Abstract:
An aircraft antenna includes an aerodynamic housing structured for attachment to an outer surface of an aircraft, and the housing contains an electromagnetic radiator and tuned over a first band of frequencies to produce a first function, and a second electromagnetic radiator to produce a second function, said radiators being arranged to decouple the first radiator and the second radiator from each other.

Description:
RELATED APPLICATIONS 
   This application relates to U.S. application Ser. No. 60/589,842 filed Jul. 20, 2004. This application also relates to U.S. application Ser. No. 10/755,033 Filed Jan. 9, 2004 For “Combination Aircraft Antenna Assemblies”, which claims the benefit of Ser. No. 60/439,252 filed Jan. 10, 2003 entitled “Combination Antennas” and U.S. Application Ser. No. 60/439,381 filed Jan. 10, 2003 entitled “Combination Antennas”. This invention also relates to U.S. Applications Ser. No. 60/533,113, filed Dec. 29, 2003, U.S. Application Ser. No. 60/530,124 filed Dec. 17, 2003, a provisional application entitled Multiple Aircraft-Antenna Assemblies Ser. No. 60/589,842 filed Jul. 20, 2004, a provisional application entitled Multifunction Combination Aircraft Antennas Ser. No. 60/606,598 filed Sep. 1, 2004, a non-provisional application entitled Multifunction Combination Aircraft Antennas filed Oct. 7, 2004 Ser. No. 10/960,394, and a provisional application filed Oct. 1, 2004 entitled Multi-Operational Combination Aircraft Antennas Ser. No. 60/615,404. The content of these applications are hereby incorporated by reference into this application as if fully recited therein. 
   Applicant claims the benefit of all these applications under 35 USC 120. 
   FIELD OF THE INVENTION 
   This invention relates to multi-operational combination aircraft antennas, and particularly to individual aircraft antennas operational in multiple frequency bands and performing multiple functions. 
   BACKGROUND OF THE INVENTION 
   Aircraft require a large array of antennas for navigational, communication, entertainment, and other purposes. The antennas perform various specialized functions at individual frequency bands that must not interfere with each other. Each antenna represents a potential projection from the surface of the aircraft, and such projections may create drag and instabilities that slow and otherwise affect the aircraft&#39;s performance adversely. A single aircraft may support as many as twenty antennae that extend from the aircraft surface into the airstream about the surface. 
   SUMMARY OF THE EMBODIMENTS OF THE INVENTION 
   According to an embodiment of the invention antenna projections from the surface of an aircraft are reduced by combining multiple antenna functions under one aviation radome and arranging the systems inside the radome to limit interference and crosstalk. 
   These and other features of the invention are pointed out in the claims. Other aspects of the invention will become evident from the following detailed description when read in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a generalized schematic illustration of an antenna mounted on an airframe and embodying features of the invention. 
       FIG. 2  is a generalized schematic diagram of another antenna mounted on an airframe and embodying features of the invention. 
       FIG. 3  is a perspective view of an example of an antenna in  FIG. 1  and  FIG. 2 . 
       FIG. 4  is a plan of the example of the antenna in  FIG. 3  embodying features of the invention. 
       FIG. 5  is an elevation of the antenna in  FIGS. 4 and 5  mounted on an airframe and embodying features of the invention. 
       FIG. 6  is another example of an antenna shown in  FIGS. 1 and 2  mounted on an airframe and embodying features of the invention. 
       FIG. 7  is a plan view of the antenna in  FIG. 6 . 
       FIG. 8  is another example of an antenna shown in  FIGS. 1 and 2  mounted on an airframe and embodying features of the invention. 
       FIG. 9  is a bottom view of the antenna in  FIG. 8 . 
       FIG. 10  is a schematic plan of an example of an arrangement inside the antenna in  FIGS. 1 to 5 . 
       FIG. 11  is a schematic plan of another example of an arrangement inside the antenna in  FIGS. 1 to 5 . 
       FIG. 12  is a diagram showing the frequency bands of XM satellite radio and Sirius Satellite Radio. 
       FIG. 13  is a schematic diagram showing an example of two radiators mounted in an antenna embodying features of the invention. 
       FIG. 14  is a schematic the relationship of dimensions in a radiator of the antennas in  FIGS. 1 to 13 . 
       FIG. 15  is a schematic diagram showing the radiation pattern of a helix radiator. 
       FIG. 16  is a schematic diagram of a pair of patch radiators in an antenna showing problems of shadowing. 
       FIG. 17  is a plan schematic diagram of a pair of patch radiators in an antenna arranged to alleviate problems of shadowing according to the invention. 
       FIG. 18  is a perspective view of a platform to alleviate problems of shadowing according to the invention as shown in  FIG. 17 . 
       FIG. 19  is an elevation of radiators, having platforms to alleviate problems of shadowing according to the invention as shown in  FIG. 17 . 
       FIG. 20  is a perspective view of  FIG. 19 . 
       FIG. 21  is elevation of  FIG. 20   
       FIG. 22  is a schematic diagram illustrating radiator orientation according to an embodiment of the invention. 
       FIGS. 23 to 26  illustrate the effects of patch dimensions and positions. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a schematically-illustrated aircraft AC 1  embodying the invention includes a schematically exemplified airframe AI 1  and a schematically-shown multi-operational combination antenna AN 1  also embodying the invention. The antenna AN 1  includes an antenna housing or radome RD 1  that and rests securely on the outer and upper surface of the airframe AI 1  such as on a wing or fuselage. The term airframe includes all parts of the aircraft including its outer shell. The term radome as used herein is not limited to any particular shape. The radome RD 1  includes a base plate BP 1 . Suitable means secure the radome RD 1  to the outer surface or the shell of the airframe AIL A transmitter/receiver system (not shown), which may be located in the antenna AN 1  or connected to the antenna from inside the aircraft, may include one or more transmitters or receivers, drives and receives signals from the antenna AN 1 . 
   The antenna system AN 1  includes a radiator RA 1  and a separate radiator RA 2  mounted on the base plate BP 1 . The term radiator is intended to include both a transmitting antenna element and a receiving antenna element. According to one embodiment of the invention, each radiator RA 1  and RA 2  includes an internal amplifier and according to another embodiment it operates without an internal amplifier but uses the receiver or transmitter, located inside the airframe AI 1 , to which it is connected. Connectors CT 1  and CT 2  connect the radiators RA 1  and RA 2  to the receiver or transmitter through the base plate BP 1 . 
     FIG. 2  illustrates another aircraft AC 1  with an airframe AI 1  supporting an antenna AN 1  with a radome RD 1  that envelops an antenna system AS 1 . However here the antenna system includes N radiators RA 1 , RA 2 , . . . RAN. As in  FIG. 1 , each radiator RA 1 , RA 2  . . . RAN may include an internal amplifier or it may operate without an internal amplifier and use a receiver or transmitter, which is located inside the airframe AI 1  and to which it is connected. Connectors CT 1 , CT 2 , . . . CTN connect the radiators RA 1 , RA 2  . . . RAN to the receiver or transmitter through the base plate BP 1 . 
   According to various embodiments of the invention, the radome RD 1  takes any of a number of forms. For example, according to one embodiment, the antenna housing or radome RD 1  exhibits a high-speed low-profile bar-of-soap-shaped structure, a perspective view of which appears in  FIG. 3 , a plan view in  FIG. 4 , and an elevation in  FIG. 5 . According to another embodiment the radome RD 1  assumes a teardrop shape as shown in elevation in  FIG. 6 , an in plan view in  FIG. 7 . According to another embodiment, the radome RD 1  forms a blade housing BH 1  and appears in cross-sectional elevation in  FIG. 8  and a view from below in  FIG. 9 . According to other embodiments of the invention, the antenna forms a whip housing, or other appropriate shape for aircraft AC 1 . The base plate BP 1  in  FIG. 8  forms part of the housing or radome RD 1  and supports the radiators RA 1 , RA 2 , and RA 3 . In this case the radiator RA 1  is a monopole. Suitable means, such as bolts BT 1  shown in  FIGS. 3 ,  4 , and  5  secure the radome RD 1  to the outer surface of the shell of the airframe AI 1 . Connectors CT 1  appearing for example in  FIGS. 5 ,  6 ,  8 , and  9  project from the radiators RA 1 , RA 2 , and RA 3  through the base plate and the shell of the airframe AI 1  to furnish signals to a receiver or transmitter. 
   In the blade-shaped radome or housing RA 1  in  FIGS. 8 and 9  the radiator RA 1  takes the form of a VHF monopole with a communications conductor antenna CA 1  that extends from the base plate BP 1  at the airframe AI 1  upwardly along the length of the blade-shaped radome. Two or more patch radiators RA 2 , RA 3 , . . . RAN extend parallel to the base plate BP 1 . 
   The radiators RA 1 , RA 2 , . . . RAN may take various forms and perform various functions. According to an embodiment, for example, one of the radiators RA 1 , RA 2 , . . . RAN in  FIGS. 1 to 7  may constitute a helix or quadrifilar-helix antenna element with right hand circular polarization (RHCP) or left hand circular polarization (LHCP) or linear polarization. According to another embodiment one of the radiators RA 1 , RA 2 , . . . RAN is a patch radiator element or a stacked patch arrangement. 
   According to various embodiments of the invention, the radiators RA 1 , RA 2 , . . . RAN perform any one of a number of functions. In one example, any one of the patch radiators RA 1 , RA 2 , . . . RAN in  FIGS. 1 to 9  functions as a GPS L1 device operating for example in a range 1575.42±3 MHz. According to another embodiment any one of the radiators RA 1 , RA 2 , . . . RAN operates in the weather service range from 1544.5 to 1558 MHz. According to another embodiment the any one of the radiators RA 1 , RA 2 , . . . RAN functions as and ELT or Emergency Locator Transmitter operating for example at 121.5 MHz, 243 MHz, and 406 MHz. According to another embodiment the one of the radiators RA 1 , RA 2 , . . . RAN functions in the XM Satellite range at 2332.5 to 2345.0 MHz. According to another embodiment the one of the radiators RA 1 , RA 2 , . . . RAN operates in the Sirius range at 2330.0 to 2332.5 MHz. According to another embodiment the one of the radiators RA 1 , RA 2 , . . . RAN functions as a Military GPS L2 device operating for example at 1,227.60 MHz. According to still another embodiment the one of the radiators RA 1 , RA 2 , . . . RAN functions in the GLONASS Russian GPS service operating for example at 1,602.5625-1615.5 and 1240-1260 MHz. According to still another embodiment the one of the radiators RA 1 , RA 2 , . . . RAN is a VHF radiator operating for example at 118-137 MHz. The frequencies here are given only as examples, where appropriate, and other frequencies may be substituted therefor. In each radome, each radiator RA 1 , RA 2 , . . . RAN performs a different one of these functions, although it is possible for two radiators to perform the same function. 
   The shape of the radome RD 1  is as symmetrical as possible and of uniform thickness to preserve radiation pattern symmetry. A dielectric material DM 1  fills the radome RD 1  up to the radiators RA 1  and RA 2 , and RA 1 , RA 2 , . . . RAN, and other antenna elements, to form a moisture barrier, to hold the components together, to control any frequency shift, and to adjust the radiators or other antenna elements to compensate for tuning shifts. 
   According to embodiments of the invention, where a number of radiators RA 1  and RA 2  of  FIG. 1 , or RA 1 , RA 2  . . . RAN of  FIG. 2  are patches, adjacent patches assume the positions shown in  FIG. 10  or  FIG. 11  to decouple their radiation and limit crosstalk. Here, each radiator performs a distinct function and constitutes one of the patch radiators RA 1  and RA 2 , or RA 1 , RA 2  . . . RAN in any of  FIGS. 1 to 9 . The orientations and distances between the patches or any of the radiators RA 1  and RA 2 , or RA 1 , RA 2  . . . RAN of  FIGS. 1 to 9  effect decoupling between the radiators. Other embodiments achieve additional decoupling by the use of filters. 
   In  FIG. 10  two radiators RA 1  and RA 2  perform different functions, such as operating as GPS and XM radiators. The point to edge orientation as shown represents relative positions producing low crosstalk and coupling. This permits small spacing between the elements for a specific low coupling and crosstalk. The distance between the two elements may for example be ⅜″±⅛″. 
     FIG. 11  illustrates yet another embodiment of the invention. Here the antenna AN 1  includes patch radiators RA 1  and RA 2  in tip-to-tip or point-to-point relationship. This orientation helps minimize crosstalk and coupling between the radiators. In  FIG. 11 , one of the radiators RA 1 , RA 2 , . . . RAN encased in the radome RD 1  takes the form of a GPS patch radiator PRG (1,575.42 MHz). The other radiator adjacent the patch radiator PRG is a satellite patch radiator PRS, tuned to receive both the Sirius Satellite Radio (2320.0 to 2332.5 MHz) frequency band and the XM Satellite Radio (2332.5 to 2345.0 MHz) frequency bands. These ranges appear in  FIG. 12 . 
   In the GPS radiator RA 1 , RA 2 , . . . RAN, a GPS preamplifier PA 1  under the GPS patch radiator PRG receives GPS signal input via a GPS patch feed point FP 1  and outputs amplified signals to the GPS receiver RE 1  via a connector CT 1 , CT 2 , CT 3  . . . In the radiator RA 2 , a satellite preamplifier PA 2  under the satellite patch radiator PRS receives satellite signal input via a satellite patch feed point and outputs amplified signals to the satellite radio receiver via connector CT 1 , CT 2 , CT 3 . . . . Respective shorting pins in the patch radiator PRS and patch radiator PRG serve as DC grounds. According to an embodiment, a can surrounds the GPS preamplifier under the GPS patch radiator PRG to shield the GPS preamplifier from radiation, and a can surrounds the satellite preamplifier under the satellite patch radiator shield the satellite preamplifier from radiation. 
   The satellite radio receives both audio entertainment and digital data channels from one or both the Sirius and XM Satellite Radio satellites. The GPS receiver GP 1  receives navigation data from the GPS constellation of satellites. 
   In  FIGS. 10 and 11 , the radiators RA 1  and RA 2  are described as GPS and 
   PRS satellite radiators only as an example of the functions they can perform. According to embodiments of the invention the radiators RA 1  and RA 2  can have the structure or function of any patches described in  FIGS. 1 and 2 . 
   In one embodiment of the antenna as shown in  FIGS. 10 and 11 , the one of the radiators RA 1 , RA 2 , . . . RAN operates at GPS over the GPS frequency range and the radiator RA 2  operates in the WSI (Weather Data) range. The orientation of the radiators RA 1  and RA 2  limits the interference and cross talk between these two bands. 
     FIG. 13  illustrates another embodiment of the invention. Here the radome RD 1  encloses a Quadrifilar Helix QH 1  with a built-in Balun transformer, and a patch RA 1 . The patch radiator RA 1  exhibits a narrow bandwidth and a hemispherical radiation pattern RP 1 . Making the patch thicker permits increasing the bandwidth. The Quadrifilar Helix QH 1  exhibits a broad bandwidth whose operation may be modified by selecting the helix pitch. The Quadrifilar Helix QH 1  helix exhibits a cardioid radiation pattern RP  1  when viewed from the side. 
   All of these embodiments with patch radiators involve any of patch radiators with right hand circular polarization (RHCP) or left hand circular polarization (LHCP). In other embodiments a monopole produces linear polarization. 
     FIG. 14  illustrates the effect of the dimensions of the metal electrode of a patch relative to its supporting dielectric. Where A&gt;B the polarization is RHCP and where A&lt;B the polarization is LHCP. 
   According to another embodiment of the invention, any one of the radiators 
   RA 1 , RA 2 , RA 3 , . . . may be a simple helix with right hand circular polarization (RHCP) or left hand circular polarization (LHCP). A helix antenna HA 1  with an RHCP or LHCP exhibits a radiation pattern RP 3  as shown in  FIG. 15 . 
   In some instances the top of one patch radiator towers over an adjacent patch radiator and produces a type of shadowing shown in  FIG. 16 . There, the top of an XM satellite radiator RA 1  (for example) is lower than a GPS radiator RA 2  and the thicker or higher GPS radiator forms line-of sight obstruction of the XM satellite radiator RA 1  at low angles of elevation. Both radiators rest on low noise amplifiers LNA. The difference in the levels of the tops of the radiators RA 1  and RA 2  in  FIG. 16  forms a radio-frequency shadow to XM radiation, which distorts the radiation pattern RP 4  of the XM radiator RA 1 . Optimizing performance of an antenna with adjacent patch radiators requires eliminating the shadowing of  FIG. 16 . An embodiment of the invention involves placing the tops of the adjacent radiators at the same level as shown in  FIG. 17 . According the various embodiments, this is accomplished by making the patch XM satellite radiator RA 1  thicker, by lowering the GPS radiator RA 2 , or by raising the XM satellite radiator RA 1 . The arrangement in  FIG. 17  alleviates the shadowing of  FIG. 16  so that acceptable radiation patterns RP 5  and RP 6  result. Accomplishing the end of keeping the levels of the tops of the radiators equal may involve using an empty can to form a support platform SP 1  under the structure of the XM satellite radiator RA 1  to raise its top to the level of the top of the GPS radiator RA 2 , or by using empty cans under both patch structures to form support platforms to bring their tops to same level. Other embodiments involve adjusting the thicknesses of the patch dielectrics to produce tops at equal heights and adjusting the dielectric constants of each patch dielectric to accommodate the thickness changes. 
     FIG. 18  illustrates a support or platform SP 1  in the form of a hollow brass can CN 1 , for example, for raising the top of XM radiator to the level of the top of the GPS radiator. The support can CN 1  is cut out on top and contains flanges FL 1  at the bottom for fastening, such as by soldering, to the base plate BP 1 . In one embodiment, separate platforms in the form of cans maintain the tops of both the XM radiator and the GPS radiator at the same level.  FIG. 19  is an elevation showing the arrangement with two separate support cans CN 1  and CN 2 .  FIG. 20  illustrates the separate cans CN 1  and CN 2  mounted on the base plate BP 1  with machined or cutout cavities in the base plate for preamplifiers PA 1  and PA 2 .  FIG. 21  shows another elevation with cans CN 1  and CN 2  on a base plate BP 1 . 
   Adjusting the coupling between adjacent patches involves spacing the patches from each other. As shown in  FIG. 22 , it also entails varying the angular relationship of the patch edges relative to each other. In  FIG. 22  radiator RA 1  is oriented 45 degrees relative to the radiator RA 2 . Such relationship may be further shifted 10 degrees. A combination of spacing and angular relationship can achieve a desired end. 
   According to another embodiment of the invention, the gain of the XM patch and the GSM patch are optimized, while minimizing shadowing, by adjusting the patch dimensions to the patch dielectric constant ∈ r  of each patch&#39;s dielectric material. Increased patch dimensions accompany decreasing ∈ r . Decreased patch dimensions accompany an increasing ∈ r  as shown in  FIGS. 23 and 24 . Increasing the patch thickness can make the patch heights of adjacent patches equal and thereby reduce shadowing. It also increases the bandwidth and lowers the gain. 
   A pair of patches mounted on a base plate at unequal heights appears in  FIG. 25 . The higher GPS patch PGR can cause shadowing of the XM patch PRS. The height of the GPS patch PRG arises from a large fiber or large PCB compound supporting the patch or from a large TNC connector projecting into the base plate.  FIG. 26  shows the XM patch PRS and the GPS patch at the same level. Increasing the XM patch thickness may result in a drop in the gain of the XM patch. However raising the XM patch with a can avoids this drop in gain. 
   The references to GPS and XM patches in the above are only examples and the invention contemplated other pairs of adjacent patches. 
   According to various embodiments, the patch radiators are grounded or not. Repeatable accurate positioning of patches on manufactured base plates involves machining or casting precision cavities in the base plates. Placing any radome mounting hardware at a level below the patch radiator prevents shadowing from such hardware. The radomes exhibit symmetry and uniform thickness as much as possible to preserve the radiation pattern symmetry. A dielectric material fills all radomes, forms a moisture barrier, holds the components together, but introduces a dielectric frequency shift. Compensating for this shift, according to an embodiment, entails adjusting the antenna elements. 
   While embodiments of the invention have been described in detail, it will be evident to those skilled in the art that the invention may be embodied otherwise within its spirit and scope.