EP2485329B1 - Array antenna - Google Patents

Description

The invention relates to a group antenna with a WAIM layer for impedance matching for large tilt angles according to the preamble of claim 1.

An often observed phenomenon in the transmission behavior of a group antenna during the electronic pivoting of the main beam is the difference in transmittance, depending on the direction in which the antenna is pivoted. Usually, an antenna has a defined polarization orientation, eg vertical or horizontal polarization. In order to explain the said phenomenon, it is sufficient, in the thought, the main ray of such a group antenna along this
both levels (vertical & horizontal) to pivot electronically. If the vector of the radiated electric field strength forms within the pivoting plane, defined from the pivoting direction and antenna normal, one speaks of the transverse magnetic polarization (TM). If the vector of the electric field strength is perpendicular to this plane, the designation is transversely electric (TE). All sorts of other polarization states can be in these two
Disassemble polarization components. In principle, conventional array antennas (as well as other related structures such as dielectric or frequency-selective radomes) tend to form a worse transmittance with increasing tilt angle in TE than in TM.

A so-called WAIM layer (WAIM: Wide Angle Impedance Match), which is arranged in front of the radiator elements, can counteract this effect. With reference to the two polarization cases TE and TM, the WAIM layer, in analogy to a replacement line model of the antenna, functions like a parallel-connected capacitance whose relative susceptance (relative to the characteristic impedance) changes with the swivel angle θ. In the case of the TE polarization, this change is with the factor 1 / cos (θ), but in the case of the TM polarization with the factor cos (θ), provided the dielectric constant of the WAIM layer is sufficiently high and the thickness the WAIM layer is sufficiently low. The described reciprocity of the factors now leads, with a suitable design of the WAIM layer, to the fact that the transmittance of the antenna when swinging between TE and TM polarization align with each other. This applies to all possible tilt angles within a technically meaningful range of, for example, θ = 0 ° to θ = 60 °. This matching then results in the usually desired broad single emitter diagrams of emitter elements of a group antenna in all important cutting planes.

The solutions used so far are essentially based on the theoretical elaborations of Magill & Wheeler, ( E. Magill and H. Wheeler, "Wide-angle impedance matching of a planar array antenna by a dielectric sheet," IEEE Transactions on Antennas and Propagation, Vol. 14, No. 1, pp. 49-53, 1966 ). A WAIM layer only serves the purpose of transmission compensation between TE and TM polarization if it maintains a small but well-defined distance to the antenna elements of the array antenna.

• Hygroskopie: Viele Schäume neigen dazu, mit der Zeit Feuchtigkeit aus der Umgebung aufzunehmen, was zu einer starken Veränderung der dielektrischen Eigenschaften führt. Aufwändige Maßnahmen zur Kapselung der SchaumSchicht sind die Folge.
• Toleranzen: Die Herstellung von Schaumschichten mit wenigen Millimetern Dicke ist nur in einem moderaten Toleranzbereich möglich.
• Verklebung: Für die WAIM-Schicht prinzipiell geeignete Standardmaterialien (kommerziell erhältliche HF-Leiterplattenmaterialien mit hoher dielektrischer Konstante, z.B. Rogers RT/duroid 6010, enthalten Teflon, welches im Sinne einer haltbaren und zuverlässigen Verklebung mit dem Schaummaterial ein Problem darstellt. Zwar ist es prinzipiell technisch möglich, solche Verklebungen durchzuführen, jedoch nur mit aufwändigen Maßnahmen wie PlasmaAktivierung der teflonhaltigen WAIM-Bestandteile.

The standard solution for creating the necessary spatial separation is the use of RF foam materials, eg US 7,580,003 B1 , While the availability of such foams is not a problem, there are a number of disadvantages to using such foams:

• Hygroscopy: Many foams tend to absorb moisture from the environment over time, resulting in a large change in dielectric properties. Elaborate measures to encapsulate the foam layer are the result.
• Tolerances: The production of foam layers with a thickness of only a few millimeters is only possible within a moderate tolerance range.
• Bonding: Basically suitable standard materials for the WAIM coating (commercially available HF printed circuit board materials with a high dielectric constant, eg Rogers RT / duroid 6010, contain Teflon, which is a problem in terms of a durable and reliable bonding with the foam material technically possible to perform such bonds, but only with complex measures such as plasma activation of the teflon-containing WAIM components.

The US 3,605,098 A describes a group antenna in which there is a separate WAIM element in front of each radiator element. Such a WAIM element comprises in each case a WAIM layer parallel to the plane of the radiator elements and spacers on which the WAIM layer is arranged.

In MCGRATH DT: Accelerated periodic hybrid finite element method analysis for integrated array element and radome design, PHASED ARRAY SYSTEMS AND TECHNOLOGY, 2000. PROCEEDINGS 2000 IEEE INTERNATIONAL CONFERENCE ON DANA POINT, CA, USA 21 -25 MAY 2000, PISCATAWAY, NJ, USA, IEEE, US, May 21, 2000 (2000-05-21), pages 319-322, XP010504600, DOI: DOI: 10.1109 / PAST.2000.858965, ISBN: 978-0-7803-6345-8 a group antenna is described with waveguide radiating elements, wherein the waveguide radiator elements have dielectric filling elements to change the radiation properties of the antenna targeted. The dielectric filling elements project out of the antenna. On top of these overhanging dielectric filling elements, a WAIM layer is arranged.

The JP 2007013311 A describes an arrangement of a plurality of individual antennas arranged in a fixed grid, whose radiations are each decoupled from one another. The individual antennas are covered by a radome, which has spacers in relation to an antenna base plate in a corresponding grid.

The object of the invention is to provide a group antenna with WAIM layer, which avoids the disadvantages occurring in the use of foams as an intermediate layer between radiator elements and WAIM layer disadvantages.

This object is achieved with the subject matter of patent claim 1. Advantageous embodiments are the subject of further claims.

According to the invention spacers are machined in a regular pattern from the material of the WAIM layer. Spacer and WAIM layer are therefore integrally connected to each other (monolithic), wherein the grid of the spacers corresponds to the grid of the radiator elements. and the spacers are disposed in the spaces between the individual radiating elements. The grid may e.g. square, rectangular or hexagonal. The spacers may in particular be of columnar design with a round cross section. The attachment of the WAIM layer to the antenna baseplate advantageously takes place on the spacers by mechanical connection means (e.g., screws), the numbers of which spacers on which a connection means is present depend on the specific requirements. In particular, therefore, a connecting means does not have to be present on each spacer.

According to the invention thus takes the place of the known multi-layer structure (WAIM layer - adhesive film - foam), which comprises different materials, only the material of the WAIM layer, in which the spacers already are integrated. The spacers realize an air- or vacuum-filled separator between the WAIM layer and the antenna elements. The disadvantages described in connection with the previously used foams are completely avoided. Furthermore, expensive adhesive processes for connecting the WAIM layer with a foam separator are eliminated.

The spacers give the WAIM layer the required mechanical stability. It is therefore insensitive to vibration, shock, etc., making it suitable for robust application scenarios.

Since the grid in which the spacers are arranged corresponds to the grid of the radiator elements, the natural periodicity of the array antenna is not disturbed, so that within the frequency range for which the array antenna is designed, no Bragg reflections can occur on the antenna surface. There is no loss in Radarrückstreuquerschnitt be accepted. If there are no increased requirements for the radar backscatter cross section (RCS), embodiments are alternatively possible in which the grid of the spacers and the grid of the radiator elements do not correspond. However, this changed grid must continue to be based on the grid of the radiator elements. For this purpose, the grid of the spacers is derived from the grid of the radiator elements such that only a corresponding spacer is present for every nth radiator element (and, moreover, no further spacers are present). It is therefore a defined thinning of the original grid of the spacers. In other words: the basic grid structure is retained, but the grid dimension (grid constant) changes by the factor n. N is a natural number greater than 1.

The described shape of the WAIM layer can be achieved in particular by mechanical processing techniques, such as milling. According to its function as a WAIM layer, the material should have the highest possible dielectric constant and a low loss angle, and its layer thickness should be as low as possible. Such dielectric materials are commercially available as semi-finished products.

A suitable material for the WAIM layer is e.g. the dielectric material (semi-finished product) "C-Stock AK" of the company. Cuming Microwave Corporation, which is available with customized dielectric constant and in different semi-finished sizes. Such materials can be readily processed by mechanical means (e.g., milling).

For further mechanical stabilization, additional stiffening structures in the form of ribs can be formed out of the material of the WAIM layer. So that these have no negative effects on the transmittance of the antenna during electronic panning, these structures must also follow the periodicity in the arrangement of the antenna elements. The ribs are formed so that they each connect two adjacent spacers.

The WAIM layer does not necessarily have to be flat. It may also have a one-dimensional or two-dimensionally curved surface, for use in structurally-conforming curved array antennas.

The WAIM layer can be expanded to a multi-layer WAIM block by connecting to further dielectric layers.

Fig. 1

eine erfindungsgemäße WAIM-Schicht in 3D-Darstellung mit periodisch angeordneten Abstandshaltern;

Fig. 2

eine erfindungsgemäße Gruppenantenne in Querschnittsdarstellung:

1. a) ohne Darstellung der Befestigungsmittel für die WAIM-Schicht;
2. b) mit Befestigung der WAIM-Schicht von hinten;
3. c) mit Befestigung der WAIM-Schicht von vorne;

Fig. 3

eine erfindungsgemäße Gruppenantenne sowie die zugehörige WAIM-Schicht jeweils in Draufsicht:

1. a) Antennengrundplatte ohne WAIM-Schicht,
2. b) mit davor angeordneter WAIM-Schicht (letzere transparent dargestellt),
3. c) WAIM-Schicht allein.

Concrete embodiments of the invention are explained in more detail below with reference to figures. Show it:

Fig. 1

a WAIM layer according to the invention in 3D representation with periodically arranged spacers;

Fig. 2

a group antenna according to the invention in cross-sectional representation:

1. a) without showing the fasteners for the WAIM layer;
2. b) with attachment of the WAIM layer from behind;
3. c) with attachment of the WAIM layer from the front;

Fig. 3

a group antenna according to the invention and the associated WAIM layer each in plan view:

1. a) antenna base plate without WAIM layer,
2. b) with WAIM layer arranged in front of it (the latter shown in transparent),
3. c) WAIM layer alone.

Fig. 1 shows an example of the inventive WAIM layer W. The layer W itself is shown transparent (lying in the plane of the paper). Exalted protruding from this layer W can be seen in this embodiment post-shaped (with a circular cross-section) spacers A and each connecting a spacer A reinforcing ribs R recognize. Spacers A and reinforcing ribs R were machined out of a block of material.

Fig. 2 shows cross-sectional representations of a group antenna according to the invention with WAIM layer W arranged in front of it. The terms "before" and "behind" with respect to the antenna are used in the sense that "before" means the side of the antenna into which the radiation takes place.

It can be seen arranged in a regular grid spacers A, which are arranged in the spaces between the individual radiator elements SE and abut there on the antenna base plate P.

The attachment of the WAIM layer W with the metallic antenna base plate P of the array antenna is carried out by means of a plurality of screws S (FIG. Fig. 2b . c ), which are driven in the area of the spacer A. Screws made of a plastic material are preferably used in order not to influence the antenna pattern. The screws S in their entirety provide for a very stable anchoring of the WAIM layer W to the base plate P. Advantageously, the material properties of the screws should be as similar as possible to those of the WAIM layer.

The number and position of each screw is chosen based on the antenna stability requirements. In particular, there need not be a screw on each spacer.

However, in order to keep an influence on the antenna pattern as small as possible, the arrangement of the screws will preferably be selected in the same grid as the grid prescribed by the radiator elements.

If, however, the number of screws required is less than the number of spacers selected, the arrangement of the screws will continue to be oriented at the grid of the radiator elements. The arrangement of the screws will then be thinned out in such a way that a screw is provided only on every nth (n = 2,3,4 ...) spacer.

The Fig. 2b . c differ with respect to the question from which direction the attachment of the WAIM layer should take place. This can be done both from the back ( Fig. 2b ) or from the front of the antenna ( Fig. 2c ) ago. In case of Fig. 2b the screws S are driven through the base plate P into the spacers A. In case of Fig. 2c The screws S are driven through the WAIM layer W in the base plate P.

In view of possible losses in the radar backscatter cross section (RCS), the attachment from the rear is preferred, but the attachment from the front naturally has advantages in terms of accessibility.

Fig. 3a shows in plan view the antenna base plate P with the arranged thereon in a regular grid elements elements SE.
Fig. 3c shows the matching WAIM layer W with associated spacers A. The grid of the spacers A on the WAIM layer corresponds to the grid of the radiator elements SE.
In Fig. 3b For example, the WAIM layer W (shown in transparent) is mounted on the antenna base plate P, whereby the correspondence of the two screens can be seen very well.

Claims (8)

1. Array antenna, comprising

   - an antenna base plate (P) having multiple radiating elements (SE) arranged in a regular grid, a main beam of the array antenna being electronically pivotable, and

   - a dielectric WAIM (Wide Angle Impedance Match) layer (W) arranged in front of the radiating elements (SE) for impedance matching at large pivot angles, which maintains a low but well-defined distance from the antenna elements of the array antenna,

   - the WAIM layer (W) covering all the radiating elements (SE),

   spacers (A) being machined out of the material of the WAIM layer in a regular grid,
   the grid of the spacers (A) corresponding to the grid of the radiating elements (SE),
   characterized in that WAIM layer (W) and spacers (A) together form an integral monolithic workpiece, and wherein the spacers (A) are arranged in the interspaces between the individual radiating elements (SE).
2. Array antenna according to Claim 1, characterized in that the grid of the radiating elements (SE) is square, rectangular or hexagonal.
3. Array antenna according to Claim 1 or 2, characterized in that the grid of the spacers (A) is not equal to the grid of the radiating elements (SE), wherein the grid of the spacers (A) is derived from the grid of the radiating elements (SE) in such a way that there is a corresponding spacer (A) only for each nth radiating element (SE), with n = 2, 3, 4,....
4. Array antenna according to one of the preceding claims, characterized in that reinforcing ribs (R) which each connect two adjacent spacers (A) are machined out of the WAIM layer (W).
5. Array antenna according to one of the preceding claims, characterized in that the fixing of the WAIM layer (W) to the antenna base plate (P) at multiple spacers (A) is carried out by mechanical connecting means (S).
6. Array antenna according to Claim 5, characterized in that the mechanical connecting means (S) are arranged in a grid which corresponds to the grid of the spacers (A).
7. Array antenna according to Claim 5, characterized in that the grid of the mechanical connecting means (S) is not equal to the grid of the spacers (A), wherein the grid of the mechanical connecting means (S) is derived from the grid of the spacers (A) in such a way that there is a corresponding mechanical connecting means (S) only at each nth spacer, where n = 2, 3, 4,....
8. Array antenna according to one of the preceding claims, characterized in that the spacers (A) have a round cross section.

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