Abstract:
Apparatus and method improving the performance and allowing increased directionality and bandwidth via display-like software defined antenna. A surface is composed of an array of interconnected pixels which are capable of either becoming conducting or resistive allowing arbitrarily sized and shaped antenna structures. Each pixel is controlled by biasing the base which alters the conductivity on the top portion of the pixel. The specific pattern which is active on the display style antenna is based on the desired direction, frequency range, and waveform necessary for a required transmit and receive function.

Description:
PRIORITY CLAIM UNDER 35 U.S.C. §119(e) 
       [0001]    This patent application claims the priority benefit of the filing date of provisional application Ser. No. 61/927,066, having been filed in the United States Patent and Trademark Office on Jan. 14, 2014 and now incorporated by reference herein. 
     
    
     STATEMENT OF GOVERNMENT INTEREST 
       [0002]    The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    This invention relates generally to software definable antennas capable of functioning across a wide range of frequency ranges and environmental conditions. 
         [0004]    That there is a need for a software defined antenna system to pair with the growth in software based radios is well known across both government and industry. Efforts have been started through both public agencies such as DARPA as well as private, corporate entities. In order to gain the full benefit of these novel radios, flexible antenna hardware is urgently in need. 
         [0005]    It is desirable to provide geometrically flexible antenna hardware capable of functioning efficiently across a broad range of frequencies, signal types, and environmental conditions. 
         [0006]    An optimal solution to the problem of building communications hardware that is functional across a wide bandwidth, with variable power transmit and receive and capable of functioning in degraded or cluttered environments, is a maximally adaptive radio system. The prior art has embarked upon a quest to engineer this very approach but while it has succeeded in building a software defined (thus highly adaptive) radio, it has failed to generate an antenna system which would allow the software radio to function to its full potential. Specifically, the prior art still utilizes such standard hardware as patch antennas and as such, the prior art forms are still unable to gain full usage from these novel software defined radio systems. Additionally, the majority of the explorations into the field of reconfigurable antennas have been in one or two forms: either a short antenna which can be connected to a longer antenna section via a switch (see U.S. Pat. No. 6,195,065 B1) or narrow bandwidth antennas at the lower end of the size and power scale, leaving unaddressed the needs of larger, higher power applications. 
         [0007]    The other background from which the motivation for this invention is drawn is nonemissive display technology as described in U.S. Patent Application Publication US005930026A and utilized in several electronic book systems. These displays utilize electrically charged ink (with opposite charges and different colors) suspended in spheres of fluid. When an electrode beneath the sphere becomes positively or negatively charged it draws a specific color of ink to the bottom of the sphere while forcing the other color to the top. In this way each sphere becomes a pixel on the display controlled by the matrix of electrodes set beneath the spheres. While these displays are quite effective at visible wavelengths they are all completely ineffective at interfering with longer wavelength radio frequencies as used in communications antennas. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to provide an apparatus that overcomes the prior art&#39;s dependency in reconfigurable antenna systems to perform precise, on-the-fly geometrical alterations to the antenna. 
         [0009]    It is a further object of the present invention to provide “display” type antennas, capable of being any flat antenna system capable of taking on arbitrary two dimensional geometries, analogous to optical class emissive and nonemissive displays. 
         [0010]    It is yet a further object of the present invention to provide the capability of increasing the signal to noise ratio of received signals, the directionality of both transmit and receive communications, and broadening the functional bandwidth of the antenna in dynamically changing interference environments by adapting the antenna electrical geometry in real time to maximize these capabilities. 
         [0011]    It is still a further object of the present invention to provide novel means to selectively switch individual antenna radiating pixels into and out of a radio frequency radiating or receiving mode. 
         [0012]    Briefly stated, the present invention, a radio frequency emissive display antenna and system for controlling it provides an apparatus for improving the performance and allowing increased directionality and bandwidth via display-like software defined antenna. A surface is composed of an array of interconnected pixels which are capable of either becoming conducting or resistive allowing arbitrarily sized and shaped antenna structures. Each pixel is controlled by biasing the base which alters the conductivity on the top portion of the pixel. The specific pattern which is active on the display style antenna is based on the desired direction, frequency range, and waveform necessary for a required transmit and receive function. 
         [0013]    The present invention, a Radio Frequency Emissive Display (RFED) and system for controlling it, comprises in its preferred embodiment, an array of addressable pixels with microwires connecting the top of each pixel, as seen in  FIG. 3 , with a control mechanism. A key feature is that when a pixel is switched it becomes a conductive connection between the wires attached to the top of the pixel. 
         [0014]    In a preferred embodiment of the present invention, an electronically directed antenna apparatus comprises an antenna having an array of radiating pixels, each capable of being switched between conductive and resistive states so as to permit and inhibit radio frequency radiation, respectively, therefrom as well as an antenna control subsystem that cooperates with the antenna, a radio frequency source, and a data source to enable switching of the pixels. 
         [0015]    In the preferred embodiment, the radiating pixels comprise a pixel, a biasing element, and a column comprising a switching element where the biasing element receives control signals and transmits state signals to the antenna control subsystem. 
         [0016]    In alternate embodiments, the radiating pixels replace the biasing element with alternative means for switching the pixel into a conductive state. 
         [0017]    The present invention is capable of an extremely wide range of antenna geometries and on-the-fly signal maximization and has the flexibility for use in highly mobile applications where weight is a major factor. It would be most apt for applications requiring flat profile, quick response directionality and multi-band capability as in high-performance military aircraft, for example. The dynamic capabilities of the present invention would enhance mitigation of atmospheric and environmental signal distortions and degradations, while providing a high degree of angular directivity. Additionally, the present invention could be layered, and if properly controlled in parallel, would yield three dimensional (although still flat surfaced) antenna geometries. 
         [0018]    There are a variety of possible embodiments of the present invention, most having to do with the mechanism for activation of each pixel once selected for conductivity. In non-emissive displays the switching system relies on charged ink which moves to the bottom and top of each pixel (see above mentioned patent). The emissive display proposed here must function quite differently to produce a conductive surface with similar responsiveness as its non-emissive counterpart. 
         [0019]    The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic diagram representation of the present invention including transmit and receive and control modules. 
           [0021]      FIG. 2  is a schematic diagram representation of the interconnection between the RFED antenna and the control and radio frequency (RF) pathways of the present invention. 
           [0022]      FIG. 3  is a schematic diagram representation showing the array system of the pixels in the present invention. 
           [0023]      FIG. 4  is a schematic diagram showing the preferred embodiment of the present invention, further depicting an individual pixel with its set of charged, nonconductive displacers. 
           [0024]      FIG. 5  is a schematic diagram showing an alternative embodiment of the present invention having an individual pixel utilizing a bimodal sphere. 
           [0025]      FIG. 6  is a schematic diagram showing another alternative embodiment of the present invention having an individual pixel utilizing a bimodal plunger. 
           [0026]      FIG. 7  is a schematic diagram showing another alternative embodiment of the present invention having an individual pixel utilizing a ferro-fluid and a piezoelectric cap. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    The preferred embodiment is the initially described reflecting system seen in  FIG. 1  through  FIG. 4 . 
         [0028]      FIG. 1  shows a detail of the overall system comprising the present invention. The present invention&#39;s antenna  100  requires sources of input from an RF source such as the RF coming from the transmitter (Tx) portion of the Receive-Transmit (Rx/Tx)  120  module, and the Display Control Signals  220  coming from the Antenna Control Module  210 . The Rx/Tx  120  module can be any of a number of systems capable of receiving and transmitting across a wide bandwidth and a large variety of waveforms (e.g. TR Modules, Traveling Wave Tube amplifiers, etc.). Software radio applications of the present invention, and perhaps some radar applications, would require RF connections to and from an RF receiver/transmitter. Both the outgoing data to be transmitted  150  and the received data  130  from the present invention&#39;s antenna  100  are fed through the Input/Output (I/O) Adaptor  140  which ensures proper connection between the present invention and the rest of the system to which it is attached (i.e. an aircraft or ground vehicle). The I/O Adaptor  140  also provides the control signals to the Signal Antenna Matching (SAM)  170  module. This module is responsible for aligning the antenna  100  with the desired Rx/Tx requirements. In order to do so, it accepts Control Signals  160  from the I/O Adaptor  140  which includes the desired direction, waveform, and the frequency band that needs to be utilized. I/O Adaptor  140  typically interfaces with some form of data source such as a computer (not shown) under autonomous or interactive software control and from which control signals and commands originate. The SAM  170  module then determines the proper antenna geometry to be utilized and generates an appropriate Antenna Selection  190  signal to send to the Antenna Control  210 . The SAM  170  module is also responsible for ensuring time alignment between the present invention&#39;s antenna  100  and the Rx/Tx  120  system, thus ensuring the proper geometry is in place on the present invention&#39;s antenna  100  before the Rx/Tx  120  tries to operate. To perform this alignment the SAM  170  reads the current state of the present invention&#39;s antenna  100  from the Combined State Signal  200  passed along from the Antenna Control  210  and utilizes this information to generate the Rx/Tx Pre-Trigger, which along with the Frequency Selection signal, is sent via signal path  180  to the Rx/Tx module  120 . The Antenna Control  210  performs two basic functions: converting the Antenna Selection  190  signal to appropriately routed Display Control  220  signals to switch individual RFED  100  pixels, and amalgamation of the separate State Signals  230  into a Combined State Signal  200  for the SAM  170 . Antenna Control  210 , Display Control  220 , Signal Antenna Matching (SAM)  170 , and I/O Adaptor  140  are functionally and collectively referred to as an antenna control subsystem. 
         [0029]      FIG. 2  shows the interconnections between the present invention&#39;s antenna  100  and the other modules. At the top of the diagram, the RF signals  110  from both the Tx and Rx is shown entering and leaving the antenna via the Splitter/Combiner  240  which distributes the Tx RF signals to the elements of the present invention&#39;s antenna array  100  and combines the Rx signals to a single output (the RF going to and from each segment of the array is seen in  250 ). The RF signals are conducted along wires  260  to the radiating pixels  270  which when activated, are conducting. The column  280  contains the mechanism to switch the pixel  270  several alternate embodiments which are described below. While the shape column  280  is shown in the attached diagrams as cylindrical, it need not be. Shown at the bottom of  FIG. 2  are the Display Control Signal  220  inputs and the State Signal outputs  230  seen connecting to the Biasing Element  290  which is used to power the pixel switching element  290 . This control system functions in a manner similar to non-emissive displays, and would be modeled on them. 
         [0030]      FIG. 3  shows how all of the pixels  270  are arranged and interconnected using the wires  260 . The shape of the conducting portion of the array is constructed by switching the proper arrangement of pixels  270  into a conducting mode, while ensuring that the others are simultaneously non-conducting. 
         [0031]      FIG. 4  through  FIG. 7  shows a series of alternate embodiments of the pixel  270  switching elements which are contained in the cylinders  280 . One alternate embodiment is shown in  FIG. 4  in which the cylinder  280  contains a conducting fluid  300  in which are suspended charged, non-conducting spheres  310 . The spheres are forced towards the top of the cylinder  280  when the Biasing Element  290  is biased with the same charge as the spheres. These non-conducting spheres then displace the conducting fluid  300  from the pixel  270  thereby greatly decreasing the conductivity across the pixel. When the Biasing Element  290  has a charge opposite of the spheres  310  it draws them to the bottom of the cylinder  280  thereby increasing the conductivity across the pixel  270 . Note that the non-conducting displacing elements  310  need not be spherical as shown in  FIG. 4 , but rather should be shaped in such a way as to achieve the best displacement of the conducting fluid  300  while still moving effectively in response to the charge on the Biasing Element. 
         [0032]      FIG. 5  shows another alternate embodiment of the pixel  270  switching elements in which a cylinder  280  contains a sphere which itself is composed of two sections: a conducting hemisphere  330  and a charged, non-conductive hemisphere  320 . In this embodiment, the Biasing Element  290  is used to rotate the sphere so that either the conducting portion  330  or non-conducting  320  hemisphere is touching the pixel  270  thereby increasing or decreasing its conductivity. 
         [0033]      FIG. 6  depicts yet another alternate embodiment of the pixel  270  switching element but instead of a sphere, there is a bi-modal plunger composed of a broad head conducting element  350  and a smaller non-conductive charged tail  340 . In this set-up the Biasing Element  290  moves the plunger up and down the cylinder  280  using the charged tail.  FIG. 7  depicts still yet another alternate embodiment of the pixel  270  switching element. It is composed of two sections, the portion of the cylinder  280  adjacent to pixel  270  is composed of a material  380  which becomes conducting to varying amounts under physical pressure, such as a piezoelectric material. Below that is a hollow filled with ferrofluid  360  which produces the force on the upper portion of the cylinder  280 . Instead of the Biasing Element  290  (not present in this alternate embodiment) seen in the other figures, the control mechanism is a small wire wrap  370  which generates a magnetic field through the ferrofluid  360 . When current is sent through the wire wraps  370  the ferrofluid  360  attempts to align itself to the field, in so doing it applies force to the top portion of the cylinder  280 , allowing it to become conducting. 
         [0034]    Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.