Abstract:
A hand held Radio Frequency Identification (RFID) reader is provided. The reader includes a housing having a perimeter around an inner edge. The reader also includes a full-sized dipole antenna including two antenna elements coupled by a balun transformer. The antenna has nearly a unity gain over a range of angles. The reader also includes a transceiver, coupled to the dipole antenna by a suitable cable, the transceiver adapted to send and receive signals. The reader further includes a processor for processing signals received at the antenna. The first and the second antenna segments of the dipole antenna are wrapped along the perimeter around the inner edge of the housing.

Description:
GOVERNMENT LICENSE RIGHTS 
   The U.S. Government may have certain rights in the present invention as provided for by the terms of Contract No. N00174-01-D-0016 awarded by the Dept. of Navy. 

   TECHNICAL FIELD 
   The present invention relates generally to the field of contact-less identification such as Radio Frequency Identification (RFID) and, in particular, to hand held RFID readers. 
   BACKGROUND 
   Identification and tracking of tangible objects are essential in a multiplicity of industries. Automatic identification systems are replacing manual identification as automatic systems are more accurate, more efficient and more cost-effective. A key feature of automatic identification systems is remote or contact-less identification. Remote identification improves the accuracy of inventory identification, dramatically reduces the effort required, and allows potentially instant verification of inventory. Typical remote identification systems include Radio Frequency Identification (RFID) technology. Incorporating RFID technology reduces the time, cost and effort for performing identification and tracking when compared to manual methods while significantly improving the accuracy. RFID technology also provides a safer means for identification and tracking both in hazardous environments and identification and tracking of hazardous materials. 
   In general, a typical RFID systems consists of a transmitter (tag) and a receiver (reader). The tag can be either a passive identification device or an active identification device. A passive tag typically is powered by an external means. One embodiment powers the tag from the reader via a magnetic field generated by the reader. A typical active RFID tag contains its own battery for power. A tag is affixed to an object to be identified. The transmitter sends a radio frequency interrogation signal that activates the tag and the tag emits a signal that identifies the object to which it is attached. The reader could be able to distinguish the identification signals from a single tag or a group of RFID tags. RFID tag readers can be found in two manifestations: hand held readers and fixed readers. The selection of a fixed or handheld reader depends on the application in which it is used. 
   When designing a handheld reader, there are a multiplicity of factors that need to be taken into account. One of the paramount considerations is that the size, weight, and shape of the reader is manageable by a typical user without excessively compromising the functionality of the reader. A key area for size reduction is the antenna used by a handheld reader. The antenna is used to excite the tag in order to elicit a response that identifies the item to which the tag is attached. Unfortunately, reductions in antenna size also result in reductions in antenna efficiency. Antenna efficiency is a measure of the amount of signal power that an antenna radiates to its environment relative to the amount of power supplied to the antenna. It is desirable to keep antenna efficiency as high as possible as low antenna efficiency requires higher power transmitters and this directly reduces battery life in a handheld reader. Frequently, the antenna size is so small and antenna efficiency is so low that the performance of the handheld reader as measured by its usable range is inadequate for many applications. 
   For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a hand held RFID reader that provides better performance over existing RFID readers in a variety of environments. 
   SUMMARY 
   Embodiments of the present invention provide a hand held RFID reader with better performance over existing readers. In one embodiment, a hand held RFID reader is provided. The reader includes a housing having a perimeter around an inner edge. The reader also includes a full-sized dipole antenna including two antenna elements coupled by a balun transformer. The antenna has nearly a unity gain over a range of angles. The reader also includes a transceiver, coupled to the dipole antenna by a suitable cable, the transceiver adapted to send and receive signals. The reader further includes a processor for processing signals received at the antenna. The first and the second antenna segments of the dipole antenna are wrapped along the perimeter around the inner edge of the housing. 

   
     DRAWINGS 
       FIG. 1  is an illustration of one embodiment of an antenna gain pattern of a compact antenna. 
       FIG. 2  is an illustration of one embodiment of antenna gain pattern full sized dipole antenna. 
       FIG. 3  is a block diagram of one embodiment of a RFID reader system. 
       FIG. 4  is an illustration of one embodiment of a dipole antenna. 
       FIG. 5  is a perspective view of one embodiment of the back of a hand held RFID reader with the back cover removed and showing one embodiment of a full sized dipole antenna installed in the RFID reader. 
       FIG. 6  is a perspective view of one embodiment of the front of a hand held RFID reader. 
       FIG. 7  is an illustration of one embodiment of an environment where RFID readers are used. 
   

   DETAILED DESCRIPTION 
   In the following detailed description of the preferred embodiments, reference is made to accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
     FIG. 1  is an illustration of the antenna gain pattern of a compact antenna that enables receiving signals by a hand held RFID reader, indicated generally at  100 . As illustrated, the gain is sub-optimal in that the antenna gain never approaches unity. This indicates that the antenna does not efficiently receive or transmit signals. Low antenna efficiency can degrade battery life in portable devices such as an handheld RFID reader by requiring a higher power transmitter to achieve a radiated signal power equivalent to that produced by a lower power transmitter and a more efficient antenna. Also, low antenna gain impacts the apparent usable range of the receiver as some of the signal that reaches the antenna is lost and causes the receiver to be unable to detect weak signals. The overall result of this is lower performance in the handheld reader and the performance may become sufficiently impaired as to affect the usability of the handheld reader. 
     FIG. 2  is an illustration of the antenna gain pattern of a full-sized dipole antenna, indicated generally at  200  that enables receiving signals in a hand held RFID reader. Antenna gain pattern  200  indicates the antenna gain is nearly unity at a range of angles. This indicates that the antenna has a preferred orientation for optimum gain and is very efficient at receiving signal from those directions. In a typical RFID reader, the antenna is oriented so that the antenna “points” in the direction from which RFID tag signals are most likely to originate. This results in efficient radiation of transmitted signals and also results in best sensitivity of the reader when receiving signals from tags. Generally speaking, a full-sized antenna has higher gain than a compact antenna and results in improved performance of the RFID reader vis-à-vis a compact antenna. 
     FIG. 3  is a block diagram of one embodiment of a hand held RFID reader, indicated generally at  300 . As illustrated, the hand held RFID reader in  300  comprises a housing  305 , power source  307 , antenna  310 , a transceiver  312 , an interface module  314 , a processor  315 , a bus  316 , a memory  317 , a display  318  and an input/output device  320 . Power source  307  provides power required for the operation of the hand held RFID reader  300 . In one embodiment, antenna  310  is coupled to transceiver  312  using a coaxial feed-line  311 . Transceiver  312  both receives and generates the radio frequency signals from antenna  310 . The interface module  314  facilitates the communication of signals between the transceiver  312  and other modules in the reader. 
   In one embodiment, display  318  and input/output device  320  are coupled to processor  315  and memory  317  through bus  316 . Display  318  is used to display RFID tag identification information and sundry other information received from interface module  314 . Input/Output device  320  could be used to select which programs stored in memory  317  to run in order to perform desired operations and could also allow the reader to be connected to outside devices via input/output device  320  for purposes such as loading new programs, offloading data from tags that have been read, and other tasks as desired. The programs accessed in memory  317  are processed in processor  315 . Data may be entered at the input/output device  320  using a keypad, touch screen, or other type of data entry device. 
   In operation, dipole antenna  310  of the RFID reader  300  receives signals transmitted by RFID tags. The tag signals contain tag identification and other information. The tag signals received at dipole antenna  310  are received by transceiver  312 . Transceiver  312  passes the data contained within the terminated RFID tag signal to interface module  314 . Interface module  314  receives the data from the tags and presents this data to internal databus  316  where it is manipulated by processor  315 . Processor  315  may translate the data to a format recognizable by display  318 , prepare the data for input/output device  320 , store the data in memory  317 , or any admixture of the aforementioned processes. In one embodiment, display  318  displays a list of all the RFID tag information carried by the signals from the tag and received at the RFID reader. In another embodiment, RFID reader  300  creates a list of RFID tags that is has received after interrogating the RFID tags and then compares the received list of RFID tag identification to a pre-selected list of RFID tag information stored in memory  317  to check for the presence or absence of specific RFID tags. 
     FIG. 4  is an illustration of one embodiment of a dipole antenna assembly, indicated generally at  400 . As illustrated, dipole antenna assembly  400  comprises a coaxial feed-line  311 , a balun  412  and antenna wires  410  and  414 . Antenna wires  410  and  414  receive signals from RFID tags and couples the signal to coaxial feedline  311 . Coaxial feed-line  311  carries the signal to a transceiver located within the RFID reader. Balun  412  is a balanced-unbalanced transformer. Balun  412  enables coupling balanced antenna wires  410  and  414  to unbalanced coaxial cable  311 . In one embodiment, antenna wires  410  and  414  are made of equal lengths. In a full-sized antenna, each of antenna wires  410  and  414  are very nearly equal in length and the length is governed by the frequency at which the antenna is designed to operate. 
     FIG. 5  is a perspective view of one embodiment of the dipole antenna installed inside a hand held RFID reader  500  with the back cover  504  removed. As illustrated, hand held RFID reader  500  includes a non-conductive hand held RFID reader housing  510 , a separation  511  between antenna wire  410  and the inner edge  513  of the housing. An identical separation exists between antenna wire  514  and the inner edge  513  of the housing. The size of the separation  511  is not important. The coaxial cable  311  passes through an orifice  512  into an inner cavity  514 . In one embodiment, the orifice is replaced with a connector that effectively connects the coaxial cable  311  to the inner cavity. In this illustration, the dipole antenna assembly  400  includes antenna wires  410  and  414 , a balun  412 , and a coaxial feed-line  311 . 
   In one embodiment, antenna wires  410  and  414  are wrapped along a perimeter  511  of the inner edge  513  inside housing  510  of hand held RFID reader  500  to provide a compact design for hand held RFID reader  500 . Placing of full sized dipole antenna assembly  400  in this manner inside hand held RFID reader  500  takes advantage of the antenna gain inherent in a full-sized antenna and enables better performance of hand held RFID reader  500 . Antenna wires  410  and  414  are coupled to a balun  412  which in turn is coupled to a coaxial feed-line  311 . Hand held RFID reader housing  510  includes an inner cavity  514  that contains the necessary components required for the operation of the RFID reader  500 . In one embodiment, coaxial feed-line  311  enters into inner cavity  514  through an orifice  512  to connect with a transceiver located within inner cavity  514 , balun  412  is mounted on housing  510 . Other embodiments are possible. Back cover  504  attaches to the back of housing  510  and protects antenna assembly  400 . 
     FIG. 6  is a perspective view of one embodiment of the front of a hand held RFID reader, indicated generally at  600 . In this embodiment, the front view of hand held RFID reader  600  includes housing  510 , display  602 , key pad  604  and keys  606 . Display  602  lists the RFID tag information captured by the hand RFID reader  600 . Key pad  604  includes a number of individual keys  606  that may be used to operate the RFID reader and may also be used to enter data that is to be programmed into the RFID tag. Other embodiments are possible where the usage of the keypad and display vary from this illustrative example. 
     FIG. 7  is an illustration of one embodiment of an environment where handheld RFID readers are used, indicated generally at  700 . In this illustrated, environment  700  includes building  720 , a reflecting wall  730  forming an enclosure  740 , a person  750  carrying a hand held RFID reader  760 , RFID tags  722 - 1  through  722 -N that are attached to objects. Transmitted RFID tag signals are received by hand held RFID reader  760  carried by person  750 . The RFID tags transmit unique identification numbers and possibly additional information related to or derived from the object to which they are attached. 
   In operation, person  750  moves within enclosure  740  of building  720  to capture the transmitted RFID tag information using hand held RFID reader  760 . In one embodiment, building  720  is an ammunition magazine with an igloo shaped structure. RFID tags  722 - 1  through  722 -N are attached to ammunition containers which may or may not have metal casings. The RFID tags transmit signal and some of the transmitted signals are received directly at hand held RFID reader  760  whereas others are reflected by either the wall  730  or other objects which could be the items to which RFID tags  722 - 1  through  722 -N within enclosure  740  of building  720  are attached. 
   Because of possible multiple reflections (multipath) of transmitted RF signals from both the tags  722 - 1  through  722 -N and the handheld reader  760 , the strength of the signal received by the handheld reader may be very weak. If a compact antenna were used in the handheld reader, the attendant reduction in antenna gain could cause these signals to be sufficiently weak as to prevent accurate reception and correct decoding. Because of the higher antenna gain of a full-sized dipole antenna, the handheld reader is capable of reading RF signals that are much weaker than could be read by a handheld reader with a compact antenna. Thus, the useful range of the handheld reader is increased and this increases the utility of the handheld reader.