Planar high-frequency antenna

[0002] This invention claims priority to the following co-pending U.S. provisional patent application, which incorporated herein by reference, in its entirety:

[0003] Shor, et al., Provisional Application Serial No. 60/289,448, entitled “PLANAR HIGH-FREQUENCY ANTENNA,” filed May 7, 2001.

[0004] The present application is related to U.S. patent application Ser. No. 10/140,336, entitled “PARALLEL-FEED PLANAR HIGH FREQUENCY ANTENNA”, filed on the same date as the present application; and Ser. No. 10/140,339, entitled “DUAL-BAND PLANAR HIGH FREQUENCY ANTENNA”, filed on the same date as the present application, the contents of each are incorporated herein by reference in their entirety.

[0005] 1. Field of Invention

[0006] The present invention relates generally to the field of high frequency antennas, and more particularly to the field of high-gain, multi-dipole array antennas constructed using inexpensive manufacturing techniques.

[0007] 2. Discussion of Background

[0008] The U.S. Federal Communications Commission (FCC) allocates a certain number of frequency bands where a license is not required for use. For example, many garage-door openers operate in the unlicensed 49 MHz band. Similarly, the unlicensed 2.4 GHz frequency band has become popular for connecting computers to a wireless LAN.

[0009] Unfortunately, the 2.4 GHz band available in the U.S. and worldwide hosts a myriad of devices and competing communications standards that have led to increasing interference and degraded performance in the wireless networking world. Devices operating at 2.4 GHz include common household items such as microwave ovens, cordless phones and wireless security cameras, in addition to the myriad computing devices that are wirelessly networked together. To add to the confusion, the industry has deployed multiple standards for wireless networking at 2.4 GHz. The IEEE 802.11b standard is, as of the filing date hereof, most commonly used for enterprise wireless LANs. The Home RF standard also exists for wireless LANs in the home, and Bluetooth has been developed as a short-distance wireless cable replacement standard for short-range, low-rate applications.

[0010] The interference and performance issues at 2.4 GHz have the wireless LAN industry headed for the open 5.15 to 5.35 GHz frequency band, where the opportunity exists for a much cleaner wireless networking environment. The allocated unlicensed 5 GHz band is devoid of interference from microwave ovens and, in the U.S., provides more than twice the available bandwidth of the allocated unlicensed 2.4 GHz band, thereby allowing for higher data throughput and more simultaneous users, and the potential for multimedia application support. This open 5 GHz spectrum provides an opportunity for the potential creation of a unified wireless protocol that will support a broad range of devices and applications. Everything from cordless phones to high-definition televisions and personal computers can communicate on the same multipurpose network under a single unified protocol. As a result, an antenna operating in the unlicensed frequency band above 5 GHz would encourage the creation and support of a wide range of low and high data rate devices that could all communicate on a single wireless network.

[0011] As to antenna design to take advantage of the above described opportunity for high-frequency wireless communication, the industry's foremost objective is to provide antennas having (1) the lowest possible manufacturing costs with consistently uniform performance, (2) high gain, (3) high directivity when desired, and (4) design characteristics that can be applied in both the current majority-used frequency bands (such as 2.4 GHz) and the newly utilized bands (particularly between 5 GHz and 6 GHz).

[0012] Conventional dipole antennas (also commonly known as Franklin antennas), in which each member of a pair of fractional wavelength radiators are fed in anti-phase, produce a substantially omni-directional radiation pattern in a plane normal to the axis of the radiators. However, providing such an omni-directional structure on a substantially planar (and inexpensively produced) surface, such as a printed circuit board substrate, has proven a challenge. Existing attempts to achieve such planarity and performance rely on vias that penetrate the substrate to interconnect a plurality of conducting planes, thereby adding substantially to the cost of the antenna.

[0013] U.S. Pat. No. 5,708,446 discloses an antenna that attempts to provide substantially omni-directional radiation pattern in a plane normal to the axis of the radiators. The patent discloses a corner reflector antenna array capable of being driven by a coaxial feed line. The antenna array comprises a right-angle corner reflector having first and second reflecting surfaces. A dielectric substrate is positioned adjacent the first reflective surface and contains a first and second opposing substrate surfaces and a plurality of dipole elements, each of the dipole elements including a first half dipole disposed on the first substrate surface and a second half dipole disposed on the second substrate surface. A twin line interconnection network, disposed on both the first and second substrate surfaces, provides a signal to the plurality of dipole elements. A printed circuit balun is used to connect the center and outer conductors of a coaxial feed line to the segments of the interconnection network disposed on the first and second substrate surfaces, respectively.

[0014] However, in order to connect the coaxial cable to the interconnection network, U.S. Pat. No. 5,708,446 requires a via to be constructed through the substrate. This via's penetration through the substrate requires additional manufacturing steps and, thus, adds substantially to the cost of the antenna.

[0015] Furthermore, other attempts require branched feed structures that further increase the number of manufacturing steps and thereby increase the cost of the antenna. A need exists to use fewer parts to assemble the feed so as to reduce labor costs. Present manufacturing processes rely on a substantial amount of human skill in the assembly of the feed components. Hence, human error enters the assembly process and quality control must be used to ferret out and minimize such human error, which adds to the cost of the feed.

[0016] Such human assembled feeds also provide inconsistent performance. For example, U.S. Pat. No. 6,037,911 discloses a phased array antenna comprising a dielectric substrate, a plurality of dipole means, each comprising a first and a second element, the first elements being printed on the front face and pointing in a first direction and the second elements being printed on the back face, and a metal strip means comprising a first line printed on the front face and coupled to the first element and a second line printed on the back face and coupled to the second element. A reflector means is also spaced to and parallel with the back face of the dielectric substrate and a low loss material is located between the reflector means and the back face, whereby the first and second lines respectively comprise a plurality of first and second line portions and the first and second line portions respectively being connected to each other by T-junctions. However, in order to provide a balanced, omni-directional performance, U.S. Pat. No. 6,037,911 requires a branched feed structure through the utilization of T-junctions. These T-junctions add complexity to the design and, again, increase the cost of the antenna.

[0017] To address the shortcomings of the available art, the present invention provides a planar antenna having a scalable multi-dipole structure for receiving, and transmitting high-frequency signals, including a plurality of opposing layers of conducting strips disposed upon either side of an insulating (dielectric) substrate.

[0018] In one embodiment, the present invention is an antenna in which each dipole is bifurcated along a horizontal axis, with one half of a dipole disposed on one side of a substantially planar insulating layer and the other half disposed on the other side of the insulating layer. Additionally, each dipole half is in electrical communication with a feed structure independent of its other half, and a plurality of dipoles are preferably dispersed symmetrically along the feed structure.

[0019] In another embodiment, the present invention is an antenna that is optimized to function between 5.15 and 5.35 GHz, preferably with a center frequency of 5.25 GHz. In an alternative, higher gain embodiment of the present invention, a plurality of dipoles is vertically integrated along the feed structure to create a serial, co-linear antenna.

[0020] Advantages of the present invention include: provision of a highly effective dipole structure in an inexpensive, printed implementation (printed radiating elements on opposing sides of a planar, insulating substrate); the integration of a balun with an antenna feed on a planar substrate; and, provision of a feed line and feed line branches to each of a plurality of radiating elements such that an excellent impedance match is obtained over a wide frequency range. Also, the inventive antenna's lack of vias and inclusion of balanced, independent feed structures significantly reduces system design time, manufacturing costs and utilized materials. Preferably, cost is further minimized through the use of standard manufacturing processes and eliminating the introduction of human error.

[0021] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0022] FIG. 1 illustrates in two views a preferred embodiment of the invention, providing separate views of either side of a thin, planar dielectric substrate having the antenna structure deposited thereupon, including dipoles and feed structures;

[0023] FIG. 2 illustrates in a single view the equivalent structure of FIG. 1 without illustrating the dielectric substrate or bifurcation of the dipoles, including dimensions of an embodiment preferred for application to the frequency range from substantially 5.15 to 5.35 GHz;

[0024] FIG. 3 illustrates an alternative, higher gain embodiment of the present invention, wherein additional dipole structures are included in series with primary dipoles as illustrated in FIGS. 1 and 2.

[0025] It should be understood that the figures are intended only to illustrate the invention. Only any claims that issue henceforth and their equivalents should be used to limit the invention and the coverage provided by any issued patent.

[0026] FIG. 1 illustrates a planar antenna 1 having a scalable, half-wavelength multi-dipole structure for receiving and transmitting high-frequency signals. Two sides, Side A and Side B, provide two views of the dielectric substrate 5's opposing sides, flipped along vertical axis Y. Antenna 1 includes two layers of conducting (preferably) metallic strips disposed upon opposing sides of the insulating substrate 5. A plurality of half wavelength dipoles 2, 4, 6, and 8 are positioned in series along feed structures 10 and 12. Each dipole is preferably bifurcated between side A and side B of substrate 5 and each quarter-wavelength dipole half (e.g., 2A and 2B) is separately connected to either of feed structures 10 and 12, respectively. Dipoles 2 and 4 are bifurcated along a horizontal axis 32 and dipoles 6 and 8 are bifurcated along a horizontal axis 34. The dipoles' bifurcation and placement along opposing sides of substrate 5 eliminates the need for additional substrate layers and vias to accommodate a singular antenna feed structure.

[0027] To ensure balanced, omni-directional performance, the dipole parts are symmetrically positioned about a line of symmetry 30, which oriented along the vertical centerline of the feed structures 10 and 12. The provided structure thereby compensates for the phase shift of approximately 180 degrees between stacked dipoles (since the distance between the two adjacent stacked dipoles is about one-half of a wavelength). Since alternate radiating elements of adjacent dipoles are connected to the same feed line, an additional 180 degrees of phase shift is provided, thereby providing a total phase shift of 360 degrees between adjacent dipoles in the stack, that is, equal phase for all radiating dipoles at the center frequency of the operating range.

[0028] Balun structure 14, including tapered portions 16 and 18 and lower portion 20, provides the balanced performance characteristics required of feed structures 10 and 12 above designated balance point 24 on both structures. Feed structures 10 and 12 are preferably connected to two conductors in electrical communication with a transceiver, which conductors are presented in a coaxial configuration (not shown), with an outer conductor (typically ground) in communication with antenna side A and an inner conductor (typically an active signal) in communication with antenna side B. In the illustrated example, structure 10, including tapered balun structure 14, is connected to the outer-grounded conductor, while structure 12 is connected to the inner conductor. Contact points 22 are preferably, though optionally, provided for testing and to fine-tune input/output impedance matching as needed.

[0029] Balun structure 14 includes two sub-parts, one on each side of substrate 5 and best illustrated with reference to FIG. 2. The side A (grounded) tapered balun components comprise rectangular conductors 19 and 21 (disposed on each side of the antenna longitudinal plane of symmetry) that provide a soldering surface for the coaxial connection described above (not shown). On the grounded side A, each rectangle is joined with gradually tapering structure 14 and converges towards the antenna centerline, eventually merging to a single conducting strip opposite the “signal” strip on the opposite side of substrate 5. This twin-symmetric, converging balun structure provides a transition from the unbalanced coaxial cable (or other feed configuration) to a balanced parallel strip feed line and also provides proper wideband impedance matching for the desired transceiver.

[0030] Side B provides a complementary feed structure and rectangular traces for receiving, for example, the coaxial connector.

[0031] Balun 14 is therefore a significant component of the inventive antenna, as it allows the antenna to operate equally well with or without a ground plane. In a preferred embodiment, the balun and feed line dimensions are optimized to provide a wideband impedance match while maintaining a very small balun size. Typically, printed planar baluns are one to two operating wavelengths long, while the preferred inventive embodiment is about one-quarter wavelength long and thus enables, in part, substantial (about a factor of two) reduction of the overall antenna length.

[0032] Additionally, because antenna 1 provides a low loss line structure, it is possible to use for the substrate 5 a dielectric of a standard quality, and thus of low cost, without considerably reducing the efficiency of the antenna. Substrate 5 is preferably between approximately 100 and 700 micrometers thick to provide sufficient rigidity to support the antenna structure. Because of the simplicity of production and elements and the low cost of the raw materials, the cost of the antenna is considerably lower than for more complicated high frequency antennas.

[0033] FIG. 2 provides an idealized illustration of antenna 1 having dimensions optimized for a transceiver functioning between 5.15 and 5.35 GHz, the two sides A and B being superimposed onto a single line drawing. Feed structure 10 includes tapered balun 14 and a vertical portion 1-mm wide and horizontal portions each 0.5-mm wide. Feed structure 12 also includes vertical and horizontal portions having preferably the same dimensions as feed structure 10. However, as with each of the preferred dimensions discussed herein, other lengths or widths may be utilized depending on the desired center frequency of the antenna. The length of the horizontal portions spacing the dipoles is preferably 8.4 mm, while each dipole quarter-wavelength portion is preferably 1.8 mm wide and 13 mm long. The preferred structure thereby provides a total end-to-end horizontal spread between dipoles of 12 mm (thereby optimizing gain without diminishing the omni-directional nature of the intended performance characteristics) and vertical spread of 43 mm (providing full wavelength vertical separation between the dipole pairs while accommodating the imperfect insulating properties of dielectric substrate 5).

[0034] Wireless devices typically include a transmitter and receiver to an antenna that emits and receives signals to and from a base station. For example, in the wireless environment, designers are often interested in maximizing the uplink (mobile to base station) and downlink (base station to mobile station) range. Any increase in range means that fewer cells are required to cover a given geographic area, hence reducing the number of base stations and associated infrastructure costs. The link's range, either the uplink or the downlink, and the network's overall strength can be improved via two approaches. One approach is to increase the transceiver's power in order to increase the range and thus the overall strength of the network. The second approach is to increase the receiver's gain.

[0035] FIG. 3 illustrates an alternative, higher gain embodiment of the antenna, wherein additional dipole structures (e.g. 40, 42, 44, 46) are included in a co-linear series with the primary dipoles (e.g. 2, 4, 6, 8) illustrated in FIGS. 1 and 2. This co-linear, serial embodiment continues to provide full in-phase feeding of the array elements. The antenna's gain is enhanced without disturbing other antenna performance characteristics by vertically stacking a second set of dipoles separated from the first set by a dipole separation distance, preferably an approximate distance of 43 mm. Separation distances may be calculated based on same phase 360-degree phase differential of signals emanating from the dipoles. Bifurcated dipoles symmetrically opposed (e.g., dipole 2 and dipole 4) are fed in phase, while the individual dipole elements of a single bifurcated dipole (e.g. element 2A and element 2B of dipole 2) are fed in anti-phase. The physical distance between the dipoles (see FIG. 2) is approximately 43 mm, which is less than one wavelength (˜0.7 of a wavelength). The dielectric constant of the feed lines is approximately 3.4 and thus causes a shortening of the wavelength in the feed lines compared to the wavelength in air (with a dielectric of 1), and the physical distance between dipoles is set accordingly. With a dielectric constant of approximately 3.4, the illustrated feed structures shorten the wavelength to approximately 70-80% of the wavelength in air, which corresponds approximately to the 43 mm physical distance between dipoles. Other dipole separation distance values may vary depending on the desired frequency.

[0036] It should be noted that a significant goal of the wireless communication industry is to manufacture antennas that provide superior directivity. The antenna of the present invention satisfies this goal as well. The antenna's combination of multiple, co-linear dipoles in series provides enhanced antenna directivity: that is, the elevation pattern is highly focused. However, by varying the vertical distance between dipoles, the elevation pattern can be altered. If, for example, a transceiver is located at a high point substantially above a wireless network dispersed on a lower plane, the elevation pattern may be directed downward to increase effectiveness by tilting the beam.

[0037] Finally, it will be clear that the invention is not limited to the transmission or reception of ˜5 GHz low power signals. The invention can be used with all types of high-frequency transmission networks. Also, the exemplary choice of the frequency of 5.15 to 5.35 GHz should not exclude coverage for other operating frequencies in the high-frequency range. For example, by turning the illustrated antenna on its side and connecting the balun at the center of the structure, a broader bandwidth embodiment could be constructed, as will be understood by those skilled in the art to which the present invention pertains.

[0038] In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. For example, when describing a feed line, any other device having equivalent structure, function, or capability, whether or not listed herein, may be substituted therewith. Furthermore, the inventors recognize that those newly developed technologies not now known may also be substituted for the described parts and still not depart from the scope of the present invention. All other described items, including, but not limited to feed lines, horizontal portions, balun, dipoles, substrates, etc should also be consider in light of any and all available equivalents.

[0039] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings.

[0040] It will be understood that the disclosed embodiments are of an exemplary nature and that the method and system is to be limited only by any claims that issue henceforth and their equivalents. The invention may be practiced otherwise than as specifically described herein.