Patent Publication Number: US-6989794-B2

Title: Wireless multi-frequency recursive pattern antenna

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to wireless communications antennas and, more particularly, to a multi-frequency recursive pattern antenna and a method for forming the same. 
     2. Description of the Related Art 
     As noted in U.S. Pat. No. 6,140,975 (Cohen), antenna design has historically been dominated by Euclidean geometry. In such designs, the closed antenna area is directly proportional to the antenna perimeter. For example, if one doubles the length of an Euclidean square (or “quad”) antenna, the enclosed area of the antenna quadruples. Classical antenna design has dealt with planes, circles, triangles, squares, ellipses, rectangles, hemispheres, paraboloids, and the like. Similarly, resonators, typically capacitors coupled in series and/or parallel with inductors, traditionally are implemented with Euclidian inductors. The prior art design philosophy has been to pick a Euclidean geometric construction, e.g., a quad, and to explore its radiation characteristics, especially with emphasis on frequency resonance and power patterns. The unfortunate result is that antenna design has far too long concentrated on the ease of antenna construction, rather than on the underlying electro-magnetics. 
     One non-Euclidian geometry is fractal geometry. Fractal geometry may be grouped into random fractals, which are also termed chaotic or Brownian fractals and include a random noise components, or deterministic fractals. In deterministic fractal geometry, a self-similar structure results from the repetition of a design or motif (or “generator”), on a series of different size scales. This repetition of a pattern into different size scales is referred to herein as recursively generated patterns. 
     Experimentation with non-Euclidean structures has been undertaken with respect to electro-magnetic waves, including radio antennas. Prior art spiral antennas, cone antennas, and V-shaped antennas may be considered as a continuous, deterministic first order fractal, whose motif continuously expands as distance increases from a central point. Unintentionally, first order fractals have been used to distort the shape of dipole and vertical antennas to increase gain, the shapes being defined as a Brownian-type of chaotic fractals. First order fractals have also been used to reduce horn-type antenna geometry, in which a double-ridge horn configuration is used to decrease resonant frequency. The use of rectangular, box-like, and triangular shapes as impedance-matching loading elements to shorten antenna element dimensions is also known in the art. 
     Whether intentional or not, such prior art attempts to use a quasi-fractal or fractal motif in an antenna employ at best a first order iteration fractal. By first iteration it is meant that one Euclidian structure is loaded with another Euclidean structure in a repetitive fashion, using the same size for repetition. 
     Antennas designed with fractal generators and a number of iterations, which is referred to herein as fractal geometry, appear to offer performance advantages over the conventional Euclidian antenna designs. Alternately, even if performance is not improved, the fractal designs permit antennas to be designed in a new form factor. However, the form factor of a fractal antenna need not necessarily be smaller than a comparable Euclidian antenna, and it need not fit within the constraints of a portable wireless communication device package. 
     More critically, a fractal geometry antenna has limitations with respect to the resonating frequency bands. Fractal pattern iterations have a precise mathematical relationship. As a result, the resonating frequencies of a fractal antenna have a predetermined spacing between resonances. For example, the fundamental antenna structure may resonate at cellular band frequencies of 824 to 894 megahertz (MHz). The first fractal pattern iteration of such an antenna would create structures that resonant at 1648 to 1788 MHz (twice the initial frequency). This higher frequency band is of little use if the antenna is expected to operate in the cellular band and either the PCS band (1850 to 1990 MHz), or the global positioning satellite (GPS) band at 1565 to 1585 MHz. 
     It would be advantageous if some of the general concepts of fractal geometry antennas could be used to build an antenna that resonated at frequency bands non-proportionately related. 
     SUMMARY OF THE INVENTION 
     The present invention describes a recursive pattern antenna that resonates at a plurality of non-harmonically related frequencies, as well as at frequencies that are not necessarily proportionately related. The recursive patterns are typically modifications of fractal geometry iterations that permit the antenna to be tuned to selected frequency bands. 
     Accordingly, a recursive pattern antenna is provided comprising a radiator having a first shape and a first effective electrical length and at least one radiator having a second shape, typically modified from a recursively generated pattern of the first shape, with a second effective electrical length. The radiator first shape can be triangles, rectangle, or ovals, for example. In some aspects, the antenna further comprises at least one radiator having a third shape, typically modified from a recursively generated pattern of the first shape, with a third effective electrical length. Other aspects include at least one radiator having a fourth shape, typically modified from a recursively generated pattern of the first shape, with a fourth effective electrical length. 
     In one aspect, the radiator first shape has a first effective electrical length conducive to electro-magnetic communications in the range between 824 and 894 MHz. The radiator second shape has a second effective electrical length conducive to electro-magnetic communications in the range between 1565 and 1585 MHz. The radiator third shape has a third effective electrical length conducive to electro-magnetic communications in the range between 1850 and 1990 MHz. The radiator fourth shape has a fourth effective electrical length conducive to electro-magnetic communications in the range between 2400 and 2480 MHz. 
     Additional details of the above-mentioned recursive pattern antenna, a transceiver system using a recursive pattern antenna, and a method for forming a recursive pattern antenna for wireless communications are provided below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  through  1   c  are exemplary plan view versions of the recursive pattern antenna of  FIG. 1  depicted as a monopole antenna. 
         FIG. 2  is a schematic block diagram of the present invention transceiver system with a recursive pattern antenna. 
         FIGS. 3   a  through  3   c  are exemplary plan view versions of the recursive pattern antenna of  FIG. 1  depicted as a bow tie dipole antenna. 
         FIGS. 4   a  through  4   c  are exemplary plan view versions of the recursive pattern antenna of  FIG. 1  depicted as a rectangular patch antenna. 
         FIG. 5  is a flowchart illustrating the present invention method for forming a recursive pattern antenna for wireless communications. 
         FIG. 6  is a perspective view of the present invention recursive pattern triangular patch antenna. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  is a schematic block diagram of the present invention transceiver system with a recursive pattern antenna. The system  200  comprises a wireless communication device transceiver  202  and a recursive pattern antenna  204 . As explained in more detail below, the recursive pattern antenna  204  includes a plurality of radiators having a recursive pattern relationship. Alternately as explained below, the recursive pattern antenna  204  includes a plurality of radiators having a modified recursive pattern relationship. 
     In some aspects of the system  200 , the transceiver  202  has a wireless communications port on line  206  and the antenna  204  has an interface connected to the transceiver communications port on line  206  for radiating electro-magnetic energy in the frequency range between 824 and 894 MHz. That is, the antenna  204  has a first effective electrical length approximately equal to one-half of a wavelength in the frequency range between 824 and 894 MHz. It is assumed herein that other half wavelength measurements, such as 3/2 or 5/2 of a wavelength, are equivalent to one-half (½) wavelength. In other aspects, the antenna  204  has an interface connected to the transceiver communications port on line  206  for radiating electro-magnetic energy in the frequency range between 1850 and 1990 MHz. That is, the antenna  204  has a third effective electrical length approximately equal to one-half of a wavelength in the frequency range between 1850 and 1990 MHz. 
     In some aspects, the system  200  includes a global positioning system (GPS) receiver  208  with a wireless communications port on line  206  and the antenna  204  has an interface connected to the GPS receiver communications port on line  206  for accepting electro-magnetic radiated energy in the frequency range between 1565 and 1585 megahertz (MHz). The antenna  204  has a second effective electrical length approximately equal to one-half of a wavelength in the frequency range between 1565 and 1585 MHz. 
     In some aspects, the system  200  includes a Bluetooth transceiver  210  with a wireless communications port on line  204  and the antenna has an interface connected to the Bluetooth transceiver communications port for radiating electro-magnetic energy in the frequency range between 2400 and 2480 MHz. The antenna  204  has a fourth effective electrical length approximately equal to one-half of a wavelength in the frequency range between 2400 and 2480 MHz. 
       FIGS. 1   a  through  1   c  are exemplary plan view versions of the recursive pattern antenna  204  of  FIG. 1  depicted as a monopole antenna. Generally, whether the antenna  204  is a monopole antenna, a dipole antenna (see  FIGS. 3   a – 3   c ), or a patch antenna (see  FIGS. 4   a  through  4   c  or  FIG. 6 ), the antenna  204  (see  FIG. 1   a ) comprises a radiator  100  having a first shape and the first effective electrical length  104  (as explained above in the description of  FIG. 2 ). The antenna  204  also includes at least one radiator  106  having a second shape, from a recursively generated pattern of the first shape, with the second effective electrical length  108  as described above. Note that the second electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. 
     The radiator  100  is in the proximity of a groundplane  109 . By recursively generated pattern it is meant that the shape dimensions have a constant proportional relationship between iterations, typically but not always based on an integer or whole-number. For example, the first shape can be twice the size of the second iteration shape, or the second shape can be one-half the size of the first shape. In some aspects as explained below, the second shape radiator  106  is a modified recursively generated pattern of the first shape. 
     The radiator  100  first shape can be any one of a number of conventional shapes such as a triangle, a rectangle, or oval, where a circular shape is considered to be a special case of an oval. As shown in the example of  FIG. 1   a , the first shape is a triangle. Depending on the placement of the feedpoint  110  and nature of the first shape, the electrical length can vary. For example, the electrical length  104  is slightly different than the length  104   a . It should also be understood that current flow through different regions of the radiator  100  may tend to emphasize one variation of electrical length over another. 
     It should also be understood that when modified, the second shape radiator(s)  106  is not truly recursively generated from the first shape radiator  100 . That is, the second shape triangle dimensions are not exactly whole-number proportional to the first shape triangle. Neither are the proportional relationships between iterations necessarily the same. Further, the proportional relationship between the first shape radiator and particular second shape radiators may vary. In the case shown, the second shape triangle is not exactly one-half of the first shape triangle. That is, the recursive pattern is a modification of a ½ recursive iteration. The generation and placement of the second shape radiator(s)  106  necessarily changes the first effective electrical length from the initial condition (see electrical length  104   b ), before the placement of the void area  111  associated with the formation of the second shape radiators. The void areas can be areas of exposed dielectric or groundplane where the conductive surface of radiator  100  has been removed. Likewise, the exact dimensions of the second shape radiator(s)  106  typically need to be adjusted to achieve the desired second effective electrical length. It should also be noted that the second shape radiators  106  need not have identical shapes. The present invention antenna recursive patterns are not limited to a modification of any particular whole-number, or any other number relationship. 
     As seen in  FIG. 1   b , in some aspects the antenna  204  includes at least one radiator  112  having a third shape, from a recursively generated pattern of the first shape, with the third effective electrical length  114  as described above in the explanation of  FIG. 2 . Note that the third electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. In some aspects, the third shape radiator is modified from a recursively generated pattern of the first shape, as explained above. 
     As seen in  FIG. 1   c , in some aspects the antenna  204  includes at least one radiator  116  having a fourth shape, either from a recursively generated pattern of the first shape or modified from a recursively generated pattern of the first shape, with the fourth effective electrical length  118  as described above. Note that the fourth electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. Although three recursive iterations are demonstrated in  FIG. 1   c , it should be understood that the present invention antenna  204  is not limited to any particular number of recursive pattern iterations. Generally, the radiator (or counterpoise, see  FIGS. 3   a – 3   c ) includes X second shape sections, (up to a maximum of) X 2  third shape sections, and (up to a maximum of) X 4  fourth shape sections. As shown, X is equal to three. 
       FIGS. 3   a  through  3   b  are exemplary plan view versions of the recursive pattern antenna  204  of  FIG. 1  depicted as a bow tie dipole antenna. The explanation of the radiator first and second shapes, with corresponding first and second effective electrical lengths, mirrors the description of  FIG. 1   a  and will not be repeated in the interest of brevity. As with the radiator, the recursive pattern antenna  204  includes a counterpoise having the first shape and the first effective electrical length and a plurality of counterpoises having a recursive pattern relationship with the first shape. Although a triangular shape is shown, the antenna could alternately be enabled with other shapes. In  FIG. 3   a  the antenna  204  further comprises a counterpoise  300  having a first shape and the first effective electrical length  302 . The antenna  204  includes at least one counterpoise  304  having a second shape, either from a recursively generated pattern of the first shape or modified from a recursively generated pattern of the first shape, with the second effective electrical length  306 . Also shown is feed point  110  and void area  111 . In other aspects of the invention as shown, the second shape radiator  304  has the fourth electrical length. That is, the antenna resonates in the cellular band and in the Bluetooth band of frequencies. Also shown are some key antenna dimensions in inches. Note that the second electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. 
     As shown in  FIG. 3   b , the antenna  204  includes a radiator  100  as explained in the description of  FIG. 1   b , and further comprises at least one counterpoise  308  having a third shape, from a recursively generated pattern of the first shape or modified from a recursively generated pattern of the first shape, with the third effective electrical length  310 . Also shown are some key dimensions in inches. Note that the third electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. 
     As shown in  FIG. 3   c , the antenna includes a radiator as explained in the description of  FIG. 1   c , and further comprises at least one counterpoise  312  having a fourth shape, either from a recursively generated pattern of the first shape, or modified from a recursively generated pattern of the first shape, with the fourth effective electrical length  314 . Note that the fourth electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. Each radiator and counterpoise section is shown as a triangle. As shown, the radiator and counterpoise sections each include three second triangle sections, nine third triangle sections, and twenty-seven fourth triangle sections. The efficiency of the antenna to resonate at specific electrical lengths can be adjusted by selecting the number and placement of second, third, and fourth sections in the radiator (and counterpoise). 
       FIGS. 4   a  through  4   c  are exemplary plan view versions of the recursive pattern antenna  204  of  FIG. 1  depicted as a rectangular patch antenna. As shown in  FIG. 4   a , the antenna  204  has a radiator conductive section  400  shaped as a first rectangle having the first effective electrical length  402 . In other aspects of the antenna, the radiator conductive section  400  can be circular or triangular. Also shown is a feed point  110  and a void area  111 . Generally, the recursive rectangle pattern patch antenna  204  includes a plurality of rectangular radiators having a recursive pattern relationship, as described above. Alternately, the recursive pattern antenna  204  includes a plurality of radiators having a modified recursive pattern relationship, as described above. The plurality of radiators are conductors formed overlying a dielectric layer (not shown). The dielectric layer overlies a groundplane (not shown). As shown, the antenna  204  includes at least one conductive section  404  shaped as a second rectangle having the second effective electrical length  406 . Note that the second electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. 
     In  FIG. 4   b  the antenna  204  includes at least one conductive section  408  shaped as a third rectangle having the third effective electrical length  410 . Note that depending upon the exact size and placement of the third rectangle sections  408 , many other third electrical length paths would be possible. Also note that the third electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. 
     In  FIG. 4   c  the antenna  204  includes at least one conductive section  412  shaped as a fourth rectangle having a fourth effective electrical length  414 . As noted above, other fourth electrical length paths are possible in some aspects of the antenna. Also note that the fourth electrical length can be one of a number of half wavelength measurements, such as 3/2, 5/2, and so on, equivalent to one-half a wavelength. The antenna, as shown includes eight second rectangle sections, sixty-four third rectangle sections, and four thousand ninety-six fourth rectangle sections. However as noted above, a fewer number of second, third, and fourth rectangle sections are used in other aspects of the antenna. 
       FIG. 6  is a perspective view of the present invention recursive pattern triangular patch antenna. The patch antenna  204  has an underlying dielectric  600  and groundplane  602 . A radiator  604  has a first triangle shape and a first effective electrical length  606 . At least one radiator  608  has a second triangle shape, modified from a recursively generated pattern of the first triangle shape  604 , with a second effective electrical length  610 . 
     In other aspects not shown, but equivalent to the descriptions of  FIGS. 1   b  and  1   c , at least one radiator has a third triangle shape, modified from a recursively generated pattern of the first triangle shape, with a third effective electrical length. Likewise, in other aspects at least one radiator has a fourth triangle shape, modified from a recursively generated pattern of the first triangle shape, with a fourth effective electrical length. 
     In some aspects, the radiator first triangle shape  604  has a first effective electrical length conducive to electro-magnetic communications in the range between 824 and 894 megahertz (MHz). The radiator second triangle shape  608  has a second effective electrical length conducive to electro-magnetic communications in the range between 1565 and 1585 MHz in some aspects. In other aspects, the third triangle shape has a third effective electrical length conducive to electro-magnetic communications in the range between 1850 and 1990 MHz, and the radiator fourth triangle shape has a fourth effective electrical length conducive to electro-magnetic communications in the range between 2400 and 2480 MHz. 
       FIG. 5  is a flowchart illustrating the present invention method for forming a recursive pattern antenna for wireless communications. Although this method is depicted as a sequence of numbered steps for clarity, no order should be inferred from the numbering unless explicitly stated. It should be understood that some of these steps may be skipped, performed in parallel, or performed without the requirement of maintaining a strict order of sequence. The method starts at Step  500 . Step  502  supplies a shape. Step  504  forms conductive sections recursively generated from the shape, having effective electrical lengths. In alternate aspects, non-conductive sections are recursively generated. 
     In some aspects of the method, forming conductive sections in Step  504  includes forming a recursively generated first shape in a plurality of effective electrical lengths. Alternately, Step  504  forms a recursively generated first shape modification in a plurality of effective electrical lengths. 
     In some aspects, forming a recursively generated first shape in a plurality of effective electrical lengths in Step  504  includes substeps. Step  504   a  forms a first shape having a first electrical length. Step  504   b  forms a second shape having a second electrical length. Step  504   c  forms a third shape having a third electrical length. Step  504   d  forms a fourth shape having a fourth electrical length. As noted above, the present invention is not limited to any particular number of iterations. 
     In some aspects, forming a first shape having a first electrical length in Step  504   a  includes forming an electrical length conducive to electro-magnetic communications in the range of 824 and 894 megahertz (MHz). Forming a second shape having a second electrical length in Step  504   b  includes forming an electrical length conducive to electro-magnetic communications in the range of 1565 to 1585 MHz. Forming a third shape having a third electrical length in Step  504   c  includes forming an electrical length conducive to electro-magnetic communications in the range of 1850 to 1990 MHz. Forming a fourth shape having a fourth electrical length in Step  504   d  includes forming an electrical length conducive to electro-magnetic communications in the range of 2400 to 2480 MHz. 
     In other aspects, forming conductive sections in Step  504  includes forming an antenna selected from the group including patch, dipole, and monopole antennas. 
     In some aspects, forming conductive sections in Step  504  includes forming a bow tie dipole using a recursively generated triangular pattern. In other aspects, Step  504  forms a patch antenna using a recursively generated rectangular pattern. In other aspects, the pattern is circular, oval, or triangular. 
     A recursive pattern antenna and a method for forming the same are provided. Examples have been given of monopole, dipole, and patch antenna types. Although only one shape is typically exemplified per antenna type, the present invention can be enabled with a variety of shapes for each type. Examples have also been given of recursively generated shapes that have been modified to accommodate cellular (AMPS), PCS, GPS, and Bluetooth frequencies. However, the present invention is not limited to any particular frequencies. Other variations and embodiments of the invention will occur to those skilled in the art.