Abstract:
A system and method for wirelessly transmitting signals via antenna phased array. In order to decrease the distance between individual antennae in the array, the antennae are submersed in a high dielectric material in addition to being arranged at right angles to one another, both features precluding one or more antennae from coupling. Furthermore, wires are covered in high dielectric material in order to refract RF signals around them, allowing antennae towards the center of the array to successfully transmit signals past other layers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims the benefit of and is a continuation-in-part of U.S. provisional application No. 61/867,001 filed on Aug. 16, 2013, by the same title, which application is hereby fully incorporated in its entirety by this reference. 
     This non-provisional application also claims the benefit of and is a continuation-in-part of co-pending U.S. application Ser. No. 14/171,750 filed on Feb. 3, 2014, which claims priority to U.S. provisional application Ser. No. 61/760,648, filed on Feb. 4, 2013, both entitled “Systems and Methods for Optimally Delivering Pulsed Wireless Power”, which applications are hereby fully incorporated in their entirety by this reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to the field of wireless signal transmission, and more specifically a new and useful system and method for engineering antenna arrays. 
     BACKGROUND 
     Many useful applications are based on the transmission of wireless pulses. Examples include radar detection using transmitted and reflected pulsed microwave signals as well as medical ablation procedures that use pulsed microwave to ablate targeted body tissues. 
     The U.S. patent application Ser. No. 14/171,750 filed on Feb. 3, 2014 for Ossia, Inc., which is hereby fully incorporated, covered a transmitter that optimizes the delivery of wireless power to a plurality of receivers. In transmitting power wirelessly, phased array transmitters are used to direct the Radio Frequency (RF) power. 
     The transmission efficiency of a phased array transmitter is proportional to the number of antennae in the array. To transmit at high efficiency using, for example, a 2.4 GHz signal at a distance of 5 meters, one would theoretically need about 1 million antennae in the array to reach efficiencies greater than 90%. However, placing 1 million antennae within more or less the same distance of 5 meters from the target is a challenge. Each antenna needs its own volume of space to prevent it from directly coupling with neighboring antennae, and therefore, the size of the array could become several times larger than the 5-meter distance. Moreover, the efficiency would also disappear as the array would grow and most of the antennae would be outside the 5-meter range. As such, there is a need for a means of decreasing the size of an array while overcoming the constraints induced by antennae proximity. 
     A means of decreasing the size of an array while overcoming the constraints induced by antennae proximity is incorporated in the embodiments of this invention. 
     SUMMARY 
     In accordance with the present invention, a means of decreasing the size of an array while overcoming the constraints induced by antennae proximity is provided. In order to decrease the distance between individual antennae in the array, the antennae are submersed in a high dielectric material in addition to being arranged at right angles to one another, both features precluding one or more antennae from coupling. Furthermore, wires are covered in high dielectric material in order to refract RF signals around them, allowing antennae towards the center of the array to successfully transmit signals past layers above them. 
     Note that the various features of the present invention described above may be practiced alone or in combination. These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       In order that the present invention may be more clearly ascertained, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  features a table that displays different frequencies and corresponding wavelengths and transmission ranges for various wireless applications; 
         FIG. 2  shows a size comparison between an antenna in air and a noticeably smaller antenna submerged in a high-dielectric material; 
         FIG. 3  shows the arrangement of antennae on a printed circuit board (PCB), wherein some components of the said antennae are represented by dashed lines going through the board from front surface to back surface and laid in three dimensions in order to cover every type of polarized signal; 
         FIG. 4A  shows the density of wires required to block a polarization of RF radiation in air; 
         FIG. 4B  shows the density of wires required to block the polarization of RF radiation when the said wires are immersed in a dielectric of permittivity coefficient p; 
         FIG. 5  shows exemplar dipole antennae having been etched using the same technique that etches the conductive traces on PCB; 
         FIG. 6  shows a cross section of a PCB with four layers, the middle two layers being used to etch the antennae so as to have them immersed in the dielectric materials of the PCB; 
         FIG. 7  shows a cross section of a PCB where the internal layers of the PCB host a conductive wire surrounded by air or some other low-permittivity material; 
         FIG. 8A  shows a signal facing air as it leaves a high-dielectric material and exhibiting a high total internal reflection angle that causes signals to stay within the material; 
         FIG. 8B  shows the high dielectric material with several layers of slightly lower permittivity, causing internal signals to escape from the high-dielectric material to the air without having to face the high total internal reflection angle, a technique similar to optic lens coating; 
         FIG. 9  illustrates antennae at a right-angle orientation in accordance with a preferred embodiment of the invention; 
         FIG. 10  shows a quasi-crystalline arrangement of the antennae; and 
         FIG. 11  depicts a preferred embodiment of the entire system of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described in detail with reference to several embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to one skilled in the art, that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow. 
     Aspects, features and advantages of exemplary embodiments of the present invention will become better understood with regard to the following description in connection with the accompanying drawing(s). It should be apparent to those skilled in the art that the described embodiments of the present invention provided herein are illustrative only and not limiting, having been presented by way of example only. All features disclosed in this description may be replaced by alternative features serving the same or similar purpose, unless expressly stated otherwise. Therefore, numerous other embodiments of the modifications thereof are contemplated as falling within the scope of the present invention as defined herein and equivalents thereto. Hence, use of absolute and/or sequential terms, such as, for example, “will,” “will not,” “shall,” “shall not,” “must,” “must not,” “first,” “initially,” “next,” “subsequently,” “before,” “after,” “lastly,” and “finally,” are not meant to limit the scope of the present invention as the embodiments disclosed herein are merely exemplary. 
     The size of a phased array antenna is directly proportional to spacing between elements in the phased array. The spacing between these elements is dictated by the physics involved in radio frequency (RF) transmission in the material where the antenna elements are submersed, resulting in limits to how closely antennae can be placed together. 
     In the simplest case, two antennae facing each other can be placed only as closely as one wavelength apart. Any closer than that, and various unwanted side effects due to close proximity become significant and destroy the advantages of having two antennae. One of these effects causes the two antennae to act as one, which is counterproductive since the capability of directing wireless signals by a phased array antenna depends upon having unique phases assigned to individual antenna elements. The antenna phases are expected to be carefully controlled and distinct from one another. So, the minimum distance between antenna array elements sets the minimum size of the array. 
     Since the minimum distance between antenna elements is directly related to wavelength and the wavelength is the inversely proportion to frequency, we can determine the size of the antenna array by knowing the frequency being transmitted and the medium in which the antenna elements are submersed. There are several possible implementations of wireless signals, each with a preferred frequency, as illustrated in  FIG. 1 . The chart  100  describes antenna elements used in different wireless applications  110 . Frequencies  120  are the commonly used frequencies in conjunction with the wireless applications  110 . Wavelengths  130  are approximate wavelength values, in vacuum or air, associated to the frequencies  120 . Corresponding transmission ranges  140  are listed for wireless applications  110  when each is transmitting one Watt of power. 
     Within the home or business establishments, the frequencies of wireless signals range from 1 GHz to 8 GHz. One common frequency used is 2.4 GHz which corresponds to a wavelength of 12.5 cm in vacuum, or air, as shown in the chart  100 , in  FIG. 1 . If, for example the number of antenna elements on a side of a cube-shaped phased array is 40, and at this common frequency, thus the length of each side of this cube would be about 16 feet (12.5 cm*40=5 m). This is truly a home-sized array. However, there is no room for the home inside this giant cube, since the array must have a population of antenna elements spaced about every 5 inches apart in all three dimensions. Hence, a way must be found to decrease the distance between antenna elements and still preserve the advantageous properties of the array. 
     The distances involved in the above calculations are based the electromagnetic wavelengths in vacuum, or air. The important factor in these distance calculations has to do with the permittivity of free space. If we can change the permittivity of the material that makes up the volume of the antenna array, we can affect the distances involved while holding the frequencies constant. This is due to the reduced speed of electromagnetic waves in a dielectric medium which normally has a permittivity factor larger than that of vacuum or air because of the higher dielectric constant of the dielectric medium. 
     However, the dielectric medium must be chosen with care since there are many other side effects different materials can introduce. Metals, for instance, can have advantageously high dielectric constants. However, metals also bring along many undesired attributes that conflict with the application at hand. Metals reflect radio frequencies (RF), and can absorb RF radiation and convert it to heat. Metals are also used to build transmitting/receiving antennae by being configured into various shapes and thus cannot be used as the medium in which the antenna elements are submersed. 
     There are other classes of materials with promisingly high dielectric coefficients, but they have other problems, such as the attenuation of RF energies passing through them. High weight can be another problem. These properties are also not desired in this application. 
     However, there is a class of materials having desirable coefficients and none of the drawbacks in the realm of physics; some can even be obtained without prohibitive expense. These are the Rogers materials, from which are made FR4 fiberglass circuit boards (and other products). These materials have permittivity coefficients in the range of p=3 to p=30. A coefficient of p=30 means that the distance terms (wavelengths  130  and transmission ranges  140 ) in the chart  100  of  FIG. 1  can be reduced by a factor of √30, again at the same frequencies  120  in the chart  100 . This reduction in size is illustrated in  FIG. 2 . As an example, we consider the effect of material permittivity coefficient, p on a quarter-wavelength antennae system  200 . A quarter-wavelength antenna  210  is shown in  FIG. 2( a ) . The quarter-wavelength antenna  210  is in air and has a length l. A quarter-wavelength antenna  220  is shown in  FIG. 2( b ) , where the material used has a permittivity coefficient, p. The length of the quarter-wavelength antenna  220  is reduced by a factor 1/√p. 
     If we now consider a cube-shaped array with 40 elements, immersed in a medium with a permittivity coefficient=30, made of the quarter-wavelength antennae system  200  above, reducing this cube in size by a factor of √30 in each of three dimensions results in a new cube of about 36 inches along the height, width, and depth. The actual new calculation is (12.5 cm*40/√30=0.91 m=35.9 inches) resulting in a cube less than 36 inches along each edge. Further, if we consider that tight packing of antennae could be as close as half-wavelengths, we can halve this number to 18 inches. 
     In order for a large quantity of antennae to fit within this cube, one embodiment of the invention calls for a specific arrangement of them on a printed circuit board (PCB). In this arrangement, the antennae are laid down in three dimensions to cover every type of polarized signal, as shown in the antennae arrangement  300  depicted in  FIG. 3 . Components of the said antennae going through the board from front surface to back surface  310  are represented by dashed lines. This antennae arrangement  300  would allow a large quantity of antennae to be arranged in close proximity while minimizing the interference with one another. 
       FIG. 4  A depicts how polarization RF radiation can be blocked if its “waves”  410  are intercepted by conductive wires  420  with spacing  430  of a length d equal to the RF radiation wavelength  440  or shorter, assuming the wave polarization is perpendicular to the orientation of the wires. 
     According to an embodiment of the invention, if the wires  460  are immersed in a dielectric of permittivity coefficient p, the spacing  470  is now reduced to d/√p, allowing for denser spacing of lines as shown in  FIG. 4B . Thus decreasing the minimum size of the array unit overall. 
     As such and given the size constraints of the array, one embodiment of the invention recommends the submersion of the wires feeding and controlling circuitry on the PCB in a dielectric material of permittivity coefficient p, where p is substantially larger than 1. 
     As shown in  FIG. 5 , one embodiment of the invention has antennae  500  on a PCB etched using the same technique that etches conductive traces on the PCB, and thus allowing the antennae to be built into the board with no components added, and hence reducing the cost of producing the antennae. Patterns  510 ,  520 , and  530  are exemplar dipole antennae that can be easily built on a PCB according to this embodiment of the invention. 
     As shown in  FIG. 6 , one embodiment of the invention, in the configuration  600 , uses the internal layers  610 ,  620 ,  630 ,  640  of a PCB with multiple layers to etch antennae in order to ensure that said antennae would be fully immersed in the dielectric materials of the said PCB. 
       FIG. 7  shows an almost invisible trace  710  within the PCB material that are surrounded by a gap  720  of air or some other low-permittivity materials, thus making them highly reflective spaces, which is useful since traversing high- to low-permittivity materials means that most signals would be reflected at the boundary. 
     As shown in  FIG. 8A , a signal  810  facing a low-permittivity medium  820  such as air and leaving a high dielectric material  830  will exhibit a high total internal reflection angle  840 , causing the signal to stay within the material  830 , which is undesirable for an antennae array. 
     In order to avoid this problem, an embodiment of the invention includes configuration  850  shown in  FIG. 8B . In this configuration, outer layers of a PCB are made of a material  860  of a permittivity lower than that of the inner layers  870  which is made of high dielectric material. This causes internal signals  880  to escape from the high dielectric material  870  to the air without having to face the high total internal reflection angle, similar to optic lens coating. 
     Further reductions can be realized when one considers that antenna pairs at right angles to one another do not interfere. This permits five antennae to be placed into the same volume as one could with aligned antennae. 
     These right-angle orientations also have the advantageous effect of being able to deliver signals to a client device in any orientation in any of the three dimensions. With this invention, any angle can be used for orienting the antennae. 
     As illustrated in  FIG. 9 , even 45-degree orientations  900  can work, with the two figured patterns able to be overlaid upon one another. Not only do these patterns have antennae at 45-degree layouts, the two patterns can be placed one above another on alternate layers and the two arrays of antennae will be at right angles to one another. 
     With many antennae in close proximity to one another, all attempting to send RF signals out in various directions, it should be easy to imagine antennae near the center of the cubical array being unable to have an unobstructed path for sending a signal to a client device outside the array. After all, the number of other antennae is considerable—one embodiment of the invention would have over 150 other layers of antennae in the path from the center of a million-antenna array—and the signal has to avoid not only all the other antennae on the outgoing trip, but also the substantial power and ground wiring that supplies those antennae circuits. 
     What is needed is a way to make RF signals, which travel in straight lines, curve around all the other wiring enough to miss it all on the way out. Wires can be repeatedly coated with increasingly high dielectric materials in a manner similar to making candles. Just as light can be bent by glass, RF signal paths can be bent by high dielectric materials. If RF is refracted enough through the interfaces between each layer of a wire coated with ever-higher dielectric materials, the RF signal from any antenna will be routed around the wire inside. This would allow the array to be powered by wires that were essentially “invisible” to the RF passing through them. 
     This is improved upon by creating some traces within the PCB material that are surrounded by gaps of air or some other low-permittivity materials, making it possible to make traces within the board to be highly reflective spaces, as in the example shown in  FIG. 7 . This traversing of the signals from high- to low-permittivity materials means that most signals would be reflected at the boundary and thus they traverse around potentially interfering objects such as wires. This might affect the ability of antennae to receive signals, since only those signals aimed directly at the center of the wire will not be deflected around the antenna lead. 
     As shown in  FIG. 10 , a preferred embodiment of the invention further recommends that the antennae in an array  1000  be arranged in a quasi-crystalline manner  1010  that provides aperiodic (i.e., non-repetitive) structure in all directions. The image  1020  shows every collection of five antennae encased in a pentagon, illustrating the aperiodic nature of this arrangement. This aperiodic design maintains antenna density throughout the array&#39;s layout, while at the same time preventing antennae from coupling as a result of being too close to one another. Furthermore, such aperiodic design suppresses the natural directivity of phased arrays, allowing for greater power delivery in any direction by suppressing natural (i.e., unwanted) directions. 
     Although the said quasi-crystalline arrangement would be aperiodic, having several arrangements of the same design in layers would nonetheless create periodic directions, which is detrimental to signal amplification. To avoid this problem, a preferred embodiment of the invention would have each layer of the array made from a different section of quasi-crystal design, thus avoiding identical stacked patterns throughout the layers. 
     Another issue is that the center of quasi-crystalline designs is usually symmetric around a certain angle, which compromises the aperiodicity of their patterns. To avoid this problem, an embodiment of the invention calls for using those parts of the quasi-crystalline design that are farther from the center. 
       FIG. 11  shows a preferred embodiment of entire system  1100  of this invention. The system appears as a three-dimensional form comprising a plurality of PCBs  1110 , each PCB comprising high-dielectric material encasing an array of densely packed antennae  1120 , the antennae being oriented in angular positions with respect to each other, the antennae further being arranged in a quasi-crystalline pattern. The PCBs are electrically joined by inter-PCB connection comprising wire  1130  encased in high-dielectric material. The PCBs are enclosed in an enclosure  1140  which is made of a material that is transparent to RF so as not to interfere with signal transfer. The said enclosure can be made of a material having a permittivity lower than that of the PCBs. 
     In sum, the present invention provides a system and methods for reducing the size of an antenna phased array without compromising the range of its wireless signal transmission. The wireless signal may comprise power, data, or any other signal capable of being transmitted wirelessly. The advantages of such a system include the ability to store phased arrays in smaller spaces, thus making wireless signal transmission available in a wider range of scenarios, such as in the home or automobile. 
     While this invention has been described in terms of several embodiments, there are alterations, modifications, permutations, and substitute equivalents, which fall within the scope of this invention. Although sub-section titles have been provided to aid in the description of the invention, these titles are merely illustrative and are not intended to limit the scope of the present invention. 
     It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.