EP1202387A2 - Planar antenna array with improved directivity - Google Patents

Abstract

The device has a number of antenna elements arranged at row and column intersections and mirror symmetrically to form an orthogonal matrix. The central column(s) has a certain number of antenna elements and the outer columns have fewer and the number of elements per column is not greater than the number in the columns closer to the line of symmetry.

Description

The invention relates to a planar antenna with a Plurality of antenna elements forming an orthogonal Matrix essentially without gaps at crossing points of N columns and M rows are arranged, where the antenna elements forming at least one middle one Column mirror-symmetrical with respect to one in the direction the symmetry line of the columns is distributed are.

A planar antenna of the type mentioned at the outset is, for example known from published patent application DE 198 55 115 A1. It is used, for example, to receive satellite broadcast signals in the frequency range from 10.7 to 12.75 GHz. The planar antennas point towards the parabolic antennas Number of advantages; for example, they offer less Attack area for the wind, are not as voluminous and find wider ones due to their better visual impression Acceptance. However, planar antennas are well known Parabolic mirror LNB antennas have some disadvantages with the electrical Characteristics, for example a lower one Cross polarization decoupling, poor directional characteristics and stronger side lobes. In the case of the aforementioned disclosure Improved planar antenna described was u. a. through a special design of the patch elements the antenna elements an improved cross polarization decoupling and side lobe suppression achieved.

The multilayer known from the published patent application Antenna arrangement includes, among others, the satellite facing upper metallic layer, in the patch elements are trained. The patch elements are from, for example rectangular shape. In a view from behind the satellite The level of the patch elements is metallic Conductor tracks formed, which are the antenna elements Form dining feed line network. Are preferred under the patch elements two levels of feed line networks trained, one for feeding the horizontal Polarization and one for feeding the vertical polarization. Due to the insulation layers arranged between them the two feed line networks are different far from the patch elements arranged in the upper level spaced. This is one of the reasons why Vertical patch elements with the same excitation frequency and horizontal direction is not square, but are rectangular.

The individual multilayer antenna elements are in one level arranged in a matrix in N columns and M rows, where essentially each of the N columns M antenna elements having. A schematic diagram of the arrangement of the antenna elements is shown in Figure 1. After appropriate alignment on the satellites, the lines run in the azimuth direction and the columns in the direction of elevation. The single ones Antenna elements are preferably equidistant both arranged in the azimuth direction as well as in the elevation direction, the distances in the two directions different could be. In the known patch planar antenna arrangement is the different in the two directions Spacing of the antenna elements also partially the different distances between the feed line networks attributed to the upper level of the patch elements.

A planar antenna is, among other things, due to its radiation characteristics labeled, which results from the product the characteristics of the individual antenna element (at Use of the same antenna elements) and a group factor (a function dependent on the solid angle). The Total number of antenna elements determines the gain of the Antenna while the number in the azimuth or elevation direction arranged elements the opening angle in the respective Direction determined. The radiation pattern (Radiation diagram) contains zeros and side lobes (Maxima), which are introduced by the group factor. It has been found that for a complete, rectangular Matrix the attenuation at the first side lobe about 13 dB is. With direct satellite reception (geostationary Broadcast satellites) this value is too low; it will be one Attenuation of the first side lobe of at least 20 dB required. Such damping is at least on those Positions (solid angles) required that correspond to a position of satellites operating in the same frequency range Broadcasts should not be received.

The object of the invention is therefore to make the damping undesirable Signals and the suppression of interference signals to improve.

According to the invention, this object is achieved by a planar antenna solved with the features of claim 1. The Planar antenna has a plurality of antenna elements, essentially forming an orthogonal matrix arranged at the intersection of N columns and M rows are. An "essentially gapless" arrangement denotes an arrangement in which between two in one Column or row of adjacent antenna elements in the Usually there is no unoccupied crossing point, but there is it is possible that within the matrix due to constructive Exceptions (e.g. ordering a Feed point) some crossing points are unoccupied. The Antenna elements are forming at least one middle one Column mirror-symmetrical with respect to one in the direction the symmetry line of the columns is distributed. If the number of columns is odd, the planar antenna points at least one middle column in the sense of this definition at least with an even number of columns two middle columns. The at least one middle column has a number of M antenna elements. According to the invention have at least the two columns on the outside a smaller number of antenna elements. The number of Antenna elements in each column are not larger than the number of antenna elements in the closer to the line of symmetry lying adjacent column. This means, that the number of antenna elements starting from the center the planar antenna decreases towards the outside, but several Adjacent columns have an equal number of antenna elements can have. An exception to this basic Rule can by the aforementioned constructive exception a feed point in the middle of the matrix of antenna elements arise when a few antenna elements at this point be omitted. It has been shown that due to the symmetrical distribution of the number of antenna elements in each column, which decreases towards the outside, one Novel planar antenna with fewer side lobes in Direction of the rows of the matrix is created.

The antenna elements are preferably additionally mirror-symmetrical with respect to a line Line of symmetry arranged. This means that near the line of symmetry arranged middle lines the largest number of antenna elements have and at least the two arranged outside Lines a smaller number of antenna elements exhibit. This creates a planar antenna whose side lobe attenuation is also improved in the column direction, that means that the preferred antenna arrangement has a corresponding one Alignment to the satellite increased side lobe damping both in the azimuth direction and in the direction of the elevation.

The dependence of the number of antenna elements in the Columns from the distance from the line of symmetry represents in each If it is a monotonically falling function, that is, the number the antenna elements of a column further out is not greater than the number of antenna elements one inner column. In one embodiment can the number of antenna elements in each column each less than the number of antenna elements in the closer the adjacent column lying the line of symmetry.

In a preferred embodiment, the number is Columns N an even number. In addition, the number of antenna elements in a column either equal to the number or by a number x less than the number of antenna elements in the neighboring one closer to the line of symmetry Column. In addition, each have n neighboring ones Columns the same number of antenna elements. The number the column n is therefore equal to 2 * n times that on the next larger whole number rounded quotient M / x. The number x is preferably an even number, for example x = 2. In addition, the antenna elements are preferably mirror-symmetrical in terms of one between two middle ones Further symmetry line lying in rows, so that the antenna elements within a rhombus-shaped Outside contour are arranged. For example, one Planar antenna arrangement of this type has 32 columns and rows (N = M = 32), with four middle rows or columns each with 32 elements and two adjacent ones Columns have the same number of elements, this number being four less than that of inner column pairs (x = 4 and n = 2). in the the rest are the antenna elements in each column or each Line arranged equidistantly, resulting from the above Differences in column spacing from row spacing can. It has been shown that with such Planar antenna an opening angle between 2 ° and 3 ° can be reached (an opening angle of less than about 3.4 ° for direct satellite reception). Furthermore such an antenna arrangement showed a side lobe attenuation of at least 25 dB. Finally, the Symmetry of the antenna structure is a rotation of the antenna 90 °, whereby the rows with the columns are swapped functionally become. This antenna arrangement is therefore for satellite signals with horizontal and vertical polarization equally well suited.

In a preferred development of the antenna arrangements according to the invention mentioned above, a feed network with a feed point and a branched network of feed lines leading from this feed point to all antenna elements is provided, the network being designed in such a way that there is an essentially equally long route from the feed point to each Antenna element results. In the case of a conventional antenna arrangement with a constant number of antenna elements in each column, the design of such a feed network could be implemented symmetrically in a relatively simple manner. However, implementation becomes difficult in the case of the antenna arrangement according to the invention, in which outer columns and rows have a smaller number of antenna elements. In a preferred development, in which the number of rows and columns corresponds to powers of two (N = 2 ^a and M = 2 ^b , where a and b are integers greater than 1), the network of feed lines is formed by (a) a fictitious rectangular arrangement of N columns, each with M antenna elements, is assumed (b) a fictitious feed network is constructed by (b1) for all antenna elements of the N columns and M rows, the feed lines of two antenna elements adjacent in one row or column a first group are brought together, each forming a feed line branching point, from which feed lines of essentially the same length lead to the antenna elements, (b2) for all first groups, the feed lines of in each case two adjacent first groups in the column or row direction to a further one Group are brought together, each with a further meal line branching point is formed, from which feed lines of essentially the same length lead to the feed line branching points previously formed, (b3) this merging is repeated for all further groups until the feed lines of all antenna elements are brought together to the feed point, (b4) from the feed line thus formed fictitious arrangement of N * M antenna elements, those antenna elements are eliminated which are not contained in the planar antenna, and (b5) those branches of the fictitious feed lines which lead exclusively to the antenna elements eliminated in step (b4) are eliminated, and (c) the network of feed lines is formed in accordance with the fictitious feed network formed in step (b). In the case of a planar antenna of the preferred embodiment with a rhombus-shaped outer contour, the line sections of the fictitious dining network which extend beyond the rhombus-shaped outer contour are additionally replaced in step (c) by approximately equally long line sections within the rhombus-shaped outer contour. The configuration of the feed network according to the invention permits symmetrical feeding, which avoids phase errors and produces a good directional characteristic with low side lobes. "Essentially the same length" feed lines are to be understood in a first approximation as feed lines with the same geometric length. Of course, this should also be understood to mean those feed lines which have the same “route length” in such a way that the signals propagating along the line in the preferred frequency range arrive at the feed point with approximately the same phase position.

In a preferred development of the dining network in step (b6) each eliminated branch of the fictional Feed network through an effect of the eliminated Branch (cable + antenna element) replicating weight replaced, the weight at that feed junction point of the dining network from which a direct branch line to that fictitious feed line branch point leads to the eliminated branch ended. The addition of the compensation weights improved the directional pattern by turning the main lobe is avoided.

Advantageous developments of the invention are in the Subclaims marked.

Figur 1 eine schematische Darstellung der Anordnung der Antennenelemente bei einer bekannten Planarantenne;

Figur 2 eine schematische Darstellung der erfindungsgemäßen symmetrischen Anordnung von Spalten von Antennenelementen;

Figur 3 eine schematische Darstellung einer bevorzugten symmetrischen Anordnung von Spalten mit vorgegebenen Anzahlen von Antennenelementen;

Figur 4 eine schematische Darstellung der symmetrischen Anordnung der Antennenelemente innerhalb einer rhombusförmigen Außenkontur;

Figur 5 eine schematische Darstellung der Ausbildung des Speiseleitungsnetzwerks bei der erfindungsgemäßen Antennenanordnung; und

Figur 6 eine Darstellung des Speiseleitungsnetzwerks bei einem bevorzugten Ausführungsbeispiel der erfindungsgemäßen Planarantenne.

The invention is described in more detail below with reference to preferred exemplary embodiments described in the drawings. The drawings show:

Figure 1 is a schematic representation of the arrangement of the antenna elements in a known planar antenna;

Figure 2 is a schematic representation of the symmetrical arrangement of columns of antenna elements according to the invention;

Figure 3 is a schematic representation of a preferred symmetrical arrangement of columns with predetermined numbers of antenna elements;

Figure 4 is a schematic representation of the symmetrical arrangement of the antenna elements within a rhombus-shaped outer contour;

Figure 5 is a schematic representation of the formation of the feed line network in the antenna arrangement according to the invention; and

Figure 6 is an illustration of the feed line network in a preferred embodiment of the planar antenna according to the invention.

FIG. 1 schematically shows the known arrangement of antenna elements already described in the introduction. The planar antenna arrangement 1 has a multiplicity of antenna elements 2 which are arranged at crossing points of orthogonal rows and columns. In Figure 1, the antenna elements are shown as circular spots. However, the antenna elements can be of any suitable shape, for example the rectangular shape described in the above-mentioned laid-open publication DE 198 55 115 A1. The group antenna 1 consists of N columns, each with M antenna elements. If the antenna 1 is aligned towards a satellite, the rows extend in the azimuth direction, while the columns are aligned in the direction of the elevation. The antenna elements 2 are arranged equidistantly, the distance d _{a of} the antenna elements 2 in the azimuth direction being different from the distance d _{e of} the antenna elements 2 in the direction of the elevation.

Figure 2 illustrates a basic principle of the arrangement of the antenna elements in the planar antenna according to the invention. As in the prior art illustrated in FIG. 1, the antenna elements are arranged in columns, each column having a predetermined number of antenna elements. The columns are again arranged equidistantly with the distance d _a . The two outer columns 3 have a number A of antenna elements. Columns 4 adjacent to the outer columns each comprise B antenna elements. The subsequent columns 5 arranged further inside each have C antenna elements. This symmetry continues inwards, so that a symmetry line 6 extending in the column direction or in the direction of the elevation is formed for the arrangement of the antenna elements. The number A, B, C, ... of the antenna elements in each column increases in the direction of the line of symmetry 6, the number of antenna elements in a column being no greater than the number of antenna elements in a column closer to the line of symmetry 6.

FIG. 3 shows a schematic representation of a preferred arrangement of columns 7 of antenna elements, the number of which is distributed symmetrically to the line of symmetry 6. In this arrangement, the columns closest to the line of symmetry 6 have a maximum number M of antenna elements. The number of antenna elements then decreases outwards from column to column by x antenna elements in each case. The outer columns have M-kx antenna elements, where k is equal to half the number of columns N reduced by 1 (k = N / 2-1). The columns are again arranged equidistantly with the distance d _a .

In Figures 2 and 3 are neither the individual antenna elements still their alignment is shown in the row direction. But it should be noted that the neighboring Antenna elements of the neighboring columns (so far present) in approximately the same vertical position (Elevation). In a preferred embodiment the antenna elements are also vertical Direction symmetrically arranged so that there is an orthogonal further line of symmetry between the middle lines or on the middle row.

Figure 4 shows such a preferred arrangement of the Antenna elements in which the number M of lines and the Number N of columns are even numbers and the number of Antenna elements from column to column to the outside by each decreases two antenna elements. This results in the Figure 4 shown rhombus shape.

Figure 5 illustrates the formation of the feed lines or the symmetrically branching feed line network, for simplification only the feed lines for an excitation direction (e.g. vertical) are. First, a fictional arrangement of antenna elements in N columns and M rows where each column has M elements. The inferred from it, Antenna elements left in accordance with the invention are shown shaded in gray, while the later omitted antenna elements of the fictitious arrangement are illustrated by a dotted outline. outgoing of this fictitious overall arrangement of the antenna elements are two in each across the entire matrix Column direction adjacent antenna elements combined, that is, the feed lines of these are combined Antenna elements at a first branch point merged such that the lengths of the two feed lines from this branch point to the antenna elements are the same. After all the antenna elements of the fictional Arrangement are brought together in pairs in this way, two pairs in the row direction or Groups of two grouped together by starting the feed lines from the first branch points of these pairs a common further branch point by equal long lines are connected. Thus groups of four formed by antenna elements. Then turn again neighboring groups of 4 in the column direction summarized by equally long feed lines from the last branch points of the groups of 4 merged into another branch of a group of 8 become. Finally is on the right of Figure 5 still shown as neighboring in the row direction Groups of 8 are combined, by equally long lines from the last formed Branching points of the groups of 8 to a common one Junction point of a group of 16 can be merged. From this last branch point that was formed on the is shown in the middle of Figure 5, leads one common feeder of the group of 16 down. How from the illustration on the left-hand side of FIG. 5 there are four such groups of 16 antenna elements, the feed lines of two in each Column direction adjacent groups of 16 antenna elements be brought together. Eventually the two in each case 32 antenna elements feeding lines in the Merged in the middle of the rhombus at one feeding point (not shown in Figure 5).

From the fictitious dining network thus formed one goes to the feed network of the antenna arrangement according to the invention, by first making the outside of the rhombus-shaped Boundary antenna elements are omitted and then those feed lines are eliminated, which only lead to eliminated antenna elements. These are dotted on the right side of Figure 5 Lines shown. That in Figure 5 with solid Lines of remaining feed network shown schematically is now on. the antenna arrangement according to the invention realized. The eliminated antenna elements with their associated Feed lines are then replaced by suitable Weights on the remaining, now asymmetrical Feed lines replaced. These weights attached to appropriate Locations of the branch points are arranged in Figure 5 not shown.

FIG. 6 shows a feeder network of one level for a preferred embodiment of the invention Planar antenna. The preferred embodiment of the invention Planar antenna has 32 columns and 32 rows on (N = M = 32). There are four middle columns or Lines with 32 antenna elements each. Outwardly the number of antenna elements in the columns decreases, whereby a pair of adjacent columns the same number of antenna elements and wherein the number of antenna elements of this pair of columns is 4 less than the number of antenna elements of the closer to the line of symmetry lying pair of columns. The only exception is the two middle columns, the one on the right are arranged next to the line of symmetry. There are in the both arranged above the horizontal line of symmetry Rows the antenna elements omitted to be sufficient To create space for the assembly of the feed point. The total number the antenna elements is therefore 4 * (256-112) - 4 = 576 - 4 = 572.

Figure 6 shows the preferred embodiment of the feed network for a polarization direction. The feeding point is about in the middle of the symmetrical arrangement, at this point a group of four antenna elements was omitted. On the right side of Figure 6 an enlarged section is shown. In this enlargement are to compensate for the effect of the omitted antenna elements inserted weights 8 illustrated. These weights are called widenings of the Conductor lines of the feed line network visible. they are each formed at the feed line branching points 9, each of which has a direct branch line 10 to those Points 11 leads to where the fictional complete Feed line network each branch to the omitted Group of antenna elements. The widened Conductor tracks 8 begin at the respective branch points 9 and extend against the direction of direct branch lines 10.

In the preferred feed line network according to FIG. 6 it can also be seen that traces of the fictitious dining network the full matrix of the array antenna that extend over the edge of the rhombus-shaped outer contour would have been replaced by traces 12, 13 within the rhombus-shaped border, but still about the same length as the original fictional ladder exhibit. These ladder tracks include one nearby the rhombus-shaped outer contour 12 and a compensation for this shortening of the conductor path Meander loop 13.

Measurements on a practical planar antenna the preferred embodiment gave side lobes, which in entire frequency band (10.70 GHz to 12.75 GHz) more than 20 dB below the maximum sensitivity in the main lobe lay. At some frequencies the attenuation was greater than 35 dB. The main lobe extending in the main direction (0 °) had an opening angle between 2 ° and 3 °.

There are numerous alternatives within the scope of the inventive concept Embodiments conceivable. While the antenna elements in the preferred embodiment for a vertical and horizontal polarization are formed the principles according to the invention also apply to antenna elements use with circular polarization. The remains Arrangement of the antenna elements unchanged; it will only the type of suggestion changed.

Claims (13)

Planar antenna with a plurality of antenna elements (2) which are arranged essentially without gaps at the intersection of N columns and M rows, forming an orthogonal matrix,
wherein the antenna elements (2) are arranged so as to be mirror-symmetrical with respect to a line of symmetry (6) running in the direction of the columns, forming at least one central column
characterized, that the at least one central column has a number of M antenna elements and at least the two columns arranged on the outside have a smaller number of antenna elements and that the number of antenna elements in each column is not greater than the number of antenna elements in the adjacent column closer to the line of symmetry. Planar antenna according to Claim 1, characterized in that the antenna elements are additionally arranged in mirror symmetry with respect to a line of symmetry running in the direction of the lines. Planar antenna according to Claim 1, characterized in that the number of antenna elements in each column is in each case less than the number of antenna elements in the adjacent column which is closer to the line of symmetry. Planar antenna according to Claim 1, characterized in that the columns of antenna elements are arranged equidistantly at a first distance (d _a ) from one another and that the rows of antenna elements are arranged equidistantly at a second distance (d _e ) from one another. Planar antenna according to Claim 1, characterized in that the number of columns N is an even number. Planar antenna according to claim 5, characterized in that the number of antenna elements in a column is either equal to the number or by a number x less than the number of antenna elements in the adjacent column closer to the line of symmetry and that in each case n adjacent columns have the same number of antenna elements, the number of columns N being 2 * n times the quotient M / x rounded to the next larger integer. Planar antenna according to Claim 6, characterized in that x is an even number. Planar antenna according to claim 7, characterized in that the antenna elements are arranged mirror-symmetrically with respect to a further line of symmetry lying between two middle lines, so that the antenna elements are arranged within a rhombus-shaped outer contour. Planar antenna according to Claim 8, characterized in that N = M = 32, x = 4 and n = 2. Planar antenna according to Claim 1, characterized by a feed network with a feed point and a branched network of feed lines leading from this feed point to all antenna elements, which is designed in such a way that there is an essentially equally long route from the feed point to each antenna element. Planar antenna according to claim 10, characterized in that N = 2 ^a and M = 2 ^b , where a and b are integers greater than 1, and that the network of feed lines is formed by a) a fictitious rectangular arrangement of N columns with M antenna elements each is assumed, b) a fictitious dining network is constructed by b1) for all antenna elements of the N columns and M rows, the feed lines of in each case two antenna elements adjacent in one row or column are combined to form a first group, a feed line branch point being formed in each case, from which feed lines of essentially the same length lead to the antenna elements, b2) for all the first groups, the feed lines of two first groups adjacent in the column or row direction are brought together to form a further group, a further feed line branch point being formed, from which feed lines of essentially the same length lead to the previously formed feed line branch points, b3) this merging is repeated for all other groups until the feed lines of all antenna elements are merged at the feed point, b4) from the fictitious arrangement of N * M antenna elements thus formed, those antenna elements which are not contained in the planar antenna are eliminated, and b5) those branches of the fictitious feed lines which lead exclusively to the antenna elements eliminated in step b4) are eliminated, and c) the network of feed lines is formed in accordance with the fictitious feed network formed in step b). Planar antenna according to claim 8, characterized in that N = 2 ^a and M = 2 ^b , where a and b are integers greater than 1, and that the network of feed lines is formed by a) a fictitious rectangular arrangement of N columns with M antenna elements each is assumed, b) a fictitious dining network is constructed by b1) for all antenna elements of the N columns and M rows, the feed lines of in each case two antenna elements adjacent in one row or column are combined to form a first group, a feed line branch point being formed in each case, from which feed lines of essentially the same length lead to the antenna elements, b2) for all the first groups, the feed lines of two first groups adjacent in the column or row direction are brought together to form a further group, a further feed line branch point being formed, from which feed lines of essentially the same length lead to the previously formed feed line branch points, b3) this merging is repeated for all other groups until the feed lines of all antenna elements are merged at the feed point, b4) from the fictitious arrangement of N * M antenna elements thus formed, those antenna elements are removed which are not contained in the planar antenna, and b5) those branches of the fictitious feed lines which lead exclusively to the antenna elements eliminated in step b4) are eliminated, and c) the network of feed lines is formed in accordance with the fictitious feed network formed in step b), the line sections of the fictitious feed network extending beyond the rhombus-shaped outer contour being replaced by line sections (12, 13) of approximately the same length within the rhombus-shaped outer contour. Planar antenna according to claim 11 or 12, characterized in that in step b): b6) each eliminated branch of the fictitious feed network is replaced by a weight (8) which simulates the effect of the eliminated branch, the weight (8) being added at that feed line divergence point (9) of the feed network from which a direct branch line (10) to the fictitious feeder branching point (11) at which the eliminated branch ended.

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