RECEPTION USING FRAGMENTED APERTURE DESIGN

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. provisional patent application

61/908,770, filed on November 26, 2013, the contents of which are incorporated herein by reference.

OVERVIEW

[0002] The technology in this application relates to antennas, and more particularly, to an antenna with a fragmented aperture design to receive very-high frequency / ultra-high frequency (VHF UHF) digital TV signals.

BACKGROUND AND SUMMARY

[0003] An antenna is a device that can both transmit and receive electromagnetic (EM) energy. Antennas may be as simple as a folded wire (dipole) cut to an optimal length for receiving a specific narrow-band frequency of EM energy. Although simple in theory, however, antennas in practice must offer multiple performance criteria to be effective, including high gain in the frequency band(s) of interest, optimized impedance matching with the connector cable to minimize signal loss, minimal geometric footprint, and/or optimal lobe pattern for receiving and transmitting. The VHF band (30-300 MHz) and the lower part of the UHF band (300-3000 MHz) are widely used for transmitting television and radio signals (among other purposes) because they travel efficiently through the Earth's atmosphere. Reception of VHF and UHF signals inside a building is problematic, however, because the optimal antenna size for VHF- UHF EM waves is very large (e.g., >1 m for VHF). Indoor TV antennas that effectively meet these challenges and cover the full channel frequency range (57-803 MHz) are difficult to design and fabricate.

[0004] A relatively recent family of antennas includes fragmented aperture antennas.

U.S. patent 6,323,809, incorporated herein by reference, describes a fragmented aperture antenna that includes a planar layer having a plurality of electrically conductive and substantially non- conductive areas. These areas may be rectangles, triangles, parallelograms, or other shapes. At least two of these conductive areas are connected, and in turn connected with feed points, in a fashion that enables EM resonance at a specific range of frequencies. The locations of the conducting materials in the fragmented aperture antenna may be determined, as described in U.S. patent 6,323,809, by a multi-stage optimization procedure that tailors the performance of the antenna to a particular application. The resulting configuration and arrangement of conductive and substantially non-conductive areas enable reception and transmission of electromagnetic energy wirelessly in a specific direction to the planar layer when an electrical connection is made to at least one of the conductive areas.

[0005] The inventor used this fragmented aperture antenna approach to design a conformal antenna for digital TV signal reception. In non-limiting example embodiments, the conformal antenna is very thin (e.g., on the order of thickness of a piece of paper), wideband, possesses wide-angle lobes, and has a high gain over the VHF and UHF bands. In example embodiments, the conformal antenna is combined with a phase splitter to provide substantially omni-directional television signal reception.

[0006] Example embodiments include a conformal antenna comprising a conformal planar layer having a plurality of first areas and a plurality of second areas. The first areas are more conductive than the second areas. The conformal planar layer conforms to a surface shape to which the conformal planar layer is placed adjacent. Each area has a periphery that extends along a grid. The first and second areas are configured so that the planar layer can communicate electromagnetic energy wirelessly in a specific direction to the planar layer when an electrical connection is made to at least one of the first areas. The conformal planar layer has a thickness in the range of 0.001" to 0.01". The antenna has substantially omnidirectional coverage and sufficient gain over a frequency range to receive television (TV) signals inside a home, office, or other building.

[0007] In an example implementation, the antenna coverage is approximately 300° x

300°.

[0008] In an example implementation, the conformal planar layer has a thickness of approximately 0.005".

[0009] In an example implementation, the first areas include a conductive or

semiconductive material and the second areas include a dielectric or semiconductive material. The grid includes first and second sets of parallel lines. Each area comprises one or more contiguous elements defined by the parallel lines.

[0010] Example frequency ranges for the antenna include 150 MHz - 500 MHz or 1 10

MHz - 800 MHz.

[0011] In example embodiments, the antenna also includes a 75 ohm connector and is configured to operate with a mixture of vertical and horizontal polarization and provide a gain of approximately 0 dBd over 200-450 MHz for TV channels 1 1-14, a gain of approximately -1 to -4 dBd above 450 MHz for TV channels 14-69, and a gain of approximately -1 to -20 dBd below 200 MHz.

[0012] Another example embodiment provides an antenna apparatus having a conformal planar layer with a plurality of first areas of an antenna. The first areas being conductive or semi-conductive, and the conformal planar layer having a thickness in the range of 0.001 " to 0.01". The conformal planar layer is conformable to a shape of a surface to which the conformal planar layer is placed on, and the surface is less conductive than the first areas. When the conformal planar layer is on the surface, the surface forms a plurality of second areas of the antenna, in which case each area has a periphery that extends along a grid and the first and second areas are configured so that the planar layer can communicate electromagnetic energy wirelessly in a specific direction to the conformal planar layer when an electrical connection is made to at least one of the first areas. The antenna has substantially omnidirectional coverage and sufficient gain over a frequency range to receive television (TV) signals inside a home, office, or other building. The antenna apparatus may also include one or more phase splitters coupled to at least one of the first areas.

BRIEF DESCRIPTION OF THE FIGURES

[0013] Figure 1 shows an example of a dipole antenna.

[0014] Figure 2 shows an example of a flat indoor TV antenna.

[0015] Figure 3 shows an example embodiment of an antenna design.

[0016] Figure 4 is a picture of an example embodiment of a prototype but non-limiting antenna. [0017] Figure 5A shows a reference guide and dimensions of the example prototype antenna shown in Figure 4.

[0018] Figure 5B shows pseudo 3D normalized3D gain pattern of the example prototype antenna shown in Figure 4.

[0019] Figure 5C shows E _to tai gain patterns for the example prototype antenna shown in

Figure 4.

[0020] Figure 5D shows a graph of broadside gain versus frequency for the example prototype antenna shown in Figure 4.

DETAILED DESCRIPTION

[0021] The following description sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using electronic components (e.g., amplifiers), and hardware circuitry (e.g., matching circuits).

[0022] An antenna may be connected to or modulated through additional software or hardware components, including active matching networks, electronic steering, digital controllers, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

[0023] Historically, indoor TV antennas are of the dipole ("rabbit ears") type formed using two bent wires that are connected directly to a TV by a coaxial RG6U 75 ohm cable. An example of a dipole antenna sold today by RCA Accessories, model ANT1050R, is shown in Figure 1 and has dimensions of 28" x 4" x 0.04". Dipole antennas are highly directional and must be adjusted manually to maximize reception of signals for different frequencies (channels), depending on the angle of incidence and the frequency.

[0024] Recently, indoor TV antennas have been designed to be flat, unobtrusive, wideband, and provide "omnidirectional" coverage. This is to provide the end-user with a simple, minimized form-factor reception device that does not need manual or electronic adjustments to receive signal from multiple angles of incidence or at different frequencies (channels). An example of a flat indoor TV antenna, RCA Accessories model ANT1080, is shown in Figure 2. This antenna has dimensions of 8" x 9" x 0.75" and uses various copper pads on a fiberglass reinforced plastic (FRP) board substrate, with capacitors, resistors, and inductors of various types connecting the copper pads. Both sides of the FRP board are instrumented, and the antenna is connected to an RG6U 75 ohm cable for direct connection to a TV digital converter box or TV. Other indoor TV antenna models include an amplifier on the feed line.

[0025] An example TV digital channel range is from 2 to 69, with a frequency assigned to each channel that range discontinuously from 57 MHz to 803 MHz, with a gap from -225-450 MHz. CEA-2032-A is a specification which directs indoor antennas to provide -12 dBd for channels 2-6, -8 dBd for channels 7-13, and -8 dBd for channels 14-69. Existing indoor TV antennas, without or with amplifiers, can meet these gain requirements.

[0026] However, these known indoor TV antennas suffer from a number of problems.

Example problems involve insufficient multi-directionality capabilities (in terms of lobe angle coverage or signal polarization), inadequately large geometric footprint, or a high fabrication cost. The ANT1050R antenna shown in Figure 1 is essentially dipole type antenna and, when oriented with the long axis parallel to the ground, provides only horizontal polarization (HPol) reception and relatively narrow lobes (estimated at 60° x 90° coverage in front and behind the antenna plane). The ANT 1080 antenna shown in Figure 2 is more capable in terms of lobe coverage (estimated at 270° x 270°), and may provide fairly good reception in terms of both HPol and VPol (vertically polarized) signals, but is fairly thick at 0.75" thickness. This thickness makes the antenna difficult to conceal when connected to a television. Additionally, the

ANT1080 antenna has multiple capacitors, resistors, and inductors soldered into the structure, which are costly in terms of materials and fabrication time.

[0027] Starting from the fragmented aperture antenna methodology outlined in U.S. patent 6,323,809, but with multiple innovative changes and additions, the inventor designed a different type of TV antenna that overcomes these limitations and problems. The antenna is very thin— as thin as 0.001". However, a greater thickness of up to and including 0.01" may be desired for additional mechanical stability. This very thin antenna enables it to be conformally placed on the wall, floor, ceiling, furniture, or other object within the building interior. In other words, the thinness of the antenna gives it the flexibility to conform to the surface it is mounted or placed on. The antenna is wideband, meaning that it has a high gain across a wide band of frequencies, with a ratio of upper operating frequency to lower operating frequency of at least 2: 1. Preferably, but not necessarily, the operational band covers a significant portion of the VHF and UHF bands (50 - 1000 MHz). The antenna is based on a fragmented aperture design and is preferably combined with a phase splitter to provide substantially omni-directional (e.g., nearly equal gain over 300° of the azimuthal angle and 300° of the elevational angle) television signal reception. Additionally, the antenna has an elegant but simple design which can be fabricated at low cost, in terms of both equipment and fabrication time.

[0028] As just mentioned, the antenna preferably includes a phase splitter. A phase splitter splits a signal into two signals with opposite phases (i.e., a 180 ⁰ phase difference). For use with the antenna described in this application, a phase splitter works in reverse taking the omnidirectional signal from the fragmented aperture and converting it into one signal to provide better impedance matching at the receiver and therefore increasing the gain of the antenna. The addition of a phase splitter is advantageous to the overall performance of the antenna.

[0029] An example prototype VHF-UHF antenna was designed with length and width of

14"xl4" and a very thin thickness of 0.005". Note that the thickness is an order of magnitude less than the thickness of the antenna shown in Figure 2. Other length and width dimensions may be used and the thickness may be selected to be substantially in the range of 0.001-0.01". The example prototype was designed to be free-standing, meaning that a backing conductive plane is not included in the structure. Other thicknesses may be used. An example thickness of the non-conductive material of 0.003" (which is part of the antenna's overall 0.005" thickness) provides increased physical stability during transport, installation, and use, though other thicknesses may be used. The sheet resistance of the conductive regions is preferably in the range of 0.01 to 0.1 ohm/sq. The example prototype antenna has gain lobes that project in both directions normal to the film plane and performs more optimally with all conductive surfaces as far away as possible or practical.

[0030] The example prototype antenna was designed using custom modeling software, based on a Finite-Difference Time-Domain (FDTD) solver provided by the Georgia Tech Research Institute (GTRI). The MAX well Time Domain Analyzer (MAXTDA) suite of codes is an electromagnetic full-field Finite-Difference Time-Domain (FDTD) solver with post- processors capable of modeling antenna, material, and scattering problems. The design technology is described further in U.S. patent 6,323,809. Other data processing approaches capable of modeling EM performance through FDTD and designing iterative solutions may be used to generate similar fragmented aperture antenna designs.

[0031] The example prototype antenna was built using the following elements: copper- plated taffeta fabric laser-cut into the specified pattern or design (example conductive material) and backed with an adhesive to attach to a 0.005" PVC substrate (example non-conductive material); copper wiring and solder to connect the two sides of the pattern to a 0°/l 80° phase splitter module; and direct soldering to a center pin and outer ground of a 75 ohm RG6U cable. To provide a performance desired for the example prototype antenna, the sheet resistance of the conductive radiator was between 0.01 and 0.1 ohm/sq. The example phase splitter used is a commercial device, MiniCircuits PMT-1+, which uses coupled inductors in a bridge arrangement to transfer an input signal into two half-power output signals, one at 0° and one at 180° relative to the input.

[0032] Figure 3 shows the example prototype antenna design where black regions represent conductive regions or areas, and white regions represent substantially non-conductive regions or areas and which is based on a notion of percolation physics. Conducting material may be any material that has a higher conductivity than the substantially non-conducting material. Conductive or semiconductive material areas are shown in black, and less conductive

(semiconductive or dielectric) material areas are shown in white. As another non-limiting example, the conductive material may be a material with semi-conducting qualities, and a substantially non-conductive material may be any type of dielectric material.

[0033] Figure 3 may be viewed as a configuration of first and second areas designed so as to form a grid of elements in the horizontal and/or vertical direction. The grid in Figure 3 includes first and second sets of parallel lines. Each area comprises one or more contiguous elements defined by the parallel lines. Each area has a periphery that extends along the grid. The first and second areas are configured so that the planar layer can communicate

electromagnetic energy wirelessly in a specific direction to the planar layer when an electrical connection is made to at least one of the first areas.

[0034] As explained in the 6,323,809 patent, each site that is occupied by conducting

(conductive or semi-conductive) material has an associated probability. When that probability approaches a critical value, i.e., a percolation threshold, long chains of conducting elements are likely to be formed in the antenna design. For occupation probabilities greater than this threshold, there will be a continuous chain across the antenna design enabling direct current (DC) conduction to occur. Near the percolation threshold, conducting chains are created having a variety of lengths. These chains resonate at a wide range of frequencies and cause the resulting antenna to have a broadband response.

[0035] Figure 4 is a picture of an example prototype antenna developed using methods described herein and the antenna design in Figure 3 (with conductive and non-conductive regions) along with non-conductive backing (which is just an extension of the non-conductive material) and a phase splitter coupled to a coaxial cable.

[0036] The free-standing antenna design describe above, of which the prototype in Figure

4 is just a non-limiting example, is suitable as an indoor TV antenna since the walls, ceiling, and floor near a TV are typically non-conductive. The wideband characteristics of the example antenna are beneficial for TV reception since TV channels cover a wide range, although the antenna's gain at some frequencies in that wideband may be somewhat lower than others. The example prototype antenna uses a phase splitter limited to approximately 1 W maximum power, which is highly appropriate for TV signal reception.

[0037] The example prototype antenna uses a 75 ohm connector suitable for TV applications and operates with a mixture of vertical and horizontal polarization. The antenna provides a gain of ~0 dBd over 200-450 MHz, which covers TV channels 1 1 -14; a slightly lower gain above 450 MHz, approximately -1 to -4 dBd, to cover channels 14-69; and a lower gain below 200 MHz, approximately -1 to -20 dBd. Figure 5 presents additional details of the performance. The antenna provides "omnidirectional" coverage of approximately 300° x 300°.

[0038] Figure 5A shows a reference guide and dimensions of the example prototype antenna shown in Figure 4.

[0039] Figure 5B shows pseudo 3D normalized3D gain pattern of the example prototype antenna shown in Figure 4 (gain shown in dBi).

[0040] Figure 5C shows Etotai gain patterns for the example prototype antenna shown in

Figure 4 (gain shown in dBi).

[0041] Figure 5D shows a graph of broadside gain versus frequency for the example prototype antenna shown in Figure 4 (gain shown in dBi). [0042] In another example embodiment, the antenna is formed using a wall, ceiling, floor, or other non-conductive surface as the non-conductive element of the antenna and the conductive elements are placed on the wall, ceiling, floor, or other non-conductive surface. In other words, while the antenna with conductive elements formed on a non-conductive backing layer may be placed on a wall, ceiling, floor, or other non-conductive surface as described above, in this example embodiment, the conductive elements without a non-conductive backing may be placed on a wall, ceiling, floor, or other non-conductive surface which then performs the function of the non-conductive elements of the antenna. One example of the conductive elements for this embodiment is as a pre-cut layer, decal, or similar.

[0043] Various fabrication methods may be used to achieve the desired antenna design and performance. Various methods may be used to construct thin-film conductive or semi- conductive patterns. A few examples include: conductive printing, cutting of conductive films or meshes, photolithography, masked metal deposition, etc. A variety of devices may be used to split the signal into two phases. In some cases, no phase splitting is needed. Substrates may be stiff or flexible, transparent or opaque, curved or flat, with minimal impact on the performance. Cabling may for example be 50 or 75 ohm impedance, and of various types, and can be connected at various junctions on the pattern.

[0044] Other example embodiments include an antenna similar to the examples described above but with varied width and length dimensions, e.g., from Γ'χΓ' to 10'xlO'; an antenna similar to the examples described above but bent along a curved or 3-dimensional surface, e.g., a sheet of flat conductive elements is wrapped around a cylinder; an antenna similar to the examples described above without a phase splitter; an antenna similar to the examples described above with multiple phase splitters; an antenna similar to the examples described above including other electronic components that modify the signal; an antenna similar to the examples described above but having multiple, stacked conductive layers to modify the EM performance. Other modifications to the example antennas described above are also envisioned as known to the person skilled in the antenna art. Advantageous features shared by example embodiments include fragmented aperture type, very thin thickness, wideband operation, a capability to operate without a heavy conductive backplane, relatively simple construction, and low-cost design. [0045] The example TV antenna incorporates a fragmented design generated using computer modeling, such as described above, to provide: (1) very wide angle (nearly omnidirectional) coverage that exceeds that achievable by existing dipole or low profile antennas; (2) sufficient gain over a wide frequency range to receive TV signals indoors; (3) much thinner construction than existing low profile antennas; and (4) lower cost in terms of both materials and fabrication because it includes a single sheet of conductive material and because it does not rely on capacitors, resistors, or inductors to connect the conductive regions. This very thin, fragmented aperture design, which also preferably incorporates a phase splitter, is highly effective for digital TV signal reception in terms of performance, geometric footprint, and low- cost manufacture.

[0046] Because of the extremely wideband nature of this antenna, which translates into lower gain for any particular narrow frequency band, this type of design is primarily applicable to TV signal reception. However, it could potentially be adapted with or without design changes for any other receiving or transmitting applications in the VHF or UHF bands, including frequency modulated (FM) radio, Digital Audio Broadcasting, amateur radio, marine radio, aviation communications, military communications, and other communications. In addition, since the frequency band of maximum gain tends to scale with the dimensions of the antenna, this design can conceivably be geometrically re-scaled such that the frequency band also shifts higher or lower, and would therefore be relevant to the 3-30 MHz High Frequency (HF) or 3-30 GHz Super High Frequency (SHF) bands, for example. In addition, although this antenna is intended to function with a mixture of HPol and VPol EM radiation, other designs could easily be generated to maximize the transmission or reception of right-handed-circular polarization (RHCP) or left-handed-circular polarization (LHCP).

[0047] Although the description above contains many specifics, those specifics should not be construed as limiting but as merely providing illustrations of some presently preferred embodiments. The technology fully encompasses other embodiments which may become apparent to those skilled in the art. Reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural and functional equivalents to the elements of the above-described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed hereby. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the described technology for it to be encompassed hereby.