Abstract:
A spiral planar antenna includes more than two spiral arms. Each arm includes at least a portion that is coiled. The antenna may operate from approximately 50 MHz to upwards of several GHz within a payload space of only about 5.75 inches in diameter and less than one inch in height, with approximately 5 dBi or less of measured axial ratio. The broad frequency response in conjunction with a small space-profile improves space limitations and payload for deployable and non-deployable platforms while reducing opportunities for electromagnetic interference.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   FIELD 
   The present invention generally relates to antennas and, in particular, relates to coiled spiral antennas. 
   BACKGROUND 
   Antennas operate to control energy wave propagation. They are critical components for various wireless transmission and reception systems, for example, telecommunication, aerospace, and/or data transmission systems in general. 
   Edwin Turner is credited with first generally investigating the spiral antenna in 1954 when he wound a long wire dipole into a spiral form and connected its terminals to a two-wire feed line. Results from his experiments have spurred investigation that continues even today. 
   Spiral antennas have been designed in various planar or conical shapes, the most common being the equiangular and Archimedean. Spirals operate in three simultaneous fashions: as fast-wave, as leaky-wave, and as traveling-wave antennas. Excited currents in the antenna conductors form a traveling wave that allows for broadband performance. The wave has a phase velocity in excess of the speed of light because of the mutual coupling between neighboring arms. The antenna leaks energy while propagating on the line to produce radiation. 
   SUMMARY 
   In an exemplary embodiment of the present invention, a radio frequency antenna device is provided for transmission/reception of energy waves across a broad spectrum of frequencies with improved performance in high and/or low frequency bands within a small profile. An exemplary embodiment of the instant invention includes multiple spiral arms, at least a portion of each being coiled. The antenna is generally planar with gaps between each arm, and is typically of a small geometry. In some instances the antenna is less than 1 inch in height and less than 12 inches in diameter. In some instances the antenna is less than 6 inches in diameter. In many of the exemplary embodiments described herein the antenna is approximately 5.75 inches in diameter and about 0.75 inches in height. 
   According to an embodiment, a planar antenna device comprises more than two conductive spiral arms, each comprising a coiled portion, a plurality of spiral gaps, a center dielectric portion, and an outlying dielectric portion. Each of the more than two conductive spiral arms is configured to receive a phase shifted input signal at a beginning point of the corresponding one of the more than two conductive spiral arms in the center dielectric portion. Each of the more than two conductive spiral arms spirals from the beginning point of the corresponding one of the more than two conductive spiral arms in the center dielectric portion to an end point in the outlying dielectric portion in a radially increasing manner. Each of the plurality of spiral gaps spirals from a beginning point of the corresponding one of the plurality of spiral gaps toward an outer edge of the outlying dielectric portion in a radial manner. 
   According to an embodiment, a planar antenna device comprises a plurality of conductive spiral arms, each comprising a coiled portion, a plurality of spiral gaps, a center dielectric portion, and an outlying dielectric portion. The center dielectric portion comprises a first planar thickness, the outlying dielectric portion comprises a second planar thickness, and the first planar thickness is less than the second planar thickness. Each of the plurality of conductive spiral arms is configured to receive a phase shifted input signal at a beginning point of the corresponding one of the plurality of conductive spiral arms in the center dielectric portion. Each of the plurality of conductive spiral arms spirals from the beginning point of the corresponding one of the plurality of conductive spiral arms in the center dielectric portion to an end point in the outlying dielectric portion in a radial manner. Each of the plurality of spiral gaps spirals from a beginning point of the corresponding one of the plurality of spiral gaps toward an outer edge of the outlying dielectric portion in a radial manner. 
   According to an embodiment, a planar antenna device comprises a plurality of conductive spiral arms, a plurality of spiral gaps, a center dielectric portion, an outlying dielectric portion and a wall. Each of the plurality of conductive spiral arms is configured to receive a phase shifted input signal at a beginning point of the corresponding one of the plurality of conductive spiral arms in the center dielectric portion. Each of the plurality of spiral gaps spirals from a beginning point of the corresponding one of the plurality of spiral gaps toward an edge of the outlying dielectric portion in a radial manner. Each of the plurality of conductive spiral arms spirals at least in a first direction from the beginning point of the corresponding one of the plurality of conductive spiral arms in the center dielectric portion toward the outlying dielectric portion in a radially increasing manner. After spiraling to the outlying dielectric portion, each of the plurality of conductive spiral arms travels in the wall at least in a second direction in a coiled manner from a first point to a second point forming a coil arm between its first point and its second point. In this embodiment, the second direction is different from the first direction. 
   Additional features and advantages of the invention will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention both to its organization and manner of operation, may be further understood by reference to the drawings that include  FIGS. 1 through 27B , taken in connection with the following descriptions: 
       FIG. 1A  illustrates an aspect of an exemplary embodiment of the present invention including a housing; 
       FIG. 1B  illustrates a side view of an exemplary embodiment of the invention showing approximate dimensions; 
       FIG. 2  illustrates a top plan view of an exemplary embodiment of the invention; 
       FIG. 3  illustrates a bottom plan view of an exemplary embodiment of the invention; 
       FIG. 4  illustrates an exemplary non-coiled spiral antenna; 
       FIG. 5  illustrates a top down side view of a spiral antenna with four spiral arms according to an exemplary embodiment of the present invention; 
       FIG. 6  illustrates a top down side view of a spiral antenna with six antenna arms according to an exemplary embodiment of the present invention; 
       FIG. 7A  illustrates a top plan view of a two-arm spiral antenna according to an exemplary embodiment of the present invention; 
       FIG. 7B  illustrates a bottom plan view of the antenna shown in  FIG. 7A  according to an exemplary embodiment of the present invention; 
       FIG. 8  illustrates an exemplary embodiment of the invention showing formation of coiled spirals; 
       FIG. 9  is an illustration of an exemplary embodiment of the present invention being tested in a tapered chamber; 
       FIG. 10  shows an exemplary embodiment of the present invention being tested in a tapered chamber; 
       FIG. 11  is a graphical representation of a radiation pattern of a radio frequency wave propagated by an exemplary embodiment of the instant invention including a two-armed, coiled spiral antenna operating at 200 MHz; 
       FIG. 12  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the instant invention with four antenna arms operating at 200 MHz; 
       FIG. 13  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention with six antenna arms operating at 200 MHz; 
       FIG. 14  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention using two antenna arms operating at 400 MHz; 
       FIG. 15  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention including four antenna arms operating at 400 MHz; 
       FIG. 16  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention including six antenna arms operating at 400 MHz; 
       FIG. 17  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the instant invention including two antenna arms operating at 800 MHz; 
       FIG. 18  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention including four antenna aims operating at 800 MHz; 
       FIG. 19  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention including six antenna arms operating at 800 MHz; 
       FIG. 20  is a top plan view of an antenna according to an exemplary embodiment of the present invention; 
       FIG. 21  is another top plan view of an antenna according to an exemplary embodiment of the present invention; 
       FIG. 22  is a graphical representation of a radiation pattern propagated by an exemplary embodiment of the instant invention including propagation with four antenna arms in delta mode; 
       FIG. 23  is a graphical representation of a radiation pattern of an exemplary embodiment of the present invention including propagation with six antenna arms in delta mode; 
       FIG. 24  is a top plan view of a dual-polarized four-arm coiled antenna according to an exemplary embodiments of the present invention; 
       FIG. 25  is a graph showing a measured axial ratio compared to frequency according to various exemplary embodiments of the present invention; 
       FIG. 26  is a graph showing an axial ratio measured from an exemplary embodiment of the present invention; 
       FIG. 27A  illustrates a top plan view of an antenna according to an exemplary embodiment of the present invention; and 
       FIG. 27B  illustrates a sectional view of an antenna according to an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The following description of illustrative non-limiting exemplary embodiments of the invention discloses specific configurations and components. However, the exemplary embodiments are merely examples of the present invention, and thus, the specific features described below are merely used to describe such exemplary embodiments to provide an overall understanding of the present invention. One skilled in the art readily recognizes that the present invention is not limited to the specific exemplary embodiments described below. Furthermore, certain descriptions of various configurations and components of the present invention that are known to one skilled in the art are omitted for the sake of clarity and brevity. Further, while the term “exemplary embodiment” may be used to describe certain aspects of the invention, the term “exemplary embodiment” should not be construed to mean that those aspects discussed apply merely to that embodiment, but that all aspects or some aspects of the disclosed invention may apply to all exemplary embodiments, or some exemplary embodiments. 
     FIGS. 1A and 1B  illustrate overall dimensions of an exemplary embodiment of a planar antenna device  100 . The planar antenna device  100  may be a coiled spiral antenna including a diameter  110  of approximately 5.75 inches and a depth  120  of one inch or less. In certain exemplary embodiments the depth  120  may be 0.75 inches or less. The planar antenna device  100  is provided with an input connector  130  which may be an SMA, a TNC, or N connector, another input connector type, or other type of transmission line interface. An antenna substrate (not shown) rests within housing  140 . Housing  140  may resemble a pie tin in shape and is typically made of PVC but may be any suitable non-conductive material capable of providing structure for an antenna substrate. 
   The planar antenna device  100  typically radiates bi-directionally, with opposite polarization across two hemispheres. Many applications, however, require unidirectional radiation. In these instances a ferrite tile may be used such as shown by element  150  in  FIG. 1A . The tile need not be located inside the cavity  140  and may be positioned externally, such as shown by ferrite tiles  510  in  FIG. 5 . Tile  150  may be any suitable radiation absorbing or reflecting material in addition to ferrite. 
     FIG. 2  illustrates an exemplary top plan view of a planar antenna device with four conductive antenna arms  220 ,  222 ,  224 , and  226 .  FIG. 3  illustrates an exemplary bottom plan view of the planar antenna device of  FIG. 2 . The planar antenna device  200  may be a coiled spiral antenna having a center area I and an outer area II. In exemplary embodiments, center area I is comprised of a center dielectric portion  240 ,  340  and non-coiled center conductor portions  220   c ,  222   c ,  224   c , and  226   c . Non-coiled center conductor portions  220   c ,  222   c ,  224   c , and  226   c  may be flat conductors that are disposed on top of the center dielectric portion  240  using a deposition or other process. In exemplary embodiments, outer area II is comprised of outlying dielectric portions  210 ,  310 , tightly coiled end portions  220   a ,  222   a ,  224   a ,  226   a , and loosely coiled middle sections  220   b ,  222   b ,  224   b , and  226   b.    
   Each of the four conductive arms  220 ,  222 ,  224 , and  226  spirals in an outward, radial manner (in a radially increasing manner) in a first direction  201 . First direction  201  travels from center area I to outer area II or from the center of the coiled spiral antenna to the outlying dielectric portion  210 . While represented by a single arrow, first direction  201  represents a radial direction including 360 degrees that emanate from the center of the coiled spiral antenna on a plane created by center area I and outer area II. 
   Antenna arm  220  comprises tightly coiled end portion  220   a , loosely coiled middle section  220   b , and non-coiled center conductor portion  220   c . Antenna arm  222  is comprised of tightly coiled antenna section  222   a , loosely coiled antenna section  222   b , and center non-coiled portion  222   c , and the same goes for antenna arms  224  and  226 . The planar antenna device  200  includes outlying dielectric portion  210  that may be comprised of any suitable dielectric. For instance, the outlying dielectric portion  210  may be made of a typical fluoropolymer such as Teflon (a product of DuPont Co.) and/or fiberglass, or may be made of Duroid (a product of Rogers Corporation), or any other suitable dielectric. 
   An exemplary embodiment of planar antenna device  200  may include thin center dielectric portion  240  made of, for example, Duroid, in center area I (i.e., in the area of antenna arm sections  220   c ,  222   c ,  224   c  and  226   c ). Thin dielectric portion  240  is approximately as thin as a few thousandths of an inch, and may be 5-60 mils in thinness, where 1 mil equates to 1 one-thousandth of an inch. The thinness of dielectric portion  240  improves the high frequency propagation of the antenna aims  220   c ,  222   c ,  224   c  and  226   c . This is mainly because wavelengths at high frequencies are shorter than wavelengths at lower frequencies and the higher frequency wavelengths would see a theoretically highest-possible propagation if they were able to transmit through an environment with a dielectric  240  that approached the dielectric value of free space or air, or approximately the relative dielectric constant of 1.0. 
   Because dielectric  240  provides structure for the antenna arms, however, some solid, non-gaseous dielectric is needed. The thinness aspect of the instant invention provides a high-efficiency feed for high frequencies by making dielectric portion  240  as thin as approximately a few thousandths of an inch thick. In exemplary embodiments of the present invention the thickness of thin dielectric portion  240  is thinner than the thickness of the outlying dielectric portion  210 . The thickness of dielectric portion  210  in exemplary embodiments provides structural support for both of the outlying dielectric portion  210 , as well as for the center dielectric portion  240 . 
   As shown in  FIG. 2 , thin dielectric portion  240  may be viewed as comprising physical gaps between adjoining non-coiled center conductor portions  220   c ,  222   c ,  224   c , and  226   c . The gaps are of a first width near the center of center area I, and progressively become wider and wider the farther they are located from the center of planar antenna device  200 , including as they eventually become outlying dielectric portions  210 , and as they progress towards an outer edge of outer area II. 
   Similarly, the non-coiled center conductor portions  220   c ,  222   c ,  224   c , and  226   c  begin at a first width near the center of center area I, and they progressively become wider and wider the farther they are located from the center of planar antenna device  200 , including as they eventually become loosely coiled middle sections  220   b ,  222   b ,  224   b , and  226   b , and then become tightly coiled end portions  220   a ,  222   a ,  224   a ,  226   a , and eventually progress towards an outer edge of outer area II. Loosely coiled middle sections  220   b ,  222   b ,  224   b , and  226   b  and tightly coiled end portions  220   a ,  222   a ,  224   a , and  226   a  are comprised of multiple top segments, multiple bottom segments, and multiple vertical segments. Individual top segments are shown by the heads of arrows for elements  220   b ,  222   b ,  224   c , and  226   c . Individual bottom segments are shown by the heads of arrows for elements  320   b ,  322   b ,  324   b , and  326   b . Vertical segments are not shown because they exist within outer dielectric portions  210  and  310 . Noticeably, individual top segments of the loosely coiled middle sections  220   b ,  222   b ,  224   b , and  226   b  are spaced farther apart than are individual top segments located in tightly coiled end portions  220   a ,  222   a ,  224   a , and  226   a.    
   In exemplary embodiments of the present invention the width of certain gap areas are configured to be a certain width in relation to the width of certain antenna arm portions. In certain exemplary embodiments the width of an individual gap (e.g., element  2007  shown in  FIG. 20 ) at the center of center area I is configured to be less than the width (e.g., element  2008  shown in  FIG. 20 ) of the individual ones of non-coiled center conductor portions  220   c ,  222   c ,  224   c , and/or  226   c . This configuration may be referred to as being “non-complimentary.” 
   In certain exemplary embodiments the width (e.g., element  809  shown in  FIG. 8 ) of an individual one of tightly coiled end portions  220   a ,  222   a ,  224   a , and/or  226   a  in outer area II is configured to be approximately equal (that is, substantially equal at least in comparison to the non-complimentary aspects discussed previously) to the width of a gap (e.g., element  806  shown in  FIG. 8 ) between adjoining tightly coiled end portions  220   a ,  222   a ,  224   a , and/or  226   a . This configuration may be referred to as being “complimentary.” 
   By varying non-complimentary widths in center area I, various exemplary embodiments of the instant invention are able to make an impedance match (or an approximate impedance match) between an input signal and the antenna itself. That is, input impedance may be set by altering the difference in width between an individual gap at the very center of center area I and the width of individual ones of non-coiled center conductor portions  220   c ,  222   c ,  224   c , and/or  226   c.    
   Furthermore, an aspect of an exemplary embodiment of the present invention where the width of the gaps in outer area II approaches approximately the same widths of individual ones of tightly coiled end portions  220   a ,  222   a ,  224   a , and/or  226   a  enables the planar antenna device  200  to be efficiently fed. The impedance matching at an input to the antenna as reflected by a non-complimentary configuration of the dielectric in the center area (for example, area I in  FIG. 2 ) in conjunction with the complimentary spiral in the outer diameter area (for example, area II in  FIG. 2 ) enables various exemplary embodiments of the invention to be efficiently fed. Efficient feeding of the antenna arms is one of the aspects of the present invention enabling enhanced propagation, for instance, the enhanced propagation as shown in and as discussed in relation to  FIGS. 11-19 . 
     FIG. 3  illustrates four antenna arm portions  320 ,  322 ,  324  and  326 . Each of these four arms includes tightly coiled spiral sections  320   a ,  322   a ,  324   a ,  326   a , and loosely coiled spiral elements  320   b ,  322   b ,  324   b ,  326   b . As shown by portion  340  the non-coiled section of the antenna arms  220   c ,  222   c ,  224   c ,  226   c  of  FIG. 2  are not visible in  FIG. 3 . This is because sections  220   c ,  222   c ,  224   c , and  226   c  are on the opposite side of the substrate and their view is thus obscured by thin dielectric  340 . The dielectric  340  may be thin in the center portion of the antenna portion to allow for enhanced high frequency performance as described previously. 
   In either  FIG. 2  or  3 , the conducting material may be copper, gold, platinum, copper covered gold or platinum, or any suitable transmitting conductive material. In either  FIG. 2  or  3 , the process to manufacture an antenna would include the use of a substrate. The substrate may be of a dielectric material, and the antenna arms (e.g., tightly wound coils  220   a  or  320   a , coils  220   b  or  320   b , and/or the high frequency conductors  220   c ,  222   c , etc.) may be produced using photolithography and deposition/etch processes. 
   When creating aspects of the present invention including the coiled sections of the spiral antenna arms, two substrates may be used: a first substrate that includes the top portion of the coils, and a second substrate that includes the bottom portion of the coils. Stated differently, a substrate could be used to create the antenna portions shown in  FIG. 2 , for instance, and a separate substrate could be used to create the antenna portions shown in  FIG. 3 . These two substrates may then be placed together to create one substrate with via holes acting as potential conduits between each of the top and bottom sections of the coils. (Individual coils are shown in greater detail in  FIG. 8 .) 
   Upon completion of the deposition process and/or adhesion of the first and second substrates to each other, an electrolysis (or other) process may be used to fill each of the via holes. In addition to electrolysis, other known methods such as a deposition process may be used to place conductive material into the via holes. Deposition may also be used to fill in photo-etched sections of the substrate. In different aspects of the invention, the coiled spiral antenna elements may be made using a photolithography and/or other processes on both sides of the same substrate. 
   Once an electrolysis or other process is used to fill the via holes with conductive material the antenna arms  220  and  320  are electrically the same conductive arm from a signal input point at the center area I of the spiral to the end of the antenna arm at a very outer portion of the outer area II of the coiled spiral antenna. The same may apply for antenna arms  222  and  322 ,  224  and  324 , and  226  and  326 . 
     FIG. 4  illustrates an exemplary two arm antenna that is completely non-coiled from input feeds  410   a  and  410   b  to the end of the antenna arms  412   a  and  412   b . The non-coiled spiral antenna  400  has a diameter of about six inches. A measured axial ratio for this antenna would be similar to the measured axial ratio shown in  FIG. 25  for a two-armed coiled spiral antenna. For the exemplary two-arm non-coiled antenna, it can be expected that below about 700 MHz the measured axial ratio will start to oscillate above 5 dB, and below 500 MHz, the axial ratio will remain above 5 dB. The cross-polarization expressed by the measured axial ratio above 5 dB indicates that it is approaching or even exceeding levels of co-polarization, a state that is undesirable. This undesirable state stems from reflected currents radiating at high levels which have an extreme negative effect on the polarization purity. 
     FIG. 5  illustrates a top down side view of a planar antenna device in an exemplary embodiment of the invention including four antenna arms  520 ,  522 ,  524  and  526 . The number of antenna arms may be as many as will fit within the actual space with which they could be imprinted on an exemplary substrate. For instance while various aspects and various exemplary embodiments of the invention include descriptions of a plurality of arms, the total number may be as many as will fit within the physical limitations of mechanical processes and/or chemical processes used to create the arms on the substrate. A planar antenna device  500  may be a coiled spiral antenna which sits on four ferrite tiles  510  to allow for unidirectional radiation in a direction away from the tiles  510 . 
     FIG. 6  illustrates a top down side view of a planar antenna device in an exemplary embodiment of the invention including six antenna arms  620 ,  622 ,  624 ,  626 ,  628  and  630 . A planar antenna device  600  may be a coiled spiral antenna which sits on four ferrite tiles  610 . The radiation absorbing function of ferrite tiles  610  may be completed by use of a circular absorber within the antenna cavity, as shown in  FIG. 1A . 
     FIGS. 7A  (top plan view) and  7 B (bottom plan view) illustrate an exemplary embodiment of the present invention including a two-armed planar antenna device  200 . The antenna device  200  includes arms  220  and  222 . Each arm includes a tightly coiled portion  220   a  and  222   a , a loosely coiled portion  220   b  and  222   b , and a non-coiled section  220   c  and  222   c , respectively. The arms are supported by a dielectric substrate  210 ,  240 . Substrate portion  240  is a thin dielectric on the order of 5-60 mils thick to achieve a highly efficient high frequency feed as discussed herein in relation to  FIG. 2  (that discussion will not be reiterated for the sake of brevity). Outlying dielectric portion  210  is of a greater thickness than inner dielectric portion  240  so that the plane of the planar antenna device  200  has superior overall strength/durability. Aspects of the invention include the possibility of making the width of the dielectric portion  240  less than the width of the antenna arms  220   c ,  222   c  so that a non-complimentary effect is achieved that allows for an impedance match to be made between an input signal and the antenna (for instance, as shown in  FIG. 20  by elements  2007  and  2008 , respectively, as the width of an individual gap and the width of an individual antenna arm). Additionally, a complimentary (i.e., similar) width between gaps and individual ones of arms  220   a ,  222   a  allows for enhanced propagation of radiation waves. 
   The antenna portions shown in  FIGS. 7A  (top plan view) and  7 B (bottom plan view) may be made from one substrate or made from two or more different substrates. If they are made from two different substrates, they are attached to one another as described in relation to  FIGS. 2 and 3 , thereby allowing creation of the coiled spirals. 
     FIG. 8  is a top-down view of both loosely wound coils  810  and tightly wound coils  820  as aspects of various exemplary embodiments of the instant invention. The view is from the perspective of looking directly down at the plane of a planar antenna device, for instance, a coil spiral antenna shown in  FIGS. 2 ,  3 ,  7 A and/or  7 B. The coils  810  are farther apart from each other than coils  820 . Coils  810  are thus described as loosely wound while coils  820  are described as tightly wound. The coil portions  812  (top segments) are all located on the top side of the substrate in comparison to coil portions  814  (bottom segments) that are located on an opposite side. The opposing sections of coil  812  and  814  are connected by via holes  816  (vertical segments). During the manufacturing process coil portions  812  and  814  are filled with a conductive material and then via holes  816  undergo a further deposition, electrolysis, or other process to fill in the holes with a conductive material. In this fashion a three-dimensional coil is formed. The same or similar process is used to create the tightly wound coils  820 . Conductive coil portions  822  and  824  are on opposite sides of the substrate and via holes  826  are filled in to allow for electrical conductivity throughout the coil. 
     FIG. 9  illustrates testing of an exemplary planar antenna device in an anechoic chamber according to one aspect of an exemplary embodiment of the invention. A planar antenna cap  940  is the top piece of coiled spiral antenna  900 , which has six antennas arms. Coiled spiral antenna  900  sits atop the chamber test equipment  930 . As shown by cables  910 ,  912 ,  914 ,  916 ,  918  and  920  the antenna  900  is provided with six inputs. Each of the inputs for feed elements  910 ,  912 ,  914 ,  916 ,  918  and  920  is of equal amplitude but is phase shifted in equal amounts based on the number of antenna arms and/or inputs. Even though feed elements  910 ,  912 ,  914 ,  916 ,  918  and  920  are shown as possessing six inputs, it would be clear to one of skill in the art that a beam former could be used to vary the amplitude and phase (with N inputs) to thereby allow a six arm antenna to have a single input instead of multiple inputs. In an exemplary embodiment, a six arm antenna can form useful higher order modes, and in those instances a beamformer may be provided with several inputs. 
     FIG. 10  illustrates an exemplary embodiment of a planar antenna device. The planar antenna device  1000  may be a coiled spiral antenna including ferrite tiles  1010 . The tiles  1010  are useful for unidirectional transmission, as discussed previously. The planar antenna device  1000  sits atop the test equipment  1020 . The tapered chamber test equipment  1020  (and  930  in  FIG. 9 ) is (are) used to derive graphical representations of radiation patterns, for instance those patterns represented by  FIGS. 11 through 19 , and  FIGS. 22 and 23 .  FIGS. 11 through 19 ,  22  and  23  were each derived using coiled spiral antennas that were approximately 5.75 inches in diameter. 
   In  FIG. 11  a graphical representation of a radiation pattern propagated by an exemplary embodiment of the present invention including two coiled antenna arms at 200 Megahertz is shown. As show in the figure, the co-polarization  1110  appears to be slightly less than the cross-polarization  1120 . 
   Cross-polarization is undesired because it reduces signal strength. Additionally, cross-polarization can decrease the signal to noise ratio of the intended transmission. For the previous reasons cross-polarization is undesired. 
     FIGS. 12 through 19 ,  22 , and  23  reflect a cross-polarization comparison to co-polarization for exemplary embodiments of the present invention including planar antenna devices with more than 2 spiral antenna arms. As can be seen in these figures, the cross-polarization is much less than the co-polarization. Co-polarization is desired and as reflected in the noted figures, the patterns for the co-polarized signals are all circular and symmetrical. The patterns for co-polarized signals overlay fairly tightly as they approach their outer limits represented by the intended target 0 (zero) at the top of the graph. Because of this, the measured axial ratio for these antennas is less than 5 dB across a frequency range of 100 MHz to more than 6 GHz, as reflected by the graph of  FIG. 27 . 
     FIG. 12  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including four antenna arms and operating at 200 megahertz according to an aspect of an exemplary embodiment of the present invention. As shown in the figure, the cross-polarization  1220  is significantly less than co-polarization  1210 . 
     FIG. 13  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including six antenna arms and operating at 200 megahertz according to an aspect of an exemplary embodiment of the present invention. As shown in  FIG. 13 , the cross-polarization  1320  is significantly less that the co-polarization  1310 . Again the cross-polarization  1320  being less than the co-polarization  1310  allows for a cleaner signal to be transmitted. 
     FIG. 14  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including two antenna arms and operating at 400 megahertz according to an aspect of an exemplary embodiment of the present invention. As shown in the graph, cross-polarization  1420  is improved in relation to  FIG. 11 . Further, the co-polarization  1410  is greater than the cross polarization  1420 . 
     FIG. 15  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including four antenna arms and operating at 400 megahertz according to an aspect of an exemplary embodiment of the present invention. As shown in the figure, cross-polarization  1520  is significantly less than the co-polarization  1510 . 
     FIG. 16  illustrates a graphical representation of a radiation pattern propagated by a coiled spiral antenna including six coiled antenna arms and operating at 400 megahertz according to an aspect of an exemplary embodiment of the present invention. As shown in the figure the cross-polarization  1620  is significantly less than the co-polarization  1610 . 
     FIG. 17  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including two coiled antenna arms and operating at 800 megahertz according to an aspect of an exemplary embodiment of the present invention. The cross-polarization  1720  is less than co-polarization  1710 . 
     FIG. 18  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including four antenna arms and operating at 800 megahertz according to an aspect of an exemplary embodiment of the present invention. As show in the figure the cross-polarization  1820  is significantly less than the co-polarization  1810 . 
     FIG. 19  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including six coiled antenna arms and operating at 800 megahertz according to an aspect of an exemplary embodiment of the present invention. As shown in the figure cross-polarization  1920  is significantly less than the co-polarization  1910 . 
   In various aspects of the present invention the input signal is phase shifted for each individual antenna arm, such as antenna arms  220 ,  222 ,  224  and  226  as shown in  FIG. 2 . For instance, an input signal is phase shifted to provide a 0 degree phase shift to the input to antenna arm  220 , the same signal is phase shifted 90 degrees as the input to antenna arm  222 , the same signal is phase shifted 180 degrees for the input to antenna arm  224 , and the same signal is phase shifted 270 degrees for antenna arm  226 . For a six arm antenna the phase difference between each arm is sixty degrees, for an eight arm antenna is 45 degrees, and for a three arm antenna the phase difference between each arm is 120 degrees. Phase shifting may occur either externally to the antenna or within the antenna cavity. One of skill in the art would understand that a beam splitter, a coupler, and/or shifter may be used to split a signal to give it differently phased components. 
     FIGS. 20 and 21  describe aspects of an exemplary embodiment of the present invention including the ability to provide an impedance match (or an improved impedance match) between an input signal and the antenna itself. As shown in  FIG. 20  antenna arms  2010 ,  2012 ,  2014 ,  2016 ,  2018 ,  2020 ,  2022  and  2024  spiral outwardly from the center of the antenna device  2000  in a radially increasing manner. Between each antenna arm is a gap  2030 . Each gap  2030  has a particular width  2007  between adjoining antenna arms. Notably each of the antenna radial arms  2010 ,  2012 ,  2014 ,  2016 ,  2018 ,  2020 ,  2022 , and  2024  is of approximately identical width  2008  in relation to each other. The ability to reduce the width of the particular width  2007  in relation to an individual width  2008  of the antenna spiral arms  2010 ,  2012 ,  2014 ,  2016 ,  2018 ,  2020 ,  2022 , and  2024  allows the antenna device  2000  to provide a specific impedance match or an approximate impedance match in mind. For instance, in the antenna shown in  FIG. 20 , an impedance match is provided by virtue of the gaps  2007  being of lesser width than the width  2008  of individual antenna arms such that the impedance match approaches and/or matches approximately 50 ohms. It should be noted that while the size of gap  2007  shown in  FIG. 20  is small near the center of the antenna  2000 , the gap eventually increases as the spiral continues outward. For instance, as shown in the center portion of  FIG. 2 , the gap is non-complimentary, but the gap transitions to approximately complimentary and then to complimentary as the gap travels from the center to the outer portions of area I (shown in  FIGS. 2 and 3 ) of the coiled spiral antenna  200 . It is to be understood that the location of the non-complimentary, transitional area of approaching complimentary, and then complimentary areas may be varied based on desire or need. 
   In  FIG. 21  the spiral antenna  2100  includes antenna arms  2110 ,  2112 ,  2114  and  2116 , gap areas  2130 . Notably near the center of the antenna the gap area  2130  is of lesser width than the width of individual ones of antenna arms  2110 ,  2112 ,  2114 , and  2116 . As discussed in relation to  FIG. 20 , the widths reflects an aspect of the present invention whereby an impedance match (or an improved impedance match) can be configured for the signal provided as an input to the antenna  2100 . 
     FIG. 22  is a graph of a radiation pattern propagated at 600 megahertz by a coiled spiral antenna including four coiled antenna arms in delta mode (or what is otherwise known as mode 2) according to an aspect of an exemplary embodiment of the present invention. In  FIG. 22  the co-polarization  2210  is slightly higher than the cross-polarization  2220 . Delta mode is useful for monopulse direction finding, among other things, as would be known to one of skill in the art. Mode 2 patterns with lower cross-polarization are produced when the antenna has more than four arms. 
     FIG. 23  is a graphical representation of a radiation pattern propagated by a coiled spiral antenna including six antenna arms and operating at 600 megahertz in delta mode (or mode 2) according to an aspect of an exemplary embodiment of the present invention. The co-polarization  2310  is significantly higher than the cross-polarization  2320 . As shown by the differences between  FIGS. 22 and 23 , the cross-polarization is reduced with the additional two arms. 
     FIG. 24  illustrates an exemplary embodiment of the present invention comprising a dual polarized antenna  2400  with both right-hand circular polarization (RCP) and left-hand circular polarization (LCP) units, wherein both the RCP and LCP units each have four antenna arms with coiled portions. For ease of understanding and for clarity, the following describes one antenna arm for each of the RCP and LCP units, but it is to be understood that each of the RCP and LCP units possess four antenna arms, and that each arm comprises a flat portion, a loosely coiled portion, and a tightly coiled portion. A shown in  FIG. 24 , antenna arms  2401  and  2403  respectively comprise non-coiled portions  2401   a  and  2403   a , loosely coiled portions  2401   b  and  2403   b , and tightly coiled portions  2401   c  and  2403   c . The flat portions  2401   a  and  2403   a  begin in a circular fashion but eventually change shape such that they produces a square or an approximate square shape before becoming loosely coiled portions  2401   b  and  2403   b , respectively. One purpose for this is to better conform to a square shape at the perimeter. One of skill in the art would understand that the shape of the perimeter could be configured practically in any fashion based on need or desire. Since many of the previously described exemplary embodiments of the present invention including single polarization spiral antennas provide satisfactory co- and cross-polarization results using inductive loading, the example of the dual antennas shown in  FIG. 24  is one way to achieve dual polarization. Using a square geometry may make packaging easier, and may increase loading by 4/π (ratio of square perimeter to circle). 
     FIG. 25  is an exemplary graph that illustrates axial ratios measured from various exemplary embodiments of the present invention, including a 2-arm spiral antenna and a 4-arm spiral antenna, both operating in the first mode. As shown in the graph, the measured axial ratios remain well below 5 dB (and mostly below 3 dB) across most of the frequency spectrum. Only the 2-arm spiral antenna produces an axial ratio that is greater than 5 dB in a certain frequency range. For example, the axial ratio of the 2-arm spiral antenna oscillates above and below the 5 dB level between 500 and 700 MHz. Below 500 MHz the measured axial ratio of the 2-arm spiral antenna is typically above 5 dB, showing increased cross-polarization in relation to co-polarization. 
   Exemplary versions of the present invention with greater than two spiral antenna arms are shown to have a measured axial ratio of much less than 5 dB, and thus provide an improvement over other antennas, such as the exemplary non-coiled antenna shown in  FIG. 4 . 
     FIG. 26  illustrates axial ratio measurements obtained from an exemplary embodiment of the present invention including a 4-arm coiled spiral antenna. As shown in the graph, the measured axial ratio remains well below 5 dB across the frequency range between about 0.2 and 6 GHz.  FIG. 26  illustrates excellent transmissibility of exemplary embodiments of the present invention including 4 coiled spiral antenna arms. Exemplary embodiments of the present invention including 3 antenna arms may achieve results similar to those shown in  FIG. 26 . Superior transmissibility results for various exemplary embodiments of the present invention were found with antennas having greater than two arms while operating in a first mode (for example, mode 1, sum, or Σ) that is useful for transmission/reception, for example, during angle of arrival applications. Superior transmissibility results for various exemplary embodiments of the present invention were also found with antennas having greater than four arms while operating in a second mode (a second mode is also referred to as mode 2, difference, or delta mode). A second mode is useful, for instance, for monopulse direction finding. 
     FIGS. 27A  (top plan view) and  27 B (sectional view) illustrate a planar antenna device in accordance with an exemplary embodiment of the present invention. As illustrated, a two-armed antenna device  2900  has two antenna arms  2910   a  and  2910   b , which begin in the center of the antenna device  2900  and extend outwardly in a fairly circular fashion but become rather square-shaped at the outer edges of the antenna device  2900 . The antenna arms  2910   a  and  2910   b  conform to an outer wall  2920 . A separate exemplary illustration of an outer wall is shown as an element  140  in  FIGS. 1A and 1B . While  FIG. 27A  shows a square shape, an antenna of the present invention may have a circular shape or other shapes. 
   As shown in  FIGS. 27A and 27B , in various exemplary embodiments of the present invention the antenna arms  2910   a / 2910   b  may continue at least to the wall  2920  and travel in the square-shaped wall  2920 , which may have a depth  2930  (see  FIG. 27B ). Wall  2920  may be capped with a planar cap element  2940  (which is shown as antenna cap  940  in  FIG. 9 ). In this example, each of the antenna arms  2910   a / 2910   b  travels in a first direction  2950  outwardly toward the edge of outer dielectric portion  2915  (e.g., a point where the outer dielectric portion  2915  meets with wall  2920 ). Each of the antenna arms  2910   a / 2910   b  then enters the wall  2920  and proceeds in a second direction  2952  while coiling in the wall  2920 . 
   In comparing first direction  2950  to second direction  2952 , first direction  2950  represents a radially outwardly spiraling direction from the center of the planar antenna device  2900  on a plane created by antenna arms  2910   a / 2910   b . Second direction  2952  is generally perpendicular to first direction  2950 . Second direction  2952  may be a direction along one or more sides of a square, as illustrated in  FIG. 27A . In one aspect, second direction  2952  does not travel toward, or away from, the plane created by antenna arms  2910   a / 2910   b  but rather travels along the side of the plane created by antenna arms  2910   a / 2910   b.    
   Antenna arm  2910   a  travels in first direction  2950  on the plane created by antenna arms  2910   a / 2910   b  from the center of the planar antenna device  2900  to an edge of outer dielectric portion  2915  then travels in wall  2920  in second direction  2952 . Second direction  2952  for antenna arm  2910   a  may begin, for example, at first point  2921  and end at second point  2922 . While traveling generally in second direction  2952 , antenna arm  2910   a  may coil between a first surface  2953  and a second surface  2954  of the wall  2920 . The coil direction may include a forward direction  2902  (perpendicular to second direction  2952 ) and a reverse direction (at an angle to forward direction  2902 ). As the coiled antenna arm  2910   a  travels generally in second direction  2952 , it may have a height  2911  at an initial point and a height  2912  at a later point. Height  2912  may be greater, equal to, or less than height  2911 . The height of the coiled antenna arm  2910   a  may progressively increase from one point to another along second direction  2952 . First surface  2953  may be parallel to the plane defined by antenna arms  2910   a / 2910   b . Second surface  2954  may be at an angle to first surface  2953 . Antenna arm  2910   b  may travel in a manner similar to antenna arm  2910   a . In this example, second surface  2954  is not parallel to first surface  2953 . 
   The area  2975  illustrates an expanded view of an exemplary embodiment where the antenna arm  2910   a  travels into the wall  2920  at point  2921  and then coils within wall  2920 . As illustrated in the expanded view of area  2975 , antenna arm  2910   a  reaches point  2921 , where it travels downward into wall  2920  and then travels in a width-wise direction of wall  2920  to reach point  2978 . At point  2978  the antenna arm then travels upwards towards a top portion of wall  2920 , where it then travels in a substantially lengthwise-direction of wall  2920  to reach point  2980 . As shown in relation to  FIG. 27B , the antenna arm  2910  may travel within the wall  2920  until reaching an end-point, for instance, point  2922  (shown in  FIG. 27A ). Within the wall  2920 , the antenna arm  2910  may be either of tightly or loosely coiled, as described in previous exemplary embodiments. Further, the antenna arm  2910  may be of any height to include a consistent or varying height as generally illustrated by callouts  2911  and  2912 . 
   Wall  2920  may be a square shape as shown by  FIG. 27A , or it may be a circular shape or another shape (for example, as shown in  FIG. 1 ,  9 , or  10 ). When antenna arm  2910   a  leaves a first plane created by antenna arms  2910   a / 2910   b , it may enter a second plane created by wall  2920 . The second plane may be perpendicular to the first plane, and the top surface of the second plane may be co-planar with the top surface of the first plane. The second plane may include two sides of a cube or may have generally a tubular or cylindrical shape. 
   Each of the antenna arms  2910   a / 2910   b  may include coiled conductor portions, non-coiled conductor portions (as described with reference to  FIGS. 2 ,  7  and  8 ), a combination of both, other shapes, and/or other combinations. Each of the antenna arms  2910   a / 2910   b  may also spiral in a helical fashion within wall  2920 . Wall  2920  may be plastic and in some cases may be Rexolite (a commercially available plastic molding material made by C-LEC Plastics, Inc.). 
   Additional aspects of exemplary embodiments of the present invention may include the following: Certain exemplary embodiments may include the addition of loads at the end of the spiral arms to further attenuate cross polarized response (such as end loading with resistors for better polarization at the expense of reduced gain). Certain exemplary embodiments comprise adding coils to the arms to achieve inductive loading, thus enabling quality lower frequency patterns and making the antenna appear electrically larger than its physical size. 
   It is understood that any specific order or hierarchy or steps in the processes disclosed herein are merely exemplary illustrations and approaches. Based upon design preferences, it is understood that any specific order or hierarchy of steps in the process may be re-arranged. Some of the steps may be performed simultaneously. 
   The previous description is provided to enable persons of ordinary skill in the art to practice the various aspects and embodiments described herein. Various modifications to these aspects and embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects and embodiments. A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the invention, and are not referred to in connection with the interpretation of the description of the invention. All structural and functional equivalents to the elements of the various embodiments of the invention described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the invention. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.