Patent Grant
8618998
This invention is related to antennas, and more particularly to compact size antennas with linear dimensions less than a quarter of a wavelength, radiated in the free space, providing the circular polarization of radiation within a wide range of frequencies with good polarization quality.
New applications of antennas for use in Radio Frequency Identification (RFID) devices are imposing difficult and controversial requirements on antenna specifications.
Antennas used in passive Radio Frequency Identification Systems deliver enough energy to the passive tag in a certain frequency band to power the tag, to transmit the required commands from the interrogator to the tag, and to receive the response from the tag in the form of a backscattered wave. In the case of passive tags, there is no other method of energy delivery beyond the antenna.
Typical operational frequencies include 433-435 MHz, 865-870 MHz, 902-928 MHz, 952-955 MHz, 2400-2500 MHz, 5700-5900 MHz and the level of the radiated energy is between 0.01 Watt EIRP and 4.0 Watt EIRP, and are defined and limited by the government regulations for RFID applications.
One feature of the passive RFID system, which distinguishes it from the other wireless communication systems, is that the transceiver transmits energy and information and receives backscattered signals from the tags at the same time and on the same frequency.
The transceiver transmits the signal with the power level Ptransmit to the antenna 1. Most of the transmitted energy will be radiated from the antenna into the space. A small portion of the transmitted energy will be reflected back from the not perfectly matched input port 10 of antenna 1 to the transceiver 2. The amount of this reflected energy is defined as return loss, or voltage standing wave ratio (VSWR), of the antenna.
Conventional wireless communication systems, in which the transmitted signal and the received signal are separated in time and/or by the frequency of the carrier, may employ antennas with VSWR in the range of about 1.5 to about 2.0, because more than 90% of transceiver power will be accepted by the antenna.
For RFID systems, such a value of VSWR may be too high, as the part of the noisy transmitted signal is coming back to the sensitive receiver. This will degrade the performance of an RFID system, where a noise floor is defined not by the noise figure of the receiver low noise amplifier (LNA) or the mixer, but by the portion of the signal from the transmitter that is “leaked” into the receiver.
Antennas preferably have a VSWR of less than about 1.20 for RFID applications. For instance, the reduction of antenna VSWR from 2.0 to 1.2 may increase the signal to noise ratio in the receiver by 11.3 dB. This increase in the signal to noise ratio may significantly reduce the errors of decoding of the signals coming from the tags and increase the speed of interrogation.
The portion of the power from the transmitter, which is accepted by the antenna, may be radiated into space with some correction in regard to the efficiency of the antenna. Radiated energy will be distributed in the volume of the space according to the radiation pattern of the antenna.
The interrogated tags 4, 5, 6 are usually positioned randomly in a volume of space. The maximum interrogation distance from the antenna to the tag is related to the minimum power that is needed to turn on or activate the integrated circuit of the tag, by the maximum power generated in the transceiver 2 of the RFID interrogator, and by the maximum realized gain of the antenna 1 and the radiation pattern of the antenna 1.
The maximum interrogation distance in free space is well defined, and is further described in “Friis Transmission Equation” (J. D. Kraus, Antennas, 2d Ed., McGraw-Hill, 1988, pp. 48-49). The radiation pattern of the antenna defines the maximum interrogation distances at angles other than at the boresight direction Z. Boresight is the optical axis of a directional antenna.
Traditionally the width of the radiation pattern is defined by the level where the gain of the antenna falls by 3 dB relative to the maximum gain. For a RFID system, such a definition is too coarse. With the 3 dB gain variation, the maximum interrogation distance will vary more than about 30%, estimated for free space with the “Friis Transmission Equation.” A more practical definition for RFID systems is that the maximum distance variation is less than 10%. This may be translated in the antenna gain variation as less than 1 dB. In
Most of the tags employed in RFID systems are electrical dipoles connected to the passive RFID integrated circuit. Such tags are sensitive to the polarization of the wave of radiated energy. If the polarization of the radiated wave will be linear the maximum interrogation distance will depend on the angle Φ between polarization of the radiated wave and the tag position. This maximum distance will vary from 0 to a maximum with Φ variations from 90° to 0°. That is why most of the typical RFID systems employ circular polarized antennas. To reduce the performance degradation of RFID systems, the antenna has to provide the variation of maximum interrogation distance of less than 10% for any angle Φ for a position of the tag relative to the antenna.
In terms of parameters of the antenna, the axial ratio of the antenna has to be less than 1 dB within the interrogation angle +/−θ from boresight axis Z.
Government regulations allow interrogation on the particular frequency or channel during a short period of time only. After that, the interrogator changes the frequency of the carrier or interrogation channel within the defined Frequency Band. That means that the antenna for RFID systems may provide radiation frequency bandwidth, within which the variation of the maximum interrogation distance is less than about 10%. Or, the radiation frequency bandwidth of the antenna may be defined as the antenna gain level at a point where it falls off by 1 dB relative to the maximum gain.
Another area of consideration of the antenna specification is if the antenna is portable and/or wearable. This imposes additional desirable characteristics, such as the minimum weight and the minimum size and/or volume of the antenna. Very often, the antenna is designed to fit into an existing portable device, with a position and a space to install the antenna defined before the antenna is designed.
Portable and/or wearable applications assume that the body of the user is close to the antenna and within a relative strong electromagnetic field. That means that the user will absorb some energy radiated from the antenna, and will provide some influence on the antenna parameters, such as VSWR, the Maximum Realized Gain and the Radiation Pattern. This point of view increases the value of the front to back ratio of radiation from the antenna.
At the present moment, many circular polarized antennas have been developed. But not one of them satisfies the characteristics and parameters presented above.
Full size circular polarized patch antennas with dimensions from (λ×λ×λ/16) to (λ/2×λ/2×λ/32), where λ is the free space wavelength of a radio frequency, provide relatively high realized gains of up to 8 to 9 dBic or 5 to 6 dBi. The size is defined by the conductive ground plane size and it is relative to the free space wavelength λ of radiated signal at the central frequency. The frequency bandwidth of such antennas is +/−3% to +/−3.5% at the −1 dB level from the maximum realized radiation gain. The front to back ratio is defined by the size of the ground plane and it is within from about 12 dB to about 18 dB, typically.
Polarization quality and/or axial ratio may be within about 1 dB, if the feeding circuit of the antenna employs a good quality 90° hybrid power divider. One drawback of these antennas is the size and the weight of the conductive ground plane. It is too large and heavy for most portable applications.
Small patch antennas with the small ground plane which employ a ceramic substrate with a high dielectric constant may be designed to fit into a volume defined by λ/5×λ/5×λ/32, or less. However, this type of antenna may be quite heavy, because of the high density of the ceramic substrate and it may possess a very narrow frequency bandwidth of about +/−0.6% or less from the central frequency at the level −1 dB from the maximum radiation gain. The front to back ratio may also be very poor, about 1 dB to about 2 dB only. Polarization quality and/or axial ratio also depends on surrounding objects and will be within from about 2 db to about 4 dB. The VSWR is typically above about 1.3 to about 1.5 within the frequency band.
Helical, helix and/or quadrifilar helix antennas do not use a conductive ground plane and because of this, the footprint may be much smaller than the footprint of patch antennas. A typical size of a quadrifilar helix is from λ/6×λ/6×λ/6 to λ5×/5×λ/2 or thicker. A thicker antenna provides a wider frequency bandwidth. An antenna with longer radiating elements wound around a cylinder provides a higher gain, but a narrower radiation frequency bandwidth.
The frequency bandwidth of such antennas is about +/−1.5% to about +/−2.5% at the −1 dB level from the maximum realized radiation gain. The front to back ratio is within from about 10 dB to about 16 dB typically. Polarization quality is very good and the axial ratio may be less than about 1 dB, if the feeding circuit of the antenna employs a good quality quadrature (0°, −90°, −180°, −270°) hybrid power divider.
One of the disadvantages of using a helical antenna is the length and/or thickness of the structure. The structure does not fit into small portable designs. Squeezing the thickness less than λ/6 by reducing the pitch will dramatically reduce the frequency bandwidth. The size may be reduced by employing the central core with a high dielectric material. However, using a high dielectric material increases the weight of antenna and reduces the radiation frequency bandwidth to about 1% or less and reduces the realized gain at the same time. See GeoHelix P2 Product Specification V6 Issue 11-06 Sarantel Ltd. (HQ) Unit 2, Wendel Point Ryle Drive, Park Farm South Wellingborough, NN8 6BA United Kingdom. See also U.S. Pat. No. 7,372,427 “Dielectrically-Loaded Antenna” & U.S. Pat. No. 6,886,237 “Method of Producing an Antenna,” which are hereby incorporated by reference.
Another disadvantage of using a helical antenna is the cylindrical shape. The radiation elements wrap around the supporting cylinder. If the cylinder is not perfectly shaped, such as being elliptical, it distorts the radiation pattern, increases the axial ratio of radiated field and the impedances of the radiation elements will be not equal, which will increase the VSWR at the input port. The pitch of the radiating elements or distance between them also impacts the operation as a little inaccuracy or instability can affect the operation. Sometimes, this inaccuracy can distort the pattern, can disbalance the impedances of the radiating elements, and can increase the VSWR. To produce the antenna with the radiating elements accurately wrapped around the cylinder, special technology is used other than the standard flat PCB manufacturing process adopted for patch antenna production. See U.S. Pat. No. 6,886,237 “Method of Producing an Antenna,” which is hereby incorporated by reference. This increases the cost of producing helical antennas relative to producing patch antennas.
Another type of circular polarized antenna is a crossed dipole antenna or turnstile antennas, as shown in
The radiation pattern of the right hand circular polarized (RHCP) component is presented in
The θ component of the electromagnetic field represents the component which provides the coupling with the linear polarized antenna of the RFID tag.
It is advantageous to concentrate the propagation in one direction only. One solution to accomplish this is to position the crossed dipoles above the conductive plane or inside of the conductive cup. See U.S. Pat. No. 3,740,754 “Broadband Cup-Dipole and Cup-Turnstile Antennas,” which is hereby incorporated by reference. But this solution increases the size of the antenna further and makes it less capable of being used in portable applications.
To reduce the size, some antennas proposed to bend the dipoles. See U.S. Pat. No. 6,211,840 “Crossed-Drooping Bent Dipole Antenna” & U.S. Pat. No. 4,686,536 “Crossed-Drooping Dipole Antenna,” which are hereby incorporated by reference. Such antennas have a smaller footprint, but the ground plane is still large and the overall structure is generally too thick for portable applications.
The way to reduce the footprint of the antenna further is to completely fold the dipoles 7 of turnstile antenna and position the dipoles 7 above the small size ground plane. The antenna appears as four monopoles above the small ground plane. See Lap K. Yeung et al. “Mode-Based Beam Forming Arrays for Miniaturized Platforms” IEEE Transactions on Microwave Theory and Techniques, January 2009, volume 57, pp. 45-52. This type of antenna system is presented in
The radiating elements 7 are the thin strips of conductive material. These strips are positioned on the surface of thin dielectric substrates 9. The purpose of the dielectric substrate is to provide stability of radiating elements 7 in space. The combination of radiating elements and dielectric substrates may be produced through standard PCB manufacturing processes. The substrates 9 are assembled as a box, which provides a rigid, stable, and low weight structure. One end of the radiating elements is connected to the feeding circuit 8. The feeding circuit 8 divides the input signal into four signals with equal amplitude and phases (0°, −90°, −180°, −270°).
Such an antenna system poses the radiating patterns presented in
The θ component has an almost omni-directional radiation pattern. For some applications it may be useful, but from a RFID point of view, it is a waste of energy, with loss of the antenna gain and reduced interrogation range.
According to one embodiment, an antenna comprises a plurality of elongated side radiating elements having longitudinal axes oriented at angles of between about 10° and about 80° from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a cavity positioned between the side radiating elements defined by at least one non-radio frequency-transparent sidewall.
In another embodiment, a system comprises a plurality of elongated side radiating elements each lying along a unique side plane and having longitudinal axes oriented at angles of between about 10° and about 80° from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a cavity being positioned between the side radiating elements defined by at least one non-radio frequency-transparent sidewall, wherein the at least one sidewall has sides each lying along a plane about parallel to the unique side plane.
Other systems and antennas are described according to more embodiments.
For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings.
Various embodiments of the present invention are described in further detail below with reference to the figures, in which like items are numbered the same in the several figures.
The following description is the best mode presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.
It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified.
According to one general embodiment, an antenna includes a plurality of elongated side radiating elements having longitudinal axes oriented at angles of between about 10 degrees and about 80 degrees from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a cavity defined by at least one sidewall, the cavity being positioned between the side radiating elements, and the sidewall being non-radio frequency-transparent.
In another general embodiment, a system comprises a plurality of elongated side radiating elements each lying along a unique side plane and having longitudinal axes oriented at angles of between about 10 degrees and about 80 degrees from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a cavity defined by at least one sidewall, the cavity being positioned between the side radiating elements, and the sidewall being non-radio frequency-transparent, wherein the at least one sidewall has sides each lying along a plane about parallel to the unique side plane.
The side radiating elements 7 may be identical, nearly identical, or different. Also, there may be embodiments where there are more or less than four side radiating elements. The bottom part of each radiating element 7 begins from the feeding circuit plane XY and extends into the positive boresight Z-direction to its top end.
The length of each radiating element 7 may be about λ/4, where λ is the free space wavelength of radiation at a middle frequency of an operational frequency band of the antenna, and may vary within about +/−10%.
In some embodiments, the side radiating elements 7 each lie along a unique side plane. For example, each of the four side radiating elements 7 are shifted from the boresight axis Z along the feeding circuit plane XY from the central point of this plane in the quadrate directions 45°, 135°, 225°, 315° relative to the X axis. However, the quadrate directions are not limited by specified values and may be, for example, 0°, 90°, 180°, 270°; 30°, 120°, 210°, 300°, etc. The value of the shift from the central point of the XY plane to the bottom part of radiating elements 7 may be about λ/2.7 and may vary within about +/−30%. In some further embodiments, supporting substrates may be coupled to the side radiating elements 7, each of the substrates lying in the side plane of the associated side radiating element 7.
To compensate the cross polarized component of radiation and to concentrate most of the radiated energy into the positive boresight direction Z, each side radiating element 7 may be tilted relative to a line perpendicular to the feeding circuit plane XY in a direction opposite to a rotation of the electrical component of a field radiated by the antenna. This would be in a counter clockwise direction creating a Right Hand Circular Polarization (RHCP) if the viewer is looking into the positive boresight direction (direction of propagation) Z. The angle of the tilt in
The feeding circuit 8 with the four output ports Xp, Yp, Xn, Vn, which are electrically connected to the bottom part of radiating elements 7 in the XY plane, provides the four signals, which are equal by amplitude and have relative phases 0°, −90°, −180°, −270° distributed between the side radiating elements 7 in the clockwise direction.
In another possible embodiment of a Left Hand Circular Polarized (LHCP) antenna, the side radiating elements 7 may be tilted in the clockwise direction and the feeding circuit 8 may provide four signals, which are equal by amplitude and have relative phases 0°, −90°, −180°, −270° distributed between the side radiating elements 7 in the counter clockwise direction.
The feeding circuit 8 is the power divider/combiner with one input port 10 and four output ports Xp, Yp, Xn, Yn. The main function of this feeding circuit 8 is to accept the input power and distribute it between the four output ports with equal amplitudes and relative phases in quadrate 0°, −90°, −180°, −270° within the operational frequency band. Other characteristics of the feeding circuit 8, such as low VSWR, isolation between ports, and low ripple of transfer functions and low phase variation within the operational frequency band are useful, but should not limit the embodiment in any way.
In a receiving antenna, when energy flows in the opposite direction, the feeding circuit 8 may be considered as a power combiner from ports Xp, Yp, Xn, Yn into port 10.
The feeding circuit 8 may be the combination of transmission lines with the different lengths as used in the prior art. See U.S. Pat. No. 2,412,090 “Turnstile Antenna,” U.S. Pat. No. 2,511,899 “Antenna System,” & U.S. Pat. No. 3,906,509 “Circularly Polarized Helix and Spiral Antennas,” which are hereby incorporated by reference. Or, the feeding circuit 8 may be the combination of a balun and/or a hybrid divider or hybrid coupler circuit.
Now referring to
The four outputs of the 180° hybrid circuits 15 are connected to the inputs of the impedance matching circuits 16 through the four transmission lines 13. The outputs of the matching circuits 16 are output ports Xp, Yp, Xn, Yn.
The 90° and 180° hybrid circuits 14, 15 may be realized with a transmission line technique. See U.S. Pat. No. 3,484,724 “Transmission Line Quadrature Coupler” & U.S. Pat. No. 4,578,652 “Broadband Four-Port TEM Mode 180° Printed Circuit Microwave Hybrid,” which are hereby incorporated by reference. See also Kai Chang and Lung-Hwa Hsieh “Microwave Ring Circuit and Related Structures” John Wiley & Sons 2004, pp. 197-240.
For smaller sizes, the 90° and 180° hybrid circuits 14, 15 may be produced with a lumped components technique. See U.S. Pat. No. 4,851,795 “Miniature Wide-Band Microwave Power Divider,” which is hereby incorporated by reference. See also Fusco, V. F. and S. B. D. O'Caireallain “Lumped Element Hybrid Networks for GaAs MMICs” Microwave Optical Tech. Lett., Vol. 2, January 1989 pp. 19-23; Parisi, S. J. “180° lumped element hybrid” Microwave Symposium Digest, 1989., IEEE MTT-S International Volume, Issue, 13-15 Jun. 1989 Page(s): 1243-1246 vol. 3 Digital Object Identifier 10.1109/MWSYM. 1989.38951.
In addition, a combination of techniques may be used, such as a combination of transmission lines and lumped components techniques.
The length of the transmission lines 13 may be defined by the position of the radiating elements 7 and by the size of the hybrid circuits. Characteristic impedance of these lines 13 may be chosen according to the impedance for the hybrid circuits 14, 15. The function of the matching circuits 16 is to convert the complex impedance of the radiating elements 7 close to the characteristic impedance of the transmission lines 13 within the operational frequency band. These matching circuits may be produced with distributed and/or lumped components. See Wilfred N. Caron “Antenna Impedance Matching” The American Radio Relay League, 1989, pp. 4.1-4.11, 5.1-5.17. Any person of ordinary skill in the relevant art of RF and microwave circuitry may design the feeding circuit 8. Design techniques are well established and published in multiple sources over the past few decades.
Any person of ordinary skill in the relevant art of RF and microwave circuitry may design the feeding circuit 8. Design techniques are well established and published in multiple sources over the past few decades.
The side radiating elements 7 may be the conductive rods or wires with round or rectangular profile or the flat strips of conductive material positioned on the surface of the four non conductive substrates 9. The shape of the radiating element 7 is not limited by a straight line. It may be curved in the path from the feeding circuit 8 to its end. Width of the radiating elements 7 may be within about λ/400 to about λ/20. Substrates 9 are positioned to form the rigid box structure. Substrates 9 are generally thin, with a thickness from about λ/2000 to about λ/100, and are generally comprised of a rigid, low weight dielectric material with a relatively low effective dielectric constant (Dk) within a range of about 1.05 to about 7. The height H1 and the width W1 of the substrates 9 are defined by the length of the radiating elements 7 and by its tilt angle relative to the XY plane. The distance A1 between substrates 9 is defined by the shift of the radiating elements 7 from the boresight axis Z along the feeding circuit plane XY from the central point of this plane.
Function of the substrates 9 is to provide the support for the radiating elements 7 and the mechanical stability of the antenna. The length of the side radiating element 7 is adjusted to maintain the maximum radiation in the middle of the required operational frequency band. The flat radiating elements 7 positioned on the flat dielectric substrates 9 may be produced at low costs by using standard PCB manufacturing processes and with standard PCB materials, such as copper laminated FR4, G10, Rogers and/or other dielectric substrate materials developed for the electronics industry.
The interconnection between the feeding circuit 8 and radiating elements 7 may be accomplished as shown in
Another possible interconnection is show in
When these patterns are compared to patterns from the prior art antennas, presented in
The tilt of the side radiating elements 7 repositions the near electric and near magnetic fields and concentrates the far electromagnetic radiation field in the preferable direction.
Shown in
To achieve these goals, each side radiating element 7 is divided into two pieces, at a point where the near magnetic field falls about 60% to about 80% from the maximum, preferably between about 60% and about 70% from the maximum, and the near electric field reaches about 20% to about 40% from its maximum, preferably between about 20% and about 30% from its maximum.
The pieces of the side radiating elements 7 with the maximum near magnetic field are positioned the same way as the side radiating elements 7 in the embodiment shown in
The side radiating elements 7 may be conductive rods or wires with round or rectangular profiles or may be flat strips of conductive material positioned on the surface of the four non conductive substrates 9. Width of the side radiating elements 7 may be from about λ/400 to about λ/20. The length of the side radiating elements 7 may be about λ/5.7, +/−10%. The side substrates 9 are positioned to form the rigid box structure. The substrates are thin with thickness from about λ/2000 to about λ/100, and are comprised of a rigid, low weight dielectric material with a relatively low effective dielectric constant (Dk) of about 1.05 to about 7. The height H2 and the width of the side substrates 9 are defined by the length of the side radiating elements 7 and by its tilt angle relative to the XY plane and by the shift of radiating elements 7 from the boresight axis Z along the feeding circuit plane XY from the central point of this plane. The distance A2 between side substrates 9 is defined by the width of the side substrates 9. The shapes of side radiating element 7 and side substrate 9 are shown in
The flat radiating elements 7 positioned on the flat dielectric substrates 9 may be produced at low costs by using standard PCB manufacturing processes.
The feeding circuit 8 is similar to that described in the previous embodiment. Components of the feeding circuit 8 in one possible embodiment are shown in FIG. 9—matching circuit 16, transmission lines 13, 180° hybrid circuits 15 on one or the top side of PCB and in FIG. 12—90° hybrid circuits 14, 180° hybrid circuits 15, Port X 11, Port Y 12 and input Port 10 on the opposite or bottom side of PCB.
The interconnection between the feeding circuit 8 and side radiating elements 7 may be accomplished as shown in
Now referring to
The top radiating elements 17 with the maximum near electric field are tilted more in the direction to the feeding circuit plane XY and are rotated toward the boresight axis Z. This redistributes the near electric field relative to the near magnetic field and better concentrates the propagation in the positive boresight direction Z.
The top radiating elements 17 may be conductive rods and/or wires with a shape selected from a group consisting of straight, serpentine, rectangular, round (including oval), triangular, and combinations thereof.
In a more preferable embodiment, the top radiating elements 17 may be strips of conductive material positioned on the surface of a top nonconductive substrate 18. The shapes of the top radiating elements 17 and the substrate 18 are shown in
Width of the top radiating elements 17 may be from about λ/400 to about λ/20 and may vary along its length. The length of the top radiating elements 17 in some embodiments is about λ/2.7. This length may vary in dependence to the length of the side radiating elements 7 and may be adjusted to maintain the maximum radiation in the middle of the operational frequency band.
The interconnection between the top radiating elements 17 and side radiating elements 7 may be accomplished as shown in
The top substrates 18 are thin, with thickness from about λ/2000 to about λ/100, and are comprised of a rigid, low weight dielectric material with a relatively low effective dielectric constant (Dk) from about 1.05 to about 7. It may be the same substrate as is used for the side radiating elements 9, or may be a different substrate. The function of the top substrate 18 is to provide support for the top four additional radiating elements 17 and to increase the mechanical stability of the antenna.
In more embodiments, a width of each of the side radiating elements 7 in a direction perpendicular to the longitudinal axis thereof may be between about λ/400 and about λ/20, wherein the top radiating elements 17 are elongated, and a width of each of the top radiating elements 17 in a direction perpendicular to a longitudinal axis thereof is between about λ/400 and about λ/20. In some additional embodiments, the top radiating element 17 and the side radiating element 7 may have the same width.
In some embodiments, at least one of the side radiating elements 7 and the top radiating elements 17 are not coupled to a supporting substrate along an entire length thereof. For example, the top radiating element 17 may not have a substrate with which to support it, the substrate may have an exposed portion where the top radiating element 17 passes through, etc.
Still referring to
In more embodiments, the side radiating elements 7 may each have a protrusion extending at least partially through a supporting substrate of the top radiating elements 17, where the top radiating elements 17 are each coupled to the protrusion of the associated side radiating element 7. This connection may be similar or different from that shown in
In some further approaches, as shown in
By comparing these patterns with the patterns for the previous embodiment presented in
In addition, the axial ration, as shown in
According to another embodiment of an antenna, as shown in
The top radiating elements 17 with the maximum part of the near electric field are longer and are bended to fit on the surface of the top dielectric substrate 18.
According to another embodiment, as shown in
In another embodiment, presented in
The feeding circuit 8 has the output ports Xp, Yp, Xn, Yn as exposed conductive pads of a rectangular shape. The bottom part of the side radiating elements 7 end with exposed conductive pads of a rectangular shape also. Joints of the exposed pads of the feeding circuit 8 and of the corresponding side radiating elements 7 are electrically connected by solder material or conductive adhesive compound 22. An upscale view of one joint is shown in
To provide mechanical stability of the antenna structure, the substrate of the feeding circuit 8 has rectangular slots 29, which have a width that corresponds to the thickness of the side substrate 9. The positions of these slots 29 are illustrated in
The substrates 9 of the side radiating elements 7 have the protrusion 26 with the shape, size and position corresponding to the slots 29 in the substrate of the feeding circuit 8.
Each top radiating element 17 has an exposed conductive pad of a rectangular shape. There are rectangular slots 27, cut through the top radiating elements 17 and the top substrate 18. The width of these slots 27 corresponds to the total thickness of the side substrate 9 with the side radiating element 7 and the length of these slots 27 is shorter than the size of the conductive pads. The top part of the side radiating elements 7 end with the protrusion 23, with the shape, size and position corresponding to the slots 27 in the top radiating elements 17. This protruded part 23 of the side radiating element 7 has exposed conductive pads of a rectangular shape. Protruded part 23 of the side radiating element 7 and its substrate 9 pass through the slot 27 at the corresponding top radiating element 17. Joints of exposed pads of the top radiating elemental 7 and of the corresponding side radiating elements 7 are electrically connected by solder material or a conductive adhesive compound 24.
To provide mechanical stability of the antenna structure, the substrate 18 of the top radiating elements 17 has additional rectangular slots 28, which have a width that corresponds to the thickness of the side substrate 9. The substrates 9 of the side radiating elements 7 have the additional protrusion 25 with the shape, size and position corresponding to the slots 28 in the substrate 18 of the top radiating elements 17. The protrusion 25 of the side substrate 9 passes through the slot 28 in the substrate 18 of the top radiating elements 17. Other features of this embodiment may be the same or may be different than in previous embodiments.
Another embodiment of an antenna is presented in
In
In one embodiment, as shown in
According to another embodiment, as shown in
In
Now referring to
In some embodiments, a system may comprise a feeding circuit, a plurality of side radiating elements coupled to the feeding circuit, the side radiating elements having longitudinal axes including a median longitudinal axis for a side radiating element having a nonlinear profile oriented at angles of between about 10° and about 80° from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a plurality of top radiating elements electrically coupled to the side radiating elements, each of the top radiating elements having a different orientation than the associated side radiating element. These components of the system may be similar to those discussed in prior embodiments, such as the embodiment shown in
Now referring to
To prevent distortion of the RFID interrogation field and significant degradation of parameters of the antenna 1 employed within the RFID system 150, the distance X1 between the antenna 1 and the additional device 101 has to be more than ¼ of a wavelength radiated from the antenna 1. Any objects (conductive and nonconductive) in the strong Near Electric and Magnetic Fields of antenna 1 may degrade some or all of the parameters of the antenna 1 considered earlier, if the antenna 1 is not designed for such applications. The ¼ wavelength distance X1 increases the size and weight of the system 150. This is a factor to be considered when designing portable and/or hand held devices.
These additional devices 101 have become smaller and smaller over time, and presently appear in a size comparable to about the size of an antenna 1. These advancements in size reduction allow for the ability to position an additional device inside the antenna, rather than coupling the additional device external to the antenna, as shown in
The antennas disclosed herein above may be used in conjunction with an additional device. For example, one such antenna which can accept an additional device, according to one embodiment, is shown in
Analysis of the Near Electric and Magnetic Fields inside the antenna of
The strength of the Electric and Magnetic fields falls down at the middle area 301 of the antenna, but is still higher than at the distance ¼ wavelength on the side of the antenna. Any object, especially those with irregular, non-symmetrical shapes, inserted near the middle area 301 of the antenna will ordinarily have a significant impact on the parameters of the antenna.
The antenna may be designed as described above. According to some preferred approaches, a width of each of the side radiating elements 7 in a direction perpendicular to the longitudinal axis thereof may be between about λ/400 and about λ/20, where λ is a free space wavelength of radiation at a middle frequency of an operational frequency band of the antenna.
According to some embodiments, the side radiating elements 7 may each lie along a unique side plane. In addition, the at least one sidewall 302 may have sides each lying along a plane about parallel to the unique side plane. For example, as shown in
In more approaches, the side radiating elements 7 may be tilted, relative to the line perpendicular to the imaginary base plane (X-Y plane), towards the imaginary base plane (X-Y plane) in a direction opposite to a rotation of an electrical component of a field radiated by the antenna.
In some embodiments, the antenna may further comprise a plurality of top radiating elements 17 each electrically coupled to an associated one of the side radiating elements 7, each of the top radiating elements 17 extending in a direction that is not collinear with the longitudinal axis of the associated side radiating element 7. In addition, the at least one sidewall 302 may extend at least to an imaginary plane (which may be defined by top substrate 18) extending through the top radiating elements 17. In some further embodiments, the top and associated side radiating element together may form a radiating element, wherein a point of coupling of the top radiating element 17 and side radiating element 7 may be at a point along the radiating element where a near magnetic field of the radiating element is between about 60% and about 80% below a maximum near magnetic field of the radiating element. In some additional embodiments, the top radiating elements 17 may not extend over the cavity 301 defined by the at least one sidewall 302.
In some further embodiments, a width of each of the side radiating elements 7 in a direction perpendicular to the longitudinal axis thereof may be between about λ/400 and about λ/20, wherein the top radiating elements 17 may be elongated. In addition, a width of each of the top radiating elements 17 in a direction perpendicular to a longitudinal axis thereof may be between about λ/400 and about λ/20, where λ is a free space wavelength of radiation at a middle frequency of an operational frequency band of the antenna. In addition, in some approaches, the top and associated side radiating element together may form a radiating element, wherein a point of coupling of the top and side radiating elements is at a point along the radiating element where a near magnetic field of the radiating element is between about 40% and about 60% below a maximum near magnetic field of the radiating element.
In some other embodiments, a distance between the imaginary base plane (X-Y plane) and a plane extending through couplings of the side radiating elements 7 and the top radiating elements 17 may be between about λ/6 and about λ/32, where λ is a free space wavelength of radiation at a middle frequency of an operational frequency band of the antenna. In even more additional embodiments, the top and associated side radiating element together may form a radiating element, wherein a point of coupling of the top and side radiating elements is at a point along the radiating element where a near magnetic field of the radiating element is between about 20% and about 40% below a maximum near magnetic field of the radiating element.
According to some approaches, the at least one sidewall 302 may extend only partially along or not extend along a plane parallel to the imaginary base plane (e.g., the X-Y plane). For example, the sidewall 302 defining the cavity 301 may have one or more open ends.
The antenna may also include a ground plane 8. The at least one sidewall 302 may be electrically conductive and may be electrically coupled to the ground plane 8, e.g., via direct contact, leads coupling the parts, solder, etc., according to some approaches. Further, the at least one sidewall 302 may comprise multiple sidewalls electrically coupled together.
According to even more approaches, the antenna may further comprise a second antenna positioned in the cavity 301. Note that by “in the cavity” as used herein, what is meant is that at least a portion of the device is in the cavity 301, and some of the device may protrude from the cavity 301 defined by the at least one sidewall 302. In further approaches, the second antenna may be a patch antenna, a loop antenna, etc. See, e.g., the discussion of
The cavity 301 is formed by conductive walls 302 positioned on dielectric substrates 303 according to one embodiment. Conductive walls 302 are not electrically connected to each other, but are connected to the conductive ground plane 304 of the feeding circuit 8. Conductive joints 305 between the ground plane 304 and walls 302 may be comprised of any suitable material, such that a conductive joint may be formed.
Of course, any of the embodiments described above, such as the antenna described in
Table 1 displays results from a simulated comparison between several embodiments of an antenna with and without a cavity, such as cavity 301 shown in the several embodiments described above. The antennas have been simulated as being designed for a UHF frequency band of 900 MHz-933 MHz with a 2.4″×2.4″×1.0″ size. Table 1 illustrates how a cavity size affects the parameters of a simulated antenna for far field radiation. Table 2 illustrates the maximum near field strength inside the cavity of a simulated antenna. Power from the simulated transmitter is +30 dBm at the frequency of 915 MHz.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
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