Patent Application
20070222700
NOT APPLICABLE
1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to antennas used within wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks to radio frequency identification (RFID) systems. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, RFID, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
Since the wireless part of a wireless communication begins and ends with the antenna, a properly designed antenna structure is an important component of wireless communication devices. As is known, the antenna structure is designed to have a desired impedance (e.g., 50 Ohms) at an operating frequency, a desired bandwidth centered at the desired operating frequency, and a desired length (e.g., ¼ wavelength of the operating frequency). As is further known, the antenna structure may include a single mono pole or dipole antenna, a diversity antenna structure, or any number of other electromagnetic properties. For instance, one popular antenna structure is a three-dimensional in-air helix antenna, which resembles an expanded spring. An in-air helix antenna provides a magnetic omni-directional mono pole antenna that is well suited for portable wireless communication devices. However, such an in-air helix antenna occupies a significant amount of space and the three dimensional aspects of it cannot be implemented on a planer substrate, such as a printed circuit board (PCB).
For PCB implemented antennas, the antenna has a meandering pattern on one surface of the PCB. Such an antenna consumes a relatively large area of the PCB. For example, for a ¼ wavelength antenna at 900 MHz, the total length of the antenna is approximately 8 centimeters (0.25 * 32 cm, which is the approximate wavelength of a 900 MHz signal). Even with a tight meandering pattern, the antenna consumes approximately 4 cm2. With the never-ending push for smaller form factors with increased performance, a PCB meandering antenna is not acceptable for many newer wireless communication applications.
Therefore, a need exists for a small form factor antenna that offers the benefits of an in-air helix antenna and the convenience of PCB fabrication without the above mentioned limitations.
The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings.
Each RFID reader 14-18 wirelessly communicates with one or more RFID tags 20-30 within its coverage area. For example, RFID reader 14 may have RFID tags 20 and 22 within its coverage area, while RFID reader 16 has RFID tags 24 and 26, and RFID reader 18 has RFID tags 28 and 30 within its coverage area. The RF communication scheme between the RFID readers 14-18 and RFID tags 20-30 may be a back scatter technique whereby the RFID readers 14-18 provide energy to the RFID tags via an RF signal. The RFID tags derive power from the RF signal and respond on the same RF carrier frequency with the requested data.
In this manner, the RFID readers 14-18 collect data as may be requested from the computer/server 12 from each of the RFID tags 20-30 within its coverage area. The collected data is then conveyed to computer/server 12 via the wired or wireless connection 32 and/or via the peer-to-peer communication 34. In addition, and/or in the alternative, the computer/server 12 may provide data to one or more of the RFID tags 20-30 via the associated RFID reader 14-18. Such downloaded information is application dependent and may vary greatly. Upon receiving the downloaded data, the RFID tag would store the data in a non-volatile memory.
As indicated above, the RFID readers 14-18 may optionally communicate on a peer-to-peer basis such that each RFID reader does not need a separate wired or wireless connection 32 to the computer/server 12. For example, RFID reader 14 and RFID reader 16 may communicate on a peer-to-peer basis utilizing a back scatter technique, a wireless LAN technique, and/or any other wireless communication technique. In this instance, RFID reader 16 may not include a wired or wireless connection 32 computer/server 12. Communications between RFID reader 16 and computer/server 12 are conveyed through RFID reader 14 and the wired or wireless connection 32, which may be any one of a plurality of wired standards (e.g., Ethernet, fire wire, et cetera) and/or wireless communication standards (e.g., IEEE 802.11x, Bluetooth, et cetera).
As one of ordinary skill in the art will appreciate, the RFID system of
The baseband processing module 40, the encoding module 42, the decoding module 52 and the pre-decoding module 50 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The one or more processing devices may have an associated memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of the processing device. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the processing module 40, 42, 50, and/or 52 implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory element storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Further note that, the memory element stores, and the processing module 40, 42, 50, and/or 52 executes, hard coded or operational instructions corresponding to at least some of the steps and/or functions illustrated in
In operation, the baseband processing module 40 prepares data for encoding via the encoding module 42, which may perform a data encoding in accordance with one or more RFID standardized protocols. The encoded data is provided to the digital-to-analog converter 44 which converts the digitally encoded data into an analog signal. The RF front-end 46 modulates the analog signal to produce an RF signal at a particular carrier frequency (e.g., 900 MHz) that is provided to the antenna 60, which will be described in greater detail with reference to
The RF front-end 46 includes transmit blocking capabilities such that the energy of the transmit signal does not substantially interfere with the receiving of a back scattered RF signal received from one or more RFID tags. The RF front-end 46 converts the received RF signal into a baseband signal. The digitization module 48, which may be a limiting module or an analog-to-digital converter, converts the received baseband signal into a digital signal. The predecoding module 50 converts the digital signal into a biphase encoded signal in accordance with the particular RFID protocol being utilized. The biphase encoded data is provided to the decoding module 52, which recaptures data therefrom in accordance with the particular encoding scheme of the selected RFID protocol. The baseband processing module 40 provides the recovered data to the server and/or computer via the local area network connection module 54. As one of ordinary skill in the art will appreciate, the RFID protocols include one or more of line encoding schemes such as Manchester encoding, FM0 encoding, FM1 encoding, etc. As one of ordinary skill in the art will further appreciate, the antenna 60 has far more applications than RFID applications. For instance, the antenna 60 may be used in wireless local area network (WLAN) applications, cellular telephone applications, personal area networks (e.g., Bluetooth) applications, etc.
The first pattern 68 includes a plurality of substantially parallel traces (e.g., two or more), which may be metal traces on a PCB or integrated circuit die. The traces may be of the same length or different lengths and are angled with respect to their length axis. Note that if the traces are of the same length a periodic self resonance may develop, which is avoided by differing the lengths of the traces. Further note that if the traces are of different lengths, all of the traces may have different lengths or just adjacent traces may have different lengths. For example, if the first pattern includes six traces, the first, third, and fifth traces may be of the same length, and the second, fourth, and sixth traces may also be of the same length, but the length of the first, third, and fifth traces are different than the length of the second, fourth, and sixth traces.
The second pattern 70 includes a plurality of substantially parallel traces (e.g., two or more) that have connection nodes 76 of each trace aligned with connection nodes 74 of corresponding traces of the first pattern 68. The interconnections 72, which may be PCB or integrated circuit die vias or edge wrap-arounds, couple the connection nodes 74 of the first pattern 68 with the connection nodes 76 of the second pattern 70 to create a planer helical antenna. Note that the traces of the second pattern 70 may also have equal lengths or differing lengths and may be metal traces on a PCB or integrated circuit die. Further note that, while the traces of the first and second patterns are shown as straight lines, the traces may have different substantially parallel geometric shapes including, but not limited to, an arc, an “s” shape, or a “v” shape. Still further note that each of the plurality of traces of the first and second patterns includes a trace width and spacing from an adjacent trace based on PCB fabrication criteria (e.g., minimum spacing requirements, trace width for a certain frequency and/or current level) and wavelength of a signal being transceived by the antenna (e.g., impedance, capacitive coupling, magnetic coupling, etc).
As one of ordinary skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As one of ordinary skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of ordinary skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of ordinary skill in the art will further appreciate, the term “operably associated with”, as may be used herein, includes direct and/or indirect coupling of separate components and/or one component being embedded within another component. As one of ordinary skill in the art will still further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.
The preceding discussion has presented an antenna having a helical winding fabricated on a planer substrate. As one of ordinary skill in the art will appreciate, other embodiments may be derived from the teachings of the present invention without deviating from the scope of the claims.
