerelementen 2 und 3 wird eine gegenseitige Verkopplung durch elektromagnetische Streufelder der jeweils in der TM_n00-Resonanz schwingenden Resonatoren erzielt. Entspeehend der Verteilung der elektromagnetischen Felder in der TM_n00-Resonanz sind die elektrischen Wechselfelder an den im Abstand 1 . parallel zueinander laufenden Enden eines Resonators maximal.Figure 1 shows a microwave antenna 1, which is constructed from a plurality of radiator elements 2 and 3. The radiator elements 2 and 3 are made of a metallic material and are flat. They are arranged on the surface of a dielectric substrate 4, which is applied to a metallic base plate 5. The radiator elements 2 and 3 are designed as rectangular surfaces with essentially the same dimensions. The radiator elements 2 differ from the radiator elements 3 in that, on the one hand, they serve as central radiator elements and, on the other hand, their dimensions are slightly larger under certain conditions. For a better understanding of the antenna shown in FIG. 1, in particular its structure and mode of operation, a right-angled coordinate system X, Y and Z is arranged in FIG. The length of the radiator elements 2 and 3 extends in the X direction. Their length is labeled 1. The width of the radiator elements 2 and 3 extends in the Y direction. Their width is denoted by w. In the Z direction, the radiator elements 2 and 3 have only a slight extension of a few μm. The Z direction is perpendicular to the surface of the metallic base plate 5. The dimensions of the radiator elements, in particular their lengths 1 and their widths w, are dimensioned according to known approximate relationships from microwave stripline technology. This ensures that in the desired operating frequency range of the microwave antenna in the resonators, through the radiator elements 2 and 3, the substrate 4 and the base plate 5 are formed, TM _{n00 natural} vibrations with an odd atomic number n become oscillatory. The ordinal number n should preferably assume the values 1 or 3. The length 1 of a single uncoupled resonator results from the equation:

αg is the line wavelength of the microstrip line with the width w on the substrate with the thickness h and the dielectric constant ε _τ . A is the equivalent line length to take into account the end effect of this line. In the exemplary embodiment shown here, the radiator elements 2 and 3 or the resonators formed by them are coupled by electromagnetic stray fields. In this coupling of the resonators, depending on the number of radiator elements 2 and 3 and the coupling distances, additional circuit capacities occur, which can be compensated for by a further shortening of lengths 1, radiator elements 2 and 3 or the resonators. In the embodiment shown in FIG. 15, a total of 15 radiator elements 2 and 3 are arranged on the substrate surface. The radiator elements are positioned such that three radiator elements are positioned one behind the other in the X direction, forming a row. Viewed in the X direction, they are each at a vertical distance sx from one another. Viewed in the Y direction, five such radiator elements are also arranged one behind the other, forming a row. The vertical distance between two successive radiator elements, seen in the Y direction, is always the same size and is labeled sy. The radiator arranged in the middle of the microwave antenna 1 element 2 has a somewhat smaller distance sx ₁ in the X direction to the adjacent radiator elements ₃ , since its length 1 is slightly greater than that of the radiator elements 3. The spacings sx, sxi and s ^y have values in the range between 0.1 to 1 multiplied by the thickness h of the substrate 4. These measures ensure that coupling by electromagnetic stray fields can be achieved between all radiator elements 2 and 3. In the exemplary embodiment shown here, depending on the number of radiator elements 2 and 3 and the coupling distances, in particular the distances sx, sx ₁ and sy, additional viewing capacities occur in the X and Y directions between the radiator elements 2 and 3, which are further shortened the total length 1 of the radiator elements can be compensated. Due to the close spacing between the radiator elements 2 and 3, mutual coupling by electromagnetic stray _{fields of the} resonators that oscillate in the TM _n00 resonance is achieved. Corresponding to the distribution of the electromagnetic fields in the TM _n00 resonance, the alternating electrical fields are at a distance of 1. Maximum parallel ends of a resonator.

The radiator elements 2 and 3 used here can be made of copper, gold, aluminum or brass. The same applies to the base plate 5 serving as substrate support. The substrate 4 used in this embodiment consists of polytetrafluoroethylene and has a dielectric constant ε _τ = 2.23. Instead of this dielectric substrate 4, others can also be used whose dielectric numbers are preferably in the range between 1 and 10. The thickness of the on the Base plate applied dielectric substrate 4 should be between 0.2 and 3 mm. The thickness h of the substrate 4 applied here is 1.57 mm. The base plate 5 has a dimension of 30 x 30 mm2. To produce the microwave antenna, a metallic layer is first applied to the surface of the substrate 4. With the help of a known photo-etching process, the radiator elements 2 and 3 are worked out from this metal surface, so that only the. Radiator elements 2 and 3 are arranged on the substrate surface 4. In the embodiment shown here, the radiator elements 3 all have a width of w = 4 mm and a length 1 of 8 mm. Only the central radiator element 2 has a length 1, which is 8.8 mm. The width of the central radiator element 2 is also 4 mm. All radiator elements 3 have a vertical distance from their neighboring radiator elements 3 of sx = 0.5 mm in the X direction. The radiator elements 3, viewed in the Y direction, have a vertical distance sy = 0.5 mm from their nearest neighboring radiator elements 3. Only the central radiator element 2, viewed in the X direction, has a vertical distance sx _{l =} 0.1 mm from the adjacent radiator elements 3 on. Viewed in the Y direction, like the emitter elements 3, it has a vertical distance sy = 0.5 mm from the emitter elements 3. The microwave antenna 1 is fed via a coaxial feed line (not shown here). It is connected on the one hand to the coupling point of the central radiator element 2 and on the other hand to the metallic base plate 5. A detailed illustration of this coupling is shown in FIG. 3. The description of this figure follows below. The coupling point (not shown here) of the central one Radiator element 2 lies on the longitudinal axis of the radiator element 2, which runs parallel to the X axis. In particular, the coupling point is arranged so that it is arranged at a distance of 1 mm from the end face of the radiator element 2, which runs parallel to the Y axis.

The following electrical antenna data, which are shown graphically in FIG. 8, were determined for the microwave antenna 1 shown in FIG. 1 on a reflection-free antenna measuring station.

The diagram shows the measured frequency response of the reflection factor | r (f) | at the input of the 50 ohm line socket for the connection of the coaxial feed line (not shown here) and the change a _G (f) of the antenna gain with the frequency in the range f = 7.6 to 9.4 GHz. This resulted in | r | min and in the range of a _{Gmax determines} the resonance frequency f _{r of} the group _antenna . Furthermore, the frequency range in which | r (f) | ≤ -9.5 dB, the bandwidth Δf s≤2 '| r | ≤ -9.5 dB corresponds to | r | ≤0.33 and is synonymous with a ripple s ≤ 2 on the feed line, so in this frequency range the mismatch losses would be less than 0.5 dB or, in the case of transmission, less than 11% of the transmission power supplied to the antenna. Furthermore, directional diagrams of the radiation characteristic would be a _E (θ, φ = 0 °) in the E plane and a _H (θ, φ = 90 °) in the H plane in the range -180 ° ≤ θ ≤ + 180 °. From this, the half-value widths Δθ _E and Δθ _H (3 dB widths) as well as the secondary zip field attenuation a _{N were} determined. From the directional diagram a _H (θ, φ = 90 °), the radiation gain D of the group antenna at frequency f _{r was} determined by graphic integration.

In the diagram there is also the cross polarization a _Kp (θ, φ = 45 °), the antenna gain G at the frequency f _r and, based on the relationship G = η-D, the antenna efficiency η, and the antenna impedance Z _A - at the frequency f _r , measured at the input of the 50Ω coaxial socket.

Figur 2 zeigt einen Vertikalschnitt durch die in Figur 1 dargestellte Antenne parallel zur X-Z-Ebene des in Figur 1 dargestellten rechtwinkligen Koordinatensystems. Wie anhand von Figur 2 zu sehen ist., wird durch die TM_n00-Feldverteilung mit einer ungeradzahligen Ordnungszahl n bewirkt, daß die jeweils zu einem Resonator gehörenden elektrischen Wechselfelder an den Resonatorenden gegenphasig schwingen, so daß die verkoppelten Streufelder wie auch die Streufelder an den äußeren Resonatorenden alle gleichphasig sind und somit ihre Überlagerung eine gebündelte Strahlungscharakteristik mit einer Hauptstrahlrichtung in Richtung der Z-Achse ergibt. Bei dem in den Figuren 1 und 2 dargestellten Ausführungsbeispiel ist die Strahlungscharakteristik linear polarisierte und zwar in X-Richtung bezogen auf die Hauptstrahlrichtung in Richtung der Z-Achse. Werden in einem Sonderfall (hier nicht dargestellt) alle Strahlerelemente 2 und 3 quadratisch ausgebildet, so daß ihre Länge gleich ihrer Breite und damit w = 1 ist, so kann die zur TM_n00-Sehwingung orthogonale TMo_nO-Schwingung mit der selben Resonanzfrequenz angeregt werden. Hierdurch kann bei geeigneter Abstimmung beider Schwingungen auf Amplitudengleichheit und 900 Phasendifferenz ein zirkular polarisiertes Strahlungsfeld realisiert werden, dessen Hauptstrahlungsrichtung wiederum in Richtung der Z-Achse ausgerichtet ist.The antenna data determined in this way are:

Figure 2 shows a vertical section through the antenna shown in Figure 1 parallel to the XZ plane of the rectangular coordinate system shown in Figure 1. As can be seen from FIG. 2, the TM _{n00 field} distribution with an odd atomic number n causes the alternating electrical fields associated with a resonator to oscillate in phase opposition at the resonator ends, so that the coupled stray fields as well as the stray fields on the outer resonator ends are all in phase and thus their superimposition results in a bundled radiation characteristic with a main beam direction in the direction of the Z axis. In the exemplary embodiment shown in FIGS. 1 and 2, the radiation characteristic is linearly polarized, specifically in the X direction with respect to the main beam direction in the direction of the Z axis. In a special case (not shown here) all Radiator elements 2 and 3 are square, so that their length is equal to their width and thus w = 1, so the _TMo nO oscillation orthogonal to the TM _n00 oscillation can _be excited with the same resonance frequency. In this way, a circularly polarized radiation field can be realized with suitable matching of the two vibrations to the same amplitude and 900 phase difference, the main radiation direction of which is in turn oriented in the direction of the Z axis.

When dimensioning the microwave antenna 1, it should be noted that the shape of the radiation characteristic, in particular the half-value width and the side lobe spacing and thus also the radiation gain from the number of the rows and columns of the microwave antenna elements 2 and 3, the lengths 1 of the radiator elements 2 and 3 and the distances sx, sxi and s ^{y of} the radiator elements 2 and 3 in the X and Y directions. A higher radiation gain, ie a higher directivity or small half-widths, can be achieved by using many radiator elements 2 and 3 and primarily by selecting the antenna parameters ε _τ , h and w such that the length 1 is approximately half the free field wavelength ; Lo corresponds. This preferably applies to the dielectric numbers of the substrate 4 in the range from ε _τ = 1 to 10 and widths w of the radiator elements 2 and 3 from 0.1 to 0.4λ _o , the ordinal numbers n = 1 or 3 being chosen. The side lobe distance can be influenced by the amplitude assignment of the individual radiation sources, ie in this case by changing the widths of the coupling gaps, in particular by changing the values sx, sx ₁ and sy. The bandwidth and the efficiency of the microwave antenna is essentially due to the Dielectric constant ε _τ and the thickness h of the substrate 4 used on the base plate 5 are determined. Optimal values can be achieved here if ε _{τ can be selected} as close as possible to 1 and h in the range around 0.05; t _o .

FIG. 3 shows a vertical section through the antenna 1 shown in FIG. 1 in the area of the central radiator element 2. As can be seen from the drawing, the coupling point 11 of the central radiator element 2 is connected to the inner conductor 12I of the coaxial feed line 12. The outer conductor 12A of the feed line 12 is in electrically conductive connection with the base plate 5.

FIG. 4 also shows a cross section through an antenna 1 according to the invention, which is equipped with two central radiating elements 2. The two central radiator elements 2 are adjacent, in particular arranged next to one another at a defined distance. They are also connected to further radiator elements 3 at a defined distance. All radiator elements 2 and 3 are arranged on a dielectric substrate 4, which is applied to the metallic base plate 5. According to the invention, the inner conductor 12I of the feed line 12, which is connected to the antenna 1, is connected to the first central radiator element 2, while the outer conductor 12A of the feed line 12 is connected to the second central radiator element 2.

ausgebildet.Figure S shows the coupling of the feed line (not shown here) to two central radiator elements 2 which are electrically conductively connected to one another. This feed is preferably used when a Microwave antenna 1 has a large number of radiator elements 3. As can be seen from FIG. 5, the two central emitter elements are arranged opposite one another at a defined distance. They are each provided with a resistance transformation element 21 at their two opposite ends. These resistance transformation elements 21 are electrically connected to one another via a strip line 22. The strip line 22 has an infeed point 23. The inner conductor of the feed line supplying the microwave antenna is connected to it, while the outer conductor of this feed line (not shown here) is connected to the metallic base plate of the microwave antenna. The strip line 22 is as

educated.

FIG. 6 shows a further possibility of coupling the feed line (not shown here) to the central radiating element 2 of a microwave antenna, which is not shown here. The first end of the central radiator element 2 is connected to a relatively high-resistance strip line 22, which is connected to a 50 ohm strip line 24 via a resistance transformation element 21. The inner conductor of the feed line (not shown here) is connected to the strip line 24, while the outer conductor of the feed line (also not shown here) is to be connected to the metallic base plate 5 of the microwave antenna 1.

FIG. 7 shows a section of a microwave antenna 1 according to the invention which has a metallic base plate 5 on which a dielectric substrate 4 is applied. The section shows the area of the microwave antenna 1 in which the two central radiator elements 2 are arranged. The two radiator elements 2 are arranged adjacent to one another at a defined distance. The feed line (not shown here) which is provided for supplying the antenna 1 is connected to a slot line 30 in the exemplary embodiment shown here. The first half 30A of the slot line 30 is connected to the first central radiator element 2, while the second half of the slot line 30 is connected to the second radiator element 2. In this exemplary embodiment, the inner conductor of the feed line (not shown here) is connected to the first half of the slot line 30, while the outer conductor is connected to the second half 30B of the slot line 30. As can be seen from FIG. 7, the metallic base plate 5 has been removed in the region of the slot line 30, so that only the dielectric substrate 4 serves as a carrier for the slot line 30.

Claims (10)

1. Microwave antenna (1) with a plurality of flat metallic emitter elements (2, 3) which are arranged on a dielectric substrate (4) which is applied to a metallic base plate (5), characterized in that at least one central emitter element (2) is provided by a large number of other radiator elements (3) is surrounded, which are arranged at closely defined distances (sx, sx ₁ , sy) from the central radiator element (2) and from one another in such a way that the coupling of all radiator elements (2, 3) takes place by means of electromagnetic stray fields . 2. Microwave antenna according to claim 1, characterized in that for feeding the antenna, the central radiating element (2) to the inner conductor (12I) and the metallic base plate (5) to the outer conductor (12A) of a coaxial feed line (12) is connected. 3. Microwave antenna according to claim 1, characterized in that for feeding a first central radiating element (2) to the inner conductor (12I) and a second central radiating element (2) to the outer conductor (12A) of a coaxial feed line (12) is connected. 4. Microwave antenna according to claim 1, characterized in that at a very large number of radiator elements (3) at least two central radiator elements (2) are provided, the opposite ends of which have resistance transformation elements (21) which have a λ _g / 2 line trained stripes line (22) are electrically connected to each other, and that the inner conductor (12I) of a feed line (12) with the connection point (23) of the strip line (22) and the outer conductor (12A) of the feed line (12) to the metallic base plate (5) connected. 5. Microwave antenna according to claim 1, characterized in that with a smaller number of radiator elements (3), the central radiator element (2) via a relatively high-resistance strip line (22), a resistance transformation element (21) and a 50-0hm strip line (24) a feed line (12) is connected to the inner conductor (12I), while the outer conductor (12A) of the feed line (12) is connected to the metallic base plate (5). 6. Microwave antenna according to claim 1, characterized in that the first half (30A) of a slot line (30) with a first central radiating element (2) and the second half (30B) of the slot line (30) to a second adjacent central radiating element (2 ) is connected `that the inner conductor (12I) of a feed line (12) is connected to the first half (30A) and the outer conductor (12A) to the second half (30B) of the slot line (30), and that in the area of the slot line (30) the metallic base plate (5) is removed under the dielectric substrate (4). 7. Microwave antenna according to one of claims 1 to 5, characterized in that a plurality of radiating elements arranged at defined intervals (sx) one behind the other, forming a row, and several such rows at defined intervals (sy) perpendicular to one another are positioned on the dielectric substrate (4) and that at least one central radiating element (2) is arranged in the middle of a centrally positioned row of radiating elements (3). 8. Microwave antenna according to claim 1 to 6, characterized in that all radiator elements (2, 3) have substantially the same length (1) and the same width (w) and are preferably designed as rectangular surfaces, and that all radiator elements (2 , 3) have a thickness of 5 to 50 microns. 9. Microwave antenna according to one of claims 1 to 7, characterized in that the metallic base plate (5) and the radiator elements (2,3) are made of copper, gold, aluminum or brass. 10. Microwave antenna according to one of claims 1 to 8, characterized in that a dielectric substrate (4) is applied to the metallic base plate (5), which has a dielectric constant ε _τ preferably in the range 1 to 10 and in a thickness of 0, 2 to 3 mm is applied to the base plate (5).

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