ES2249984B2 - Flat reflecting antenna in printed technology with improved bandwidth and polarization separation. - Google Patents

Flat reflecting antenna in printed technology with improved bandwidth and polarization separation. Download PDF

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Publication number
ES2249984B2
ES2249984B2 ES200401382A ES200401382A ES2249984B2 ES 2249984 B2 ES2249984 B2 ES 2249984B2 ES 200401382 A ES200401382 A ES 200401382A ES 200401382 A ES200401382 A ES 200401382A ES 2249984 B2 ES2249984 B2 ES 2249984B2
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dipoles
feeder
polarization
reflector
printed
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ES2249984A1 (en
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Jose Antonio Encinar Garcinuño
Antonio Pedreira Rios
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Universidad Politecnica de Madrid
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Universidad Politecnica de Madrid
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00Antenna arrays or systems
    • H01Q21/29Combinations of different interacting antenna units for giving a desired directional characteristic
    • H01Q21/293Combinations of different interacting antenna units for giving a desired directional characteristic one unit or more being an array of identical aerial elements

Abstract

Flat reflector antenna in printed technology with improved bandwidth and polarization separation. This invention consists of a printed reflector antenna formed by the repetition of a unit cell consisting of several parallel metal dipoles of different lengths printed on a sheet of dielectric material on a metallic plane, which reflects the electromagnetic field from a feeder forming a beam. collimated, or shaped, by adjusting the phase of the field reflected in each element. Phase control is done by adjusting the lengths of the dipoles. The use of several dipoles allows to increase the bandwidth without resorting to multilayer structures. Since the dipoles only control the phase of a linear polarization, the orthogonal polarization is controlled by a second layer of dipoles located in the lower face of the dielectric perpendicular to those of the upper face, obtaining a low level of coupling between polarizations.

Description

Flat reflector antenna in printed technology with improved bandwidth and polarization separation

Technical sector to which the invention relates

This invention is framed in the sectors of radiocommunication technology, radar technology and technology space.

Statement of prior art

This invention is related to antennas flat reflectors formed by groups of radiant elements printed, as an alternative to parabolic reflectors or formed, which are usually used in radar systems, in terrestrial and satellite communications, both in the segment of Earth as of flight.

As the parabolic reflectors (figure 1), shaped reflectors, etc. a printed flat reflector, too called Reflectarray (figure 2) [D. G. Berry, R. G. Malech W. A. Kennedy, "The Reflectarray Antenna", IEEE Trans. on Antennas and Propagation, Vol. AP-11, 1963, pp.646-651] produces a certain radiation pattern generating a plane wavefront directed in the right direction, from the incident radiation coming from the feeder located at a point called focus (1). This is achieved providing adequate phase correction at each point of the reflective surface, in a 360º range.

To synthesize a certain radiation diagram by means of a printed flat reflector, conductive elements can be used that allow the reflection coefficient phase to be varied locally. Mainly, there are two techniques for this: (1) radiators attached to transmission lines of adequate length [RE Munson, HA Haddad, JW Hanlen, "Microstrip Reflectarray for Satellite Communications and RCS Enhancement or Reduction", US4684952, August 1987], and (2) variations in the length of the resonant element [DM Pozar, SD Targonski, "A Microstrip Reflectarray Using Crossed Dipoles", 1998 IEEE Intl. Symposium on Antennas and Propagat., pp. 1008-1011]. This last arrangement has a fairly reduced bandwidth, mainly because only a linear phase variation with the length of the element within a small range is possible. In addition, the maximum range of phases that can be achieved with a single resonant element is less than 360º, being around 330º maximum in practical embodiments. To improve these characteristics, in the patent [EP 1 120 856 Al, "Printed circuit technology multi-layer planar reflector and method for the design thereof", June 1999] a configuration of several stacked layers of metallizations of slightly different size has been proposed (Figure 3), so that the range of variation of the phase exceeds 360 degrees, being quite linear with the length of the element. With such multilayer flat reflector technology, a bandwidth of 16% has been achieved for a 16-wavelength diameter reflectarray [JA Encinar, "Design of two-layer printed reflectarrays using patches of variable size", IEEE Trans. Antennas Propagat ., Vol. 49, no. 10, pp. 1403-1410, Oct. 2001]. Additionally, improvements in bandwidth have been obtained using optimization techniques that adjust the dimensions of the patches in each layer to achieve the required phases in a frequency band [JA Encinar and JA Zornoza, "Broadband design of three-layer printed reflectarrays, " IEEE Trans. Antennas Propagat ., Vol. 51, no. 7, pp. 1661-1664, July 2003]. However, the configuration of several stacked layers has greater manufacturing times and costs, because the processes must be repeated for each layer. It can also increase the weight and dissipative losses in the dielectric layers by the fact of having a greater number of layers.

As a dual polarization reflectarray, a configuration consisting of clusters of two orthogonal dipoles has been patented [JR Profera, E. Charles, "Reflectarray antenna for communication satellite frequency re-use applications", US5543809, August 1996]. The grouping of vertical dipoles acts as a reflector for vertical polarization and that of horizontal dipoles for the other polarization. When the orthogonal dipoles are physically separated, the adjustment of the phase on the surface of the reflectarray to collimate the beam is performed independently for each polarization. In order to reduce the coupling between orthogonal polarizations in reflectors with crossed dipoles, a configuration with two stacked layers of dipole clusters has been proposed, in which the two polarizations are separated by a grid of wires or conductive strips [KC Clancy, m . E. Cooley, D. Bressler, "Apparatus and method for reduccing polarization cross-coupling in cross dipole reflectarrays", US2001 / 0050653 Al, March 2000]. This invention also contemplates the possibility that the orthogonal dipole clusters for the two polarizations are on the same plane. In that case, each dipole is formed by very close threads, which act as a single dipole of greater width, with the sole objective of not affecting orthogonal polarization. In this configuration the phase curves depending on the length are similar to those obtained with a single dipole of greater width, but with better performance in polarization purity than the reflectors formed by cross dipoles. In order to increase the range of phases that can be achieved by varying the length of the dipoles up to 360 °, different solutions have been proposed [JP McKay et al ., "Full dynamic range reflectarray element", US Pat. No. 6,072,438, Dec. 1998]. Said solutions consist of: a) varying the width of the dipoles, and b) including in addition to the dipoles of varying length, other coupled dipoles of different length, in which the separation and / or the length of the shorter dipole is varied. However, in the previous inventions, the phase curves depending on the length of the dipoles remains similar to those obtained for single-layer reflectors based on dipoles of variable length, and consequently, the bandwidth remains insufficient for Most commercial applications.

Explanation of the invention.

In this invention a flat reflector is proposed, or reflectarray, which incorporates clusters with several dipoles printed parallels, in order to achieve an effect similar to that of have several layers of metallizations, but with a single layer, well to get the reflector with a single layer or at least get a reduction in the number of these. The reflector elements are they place in a grid, each element occupying a cell of said reticle Each element is formed by two or more parallel dipoles of slightly different dimensions printed on a sheet of dielectric material on a mass plane.

The innovation of incorporating several dipoles parallel lengths close to resonance in the same layer and in the same cell of the reflectarray allows to increase the offset entered in the field reflected at values greater than 360º required in the design of reflectarrays as well as a behavior more linear phase, because the phase is controlled with the Lengths of several resonant elements (dipoles). Thus an effect similar to that obtained for configurations of multi-layer reflectors, but using only one cap.

A main object of this invention is a flat reflector, or reflectarray, in printed technology with several parallel dipoles in the same layer and in the same cell. In the figure 4 shows a sketch of the reflectarray object of the invention. This flat reflector reflects the electromagnetic field of linear polarization, with the electric field in the direction of the dipoles, coming from a feeder (14), forming a collimated beam or shaped in a certain direction and at a certain frequency. From reciprocally, the reflector receives a beam in one direction and at a certain frequency and reflects the polarization field linear, with the electric field in the direction of the dipoles, concentrating it on the focal point where the feeder (14). To achieve the desired radiation pattern, the phase of the field reflected in each element is adjusted by varying the Length of the dipoles. The reflective element in each cell (Figure 5) is formed by two or more dipoles (15, 16, 17 ...), of dimensions I_ {i}, the length of the dipole "i", and w_ {i}, its width, printed on a sheet of dielectric material that is found at a certain distance from a metal sheet (11), which It acts as a mass plane. The dielectric sheet (9) with the dipoles printed and the mass plane can be separated by air or by another sheet of dielectric material, called separator (20, figure 7). The thickness of the metallizations is considered negligible, while that of the dielectric sheet (9), support of the dipoles, it has a thickness d. Item settings is given, then, by the number of dipoles, n, their positions and The relationship between their lengths. The element is characterized by phase of its reflection coefficient depending on the length of the  dipoles, calculated at various frequencies. Properly choosing the separation of the dipoles and the relationship between lengths, is get a linear variation of the phase depending on the length of these, in a margin greater than 360º, which results impossible with a single dipole per element. A feature notable of the reflectarray of parallel dipoles with respect to those of a single layer of variable size patches is that it allows to increase the working frequency band due to its better response of phase with the resonant length of the dipoles.

Another object of the invention consists of a reflectarray for dual polarization, formed by elements such as shown in figure 6 that are obtained by metallizing on the face bottom of the dielectric (9) another grouping of dipoles (18 and 19), arranged perpendicular to those of the upper face (15 and 16). With the dipoles printed on each face it adjusts so independent phase for each linear polarization, obtaining a very low level of coupling between polarizations and allowing eventually a separation of the two feeders, one for each polarization, located in different foci (figure 9).

Another feature of the reflectarray of Dual polarization with parallel dipoles is its low coupling between polarizations, because there is no electrical contact between the dipoles of both polarizations, and therefore these reflectors will have lower cross polarization levels than other types of reflectarrays. Consequently the synthesis of diagrams of radiation can be performed independently for each Polarization. This would allow, first to simplify the process of design and, second, design the reflectarray with diagrams of different radiation in each polarization, being able to generate beams collimated or shaped in different directions.

Another object of the invention consists of a reflectarray for circular polarization, using the same reflective element that for dual polarization. The performance circular polarization is achieved by breaking it down into two linear, parallel to the dipoles of each face. The set of orthogonal dipoles reflect the signal while retaining its Polarization.

Another object of the invention consists of a multilayer reflectarray for linear, dual or circular polarization using in each layer several parallel dipoles. In figure 7 it shows a two layer configuration for linear polarization, being (9) and (10) two dielectric sheets separated by the dielectric separator (20) and containing the metallizations (15 and 16). Similarly, Figure 8 represents a reflectarray of two layers (9 and 10) for dual or circular polarization by means of metallization, on the underside of the sheets, of the dipoles (18, 19), perpendicular to those of the upper face (15, 16). In This figure does not show the separators. Another feature of two-layer reflectarray with parallel dipoles is that it introduces more degrees of freedom, the lengths of the dipoles in the two layers, and allows adjusting the required phases at various frequencies of work, allowing to make reflectarrays designs multifrequency or wider band, with only two layers.

Another feature of flat reflectors with parallel printed dipoles is that they can be constructed in several flat panels to be folded and unfolded, since  no electrical contact is required between the dipoles of the Different cells

Brief description of the figures

Figure 1: Parabolic reflector. From the signal from the focus (1), a flat wave front is obtained (8) compensating the different distances the rays travel until reaching the reflector (2) with the distances they travel (6 and 7) until reaching the plane (8), so that the distance that they travel the rays from the plane (8) to the focus (1), Reflecting in the parable (2) is constant.

Figure 2: Flat reflector. From the signal from the focus (1), a flat wave front (8) is obtained compensating the different distances that the rays travel up to reach the reflector (2) with phase shifts introduced by the radiators that form said reflector. Each of the radiators of which the reflector consists (2) introduces the appropriate offset for shaping the reflected beam producing, in this case, a front of flat wave (8) from an approximately spherical one (3)

Figure 3: Piano reflector formed by two thin dielectric sheets (9 and 10) with printed metallizations, in order to widen the usable bandwidth.

Figure 4: Flat reflector formed by a sheet fine dielectric (9) raised on a mass plane (11), characterized by having metallic dipoles on both sides, each one of which responds to a polarization.

Figure 5: Unit cell consisting of several dipoles (15, 16 and 17) parallel. Each of them is defined by its length (I_ {i}), width (w_ {i}) and the positions of their centers, not indicated in the figure. The dimensions of the cell, long and wide, they remain constant throughout the entire surface and in all reflector layers.

Figure 6: Unit cell for dual polarization formed by two parallel dipoles (15 and 16) on the upper face of a dielectric sheet (9) and two others (18 and 19), perpendicular to them, located on the underside of (9).

Figure 7: Reflector for linear polarization formed by two sheets of dielectric (9 and 10) containing each one of them metallizations with several dipoles per cell (15 and 16). In general, the sizes of the dipoles in the different layers are different.

Figure 8: Reflector for dual polarization formed by two sheets of dielectric (9 and 10) containing, each one of them, metallizations with several dipoles per cell (15 and 16) on the upper face and perpendicular dipoles (18 and 19) on the face bottom of the sheet (9), and similarly, the sheet (10) has the dipoles (15 and 16) on their upper face and the (18 and 19), perpendicular to them on their lower face. The number of dipoles per cell may vary for each layer.

Figure 9: Reflector that divides the signal incident (12) in its two polarizations (13), which directs both feeders (14), allowing diversity by polarization or Different radiation diagram for each of them.

Figure 10: Example of the reflector embodiment flat, formed by a layer of kapton (9) with two dipoles metallized by cell in expensive masters (dual polarization), a plane of mass (11) and a separator (21), in this case expanded polystyrene. Two polycarbonate caps (22) protect the structure and give it rigidity.

Figure 11: Example of complete antenna. With a only metal support (27) is able to hold the feeder (14) in position, stiffen the reflector (23) and provide a means for installing the antenna on a wall.

Figure 12: Plan, elevation and side view of the metallic support.

Figure 13: Development of the antenna support, manufactured on sheet metal. It contains the flange (29) that holds the feeder, the four clips (24) that hold the reflector, the stops (28) to mark its position and the pins (25) that are attached to the wall.

Figure 14a. Detail of the fixing screws (30) of the antenna. Tightening the screws bends more or less the pin (25) to allow some degree of orientation. (31) are flat washers and (32) is a nylon block.

Figure 14b Fastener detail feeder (14) by means of the flange (29), tightening the feeder by means of the thyme (35), provided with nuts and washers (3. 4).

Detailed exposition of an embodiment of the invention

Here we detail the manufacture of a reflector dual polarization plane, made in a single layer to replace the paraboloid of a domestic television antenna via satelite. Therefore, being a consumer electronics product, the greatest possible economy has been sought, especially in the selected materials. As dielectric separator has been used an expanded polystyrene sheet, reaching a compromise between electrical characteristics and price. For the tapas you have chosen polycarbonate, but it could also serve PVC, polyethylene, etc.

The structure of figure 10 is made, formed by the following layers, from bottom to top: A sheet metallic (11) aluminum, which acts as a mass plane. About him place an expanded polystyrene sheet (21) of 6mm (approximately a quarter of the wavelength in the dielectric) thick, which acts as a separator. Next is a sheet of Kapton (9) with photoetched dipoles, vertical on the face upper and horizontal in the lower, to achieve polarization dual. The set is enclosed between two sheets of polycarbonate (22) that give rigidity to the structure, as well as protection for Outdoor installation.

Figure 11 shows the complete antenna. A metal support (27), obtained from a single sheet, without the need of joints or welds, holds the feeder (14) in its position and with the proper orientation, so that its center phase matches the focus of the reflector. The clips (24) they hold the reflector under pressure, and the "pins" (25) serve to separate the wall assembly where it is installed. Go crossed by two screws (26) that fix the The antenna on the wall. They also allow the orientation of the antenna, since the U-shaped pins can be bent to aim the antenna.

The reflector design with parallel dipoles is performed in the following stages:

one.
Starting from the position of feeder and antenna radiation direction is obtained the offset that each element of the reflectarray must introduce to generate the desired radiation pattern, at the frequency central.

2.
Be determine the positions of the dipole centers in each cell and the relative length between the two, so that it is obtained a phase variation with the lengths of the dipoles linear enough For this, an analysis program is used which calculates the phase of the reflection coefficient of a structure periodic with the dipoles and the different layers of dielectric using "Method of Moments in the domain spectral".

3.
In Each element of the reflectarray adjusts the dimensions of the dipoles to get the necessary offset. This is used for an optimization routine that iteratively calls the program of analysis and adjusts the dimensions of each element until get the phase defined in stage 1). The analysis program calculate the phase of the reflection coefficient in each period assuming local periodicity, that is, analyzing each element with its dimensions in a periodic environment.

From the dimensions and positions of the patches in each cell you get the photogravure mask for the realization of the reflector by conventional techniques of photoengraving.

Industrial application

This invention can be applied to manufacturing of reflectors for antennas in radar applications and communications, terrestrial and satellite, presenting important advantages over conventional reflectors that it replaces. Since it is a flat reflector, it can be constructed in several parts to be folded for transport and subsequently unfolded. The reflector surface can be adapted to the existing structures, such as building facades, panels in communications satellites, etc. It can be used as a reflector for dual polarization with an isolation level between polarizations better than what the reflectors provide Conventional and other types of reflectarrays.

The present invention can be constructed in space qualified materials. Therefore, this type of reflectors printed with parallel dipoles has an important field of application in the space industry as an alternative to the different types of reflectors shipped on satellites, parabolic, grid or shaped beam. In particular, it can be an alternative to the so-called "dual gridded" reflectors that are used when a very low cross polarization level is required. They are also an alternative to multilayer printed reflectorrays with rectangular patches, for presenting better cross-polarization performance and simplifying manufacturing processes, by reducing the number of
layers.

Claims (8)

1. Flat reflector in printed technology formed by a grouping of unit cells with conductive elements printed on a sheet of dielectric material (9), on a conductive plane (11), in which each unit cell is designed to get electromagnetic energy from a feeder (14) located at a focal point, it is reflected forming a collimated beam of linear polarization in a certain direction, and by reciprocity, which when it receives a collimated beam of linear polarization in a certain direction reflects it by concentrating it at the point focal where the feeder is located; characterized by containing several parallel dipoles (15, 16, 17, ...) of lengths slightly different from the resonance length, in the same unit cell and on the same face of a sheet of dielectric material (9), where the positions of the dipoles and their relative lengths in the unit cell are chosen to increase the offset introduced by the cell to values greater than 360º with a more linear behavior of the phase, producing an improvement in the antenna bandwidth, and where the lengths of the dipoles in each cell are adjusted to achieve an offset of the reflected field that allows collimating the electromagnetic field from the feeder or concentrating in the feeder an incident collimated beam in the reflector, at one or more frequencies within the working band of the reflector .
2. Flat reflector according to 1, characterized by having on the underside of the dielectric (9) another group of dipoles (18, 19, ...), arranged perpendicularly to those of the upper face (15, 16, 17, .. .), in which the lengths of the dipoles on the lower face (18, 19) are adjusted in each cell to achieve an offset of the field reflected in the orthogonal linear polarization that allows collimating the electromagnetic field from the feeder or concentrating on the feeder a collimated beam incident on the reflector, resulting in a dual polarization antenna with high isolation between polarizations.
3. Flat reflector according to 1, characterized by having two dielectric sheets (9) and (10) with the dipoles (15, 16, ...) of the two parallel layers, for linear polarization, separated from each other and from the conductive plane by separators (20, 21), with the aim of introducing more degrees of freedom, the lengths of the dipoles in the two layers, and allowing multi-frequency reflectorrays or wider band designs.
4. Flat reflector according to 1 and 3, characterized by having printed dipoles (18, 19, ...) on the underside of the dielectric sheets (9) and (10), perpendicular to the dipoles of the upper face (15, 16, 17, ...) in order to collimate or shape the beam for dual or circular polarization.
5. Flat reflector according to 1 to 4, in which the dipole dimensions in each cell are adjusted to get The electrical characteristics of a beam reflector conformed.
6. Flat reflector according to 1 to 5, characterized by collimating the electromagnetic field from the circular polarization feeder or concentrating on the feeder an incident collimated beam in the circular polarization reflector.
7. Flat reflector according to 1 to 5, characterized by having two feeders (14) located at two different focal points, operating in orthogonal polarizations, in which the lengths of the dipoles (15, 16, 17, ...), and (18, 19, ...) in each cell are adjusted to ensure that the beams coming from the two feeders are reflected forming collimated beams in the same predetermined direction or in different directions.
8. Flat reflector according to 1 to 7, characterized by being constructed in several pieces to be folded and unfolded.
ES200401382A 2004-06-08 2004-06-08 Flat reflecting antenna in printed technology with improved bandwidth and polarization separation. Active ES2249984B2 (en)

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Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4943811A (en) * 1987-11-23 1990-07-24 Canadian Patents And Development Limited Dual polarization electromagnetic power reception and conversion system
CA2279262A1 (en) * 1997-11-28 1999-06-10 Daimler-Benz Aerospace Ag Transmission polarizer
US20010050653A1 (en) * 2000-03-14 2001-12-13 Clancy Kevin C. Apparatus and method for reducing polarization cross-coupling in cross dipole reflectarrays
US6426727B2 (en) * 2000-04-28 2002-07-30 Bae Systems Information And Electronics Systems Integration Inc. Dipole tunable reconfigurable reflector array

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