Abstract:
An antenna system comprising a ground plane, an antenna element folded under itself and operable to transmit and receive circularly polarized signals, an air filled cavity disposed between the ground plane and the antenna element, and a radio frequency module in communication with the antenna element.

Description:
TECHNICAL FIELD 
       [0001]    The present description relates to antennas. More specifically, the present description relates to patch antennas for transmitting and/or receiving circularly polarized signals. 
       BACKGROUND OF THE INVENTION 
       [0002]    A large number of radio applications, including satellite communication, global positioning system (GPS), and radio frequency identification (RFID) base stations, utilize circularly polarized signals. Circular polarization (CP) of electromagnetic radiation is a polarization such that the electric field of the radiation varies in two orthogonal planes (the major and minor axis) with the same magnitude. Perfect CP is where the major and minor components are of equal magnitude and 90° out of phase. Most real world CP signals are not perfectly circular; rather, the signals are elliptical. That is, the orthogonal components are not of equal amplitude or not strictly 90° out of phase. The quality of circular polarization is quantified as the axial ratio. Axial ratio is defined as the voltage ratio of the major axis to the minor axis of the polarization ellipse and is expressed in decibels (dB). An axial ratio of less than 3 dB is considered sufficient for most CP applications. For a good circularly polarized antenna design, axial ratio bandwidth (the frequency band having axial ratio below 3 dB) is necessarily ranged inside the impedance bandwidth. This ensures that the received or transmitted CP signal of the antenna has maximum power transfer. 
         [0003]    Microstrip or patch antennas are increasingly used in GPS, satellite communications, personal communication systems, and other communication systems that utilize circularly polarized signals. A patch antenna is a resonator-type antenna that generally includes an electrically conductive ground layer, an electrically conductive patch antenna element, a feeding geometry, and a dielectric substrate or an air filled cavity disposed between the ground layer and conductive patch antenna element. There are two primary approaches to accomplish circular polarization in patch antennas. 
         [0004]    One approach is to excite a single patch with two feeds, with one feed delayed by 90° with respect to the other. This drives two transverse modes with equal amplitudes and 90° out of phase. Each mode radiates separately, and the modes combine to produce circular polarization. A second approach is to use a single feed but introduce an asymmetry into the patch, causing current distribution to be displaced. The resonance frequencies of the two paths can be adjusted so that the phase difference between the two paths is 90°. Thus circular polarization can be achieved by building a patch with two resonance frequencies in orthogonal directions. 
         [0005]    Prior art CP patch antennas are typically in the range of half a wavelength in length. Prior art patch antennas utilize several different technologies to enable miniaturization (length&lt;0.2λ 0 ). The most common solution is dielectric loading with high dielectric constant material, but there are several drawbacks with this method. Dielectrically loaded patch antennas often exhibit narrow bandwidth, high loss, and poor efficiency. Moreover, dielectrically loaded patch antennas are often expensive, heavy, and difficult to manufacture. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Various embodiments of the invention are directed to antenna systems that include a ground plane, an antenna element folded under itself and with asymmetries that allow the antenna element to generate and receive circularly polarized signals, an air filled cavity disposed between the ground plane and the antenna element, and a radio frequency module in communication with the antenna element and transmitting and receiving radio waves through the antenna element. 
         [0007]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1A  illustrates a side view of a circularly polarized folded patch antenna according to an embodiment of the present invention. 
           [0010]      FIG. 1B  illustrates a top view of a circularly polarized folded patch antenna according to an embodiment of the present invention. 
           [0011]      FIG. 1C  illustrates a plan view of a patch radiating element according to an embodiment of the present invention. 
           [0012]      FIG. 2A  illustrates the measured axial ratio against frequency of a prototype circularly polarized folded patch antenna built and tested according to the embodiment illustrated by  FIGS. 1A-1C . 
           [0013]      FIG. 2B  illustrates the measured return loss against frequency of a prototype circularly polarized folded patch antenna built and tested according to the embodiment illustrated by  FIGS. 1A-1C . 
           [0014]      FIG. 2C  illustrates a right hand CP radiation pattern at the phi=0° plane at 1.554 GHz for the embodiment of the prototype circularly polarized folded patch antenna built and tested according to the embodiment illustrated by  FIGS. 1A-1C . 
           [0015]      FIG. 2D  illustrates a right hand CP radiation pattern at the phi=90° plane at 1.554 GHz for the embodiment of the prototype circularly polarized folded patch antenna built and tested according to the embodiment illustrated by  FIGS. 1A-1C . 
           [0016]      FIG. 3A  illustrates an exemplary patch geometry according to an embodiment of the present invention, wherein asymmetry is introduced into the top layer of the radiating element of a circularly polarized folded patch antenna. 
           [0017]      FIG. 3B  illustrates an exemplary patch geometry according to an embodiment of the present invention, wherein asymmetry is introduced into the top layer of the radiating element of a circularly polarized folded patch antenna. 
           [0018]      FIG. 3C  illustrates an exemplary patch geometry according to an embodiment of the present invention, wherein asymmetry is introduced into the top layer of the radiating element of a circularly polarized folded patch antenna. 
           [0019]      FIG. 4A  illustrates an exemplary patch geometry according to an embodiment of the present invention, wherein asymmetry is introduced into the bottom layer of the radiating element of a circularly polarized folded patch antenna. 
           [0020]      FIG. 4B  illustrates an exemplary patch geometry according to an embodiment of the present invention, wherein asymmetry is introduced into the bottom layer of the radiating element of a circularly polarized folded patch antenna. 
           [0021]      FIG. 5A  illustrates a side view of circularly polarized folded patch antenna according to an embodiment of the present invention, wherein asymmetry is introduced into the radiating element by lengthening a vertical wall portion of the radiating element. 
           [0022]      FIG. 5B  illustrates a plan view of a patch radiating element according to an embodiment of the present invention. 
           [0023]      FIG. 6A  illustrates a side view of circularly polarized folded patch antenna according to an embodiment of the present invention, wherein the radiating element is folded downwards to form a radiating element with more than two parallel layers. 
           [0024]      FIG. 6B  illustrates a plan view of a patch radiating element according to an embodiment of the present invention. 
           [0025]      FIG. 7A  illustrates a side view of circularly polarized folded patch antenna according to an embodiment of the present invention, wherein the radiating element is folded upwards to form a radiating element with more than two parallel layers. 
           [0026]      FIG. 7B  illustrates a plan view of a patch radiating element according to an embodiment of the present invention. 
           [0027]      FIG. 8A  illustrates the perspective view of a circularly polarized folded patch antenna according to an embodiment of the present invention wherein the radiating element comprises a conductor on PCB material. 
           [0028]      FIG. 8B  illustrates a side view of the circularly polarized folded patch antenna illustrated by  FIG. 8A . 
           [0029]      FIG. 8C  illustrates the top layer of the radiating element of the circularly polarized folded patch antenna illustrated by  FIG. 8A . 
           [0030]      FIG. 8D  illustrates the bottom layer of the radiating element of the circularly polarized folded patch antenna illustrated by  FIG. 8A . 
           [0031]      FIG. 8E  illustrates the bottom layer of the radiating element of the circularly polarized folded patch antenna illustrated by  FIG. 8A  wherein the tails on the bottom layer are connected. 
           [0032]      FIG. 9  illustrates an exemplary patch geometry according to an embodiment of the present invention wherein the radiating element includes dual feed points. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      FIGS. 1A and 1B  illustrate a miniature circularly polarized folded patch antenna  100  adapted according to an exemplary embodiment of the present invention.  FIG. 1A  is a side view illustration of exemplary folded patch antenna  100 . Antenna  100  includes a ground plane  101 , a spacer layer  102 , a radiating element  103 , and a radio frequency (RF) feed  104 . As illustrated by  FIG. 1A  and discussed further with respect to  FIG. 1C , radiating element  103  is folded under itself to form a folded patch. 
         [0034]      FIG. 1B  is a top view illustration of the exemplary folded patch antenna  100 . As illustrated by  FIG. 1B , radiating element  103  includes a plurality of slots, which will be discussed further with respect to  FIG. 1C , and includes a RF feed point  104 A. As discussed further below, the center conductor of a coaxial cable is coupled to radiating element  103  at RF feed point  104 A. 
         [0035]    In the example of  FIGS. 1A and 1B , ground plane  101  includes a planar substrate, such as a printed circuit board, covered by metal (e.g., copper in the example of  FIGS. 1A and 1B ). In the embodiment illustrated by  FIGS. 1A and 1B , the square ground plane is 0.26 λ 0 . Furthermore, in some embodiments, the planar substrate and conducting material may be separated by a dielectric or by an air gap. 
         [0036]    Spacer layer  102  is composed of a porous, light weight, non-conductive material that consists primarily of air. In the exemplary embodiment of  FIGS. 1A and 1B , spacer layer  102  is a foam spacer, which has a dielectric constant similar to air. In other embodiments, spacer layer  102  can be made of, for example, glass or TEFLON®. In still other embodiments, spacer layer  102  may be created using standoffs (e.g., insulator pins, dielectric spacers, etc.) to create an air gap between ground plane  101  and radiating element  103 . And in certain embodiments, a signal line from RF feed  104  holds radiating element  103  above ground plane  101 , creating an air gap between ground plane  101  and radiating element  103 . 
         [0037]    In the embodiment illustrated by  FIGS. 1A and 1B , radiating element  103  is coupled to a transmitter or receiver by a coaxial cable which is fed to RF feed  104 . The center conductor of the coaxial cable extends vertically up through the spacer layer  102  and is fixed to radiating element  103  by soldering at RF feed point  104 A. 
         [0038]    According to the embodiment of the present invention illustrated by  FIGS. 1A and 1B , radiating element  103  is shaped into a folded patch. The radiating element  103  is formed from a conducting material (copper in the example of  FIGS. 1A and 1B ). In other embodiments the radiating element may be formed from other conductors, such as aluminum, gold, or tin plated steel. The geometry of radiating element  103  comprises a unique configuration described with reference to  FIG. 1C . 
         [0039]      FIG. 1C  shows a plan view of radiating element  103  according to the embodiment of the invention illustrated by  FIGS. 1A and 1B . As shown in  FIG. 1C , radiating element  103  is formed from a single sheet of a conductor (e.g., copper) that can be stamped, cut, or otherwise formed to provide the geometries disclosed herein. Radiating element  103  includes a plurality of slots and asymmetries cut, or otherwise formed, in radiating element  103 . The slots have several purposes. For instance, the slots lengthen the effective radiating current path of radiating element  103 , thereby allowing reduction of the radiating element&#39;s size. Also, the slots and asymmetries introduce radiating current paths of differing lengths, which allows excitation of two modes. The asymmetries are designed to ensure that the current paths produce two signals of substantially equal magnitude and 90° out of phase and are described in more detail below. 
         [0040]    In the embodiment illustrated by  FIG. 1C , radiating element  103  includes slots  105 A- 105 D. Each of slots  105 A- 105 D radiates inwardly towards the center of radiating element  103 . Each of slots  105 A- 105 D is orthogonal to adjacent slots (i.e., the slots are at 90° angles to neighboring slots). Slots  105 A- 105 D define arms  106 A- 106 D. 
         [0041]    Each of arms  106 A- 106 D includes a slot  107 A- 107 D, respectively, that defines two fingers. As shown in  FIG. 1 , each of arms  106 A- 106 D is asymmetrical—the two fingers of each arm are different lengths. This asymmetry provides for radiation paths of different lengths within radiating element  103 . That is, the different lengths of the fingers on allow radiating element  103  to generate and/or receive CP signals. The lengths are selected to cause simultaneous excitation of two orthogonal patch modes substantially equal in amplitude and 90° out of phase. 
         [0042]      FIG. 1C  illustrates the dimensions of radiating element  103  in terms of λ 0  . The dimensions of slots  105 A- 105 D are identical. Similarly, the dimensions of slots  107 A- 107 D are identical. Consequently, the dimensions of arms  106 A- 106 D and fingers  108 A- 108 D and  109 A- 109 D are identical; however, as illustrated in  FIG. 3 , the arms are oriented differently. As discussed further below, with respect to  FIGS. 2A-2D , the disclosed pattern can be used to generate and receive circularly polarized signals. 
         [0043]    To further reduce the lateral size of radiating element  103 , radiating element  103  is designed to fold under itself. According to the embodiment illustrated by  FIG. 1C , radiating element  103  is designed to fold along fold lines, which are shown as dashed lines on the illustration of radiating element  103  shown in  FIG. 1C . The dashed fold lines shown in  FIG. 1C  are for illustration only as other embodiments may be folded differently. In the embodiment of  FIGS. 1A-1C , the radiating element is designed to be folded down and under itself at approximately 90° angles along the fold lines. When folded along the fold lines, radiating element  103  includes a top layer  110 , bottom layer  111 , and vertical wall layers  112 . In certain embodiments, radiating element  103  may be folded around a spacer element (not shown). The spacer element may comprise, for example, a porous, light weight, non-conductive material that consists primarily of air (e.g., foam, non-woven fabric, etc.). 
         [0044]    As shown in  FIG. 1B , the length of the radiating element for the disclosed patch antenna is on the order of 0.15 λ 0 . Miniaturization of the disclosed circularly polarized folded patch antenna is facilitated by at least two design elements. For instance, the introduction of slots into radiating element  103  causes radiation patterns that effectively lengthen the radiating element. Furthermore, the lateral size of the patch is reduced by folding radiating element  103  under itself. It should be noted that the disclosed miniaturization of antenna  100  is facilitated without utilizing dielectric loading, in contrast to some prior art CP patch antennas. 
         [0045]    A prototype according to the design of the embodiment of  FIGS. 1A-1C  has been built and tested. The results of testing are shown in  FIGS. 2A-2D .  FIG. 2A  illustrates the axial ratio of circularly polarized patch antenna  100 . The antenna has an axial ratio of 1.18187 dB at 1554.265 MHz and exhibits an axial ratio of better than 3 dB for a range of frequencies. The antenna has a 3 dB axial ratio bandwidth of 0.26%.  FIG. 2B  illustrates the measured return loss of circularly polarized folded patch antenna  100 . As shown in  FIG. 2B , the disclosed antenna displays 1.33% impedance bandwidth of return loss below −10 dB. The axial ratio bandwidth is ranged inside the impedance bandwidth, which is the dotted line in  FIG. 2A . The prototype antenna demonstrated greater than 45% efficiency and greater than 0.5 dB gain between the axial ratio bandwidth. 
         [0046]      FIGS. 2C and 2D  illustrate actual right hand CP radiation patterns for the embodiment of the circularly polarized patch antenna  100  illustrated and described with respect to  FIGS. 1A-1C .  FIG. 2C  shows the radiation pattern for folded patch antenna  100  at the Φ=0° plane.  FIG. 2D  shows the radiation pattern for folded patch antenna  100  at the Φ=90° plane. 
         [0047]    Although exemplary circularly polarized folded patch antenna  100  includes radiating element  103  of the geometry illustrated in  FIG. 1C , folded patch antennas according to the present invention may include radiating elements of any geometry that excites two different orthogonal modes 90° out of phase and substantially equal in magnitude.  FIGS. 3A-3C  and  4 A- 4 B illustrate exemplary patch geometries for use in embodiments of the present invention. 
         [0048]      FIGS. 3A-3C  illustrate embodiments of the present invention where asymmetries are introduced to the top layer of a folded radiating element.  FIGS. 3A-3C  do not show the vertical wall layers or bottom layers of the folded patch. The disclosed geometries are examples of the top layer of a radiating element of a circularly polarized folded patch antenna according to embodiments of the present invention. 
         [0049]    A folded patch radiating element with a top layer according to the geometry illustrated by  FIG. 3A  has been shown to generate and receive circularly polarized signals. Top layer  300  includes a plurality of symmetrical slots  301 A- 301 D on each side of the top layer. These slots effectively lengthen the radiating element by creating a meandering path. Top layer  300  also includes a first slot pair (slots  302 A and  302 C) and a second slot pair (slots  303 B and  303 D). As illustrated by  FIG. 3A , the prongs of the first slot pair and second slot pair are of different lengths. The lengths of the slot prongs are selected to ensure that radiating element  300  excites two orthogonal modes 90° out of phase and substantially equal in magnitude. 
         [0050]      FIG. 3B  illustrates another top layer geometry capable of exciting two modes substantially equal in magnitude and 90° out of phase. Top layer  310  includes a plurality of symmetrical slots  311 A- 311 D on each side of the top layer. Slots  311 A- 311 D effectively lengthen the radiating element by creating longer paths. In the example of  FIG. 3B , radiating circuits of different lengths are created based on the differences in the sizes of slots  312 A- 312 D. Slots  312 A- 312 D radiate inwards and terminate in circular areas. The circular area at the end of slots  312 A and  312 C has a larger area than the circular area at the ends of slots  312 B and  312 D. In this example, the size of the circular areas is selected to ensure that the radiating element  310  excites two orthogonal modes 90° out of phase. 
         [0051]      FIG. 3C  also illustrates a top layer geometry capable of exciting two modes substantially equal in magnitude and 90° out of phase. Top layer  320  includes a plurality of symmetrical slots  321 A- 321 D on each side of the top layer. Slots  321 A- 321 D effectively lengthens the radiating element by creating a meandering path. In the example of  FIG. 3C , slots  322 A- 322 D radiate inwards and turn outwards at approximately 45° and then inwards at approximately 90° to form a pinwheel-like pattern. The asymmetry in direction of the patches is selected to ensure that the radiating element excites two orthogonal modes 90° out of phase. 
         [0052]      FIGS. 4A and 4B  illustrate plan views of radiating elements according to embodiments of the present invention. Radiating elements  400  and  410  are designed to be folded along the illustrated fold lines to form a folded patch with a top layer (top layers  401  and  411 ), a vertical wall layer (vertical wall layers  402  and  412 ), and a bottom layer comprising four arms (bottom layer  403  and  413 ). As illustrated by  FIGS. 4A and 4B , the top layers of radiating elements  400  and  410  are symmetrical. In these examples, the asymmetries that drive two orthogonal modes 90° out of phase are introduced in the bottom layers ( 403  and  413 ) of the folded patch radiating elements  400  and  410 . 
         [0053]    In the example of  FIG. 4A , the asymmetry that facilitates circular polarization in radiating element  400  is introduced in each arm of bottom layer  403 . Fingers  404 A- 404 D and  405 A- 405 D are defined by slots  406 A- 406 D. As shown by  FIG. 4A , fingers  404 A- 404 D are longer than fingers  405 A- 405 D. The lengths of the fingers are selected to cause radiating element  400  to excite two orthogonal modes 90° out of phase and substantially equal in magnitude. 
         [0054]    In the example of  FIG. 4B , the asymmetry that facilitates circular polarization in radiating element  410  is introduced in each arm of bottom layer  413 . As shown by  FIG. 4B , tails  414 A- 414 D are longer than tails  415 A- 415 D. The lengths of the tails are selected to cause radiating element  400  to excite two orthogonal modes 90° out of phase and substantially equal in magnitude. 
         [0055]      FIGS. 5A and 5B  illustrate a circularly polarized folded patch antenna according to an embodiment of the present invention where the asymmetries are introduced using unequal wall heights. As shown in  FIG. 5A , circularly polarized folded patch antenna  500  includes a ground plane  501 , spacer layer  502 , radiating element  503 , and feed element  504 . Radiating element  500  includes vertical walls  505 A and  505 B of different heights. The differences in vertical wall height create radiation circuits of different lengths and are selected to excite two orthogonal modes 90° out of phase. 
         [0056]      FIG. 5B  illustrates a plan view of radiating element  503 . Radiating element  503  includes slots  506 A- 506 D that defines arms  507 A- 507 D. Each of arms  507 A- 507 D includes two fingers of different lengths defined by slots  508 A- 508 D. As shown in  FIG. 5B , the dashed fold lines define vertical walls of unequal height. When radiating element  503  is folded under itself along the fold lines, walls  505 A and  505 B are formed with differing heights. 
         [0057]    Turning now to  FIGS. 6A-6B  and  7 A- 7 B, embodiments of the present invention are illustrated wherein radiating patch elements are folded multiple times to provide a plurality of horizontal layers. By increasing the number of folds, the lateral dimensions of a patch may be further reduced, allowing for more compact packaging of the folded patch antenna. Although  FIGS. 6A-6B  and  7 A- 7 B present embodiments with three horizontal layers and two vertical wall layers, various embodiments of the present invention do not limit the number of times a patch radiating element may be folded. 
         [0058]      FIG. 6A  illustrates a circularly polarized folded patch antenna  600  according to one embodiment of the present invention. The embodiment shown in  FIG. 6A  comprises a ground plane  601 , a spacer layer  602 , a radiating element (patch)  603 , and a feed element  604 . As shown in  FIG. 6A , radiating element  603  is folded to include three horizontal layers (a top layer  605 , a middle layer  606 , a bottom layer  607 ) and two vertical wall layers (first vertical wall layer  608  and second vertical wall layer  609 ). In this embodiment, the feed element is fed upward through space in radiating element  603  to top layer  605 .  FIG. 6B  illustrates a plan view for radiating element  603 . As shown by the dashed fold lines, radiating element  603  is designed to be folded downwards as shown in  FIG. 6A . 
         [0059]      FIG. 7A  illustrates a circularly polarized folded patch antenna  700  according to an embodiment of the present invention. The embodiment shown in  FIG. 7A  comprises a ground plane  701 , a spacer layer  702 , a radiating element (patch)  703 , and a feed element  704 . As shown in  FIG. 7A , radiating element  703  is folded to include three horizontal layers (a top layer  705 , a middle layer  706 , a bottom layer  707 ) and two vertical wall layers (first vertical wall layer  708  and second vertical wall layer  709 ). In this embodiment, feed element  704  is not fed through the radiating element as with the embodiment illustrated by  FIG. 6A ; rather, the feed element is fed directly to top layer  705 . Thus, as illustrated by  FIG. 6A  and  FIG. 7A , radiating elements according to the present invention may be folded upward or downward.  FIG. 7B  illustrates a plan view for radiating element  703 . As shown by the dashed fold lines, radiating element  703  is designed to be folded upwards as shown in  FIG. 7A . 
         [0060]    Embodiments of the present invention are not limited to radiating elements comprised of a single conducting element. According to embodiments of the present invention the radiating element may comprise a conductor on printed circuit board (PCB) material. In other embodiments the radiating element may comprise a plurality of conducting layers connected by conducting connectors or pins. 
         [0061]      FIGS. 8A-8E  illustrate a miniature circularly polarized patch antenna adapted according to an embodiment of the present invention wherein the radiating element includes conductors printed on PCB material. As illustrated in  FIG. 8A , the radiating element of a circularly polarized folded patch antenna according to embodiments of the present invention can be fabricated using PCB material. The circularly polarized folded patch antenna  800  includes a ground layer  801 , a spacer layer  802  (more clearly shown in  FIG. 8B ), a radiating element  803 , and a feed element  804 . In the embodiment illustrated by  FIG. 8A , radiating element  803  includes a top layer  805 , a bottom layer  806 , and conducting pins  807 . 
         [0062]    As more clearly illustrated by  FIG. 8C , top layer  805  includes an antenna pattern etched onto PCB. In the embodiment illustrated by  FIGS. 8A-8D , the asymmetry in radiating element  803  is introduced in top layer  805  of radiating element  803 . As shown in  FIG. 8C , asymmetry is introduced at elements  808 A- 808 D etched into top layer  805 . The slots defining elements  808 B and  808 D are smaller than the slots defining  808 A and  808 C. Elements  808 A- 808 D are selected to excite two orthogonal modes 90° out of phase and of substantially equal magnitude. 
         [0063]      FIG. 8D  illustrates bottom layer  806  according to the embodiment illustrated by  FIGS. 8A-8D . As shown in  FIG. 8D , each of arms  809 A- 809 D is symmetrical in this embodiment. The radiation paths of bottom layer  806  are connected to the radiation paths of top layer  805  by conducting pins  807 . In certain embodiments, as illustrated by  FIG. 8E , portions of the radiation paths may be connected to alter, or tune, the radiation element. In the example of  FIG. 8 , tails  808 A and  808 C are connected at soldering points  809 A and  809 B and tails  808 B and  808 D are connected at soldering points  810 A and  810 B thereby tuning the response of the radiating element shown in  FIGS. 8A-8E . 
         [0064]    As illustrated in  FIG. 9 , embodiments of the present invention may include two orthogonal feeds. In the embodiment illustrated by  FIG. 9 , radiating element  900  includes dual feed points  901 A and  901 B, and radiating element  900  is fed two signals, one at feed point  901 A and the second at feed point  901 B. In embodiments utilizing a dual feed, the radiating element&#39;s geometry can be both symmetric and asymmetric. Dual feed embodiments of the present invention exhibit wider axial ratio and impedance bandwidth when fed with signals substantially equal in magnitude but 90° out of phase. 
         [0065]    Various embodiments of the invention provide advantages over prior art antenna systems. For instance, various disclosed folded patch antennas are smaller than other air substrate CP antennas. Furthermore, various disclosed folded patch antennas do not require expensive dielectrics to facilitate miniaturization. Moreover, various disclosed miniature folded patch antennas have simple antenna structures that can be quickly and inexpensively manufactured. Although the embodiments of the present invention may be used in any number of applications, the circularly polarized folded patch antenna disclosed herein may find particular use in GPS units, satellite televisions, RFID base stations, satellite communications, cellular telephones, or other mobile communication devices. 
         [0066]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.