Abstract
A multiband resonator element which, on the one hand, compensates the components of an electromagnetic field radiated from its phase centre, located on the axis of symmetry of the resonator, to control the polarization purity of a radiating element. On the other hand, it enables the selection of the electromagnetic fields reflected and transmitted on a frequency- and multiband-selective surface. In this sense, this is an innovative element that enables the design of directive radiating elements and with an axial ratio for its circular polarization less than or equal to 1.5 dB for all the angles belonging to the hemisphere centred on broadside. Thus, it can be used in the design of reflectarrays, transmitarrays and any dichroic multiband surface, likewise on metamaterial surfaces.
Claims
1. A cavity filter comprising a plurality of resonator elements, wherein each resonator element comprises a plurality of stubs adjusted in frequency and arranged according to a geometric shape to be selected from an ellipse or a rectangle, wherein each resonator element is disposed on a layer of dielectric material and separated from each other by a layer of foam-type material or air, wherein the dielectric materials include a variable dielectric constant to change the working frequency or its phase response, to perform low-pass, high-pass, band-pass or multiband-pass filters.
2. A radiating element formed by the filter cavity according to claim 1 for single or multiband applications.
3. A radiating element comprising a resonator element, wherein the resonator element comprises a plurality of stubs adjusted in frequency and arranged according to a geometric shape to be selected from an ellipse or a rectangle, wherein the radiating element further comprises an aperture polarizer configured to improve the axial ratio of the circular polarization of the radiating element up to angles of 90 degrees from a broadside axis.
4. A frequency-selective surface for one or multiple bands formed by a plurality of periodic cells each comprising: a resonator element, wherein each resonator element comprises a plurality of stubs adjusted in frequency and arranged according to a geometric shape to be selected from an ellipse or a rectangle, wherein the frequency-selective surface further comprises a dielectric material with a variable dielectric constant.
5. A resonator element comprising: a plurality of stubs adjusted in frequency and arranged according to a geometric shape to be selected from an ellipse or a rectangle wherein the resonator element further comprises an adjustable dipole to favour a polarization or application.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
(1) To complement the description of the invention and for the purpose of aiding the better understanding of its characteristics, in accordance with a preferred example of embodiment thereof, a set of drawings is attached wherein, by way of illustration and not limitation, the following figures have been represented:
(2) FIG. 1 shows the resonator element formed by a series of stubs (13.a or 13.b) adjusted in frequencies and arranged radially between inner rings (12.a) and outer rings (11.a), thus forming a ring of stubs. They can also be arranged linearly on the four sides of a rectangle, with lower rings (12.b) and outer rings (11.b), thus forming a rectangle of stubs.
(3) FIG. 2 shows a possible embodiment of the dual-band and dual-polarization radiating element (20) formed with a resonator with C-type sections joined with stubs (21) formed with copper lines, it is superimposed on a corrugated cone of a Teflon-type material (22), in order to adapt the impedance seen inside the cavity (24) with the one outside the resonator, inside the cavity there is a filter (23) formed by 4 circular resonators (23.a, 23.d, 23.g and 23.k) the same as those of FIG. 1, supported on a layer of ceramic dielectric (23.b, 23.e, 23.h and 23.j), and separated with a foam-type material (23.c, 23.f and 23.i), whose purpose is to decrease the distance between each filter of the cavity by the dielectric constant of the latter, even if it is close to one. Therefore, with dielectric materials of higher dielectric constant, we will obtain a more compact filter, but this can significantly increase the losses. This design obtains circular polarizations with a purity less than or equal to 2 dB for all angles belonging to the viewing cone centred on Broadside. The feeding of the design could be carried out by different techniques, such as for example by capacitive coupling with a feeder formed by a stub and a slot.
(4) FIG. 3 shows the design of the unit cell (30) that would configure a frequency-selective surface, to be used in dichroic subreflectors. The component (31) is a layer of dielectric material (e.g kapton), it is located in front of the copper resonator (32) to protect it from possible deterioration due to weather phenomena, then there is another layer of dielectric material (e.g. kevlar) (33) and as in FIG. 2 a foam or honeycomb type material (34) is placed to adjust the space with the next layer of kevlar (35) and kapton (36).
(5) FIG. 4 shows the two unit cells (40), formed by two elements that are the same as those of FIG. 3, placed opposite one other, being the same element, the distance that separates element (41) from (42) is approximately half a wavelength because its impedances are the same. The layers that make up the two cells are: (41.a) and (42.f) consisting of a layer of dielectric material (e.g. kapton), (41.b) and (42.e) which are the copper resonator, (41.c) and (42.d) are another layer of dielectric material (e.g. kevlar), (41.d) and (42.c) are a foam or honeycomb type material, (41.e) and (42.b) are again a kevlar layer, and finally layers (41.f) and (42.a) are a new kapton layer. This distribution is used on a frequency-selective dichroic surface of a communications system which can work simultaneously in both transmission and reflection, having a dual working band in the case of reflection, and a working band in the case of transmission, the two reflection bands being separated from each other by the transmission band. The two reflection bands could be fed by a coaxial system, having the advantage of a simpler feeder design than is necessary for FIG. 4 since the two frequency bands reflecting the signal are more spaced out from one other. For the feed of the transmission band, any feeder dedicated to the band to which it has been tuned could be used.
(6) FIG. 5 shows two symmetrical unit cells (50); this design has a variation with respect to FIG. 4, and it is the replacement of the resonator element (42.e) by a ring (52.e), the layers that form the design are: (51.a) and (52.f) consisting of a layer of dielectric material (e.g., kapton), (51.b) copper resonator, and (52.e) which is a copper ring, (51.c) and (52.d) are another layer of dielectric material (e.g. kevlar), (51.d) and (52.c) are foam or honeycomb type material, (51.e) and (52.b) is again a layer of kevlar, and finally layers (51.f) and (52.a) are a new layer of kapton. In this case the distance that separates element (51) from (52) is not half a wavelength, since the impedance of the ring (52.e) is not the same as that of the resonator element (51.b), so this distance will vary depending on the specifications to be obtained. With this variation, the unit cells placed on a frequency-selective dichroic surface of a communications system that can act simultaneously in transmission and reflection are obtained, having in this case dual reflection work band and a work band for transmission, in this case the two reflection bands are closer than in the case of FIG. 4 the reflection bands. For the feeding of the reflection bands, the same strategy would be used as that proposed for FIG. 4, or a dual-band non-coaxial feeder. For the transmission band the same strategy is followed as for FIG. 4.
(7) FIG. 6 shows the response in adaptation (60) and reflection (61) of the design of FIG. 5, thus showing the three operating frequencies: two for reflection (61) and one for transmission (60).
(8) FIG. 7, shows the response in adaptation (70) and reflection (71) of the design of FIG. 4, thus showing the three operating frequencies: two for transmission (70) and one for reflection (71).
(9) FIG. 8 shows the axial ratio response optimized by the resonant element as a polarizer aperture, for the first design frequency (80) and the second design frequency (81), of FIG. 2.
(10) FIG. 9 shows the negative image of the two resonant elements presented in FIG. 1, i.e. in the circular resonator, the new metal section is (91.a), while (92.a) is of air or in a slot of a metal structure, in the same way in the rectangular resonator, due to the structure of the design, metal lines (93.a) must be added to support the interior part of the design. Incorporation of these lines does not significantly affect the radiation characteristics of the element. Likewise, in the square design the new metal section is (91.b) and the air section is (92.b), it is also necessary to incorporate the metal lines (93.b) to be able to support the Inner part.
(11) FIG. 10 shows a multiband dipole that can be implemented as a complement to the above resonators by joining two half-rings (102) and (103) through a stub (101), both in copper and in its negative (slot) version.
DETAILED DESCRIPTION OF THE INVENTION
(12) With reference to the numbering adopted in the figures described above, the description of the present invention will be described in greater detail, which is based on a multiband resonator element, such as that represented in FIG. 1, which is formed by a series of stubs (13.a or 13.b) adjusted in frequencies and arranged on what would be a ring or a rectangle, thus making a ring or rectangle of stubs.
(13) This element may be implemented to improve the axial ratio within an enlarged viewing cone of the radiating element under analysis, such as that shown in FIG. 2, consisting of an iris filter 23.a, 23.g, 23.d, and 23.k, in the dielectric load at aperture 22 which may be a shaped or corrugated cone, in a cavity 24 containing the foregoing elements, for working at two separate frequencies, and the multiband resonator element at aperture 21 which improves the ratio between the field components for large angles relative to the axis or elevation angles. This improvement of the axial ratio consists of obtaining a circular polarization purity less than or equal to 1.5 dB for an observation range of +/75 degrees, or less than or equal to 2 dB for an observation range of +/85 degrees, with respect to the axis or broadside or axis.
(14) This element can also be implemented in multiband dichroic subreflector designs. These multiband subreflectors can be made for virtually any band ratio with the normalized frequency response shown in FIGS. 6 and 7, for the non-symmetrical and symmetrical configurations, respectively. These bands may be, for example: [S, C, X], [Ku, K, Ka], [X, K, Ka], etc. These implementations in dichroic subreflectors being limited in the upper bands by the physical dimensions and manufacturing technologies available.
(15) For the case of application in the aperture of radiating elements to improve the axial ratio of radiating elements or antennas, the length of the stubs in FIG. 2, the width and spacing of the nearest tracks in FIG. 1, and the radius of the ring that the set of stubs forms, are adjusted to improve adaptation of the resonant patch or cavity with the medium at the antenna aperture. In addition, they optimize the axial ratio with respect to the axis of symmetry or direction of broadside as explained above.
(16) In the case of application in dichroic subreflectors, we can start from the resonator of FIG. 1, but now adding to this element (32) the layers corresponding to the dielectric materials, which can be, according to design and for a manufacture with classic technology of the embodiment presented in FIG. 3: Kapton (31), Kevlar (33), Foam or Honeycomb (34), Kevlar (35), and Kapton (36). These materials may change depending on the selected manufacturing technique or technology. Now, the length of the stubs adjusts the central band of FIG. 6, while the separation of the tracks of the stubs adjusts the central and upper bands of FIG. 6. The radius of the ring formed by the stubs adjusts the lower and upper bands of FIG. 6. Finally, another important variable for the design of a dichroic subreflector, using any resonator, is that of the period of the cell used (symmetrical sides of the cell of FIGS. 3, 4 and 5). This variable, for the specific case of the invention presented here, adjusts all the bands, but it is its greatest impact on the lower and upper bands. With this set of parameters and knowing its effects on the response of the element, it is possible to design the resonant element within a periodic cell for implementation in a dichroic subreflector working on a set of specific bands.
(17) In order to maximize transmission in a dichroic subreflector, it is demonstrated that it must have symmetry with respect to the impedances seen on both sides thereof, and these must be spaced at an effective distance of approximately half a wavelength in practice as depicted in FIGS. 4 and 5. Thus, it is possible to implement two classes of dichroic subreflectors based on the multiband resonator elements of FIG. 1 and the periodic cell of FIG. 3. That is, a symmetrical one with two resonators formed by stubs 41.b and 42.e on both sides in FIG. 4, or a non-symmetrical one with a resonator formed by stubs 51.b on one side and a smooth resonator ring 52.e on the other side in FIG. 5.
(18) The symmetrical configuration allows the lower and upper bands to be adjusted in reflection, while the central one is adjusted in transmission as can be seen in FIG. 7. On the other hand, the non-symmetrical configuration allows adjusting the lower band in transmission, while the central and upper bands in reflection as can be seen in FIG. 6.
(19) For the above, the slots shown in FIG. 9 can also be implemented, to implement different designs and manufacturing techniques. Likewise, the adjustable dipole of FIG. 10 can be introduced into the above elements depending on the polarization of the system and its multiband application.
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