Radio frequency lens and method of suppressing side-lobes

ES 2 575 360 T3

DESCRIPTION

Radio Frequency Lenses and Side Lobe Suppression Method

Background of the invention

1. Technical field

The present invention relates to lenses for radio frequency transmissions. In particular, the present invention relates to a radio frequency (RF) lens that includes a photonic crystal structure and suppresses side lobe characteristics.

two. Discussion of Related Art

Radio frequency (RF) transmission systems generally use satellite dishes that reflect RF signals to transmit an outgoing collimated beam. However, these types of antennas tend to transmit a substantial amount of energy within the side lobes. Side lobes are the part of an RF beam that are dictated by diffraction when necessary to propagate the beam from the antenna aperture. Typically, sidelobe energy suppression is problematic for RF systems that require tolerance to interference, and is critical to reducing the likelihood of detecting the transmitted beam (for example, an RF beam is less likely to be detected, has interference or is spied on in response to the suppression of lobe energy).

US 2006/202909 A1 discloses an RF antenna apparatus comprising a dielectric lens that can be manufactured from a photonic crystal and US 2002/084869 A1 discloses a beam manipulation device for manipulating an Rf beam using a plurality of refractive layers fabricated with those of photonic crystal.

Summary of the invention

The invention relates to a lens and a method for manipulating a radio frequency beam according to the independent claims.

The beam manipulation device may be part of a system that includes the signal source that provides the RF beam.

The beam manipulation device is constructed with a lightweight mechanical arrangement of two or more materials, in which the materials are arranged to form a photonic crystal structure (eg, a series of defined holes within a precursor material). The beam manipulation device includes impedance matching layers, although an absorption or apodization mask is applied to the lens to create a specific energy profile through the lens. The impedance matching layers and apodization mask likewise include a photonic crystal structure. The function of the energy profile through the lens aperture is continuous, although the derivatives of the energy distribution function are continuous in the same way. This lens arrangement produces a substantial reduction in the amount of energy that is transmitted in the side lobes of an RF system.

The photonic crystal structure of embodiments of the present invention provides several advantages. In particular, the lens structure provides precise control of the phase error across the aperture (or phase narrowing at the aperture) simply by changing the spacing and size of the hole patterns. This allows a lens design with limited diffraction wavefront qualities, thereby ensuring the narrowest possible beams. Furthermore, the inherent lightweight nature of the lens precursor material (and defined holes in it) allows the creation of an RF lens that is lighter than that of a corresponding solid counterpart. The structural shape of the holes allows the lens to contain greater structural integrity in the rim portions than a lens with a similar function that is generally thin at the edges. These types of thin-edged lenses can loosen slightly, thus creating errors within the wavefront. Furthermore, the photonic crystal structure is generally smooth or flat, thus providing easy fabrication, preferably through the use of computer aided fabrication techniques. Furthermore, the photonic crystal structure directs the entire RF beam without creating side lobes (or with these basically reduced).

The aforementioned and further features and advantages of the present invention will become apparent after considering the following detailed description of specific embodiments thereof, in particular when taken in conjunction with the accompanying figures in which similar reference numerals in the various figures are used to designate similar components.

ES 2 575 360 T3

Brief description of the figures

Fig. 1 is a schematic illustration of an RF lens of one embodiment of the present invention that is being illuminated by an RF signal source.

Figs. 2A-2C are elevational views of exemplary photonic crystal structures of the type employed by the lenses of embodiments of the present invention.

FIG. 3A is a side elevational view of an exemplary optical lens.

Fig. 3B is a diagrammatic illustration of a beam being directed by a lower portion of the lens of Fig. 3A.

Fig. 4 is a side elevational view of a portion of the lens of Fig. 3A.

Fig. 5 is a graphic illustration of a far field intensity pattern generated by a conventional satellite dish.

Fig. 6 is a graphic illustration of a far field intensity pattern generated by the lens of one embodiment of the present invention.

Fig. 7 is a graphical illustration of a cross-sectional profile of the far field intensity patterns of Figs. 5 - 6.

Fig. 8 is a graphical illustration of apodization profiles of a beam along Cartesian axes (eg, X and Y) of an aperture of a conventional parabolic antenna and lens of one embodiment of the present invention.

Fig. 9 is a graphic illustration of the apodization attenuation factor necessary to achieve an aperture illumination function.

Detailed description of the preferred embodiments

Embodiments of the present invention relate to a radio frequency (RF) lens that includes a photonic crystal structure and suppresses side lobe characteristics. An exemplary lens in accordance with one embodiment of the present invention that is being illuminated by an RF signal source or Power Horn is illustrated in Fig. 1. specifically, the configuration includes a signal source 26 and an RF lens 20 in accordance with one embodiment of the present invention. Signal source 26 can be implemented by any conventional signal source or any other signal source (eg, feed horn, antenna, etc.) and preferably provides an RF signal or beam 28. Lens 20 receives the beam signal from signal source 26 and refracts the beam to produce a collimated RF 30. Lens 20 can be used for any RF transmission and / or reception system.

Lens 20 includes a lens portion or layer 10, a plurality of impedance matching layers 22, and an absorption or apodization layer or mask 24. Lens layer 10 is positioned between and attached to impedance matching layers 22 . Absorption layer 24 is bonded to impedance matching layer in front of signal source 26, wherein RF beam 28 enters lens 20 and passes through absorption layer 24, impedance matching layer 22 and lens layer 10, and exits through the remaining impedance matching layer as a collimated beam. However, the lens layers 20 can be of any quantity, shape, or size, can be positioned in any suitable manner, and can be attached by any conventional or other suitable techniques (eg, adhesives, etc.).

Lens layer 10 includes a photonic crystal structure. An exemplary photonic crystal structure for lens layer 10 is illustrated in FIG. 2A. Initially, photonic crystal structures use a variety of materials, in which the characteristic dimensions of, and spacing between, the materials are generally on the order of, or less than, the wavelength of a signal (or photon) of interest. (for example, for which the material is designed). Materials generally include varying dielectric constants. Some photonic crystal structures can be engineered to include size characteristics, which are reported to be desirable for certain applications. Specifically, lens layer 10 is formed by definition of a series of holes 14 within a precursor material 12, preferably by piercing techniques. However, the holes may alternatively be defined within the precursor material by any conventional technique or machine (eg, computer aided manufacturing, two-dimensional machines, water jet cutting, laser cutting, etc.). In this case, the two materials that make up the photonic crystal structure include air (or possibly vacuum for space applications) and the precursor material 12. The precursor material is preferably an RF laminate and includes a high dielectric constant (eg, in the range of 10-12). The precursor material may alternatively include plastics, a high-density polyethylene, glass, or other materials with a low loss tangent in the frequency range of interest and a suitable dielectric constant. The hole placement can be adjusted to alter the behavior of the lens layer as described below.

The precursor material 12 can be of any suitable size or shape. By way of example only, the precursor material 12 is substantially cylindrical in the shape of a disk that includes an inner region 16 positioned near the center of the disk and an outer region 18 positioned toward the periphery of the disk. Holes 14 are defined within inner and outer regions 16, 18. The holes are generally defined through the precursor material in the direction of (or substantially parallel to) the propagation path of the beam (e.g., along

ES 2 575 360 T3 along an axis of propagation, or from the front surface of the lens through the thickness of the lens towards the rear surface of the lens). The holes 14 within the outer region 18 include dimensions less than the wavelength of the signal or beam of interest, while the spacing between those holes is likewise on the order of or less than the wavelength of the signal of interest. For example, a hole dimension and spacing of less than one centimeter can be used for an RF beam with a frequency of 30 gigahertz (GHz). Greater lens efficiency can be achieved by reducing the dimensions and spacing the holes with respect to the wavelength of the signal of interest as described below.

As a photon reaches material 12, an electromagnetic field close to the material essentially experiences an averaging effect from the varying dielectric constants of the two materials (e.g., material 12 and air) and the resulting dielectric effects. of those materials are proportional to the mean of the volumetric capacities of the materials within the lens layer. In other words, the resulting dielectric effects are comparable to a dielectric with a constant derived from a weighted average of the material constants, where the material constants are weighted based on the percentage of the corresponding volumetric capacity of the material with with respect to the volume of the structure. For example, a structure that includes 60% by volume of a material with a dielectric constant of 11.0 and 40% by volume of material with a dielectric constant of 6.0 will provide properties of a dielectric with a constant of 9.0 (for example, (60% x 11.0) + (40% x 6.0) = 6.6 + 2.4 = 9.0).

Since an optical lens includes material of higher refraction near the center portion of the lens than that near the edge of the lens, the photonic crystal structure for lens layer 10 is constructed in the same way to include (or emule) this property. Consequently, the holes 14 defined within the outer region 18 are significantly more closely spaced as a whole than the holes 14 defined within the inner region 16. The spacing of the holes 14 and their corresponding diameters can be adjusted as a function of the radius of the frame to create a lens effect from the entire frame. Therefore, the electromagnetic fields produced by the photonic crystal structure essentially emulate the effects of the optical lens and allow the entire beam to be directed or refracted. Since the photonic crystal structure is generally flat or smooth, the photonic crystal structure is simple to manufacture and can be made using computer aided manufacturing techniques as described above.

The manner in which holes 14 are defined in lens layer 10 is based on the desired direction or refraction of the RF beam. An exemplary optical lens 25 that directs or refracts a beam is illustrated in Figs. 3A-3B and 4. Initially, lens 25 is substantially circular and includes generally curved or spherical surfaces or faces. The lens can be considered as a plurality of differential sections 61 for purposes of describing the steering effect. Each differential section 61 of lens 25 (Fig. 3A) includes a generally trapezoidal cross section and directs a beam as if the lens were actually a wedge prism, in which an equivalent wedge angle for that section is a function of the distance of the differential section from the center of the lens (for example, the wedge angle is measured with respect to a surface tangent for the curved surfaces of the lens). In other words, a beam is refracted according to a local surface gradient of the lens in a manner basically similar to refraction from a flat surface.

Specifically, a beam 7 is directed to pass through lens 25. The spread of the beam exiting the lens can be determined from Snell's Law as follows.

«Sen - /_I;sin (Equation 1) in which m is the refractive index of the first material crossed by the beam, m is the refractive index of the second material crossed by the beam, Si is the angle of the beam enters the second material, and 02 is the angle of the beam refracted within that material. Direction angles of interest for beam 7 directed toward lens 25 are determined relative to axis of propagation 60 (eg, an axis perpendicular and extending through the lens front and back faces) and according to with Snell's Law. Therefore, each of the equations based on Snell's Law (for example, as visualized in Fig. 3B) has two angles from the equation adjusted by the wedge angle (eg, β as displayed in Fig. 3B) to get the beam direction value with respect to the axis of propagation as described below.

Beam 7 enters lens 25 at an angle, Qia, that is within a plane that contains the optical axis 80 for the lens (e.g., the vertical line or axis through the center of the lens from the thinnest part to the thickest part) and the axis of propagation of the lens 60. This angle is the angle of the entrance of the beam. Since lens 25 changes refraction with a function of radius from the center of the lens, a beam is normal to the particular point the beam is incident on. Consequently, the beam entrance angle, Θ ™, with respect to the axis of propagation 60 is simply the wedge angle; β, from the lens (for example, Θμ = -β as displayed in Fig. 3B). The beam is refracted at an angle, & 2A, relative to the surface normal 70 of the front surface of the lens is determined based on Snell's Law as follows.

ES 2 575 360 T3 f

sen

Λ

<img file="ES2575360T3_D0001.tif" />

^ Éesen (0! A) n ·

V,

A (Equation 2) in which n_to¡Re is the refractive index of air, n is the average refractive index of the lens material at the radial impact position described below, and Θια is the beam entry angle.

The beam passes through the lens and is directed toward the rear surface of the lens at an angle, Oíb, relative to the normal of surface 70 of that rear surface. This angle is the angle of refraction down the front surface of the lens, Θ24, combined with wedge angles, β, from the front and back lens surfaces and can be expressed as follows.

Θ1Β - &amp; 2A ⁺ 2β (Equation 3)

The beam passes through the rear surface of the lens and is refracted at an angle, 02s, relative to the normal of the surface 70 of the rear surface of the lens and is determined based on Snell's Law as follows.

Θ2Β =

<img file="ES2575360T3_D0002.tif" />

(Equation 4) where n is the mean index of refraction of the lens material at the radial position of the impact described below, n_to/ re is the index of refraction of air, and Oís is the angle of entry of the beam. The angle of refraction, 0r, with respect to the axis of propagation 60 is simply the angle refracted with respect to the normal of the surface 70 of the posterior surface of the lens, 02s, minus the wedge angle, β, of the posterior surface of the lens (eg, as displayed in Fig. 3B) and can be expressed as follows.

<img file="ES2575360T3_D0003.tif" />

(Equation 5)

Referring to FIG. 4, the cross section of a differential section 61 of exemplary optical lens 25 is symmetrical about a plane perpendicular to axis of propagation 60. Generally, the lens includes a nominal thickness, t edge. , on the periphery of the lens. The lens material includes an index of refraction, ru, while the surrounding medium (eg air) includes an index of refraction, no, usually around 1.00. A mean index of refraction for lens 25 can be determined from a se differential section 61 or line (eg, along the dotted line as displayed in Fig. 4) as a function of distance. , r, of that line from the center of lens 25 (for example, as displayed in Fig. 4) as follows (eg, a weighted average of the index of the refractive values ​​for line segments along the line based on the length of the line segment).

2 «, (r - -¿ϋ4) + 2 ^ (ς - / 4}

Mu = -; ---------—-— --- (Equation 6)

L ', edge where ru is the refractive index of the lens 25, rio is the refractive index of air, R_c is the radius of curvature of the lens surface, D is the diameter of the lens, Ct is the center thickness of the lens, t edge is the thickness of the lens edge, and β is the wedge angle of section 61. The edge thickness, t edge, of the lens 25 does not contribute to the mean refractive index since the lens refractive index remains relatively constant in the areas included by the edge thickness (for example, between vertical dotted lines such as is displayed in Fig. 4).

ES 2 575 360 T3

The wedge angle, β, is a function of the distance, r, from the center of the lens as follows, p (r) = arcco $ (r / í_c) (Equation 7) where Re is the radius of curvature of the lens surface. Consequently, the mean refractive index can be expressed as a function of the wedge angle, β, as follows.

C "edge (Equation 8) in which m is the refractive index of the lens 25, not the refractive index of air, R_c is the radius of curvature of the lens surface, D is the diameter of the lens, Ct is the thickness of the center of the lens, t edge is the thickness of the lens edge, and β is the wedge angle of section 61. Therefore, a photonic glass lens with a particular refractive index profile provides the same beam direction characteristics as lens 25 (or sections 61) with wedge angles, β, derived from Equation 8.

The mean refractive index for lens 25 is a function of the radius or distance, r, from the center of the lens. This function is not a constant value, but instead follows a function that needs to meet the requirements of the lens. The function of an optical lens is either to focus collimated light on a feed or to re-image the energy from one feed to another. For the case of collimated light focusing, the curvature of the rays follows a simple formula. A ray striking the optical lens at a radius or distance, r, from the center of the lens is deflected by an angle, 0l, which is a function of the lens focal length, Fi, as follows.

<img file="ES2575360T3_D0004.tif" />

(Equation 9)

As described above, Equation 5 provides the angle of the directed or refracted beam, 0r, based on Snell's Law.

The properties for the lens layer 10 can be obtained iteratively from the equations mentioned above, in which the refractive index for a photonic crystal structure is equivalent to the square root of the dielectric constant as described. previously. In particular the process begins with a known or desired optical lens function for emulation by lens 20 (eg Equation 9) and the requirements or properties for the focal length of the optical lens. A given radial value, r, is used to obtain the angle of deviation, Ol, from Equation 9, where the angle of deviation is equal to the angle of refraction, 3r, and is inserted into Equation 5. Since the mean refractive index is a function of the wedge angle, β, the wedge angle and / or mean refractive index required to perform the lens function for the radial value can be determined from Equation 8. This process it is performed iteratively for radial values, r, to provide an end of refractive index for the lens (eg, the mean index of refraction for radial positions on the lens).

To create photonic glass lens 20 that emulates the physical properties of lens 25, holes 14 are positioned within precursor material 12 (FIG. 2A) of lens 20 to create the mean refractive index profile described above. Lens 20 generally includes substantially flat front and back faces normal to the axis of propagation (or direction of the beam propagation path) and emulates the physical properties of the optical lens through produced electrical fields. However, the refractive index for a photonic glass lens is equivalent to the square root of the dielectric constant of the lens (for example, for materials exhibiting low loss agents that are preferred for refraction or direction of RF beams) . In the case of materials that include significant absorption or dispersion, the refractive index is a complex value with real and imaginary components. The imaginary component provides a measure of the loss. Since the magnitude of the imaginary component (or loss) detracts from the real component (or dielectric constant), the dielectric constant differs from the aforementioned relationship in response to significant losses.

ES 2 575 360 T3

The effective refractive index along a part or line of the photonic glass lens is obtained by taking the mean volumetric refractive index along that line (for example, a weighted average of the refractive index (or dielectric constants of materials and orifices) along the line based on volume in a manner similar to that described above). The direction angle, 0r, of the resulting photonic glass lens can be determined based on Snell's Law using the effective refractive index of of the photonic glass lens as the mean refractive index, n, within Equation 5 described above. The average volumetric determination would consider the regions above and below the line (eg, analogous to the value of distance, r, described above). The physical shape of the holes may vary depending on the manufacturing process. An exemplary manufacturing process includes drilling holes in the prism materials.

The orientation of the holes defined in the photonic glass lens may be normal to the front and rear areas of the lens (eg, in a beam axis direction or path). The dimensions of the holes are small enough to allow electromagnetic fields from photons (eg manipulated with the photonic crystal structure) to be influenced by the mean refractive index on the volume of the lens interacting with or manipulating the photons. Generally, the diameter of the holes does not exceed (for example, less than or equal to) a quarter of the wavelength of the beam of interest, while the space between the holes does not exceed (for example, less than or equal to) the wavelength of that beam.

Consequently, an interaction volume for the photonic glass lens includes a square wave (eg, an area defined by the square of the wavelength of the beam) as displayed normal to the axis of propagation. Since some changes in the photonic crystal structure can create impedance mismatch along the axis of propagation, the length or thickness of the photonic crystal lens interaction includes a short dimension. Generally, this dimension of the photonic glass lens along the axis of propagation (for example, or thickness) should not exceed 1/16 of the wavelength of the beam to avoid the impact of excessive propagation (for example , producing new reflections or etalon resonances). Therefore, drilling holes through the thickness of the material is beneficial as this technique ensures minimal changes in refractive index along the axis of propagation.

By way of example, a hole spacing in the precursor material that provides a minimum mean refractive index (e.g., defined by the largest hole diameter allowed and determined by the operating wavelength as ascribed above) includes the holes spaced from each other in a hexagonal arrangement of equatorial triangles (for example, each hole at a corresponding vertex of a triangle) with a minimum wall thickness between holes to provide adequate mechanical strength. This is a hole spacing that matches the thinnest part of a conventional lens.

In contrast, a hole spacing within the precursor material that can provide the highest mean refractive index is a photonic glass lens without the presence of holes. However, the need for a slightly changing mean refractive index and effective control of the direction of the beam energy can put limitations on this configuration. If the photonic glass lens is configured to include holes of the same size (for example, as it may be economically feasible due to manufacturing limitations in machines, such as automated drilling centers), the maximum mean refractive index would be obtained with a minimum of one orifice per interaction volume. This region of the photonic glass lens corresponds to the thickest part of the lens 25.

Referring back to Fig. 1, the use of a precursor material with a high dielectric constant value for the lens layer 10 results in a lighter lens, but tends to produce the lens without the adaptation property of impedance. The lack of impedance matching creates surface reflections and ultimately requires more power to operate an RF system. Consequently, lens 20 includes impedance matching layers 22 applied to the photonic crystal body layer 10 to minimize these reflections. The ideal dielectric constant of the impedance matching layers 22 is the square root of the dielectric constant of the lens layer 10. However, due to the variable hole spacing in the lens layer (eg, within the inner and outer regions 16, 18) as described above, the dielectric constant of the lens layer is variable.

To compensate for the varying dielectric constant of the lens layer, the impedance matching layers 22 likewise include a photonic crystal structure (Fig. 2B). This structure can be constructed in the manner described above for the lens layer and includes a precursor material 32 with a mean dielectric constant that approximates the square root of the mean dielectric constant of the precursor material 12 used for the layer. lens 10. The precursor material can be of any shape or size and can be of any suitable material, including the desired dielectric constant properties. By way of example only, the precursor material 32 is substantially cylindrical in the shape of a disk with substantially flat front and rear surfaces.

ES 2 575 360 T3

Impedance matching layers 22 generally include a hole spacing pattern similar to that of lens layer 10, but with minor variations to ensure a correct square root relationship between the local mean dielectric constant of the lens layer. lens and the corresponding local mean dielectric constant of the impedance matching layers. In other words, the hole spacing pattern is arranged to provide a mean refractive index profile (e.g. Equation 6) (or dielectric constant) equivalent to the square root of the refractive index profile (or dielectric constant). of the layer (eg, lens layer 10) having the matched impedance. In particular, the thickness of the impedance matching layer is in integer increments of (2n -λ) / 4 waves or wavelength (for example, 1/4 wave, 3/4 wave, 5/4 wave , etc.) and is proportional to the square root of the mean index of refraction of the lens layer having the Impedance adapted as follows ^ ^ / ft (r) = (2n-lX / 4 (Equation 10) in where / is the thickness of the impedance layer, A is the wavelength of the beam of interest, n represents an example of series and is the average index of refraction of the lens layer as a function of the distance, r, from the center of the lens.

Achieving a lower refractive index with an impedance matching layer can become impractical due to the number of holes required in the material. Consequently, systems requiring impedance matching layers should begin with an analysis of the minimum mean refractive index that is likely to be necessary for mechanical integrity, thus providing the required refractive index for the impedance matching layer. The mean refractive index of the device to which this impedance matching layer is adapted would consequently be the square of the value achieved by the impedance matching layer.

An ideal thickness for impedance matching layers is a quarter of the wavelength of the signal of interest divided by the square root of the (average) refractive index of the impedance matching layer (for example, Equation 10, where the refractive index is the square root of the dielectric constant as described above). Due to the variability of the dielectric constant (for example, as a function of radius) of the impedance matching layer, a secondary machining operation can be used to bend the impedance matching layers and maintain thickness. of a quarter wave from the center of the layer to the edge of the layer. Impedance matching layers can improve antenna efficiency on the order of 20% (eg 55% to 75%).

A common illumination pattern on a satellite dish is a truncated exponential field strength, or a truncated Gaussian. The Gaussian is truncated at the edge of the satellite dish since the field must obtain a limit at some point. At the edge of the satellite dish, the field strength should go to zero, however, for a typical feed horn arrangement, the field strength at the edge of the satellite dish is greater than zero. This creates a problem in the far field, where the discontinuous derivative of the aperture illumination function creates unnecessarily strong side lobes. Side lobes are the part of an RF beam that is dictated by diffraction as necessary to propagate the beam from the antenna aperture. In the far field, the main beam follows a beam divergence that is on the order of twice the wavelength of the beam divided by the diameter of the aperture. The actual intensity pattern throughout the far field, however, is accurately approximated as the Fourier transform of the aperture illumination function.

The sharp edges in the aperture lighting function or any low-order derivatives create spatial frequencies in the far field. These spatial frequencies are seen as lower power beams emanating from the RF antenna, and are called side lobes. Side lobes contribute to the detection ability of an RF beam, and make it easier for the beam to be jammed or to be eavesdropped. To reduce the occurrence of these types of adverse activities, the side lobes have to be reduced. A common technique for reducing side lobes is to create an aperture lighting function that is continuous, in which all derivatives of the function are also continuous. An example of such a lighting function is a square sine function. The center of the aperture includes an arbitrary intensity of unity, while the intensity is attenuated following a sine-squared function of the aperture radius towards the outer edge of the aperture, where the intensity equals zero.

The square sine function is a simple function that clearly has continuous derivatives. However, other functions can be used, and may offer other benefits. In either case, the lighting function should be chosen to include a certain level of absorption of the characteristic power horn lighting pattern (eg, otherwise gain would be necessary).

Another common technique for reducing the illumination function at the edge of the antenna is to configure the edge of a reflecting antenna with a series of pointed triangles (for example, a jagged edge). This provides a

ES 2 575 360 T3 narrow reflection profile and smoothly brings the illumination function of the aperture to zero at the edge of the reflector, thereby assisting in the reduction of side lobes. However, these types of structures are not feasible for lenses and can create spatial frequency effects in the far field due to their physical dimensions that are generally greater than the wavelength of the signal of interest.

To reduce side lobes, lens 20 includes apodization mask 24 which is truly absorbing for an ideal case. If the dimming of the lighting pattern occurs through the use of reflection techniques (eg metal coatings), care must be taken to control the direction of those reflections. The apodization mask is preferably constructed to include a photonic crystal structure (Fig. 2C), similar to the photonic crystal structure written above for the lens and impedance matching layers. In particular, the holes 14 can be defined within a precursor material 42 with an appropriate absorption coefficient by any suitable technique (eg, drilling, etc.). The holes are arranged or defined within the precursor material to provide the precise absorption profile desired. The precursor material can be of any shape or size and can be of any suitable material, including the desired absorption properties. By way of example only, the precursor material 42 is substantially cylindrical in the shape of a disk with substantially flat front and rear surfaces.

The absorption material is analyzed to provide the necessary absorption profile as a function of lens radius (compared to refractive index). The holes 14 are positioned in the precursor absorbent material 42 to create a mean absorption over a volume in substantially the same manner as described above to achieve the mean refractive index profile for the lens layer. The actual function of the apodization profile can be quite complex if a precise beam shape is required. However, a simple formula applied to the edge of the opening is sufficient to achieve a noticeable benefit.

An example of an apodization function that can approximate a desired edge illumination narrowing to control the side lobes is one that includes a 1 / r function², where r represents the radius or distance from the center of the lens. For example, a lens with an incident aperture illumination function that has a Gaussian profile and an edge intensity of 20% (of the maximum intensity at the center) can be associated with a narrow edge function, Ψ ^, as follow next ψ (/) = ί — L-] + i (EquationH)

The denominator multiplier term (eg three) is a consequence of the lighting function including 20% ​​energy at the edge of the opening. This multiplier can vary according to the value of the energy at the edge of the opening. Equation 11 provides the absorption ratio as a function of radius, which can be summarized as the ratio of absorbed energy to transmitted energy. The radius value is normalized (for example, radius of r_max = 1) for simplicity. This function is very close to the ideal apodization function. However, for an optimized system, minor variations in function may be desired.

To perform this function within the photonic crystal apodization mask 24, a series of holes 14 are placed within the precursor material 42 which is highly absorbent of radio waves (eg, carbon loaded material, etc.). The average absorption of the material (for example, a weighted average of the absorption of the material and the holes (for example, the holes would not have absorption) based on the volume and is determined in a similar way to the weighted average for the dielectric constant described above) with respect to the lens interaction volume provides the absorption value for the apodization mask. The absorption mask divided by the non-apodized case should provide an approximate value resulting from Equation 11. Thus, the holes 14 are placed in the precursor material 42 in a manner to provide the absorption values ​​to produce the absorption profile. wanted. The apodization mask 24 can be configured with holes 14 closely spaced together (Fig. 2C) when this layer is mounted on other layers of the lens. In this case, the mechanical integrity of the apodization mask is provided by the layers in which the apodization mask is mounted, thus allowing the closely spaced arrangement of the holes 14.

The apodization mask can be easily manufactured using computer aided manufacturing techniques as described above. Equation 11 can be modified to accommodate wire drives that do not produce energy distributions with a Gaussian profile and achieve the desired results.

Figs. 5-6 illustrate an exemplary far field intensity pattern of an unappodized aperture and an apodized aperture of lens 20, respectively. The magnitude of intensity within the pattern is indicated by the shading illustrated in the legend (eg, as seen in Figs. 5-6). The unpodized case

ES 2 575 360 T3 (Fig. 5) is for a conventional parabolic antenna illuminated with a feed horn and with a cutoff illumination of 20% at the edge. The feed horn is primarily mounted on and supported by a three-bladed spider mount. The apodized case (Fig. 6) shows the far field pattern for lens 20 (eg, a clear aperture photonic glass lens manufactured to offer diffraction limited beam divergence). Fig. 7 illustrates the cross-sectional far field intensity pattern of unappodized and apodized cases. Intensity patterns are plotted along the X and Y axes respectively representing field angle and normalized intensity (as displayed in Fig. 7). The apodized case has slightly higher main beam divergence, but with greatly suppressed side lobes, especially away from the main beam. Side lobe suppression reaches factors of about 1,000 when side lobe energy is strongest.

Fig. 8 illustrates apodization or absorption profiles of the RF beam along the Cartesian axes (eg, X and Y) of a conventional parabolic antenna aperture and the aperture of lens 20. The patterns of Illumination is plotted along the X and Y axes which we represent respectively, the pupil coordinates (eg radial normalized coordinates) and normalized intensity (eg as displayed in Fig. 8). The absorption or illumination pattern of the conventional satellite dish is truncated, while the lens 20 provides the absorption function of square sine or illumination pattern described above. Fig. 9 illustrates the apodization attenuation factor required to achieve the aperture illumination function, assuming a Gaussian beam profile truncated by approximately 20% at the aperture edge (for example, as shown in Fig. . 8 for conventional satellite dish). The attenuation profile is plotted along the X and Y axes respectively representing the pupil coordinates (e.g. normalized based on radius) and the attenuation factor (e.g. as displayed in Fig. 9).

Lens 20 can be used to create virtually any type of beam direction or pattern desired. Therefore, several lenses can be produced each with a different hole pattern to provide a series of interchangeable lenses for an RF system (Fig. 1). In this case, a photonic glass lens can easily be replaced within an RF system with other lenses that include different hole patterns to achieve desired (and different) beam patterns. Furthermore, the photonic crystal structure can be configured to create any type of device (e.g. quasi-optics, lenses, prisms, beam splitters, filters, polarizers, etc.) in substantially the same way as described above, simply by adjusting the dimensions, hole geometries and / or locations within a precursor dielectric material to achieve beam steering and / or beamforming characteristics.

It will be appreciated that the embodiments described and illustrated above in the figures represent only a few of the many ways to implement a radio frequency lens and side lobe removal method.

The lens can include any number of layers placed in any suitable way. The layers can be of any shape, size or thickness and can include any suitable material. The lens can be used for signals in any desired frequency range. The lens layer can be of any quantity, size, or shape, and can be constructed of any suitable material. Any suitable material can be used in any amount to provide the varying dielectric constants (eg, a plurality of solid materials, solid materials in combination with air or other fluid, etc.). The lens layer can be used with or without an Impedance Matching layer and / or apodization mask. The precursor material of the lens layer and / or other materials can have any quantity, size, shape or thickness, it can be any suitable material, (for example, plastic, a high-density polyethylene, RF laminates, glass, etc. .) and can include any suitable dielectric constant for an application. The precursor material preferably includes a low loss tangent in the frequency range of interest. The lens layer can be configured (or include multiple layers that are configured) to provide any desired directional effect or angle of refraction or to emulate the properties of a corresponding material or optical lens. The lens layer can be further configured to include any combination of beamforming (eg lens) and / or beam direction (eg prism) characteristics.

The holes in the lens layer can be of any quantity, size, or shape, and can be defined in the precursor material and / or other material in any arrangement, orientation, or location to provide the desired characteristics (e.g., lens orientation effect). beam, refractive index, dielectric constant, etc.). The various regions of the lens precursor material layer can include any desired hole arrangement and can be defined at any suitable location in that material to provide the desired characteristics. The holes can be defined within the precursor material and / or other material by any conventional technique or other manufacturing techniques or machines (eg, computer-aided manufacturing techniques, stereolithography, two-dimensional machines, waterjet cutting , laser cutting, etc.). Alternatively, the lens layer can include or use other solid or fluid materials to provide the varying dielectric constants.

ES 2 575 360 T3

The impedance matching layer can be of any quantity, size, or shape, and can be constructed of any suitable material. Any suitable material can be used in any amount to provide the varying dielectric constants (eg, a plurality of solid materials, solid materials in combination with air or other fluid, etc.). The precursor materials and / or other materials of the impedance matching layer can have quantity, size, shape or thickness, it can be any suitable material (for example, plastics, a high density polyethylene, RF laminates, glass, etc. ) and can include any suitable dielectric constant for an application. The precursor material preferably includes a low loss tangent in the frequency range of interest. The impedance matching layer can be configured (or include multiple layers that are configured) to provide impedance matching for any desired layer of the lens.

The holes for the impedance matching layer can be of any quantity, size, or shape, and can be defined in the precursor material and / or other material in any arrangement, orientation, or location to provide the desired characteristics (e.g., impedance matching , refractive index, dielectric constant, etc.). The holes can be defined within the precursor material and / or other material by any conventional technique or other manufacturing techniques or machines (e.g., computer-aided manufacturing techniques, stereolithography, two-dimensional machines, waterjet cutting, laser cutting, etc.). Alternatively, the impedance matching layer can include or utilize other solid or fluid materials to provide the varying dielectric constants.

The apodization mask can be of any quantity, size, or shape, and can be constructed from any suitable material. Any suitable material of any quantity can be used to provide the desired absorption coefficient or absorption profile (eg, a plurality of solid materials, solid materials in combination with air or other fluid, etc.). The precursor material and / or other material of the apodization mask can have any quantity, size, shape or thickness, it can be any suitable material (for example, plastic, a high density polyethylene, RF laminate, carbon material loaded, etc.) and can include any suitable radio or other wave absorbing characteristics for an application. The precursor material is preferably implemented with a highly absorbent material for radio waves. The apodization mask can be configured (or include multiple layers that are configured) to provide the desired absorption profile.

The apodization mask orifices can be of any quantity, size, or shape, and can be defined in the precursor material and / or other material in any arrangement, orientation, or location to provide the desired characteristics (eg, lobe removal sides, absorption, etc.). The holes can be defined within the precursor material and / or other material by any conventional or other manufacturing techniques or machines (by obscura, computer-aided manufacturing techniques, stereolithography, two-dimensional machines, waterjet cutting, laser cutting, etc.). Alternatively, the apodization mask can include or use other solid or fluid materials to provide the absorption properties. The apodization mask can be configured to provide the desired absorption properties for any suitable narrow function.

The lens layers (eg, lens layer, impedance matching, apodization mask, etc.) can be bonded in any way by any conventional or other technique (eg, adhesives, etc.). The lens can be used in combination with any suitable signal source (eg feed horn, antenna, etc.), or signal receiver to direct input signals. The lens can be used to create virtually any type of pattern desired, in which multiple lenses can each be produced with a different building pattern to provide a series of interchangeable lenses to provide multiple RF beams in other systems. In addition, the photonic crystal structure of the lens can be used to create any beam manipulation device (e.g. prism, beam splitters, filters, polarizers, etc.) simply by adjusting the dimensions, geometries and / or location of the hole. within the precursor material and / or other materials to achieve the desired beam orientation and / or beam-forming characteristics.

It should be understood that the terms top, bottom, front, back side, height, length, width, top, bottom, vertical, horizontal, and the like herein are used simply to describe reference points and do not limit the embodiments herein. invention to any particular orientation or configuration.

From the foregoing description it will be seen that the invention achieves a new radio frequency lens and method for suppressing side lobes, wherein a radio frequency (RF) lens includes a photonic crystal structure and suppresses side lobe characteristics.