Abstract:
Multi-band antennae used for television reception of at least two different frequency bands enable multi-band reception with an electrically small antenna. The designs are applicable to individual antenna elements, two dimensional arrays, three dimensional arrays, and arrays constructed for high volumetric efficiency. By using the multi-band element, greater frequency reception is achieved with greater density possible in the antenna arrays.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 61/533,813, filed on Sep. 13, 2011, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    A common application for phased array antenna systems is steerable radar systems. Typically, the antenna elements of the steerable radar system are driven from a common source or connected to a common detection channel to produce a controlled emission or detection pattern. This enables the radar system to rapidly change the detection pattern to simultaneously track multiple targets, for example. 
         [0003]    More recently, arrays of small radio frequency (RF) antennas have been used for capturing over the air content, such as broadcast television, and then streaming the captured content to users via a public network, such as the Internet. 
         [0004]    An example of a system for capturing and streaming over the air content to users via the Internet is described in, “System and Method for Providing Network Access to Antenna Feeds” by Kanojia et al., filed Nov. 17, 2011, U.S. patent application Ser. No. 13/299,186, (U.S. Pat. Pub. No.: US 2012/0127374 A1), which is incorporated herein by reference in its entirety. 
       SUMMARY OF THE INVENTION 
       [0005]    When capturing over the air content with arrays of antennas, it is important to maximize the number of antennas at the installation location. One way to maximize the number of antennas is to create a three dimensional array of antennas. The three dimensional array is created by implementing two dimensional arrays on antenna array cards, and then installing multiple antenna array cards in close proximity to create the three dimensional array. 
         [0006]    One issue is that the three dimensional arrays of antennas often are installed in or on buildings or towers where there are size and/or weight limitations. Additionally, many of the arrays will be installed in large metropolitan cities where the cost of renting/leasing space for the arrays is expensive. Furthermore, there are often power consumption limitations at the installation locations. Reducing the size of each individual antenna and also the power consumption of the supporting circuitry for the arrays make the system less costly to deploy, maintain, and operate. 
         [0007]    Another benefit of having an array with numerous small antennas is redundancy. If an antenna fails (or multiple antennas fail), then one of the other antennas is able to replace the non-functioning antenna without disrupting service. 
         [0008]    The present invention is directed to antennas for the reception of radio waves preferably of at least two different frequency bands. More specifically, the purpose of the invention is to enable reception with electrically small antennas. This invention is applicable to individual antennas, two dimensional antenna arrays, three dimensional antenna arrays, and/or other antenna array systems constructed for high volumetric efficiency and/or density. 
         [0009]    By implementing multi-band antennas, a wider frequency reception is achieved and a greater density of antennas is possible within the antenna array. Generally, the multi-band antennas are constructed from at least two electrically small loop antenna elements. Operation is based on the out of band impedance of the antenna elements. A tuning feed network is implemented with resistors, capacitors, varactors, inductors, or ferrite beads to control the tuning frequency of each antenna element. Additionally, each antenna is multiply resonant. This enables each antenna to have optimal performance and provide filtering of adjacent signals and/or avoid interference from signals that may be in the same band as the desired signal. 
         [0010]    In general, according to one aspect, the invention features an antenna system comprising a circuit board having an antenna section and a tuner/demodulator section, an array of antennas installed on the antenna section that is controlled by and provides antenna feeds to tuners and demodulators in the tuner/demodulator section, and tuning feed networks for the antennas that connect the antennas to corresponding tuners and demodulators. 
         [0011]    In general, according to another aspect, the invention features an antenna system for receiving television signals. The system includes an antenna element having a partial perimeter length of less than 4.3 centimeters and a tuning feed network for the antenna element. 
         [0012]    In general, according to another aspect, the invention features an antenna system for receiving television signals. The antenna system comprising an antenna that includes at least a pair of antenna elements connected to a common pair of feed lines and a frequency tuning section for each antenna element of the antenna that receives tuning voltage via at least one of the feed lines. 
         [0013]    The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
           [0015]      FIG. 1  is a circuit diagram of an antenna and tuning feed network for an antenna system. 
           [0016]      FIG. 2A  is a perspective view of the antenna system implemented on a circuit board (antenna array card) and illustrates how antenna elements, tuners, and demodulators are mounted. 
           [0017]      FIG. 2B  is a perspective view showing a magnified view of antenna elements of the antenna system. 
           [0018]      FIG. 3  is a schematic perspective view of a card cage structure shown in phantom, which functions as an enclosure for the antenna array cards to create a three dimensional antenna array. 
           [0019]      FIG. 4  is a perspective view of the card cage structure that illustrates how the antennas mounted on antenna array cards protrude out of the card cage and create a three dimensional antenna array. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]      FIG. 1  is a circuit diagram of a multi-band antenna  102 - 1  and tuning feed network  200  for an antenna system, which has been constructed according to the principles of the present invention. 
         [0021]    In the illustrated circuit diagram, the multi-band antenna  102 - 1  is shown as a dual band antenna, which is also referred to as an antenna element pair. In the illustrated example, the antenna  102 - 1  further includes a low frequency antenna element  102 A- 1  and a high frequency antenna element  102 B- 1 . In alternative embodiments, however, additional antenna elements could be implemented to form a tri-band antenna or a multi-band antenna with three or more antenna elements. In still other embodiments, the antenna is constructed from only a signal antenna element that covers both bands of interest or only a signal band. 
         [0022]    In a typical implementation, the low and high frequency antenna elements  102 A- 1 ,  102 B- 1  are electrically small loop antennas. Loop antennas have an inductance that is proportional to the area carved out by the loops. Here, the antenna elements  102 A- 1 ,  102 B- 1  are rectangular. Other shapes such as circular shaped loop antennas known in the art could also be implemented. Electrically small antennas are defined for a particular wavelength lambda (λ) and radius “a” of the sphere enclosing an antenna. Then, if 4πa&lt;λ(4*pi* is less than lambda), the antenna is considered electrically small. See Wheeler, “Fundamental limitations of Small Antennas, Proceedings of the IRE, Vol. 35, Dec. 1947, pp 1479-1484. 
         [0023]    Generally, the antenna  102 - 1  is multiply resonant. This enables the antenna  102 - 1  to have optimal performance at a wide range of frequencies and reject interference from other signals that may be in the same band as the desired signal. 
         [0024]    In a current implementation, the antenna elements  102 A- 1 ,  102 B- 1  are each approximately 0.5 inches in height, 0.5 inches wide, or about 1.3 centimeters (cm) by 1.3 cm, and have a thickness of approximately 0.030 inches, or about a 1 millimeter (mm). In general, the three sided length (or partial perimeter) of the antenna elements  102 A- 1 ,  102 B- 1  is less than 1.7 inches (4.3 cm), with a total length of all 4 sides being less than 2.3 inches (5.8 cm). 
         [0025]    In general, smaller antennas are preferable to achieve higher density, yet smaller antennas typically have a lower gain. As a result in other embodiments larger antennas/antenna elements are used, such as antennas/antenna elements with a total length of up to 20 cm, or even up to 50 cm or 100 cm, and possibly even larger understanding that there is a concomitant decrease in packing density. 
         [0026]    A resonance of the antenna  102 - 1 , and each antenna  102 - 1  to  102 - n , is controlled via the tuning feed network  200 . The tuning feed network  200  includes a radio frequency (RF) coupling and direct current (DC) injection section  203 , a high frequency tuning section  205 , and a low frequency tuning section  207 . 
         [0027]    In the illustrated example, the low frequency tuning section  207  and low frequency antenna element  102 A- 1  are designed to receive carrier signals in the VHF (Very High Frequency) range or 174 MHz to 216 MHz. The high frequency tuning section  205  and high frequency antenna element  102 B- 1  are designed to receive carrier signals in the UHF (Ultra High Frequency) range or 470 MHz to 700 MHz. 
         [0028]    In a typical implementation, antennas (e.g., reference numerals  102 - 1  to  102 - n  in  FIG. 2B ) are grouped together on an antenna array card (reference numeral  152  in  FIG. 2A ) to form an antenna array (reference numeral  102  in  FIG. 2A ) of antennas. Each antenna  102 - 1  to  102 - n  within the antenna array  102  is tuned by a separate tuning feed network  200 . Implementing a separate tuning feed network  200  for each antenna  102 - 1  to  102 - n  enables each antenna to be individually tuned to a different frequency. 
         [0029]    Generally, the antennas (reference numerals  102 - 1  to  102 - n  in  FIG. 2B ) are balanced fed antenna elements. In alternative embodiments, however, the antennas  102 - 1  to  102 - n  are unbalanced fed antennas. In a preferred embodiment, the antennas  102 - 1  to  102 - n are tunable antennas, but the antennas  102 - 1  to  102 - n  could also be fixed frequency antennas. 
         [0030]    Returning to  FIG. 1 , an RF connection from the low frequency tuning section  207  to low frequency antenna element  102 A- 1  is made via capacitors C 1  and C 3 . Capacitors C 1  and C 3  have a capacitance of 2.2 nanoFarads, and these capacitors form a DC block (low frequency tuning section DC block  214 ). A DC block is a frequency filter designed to filter out lower frequency signals and DC signals while allowing higher frequency RF signals to pass. Additionally, the low frequency tuning section DC block  214  prevents the low frequency antenna element  102 A- 1  from shorting out a tuning voltage sent from the RF coupling and DC injection section  203 . 
         [0031]    In alternative embodiments, the RF connection is made with band pass filters, high pass filters, diplexers and/or multiplexers. 
         [0032]    Capacitors C 1  and C 3  connect to low frequency tap points  220   a,    220   b  of the low frequency antenna element  102 A- 1 . The low frequency tap points  220   a,    220   b  are designed to present the desired impedance from the low frequency antenna element  102 A- 1  to the feed lines FEED_P, FEED_N. The location of the intersection of the low frequency tap points  220   a ,  220   b  with the low frequency antenna element  102 A- 1  and the area cut out between the tap structure contribute to the impedance transformation. 
         [0033]    Capacitors C 2  and C 212  are in parallel with the varactor diode pairs D 1  and D 2 . In the illustrated example, capacitor C 2  has a capacitance of 15 picoFarads and capacitor C 212  has a capacitance of 18 picoFarads. The varactor diodes pairs D 1 , D 2  resonate with the inductance of the low frequency antenna element  102 A- 1  to set the tuning frequency. The bandwidth is determined by the value of resistor R 4  along the parasitic resistances in the wire of the low frequency antenna element  102 A- 1  and the varactor diode pairs D 1  and D 2 . Resistors R 1 , R 2 , and R 3  provide high impedance connections for DC tuning voltages that are supplied on the feed line FEED_P to the varactor diode pairs D 1  and D 2 . The high impedance serves two purposes. First, the high impedance provides isolation to the feed lines FEED_P, FEED_N so that RF signal is not lost. Second, the high impedance provides isolation from the varactor diode pairs D 1  and D 2  so they are not disrupted by other impedance/capacitive effects. 
         [0034]    Referring to the high frequency tuning section  205 , while there are some differences in the components used and their values, the basic functionality of the circuit is the same as the low frequency tuning section  207 . For example, the high frequency antenna element  102 B- 1  is generally identical to the low frequency antenna element  102 A- 1  in a current embodiment. Additionally, capacitors C 4  and C 7  provide an RF connection from the high frequency antenna element  102 B- 1  to the high frequency tuning section  205 . Likewise, capacitors C 4  and C 7  form a DC block (high frequency tuning section DC block  216 ). Capacitors C 4  and C 7  each have a capacitance value of 24 picoFarads (compared to 2.2 nanoFarads for C 1  and C 3 ). Resistor R 7  and R 5  provide a high impedance connection for the tuning voltages provided on feed line FEED_P to varactor diode pair D 3 . The parasitic resistances in the wire of the high frequency antenna element  102 B- 1  and the varactor diode pair D 3  set the bandwidth. Lastly, high frequency tap points  222   a,    222   b  are designed to present the desired impedance from the high frequency antenna element  102 B- 1  to the feed lines FEED_P, FEED_N. 
         [0035]    The feed lines (FEED_N and FEED_P) connect the high frequency tuning section  205  and the low frequency tuning section  207  to the RF coupling and DC injection section  203 . The feed lines (FEED_N, FEED_P) carry the received RF signal from the antenna elements  102 A- 1 ,  102 B- 1 , to the RF coupling and DC injection section  203 . In a typical implementation, the physical distance from the RF coupling and DC injection section  203  and the antenna elements  102 A- 1 ,  102 B- 1  can be relatively large. For example, in one embodiment the physical distance is twenty or more inches (approximately 0.5 meters). In alternative embodiments, however, the physical distance is only a few inches (e.g., approximately 5 to 8 centimeters). 
         [0036]    The RF coupling and DC injection section  203  includes an analog control line (ACNTL) connection  206  and two logical interfaces: DIFF_N  202  coupled with DIFF_P  204 . The two logical interfaces DIFF_N  202 , DIFF_P  204  are differential radio frequency connections that carry received carrier signals to a receiver (or tuner) and demodulator (reference numerals  104 - 1  and  106 - 1  in  FIG. 2A ) that are located on an antenna array card (reference numeral  152  in  FIG. 2A ). The ACNTL connection  206  is a single-ended analog control line that is referenced to ground (e.g., GND-1) and provides the control signal, to tune the varactor diode pairs D 1 , D 2 , D 3 . In the current embodiment, the control signal is a tuning voltage. In the illustrated embodiment, the control signal from the ACNTL connection  206  is generated by an antenna optimization and control system  172 . The control signal from the antenna optimization and control system  172  is converted to a voltage by a digital to analog converter  170 . A common tuning voltage is provided to the low and high frequency tuning sections  205 ,  207  and the antenna elements  102 A- 1 ,  102 B- 1 . 
         [0037]    In an alternative embodiment, the control signal could be a differential control signal. In this embodiment, another input control signal is injected at GND-2 and connected at the end of resistor R 6  (GND-2 would be removed/replaced). 
         [0038]    Capacitors C 5  and C 8  are blocking capacitors and form a DC block (RF coupling and DC injection DC block  208 ). The RF coupling and DC injection DC block  208  provides the ability to superimpose the control signal from ACNTL connection  206  on the same feed line (FEED_P) as the received carrier signals from the low and high frequency antenna elements  102 A- 1 ,  102 B- 1 . 
         [0039]    Typically, when creating a multi-band antenna, two or more antenna elements are put in parallel. There are several important factors to account for when combining multiple antenna elements. For example, in band (where the antenna is tuned), the impedance as measured at the low frequency tap points  220 A,  220 B will look like a single pole bandpass (complex pole-pair) filter having a desired impedance at the resonant frequency. Below the tuned frequency, the impedance will look like a short circuit. Above the tuned frequency, the impedance will approach an open circuit. When implementing the low frequency tuning section DC block  214 , the low frequency tuning section  207  approaches an open circuit at higher frequencies. 
         [0040]    Because the low frequency antenna element  102 A- 1  looks like an open circuit when the tuning feed network  200  is operating at higher frequencies, the low frequency tuning section  207  is typically able to connect to the high frequency tuning section  205  without issue. However, the high frequency antenna element  102 B- 1  looks like a short circuit when the tuning feed network  200  is operating at lower frequencies. To protect the low frequency antenna element  102 A- 1  when operating at lower frequencies, high frequency tuning section DC block  216  is used to electrically open the high frequency antenna element  102 B- 1 . 
         [0041]    In alternative embodiments, different capacitors values are able to be implemented for the high frequency tuning section DC block  216 . In the illustrated example, the 24 picoFarad capacitor is selected. Similar design considerations are applied when combining additional antennas elements to create tri-band or multi-band antenna elements with, for example, three or more loop antennas. 
         [0042]      FIG. 2A  is a schematic perspective diagram illustrating how the antenna array  102 , the tuners  104 - 1  to  104 - n , and the demodulators  106 - 1  to  106 - n  are mounted on the antenna array card  152  on which the antenna system is implemented. 
         [0043]    The antenna array  102  is mounted on the antenna array card  152  to form a two dimensional array of antennas (reference numerals  102 - 1  to  102 - n  in  FIG. 2B ). In one implementation, each array  102  includes 80 antennas (for a total of 160 antenna elements). In alternative embodiments, however, the antenna array card  152  is able to hold more as many as 320 antennas (for a total of 640 antenna elements), possibly 640 antennas (for a total of 1,280 antenna elements), or more. When increased numbers of antennas are implemented on the antenna array card  152 , a selector switch (not shown) is generally included on the antenna array card to selectively connect the antennas ( 102 - 1  to  102 - n  in  FIG. 2B ) to an available tuners and/or demodulators from a pool of available resources on the antenna array card  152 . The selector switch enables additional antenna elements to be added to the array  102  without requiring additional tuners and/or demodulators. 
         [0044]    The array  102  is mounted on an antenna section  111  of the antenna array card  152 . The antenna array card is typically a circuit board for mounting electronic components such as antenna elements, tuners, demodulators, and feed lines, to list a few examples. 
         [0045]    Each antenna (reference numerals  102 - 1  to  102 - n  in  FIG. 2B ) of the array  102  is controlled by a corresponding tuning feed network (reference numeral  200  in  FIG. 1 ). Each tuning feed network  200  is connected to a corresponding tuner  104 - 1  to  104 - n  and demodulator  106 - 1  to  106 - n . Antenna feeds from the antennas ( 102 - 1  to  102 - n  in  FIG. 2B ) are sent to the corresponding tuners  104 - 1  to  104 - n  and demodulators  106 - 1  to  106 - n . Generally, the tuners  104 - 1  to  104 - n  and demodulators  106 - 1  to  106 - n  are mounted on a tuner/demodulator section  109  of the antenna array card  152 . 
         [0046]    In the illustrated implementation, the tuners  104 - 1  to  104 - n  are ATSC (Advanced Television Systems Committee) tuners. The tuners  104 - 1  to  104 - n  convert received radio frequency signals to a much lower, fixed intermediate frequency signal that the demodulators  106 - 1  to  106 - n  are able to demodulate. The demodulators  106 - 1  to  106 - n  recover synchronization and decode the signal to MPEG-2 format because it is currently a standard format for the coding of moving pictures and associated audio information. In alternative embodiments, the signal could be decoded to other audio/video formats known in the art. 
         [0047]    Typically, the antenna array card  152  is fabricated from a dielectric insulator material. The components are mounted to the antenna array card  152  and are connected via conductive pathways (or tracks). In one embodiment, the antenna array card is approximately 25 inches wide by 21 inches long, or about 0.6 meters (m) by 0.5 m. 
         [0048]    An air dam  210  divides the antenna section  111  and the tuner/demodulator section  109 . Additionally, the air dam  210  acts as part of a Faraday shield to prevent unwanted interference from the components on the tuner/demodulator section  109  leaking and interfering with the antenna section  111  (and vice versa). Additionally, the air dam  210  acts to constrain airflow to enable adequate cooling of the integrated circuits such and components (e.g.,  104 - 1  to  104 - n  and  106 - 1  to  106 - n ). 
         [0049]    A data link connector  160  is installed in a card base plate  161 , which is typically formed on the antenna array card  152 . The data link connector  160  takes the demodulated signals from the demodulators  106 - 1  to  106 - n  and pushes them to the remainder of the encoder system (reference numeral  103  in  FIG. 3 ) that is typically located in a more convenient location such as basement or ground level building, which does not require access to RF signals. The antenna array card  152  further includes locking tabs  163 ,  164  to enable the cards to be fastened within an enclosure. 
         [0050]    Referring back to  FIG. 1 , the RF coupling and DC injection section  203  is located in the tuner/demodulator section  109  of the PCB  152 . The low and high frequency tuning sections ( 205 ,  207  in  FIG. 1 ) are located adjacent to the corresponding low and high frequency antenna elements  102 A- 1 ,  102 B- 1  in the antenna section  111  of the antenna array card  152 . While most of the components of the tuning feed networks can be mounted on either side of the antenna array card  152 , the antennas  102 - 1  to  102 - n  are typically all mounted on the same side of the antenna array card  152 . 
         [0051]      FIG. 2B  is a schematic perspective diagram showing a magnified view of section  211  and the antennas  102 - 1  to  102 - n , which include antenna elements (e.g.,  102 A- 1 ,  102 B- 1 ,  102 A- 2 ,  102 B- 2  . . .  102 A- n ,  102 B- n ). 
         [0052]    The antennas  102 - 1  to  102 - n  in the illustrated example are pairs of rectangular shaped loop antenna elements  102 A,  102 B. The antennas  102 - 1  to  102 - n  are arranged create a two dimensional matrix (or array) on the antenna array card ( 152  in  FIG. 2A ). In the current implementation, the rows of antennas  102 - 1  to  102 - n  are offset to create a staggered two dimensional matrix. The staggered matrix helps with routing of the feed lines on the antenna array card (reference numeral  152  in  FIG. 2A ). 
         [0053]      FIG. 3  is a schematic perspective view of a card cage structure  151 , which is shown in phantom. The card cage structure  151  functions as an enclosure for the antenna array cards  152 - 1  to  152 - n  to create an antenna system with a three-dimensional array of antennas. 
         [0054]    The side, top, bottom and front walls  150  of the card cage structure  151  are fabricated from a conductive material to maximize Faraday shielding of the antenna elements from the active electronics. The front wall of the card cage provides an open port as the boresight of the antenna array and faces the transmitting antennas. The rear wall  156  includes data transport interfaces that connect to an encoder system  103 . 
         [0055]    The encoder system  103  is typically located in a basement or ground level building and is comprised of encoding components such as transcoders, computer servers, and storage devices. In a typical implementation, demodulated signals from demodulators  106 - 1  to  106 - n are transmitted to transcoders (not shown) of the encoding system  103 . The transcoders transcode the demodulated signals to transcoded content in real time. Typically, the transcoders transcode into MPEG-4 format (also known as H.264), but the transcoders could transcode the demodulated signals into other formats in alternative embodiments. The transcoded content is then indexed and stored in the storage devices and/or streamed to client devices via the Internet. 
         [0056]    Within the card cage structure  151 , the antenna array boards  152 - 1  to  152 - n  are generally spaced about an inch (2.5 centimeters) apart within the enclosure. This distance enables a relatively high density for the antenna array cards  152 - 1  to  152 - n , while reducing unwanted interference between antenna elements to acceptable levels. This configuration helps to further maximize Faraday shielding of the antennas from the active electronics on the antenna array cards. 
         [0057]    In a typical implementation, the air dams  210 - 1  to  210 - n  act to block the airflow for the antenna array cards  152 - 1  to  152 - n  and fill in the gap between the cards such that the air dam of each card engages the backside of its adjacent card. Additionally, the air dams  210 - 1  to  210 - n  also act as part of the Faraday shields to reduce interference between the components (e.g.,  104 - 1  to  104 - n  and  106 - 1  to  106 - n ) and the antennas. Typically, the antenna array cards  152 - 1  to  152 - n  are orientated vertically, with the antenna elements horizontal to create a horizontally polarized (Electric Field) half omni-directional antenna array. Additionally, the antennas protrude out of the front of card cage  151  to further help reduce interference between the components and the antennas. 
         [0058]    Alternatively, if over the air content from the broadcasters has a vertical polarization, which occurs in some locales, then orientation of the antenna array cards  152 - 1  to  152 - n  and antennas should be changed accordingly. The illustrated example shows the orientation of the antennas for broadcasters with horizontal polarization. 
         [0059]      FIG. 4  is a partial perspective view of the front of the card cage structure  151  that illustrates how the antennas  102 - 1  to  102 - n  protrude out of the card cage  151 . 
         [0060]    In the illustrated example, multiple antenna array cards  152 - 1  to  152 - n  are installed in the card cage structure  151  and orientated in a vertical position. While only four antenna arrays cards are shown in the illustrated example, the card cage structure  151  is capable of housing between 8 and 32 antenna array cards (or more). If the card cage structure  151  is not filled to capacity, then blank slot cards  180 - 1  to  180 - n  are installed to fill the empty slots of the card cage structure. 
         [0061]    When antenna array cards  152 - 1  to  152 - n  (and antennas) protrude from the card cage structure  151 , a three dimensional array of antennas  402  is created. 
         [0062]    In some embodiments, multiple card cage structures are housed together in rack mounted chassis (not shown) to further increase the density of antenna array cards where the card cage structures are installed. 
         [0063]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.