Patent Publication Number: US-7592963-B2

Title: Multi-band slot resonating ring antenna

Description:
FIELD 
   The present invention relates generally to antennas, and more specifically to slot resonating ring antennas. 
   BACKGROUND 
   Advances in circuit technologies and packaging technologies have allowed wireless communications devices to include more features while at the same time becoming smaller. For example, many modern, small form factor, wireless devices such as cellular telephones can transmit and receive in multiple frequency bands, whereas previous generation, larger, wireless devices may have only been able to transmit and receive in a single frequency band. Wireless devices capable of transmitting and receiving in multiple frequency bands (“multi-band”) can benefit from compact multi-band antenna designs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a circuit board cross-section; 
       FIG. 2  shows an exploded view of conductive layers of a multi-band slot resonating ring antenna; 
       FIG. 3  shows a plan view of each layer of the multi-band slot resonating ring antenna of  FIG. 2 ; 
       FIG. 4  shows an equivalent circuit for a multi-band slot resonating ring antenna; 
       FIG. 5  shows a frequency response of a slot resonating ring antenna according to various embodiments of the present invention; 
       FIGS. 6-8  show plan views of conductive layers for various multi-band slot resonating ring antenna embodiments; 
       FIG. 9  shows a circuit board cross-section; 
       FIG. 10  shows an exploded view of conductive layers of a multi-band slot resonating ring antenna; 
       FIG. 11  shows a plan view of each layer of the multi-band slot resonating ring antenna of  FIG. 10 ; 
       FIGS. 12-14  show plan views of conductive layers for various multi-band slot resonating ring antenna embodiments; 
       FIG. 15  shows a flowchart in accordance with various embodiments of the present invention; 
       FIG. 16  shows a block diagram of an electronic systems in accordance with various embodiments of the present invention; and 
       FIGS. 17-19  show various antenna/amplifier coupling schemes in accordance with various embodiments of the present invention. 
   

   DESCRIPTION OF EMBODIMENTS 
   In the following detailed description, reference is made to the accompanying drawings that show, 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 the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular, feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views. 
     FIG. 1  shows a circuit board cross section. Circuit board  100  includes three substantially parallel conductive layers  102 ,  104 , and  106 , separated by dielectric layers  103  and  105 . The conductive layers may be composed of any conductive material. For example, conductive layers  102 ,  104 , and  106  may include copper. Dielectric layers  103  and  105  may be any material suitable to electrically insulate conductive layers  102 ,  104 , and  106 . Circuit board  100  may be manufactured using any suitable circuit board manufacturing technique. 
   In some embodiments of the present invention, one or both of conductive layers  104  and  106  provide a reference voltage plane to circuits coupled to the circuit board. For example, conductive layer  106  may be a “ground” plane that provides a low impedance current return path to one or more power supplies. Further, conductive layer  106  may be a “voltage” plane that provides a low impedance current path from one or more power supplies. 
   As described further below, conductive layer  106  may have slots formed to provide a multi-band slot resonating ring antenna. In addition, conductive layer  102  may include one or more microstrip feed lines to emit signal energy to be coupled to the antenna. Further, conductive layer  104  may include one or more coupling apertures to allow the energy to pass from the feed line to the antenna. Although circuit board  100  is shown with three conductive layers, this is not a limitation of the present invention. For example, in some embodiments, circuit board  100  may include more than three conductive layers. 
     FIG. 2  shows an exploded view of the conductive layers of a multi-band slot resonating ring antenna formed in circuit board  100  ( FIG. 1 ). Conductive layer  106  is shown having concentric slots  204 ,  206 , and  208 . Concentric slots  204 ,  206 , and  208  are slot resonating rings (SRR) that form part of a compact multi-band slot resonating ring antenna (SRRA). Each of the rings is a radiation element in the antenna. In the example of  FIG. 2 , three rings are present, each having a different resonating frequency. This forms a tri-band antenna, although this is not a limitation of the present invention. The remainder of this description focuses on tri-band SSRA embodiments, however other embodiments exist that operate on fewer or more than three frequency bands. As shown in  FIG. 2 , the outer slot  204  corresponds to the central frequency of the lowest operating frequency band, the middle slot  206  corresponds to that of the middle frequency band, and the internal slot  208  corresponds to that of the highest frequency band. In this way, the radiation elements are sequentially and concentrically placed inside the other element(s) with larger physical size(s). With such configuration, the radiation volume of the proposed SRRA is reusable at all frequency bands, and the dimensions of the overall antenna are greatly reduced. In addition, since the slot resonating rings may be etched on the ground plane of the printed circuit board (PCB), the SRRA is easily integrated with the PCB. 
   Conductive layer  104  is shown having coupling apertures  214 ,  216 , and  218 . Conductive layer  102  is shown having feed line  220 . In some embodiments, feed line  220  is a signal trace that emits signal energy, and each of the slot resonating rings  204 ,  206 , and  208  is electromagnetically coupled to feed line  220  through the separate apertures  214 ,  216 , and  218 . In other embodiments, feed line  220  is a signal trace that receives signal energy from the slots through the apertures. As shown in  FIG. 2 , feed line  220  includes matching circuit  222  to increase the coupling and associated power transfer. 
   In some embodiments, the coupling apertures are aligned with an associated slot. For example, aperture  214  may be aligned with slot  204 ; aperture  216  may be aligned with slot  206 , and aperture  218  may be aligned with slot  208 . As shown in  FIG. 2 , the concentric slots in conductive layer  106  are square-shaped. In other embodiments, the concentric slots are circles, and in other embodiments, the concentric slots are elliptical. The shape of the concentric slots is not a limitation of the present invention. 
     FIG. 3  shows a plan view of each layer of the multi-band slot resonating ring antenna of  FIG. 2 . Layer  106  shows the concentric slots  204 ,  206 , and  208 ; layer  104  shows coupling apertures  214 ,  216 , and  218 ; and layer  102  shows feed line  220  with matching circuit  222 . As shown in  FIG. 3 , each of the apertures are placed beneath a corresponding one of the concentric slots to couple signal energy between the feed line and the slot resonating rings. 
     FIG. 4  shows an equivalent circuit for a multi-band slot resonating ring antenna. The top portion  402  models the feed line  220  ( FIG. 2 ). The operation of the coupling apertures  214 ,  216 , and  218  is modeled by coupling circuits  412 ,  422 , and  432 , respectively. The operation of concentric slots  204 ,  206 , and  208  is modeled by resonating circuits  410 ,  420 , and  430 , respectively. Each of the resonating circuits  410 ,  420 , and  430 , have a different resonating frequency corresponding to the resonant frequency of the associated concentric slot. 
     FIG. 5  shows a frequency response of a slot resonating ring antenna according to various embodiments of the present invention. Curves  510 ,  520 , and  530  represent power radiated from concentric slots  204 ,  206 , and  208 , respectively. The frequency axis is normalized to show that any SRRAs disclosed herein maybe formed to operate at any combination of frequencies. 
     FIG. 6  shows a plan view of conductive layers for a multi-band slot resonating ring antenna having additional apertures. Embodiments represented by  FIG. 6  include concentric slots  204 ,  206 , and  208  on a first conductive layer, feed line  220  on a second conductive layer, and apertures  214 ,  216 , and  218  on a third conductive layer, all described above.  FIG. 6  also includes additional apertures  614 ,  616 , and  618  oriented laterally from apertures  214 ,  216 , and  218 . 
   Apertures  214 ,  216 , and  218 , provide coupling between feed line  220  and the concentric slots as described above. Apertures  614 ,  616 , and  618  do not have a feed line oriented beneath them, and so do not provide coupling from a feed line to the concentric slots. Apertures without a corresponding feed line, or without a feed line that is driven by a signal, are referred to herein as “dummy apertures.” The polarization purity of the SRRA may be improved by the aperture coupling architecture of  FIG. 6 . In the dummy aperture feeding scheme, as illustrated in  FIG. 6 , two apertures are employed to feed each of the SRR elements for the same polarization operation, and only one coupling aperture is coupled with radio signal feed line. The extra dummy aperture for the same polarization operation is introduced to decrease the cross polarization level. Although a total of two coupling apertures are introduced for the same polarization operation, only one of them is actually excited by a radio signal through the aperture coupling and therefore the complexity of the feeding networks of the antenna is not increased. The rationale of the dummy aperture feeding technique is that the introduction of the dummy aperture could enhance the symmetry of electromagnetic field distribution inside the radiation element, and thereafter improve the polarization purity. 
     FIG. 7  shows a plan view of conductive layers for a multi-band slot resonating ring antenna having additional apertures and balanced feed lines. The circuits of  FIG. 7  include all of the elements of  FIG. 6 , including the additional apertures  614 ,  616 , and  618 .  FIG. 7  also includes an additional feed line  720  with matching circuit  722 . In the balanced feeding scheme illustrated in  FIG. 7 , the signals driving the two feed lines  220 ,  720 , may be out of phase with each other and may be directly connected to the differential pins of a radio frequency integrated circuit (RFIC) without using the a balun. The balanced feeding scheme of  FIG. 7  increases polarization purity. 
   In some embodiments, two microstrip feed lines are included as shown in  FIG. 7 , but only one is driven with a signal. For example, in some embodiments, feed line  720  may be included, but not coupled to a signal path. 
     FIG. 8  shows a plan view of conductive layers for a multi-band slot resonating ring antenna having dual polarization with dummy apertures. Dual polarization may be implemented for polarization diversity applications. As shown in  FIG. 8 , feed lines  220  and  820  are oriented as substantially 90 degrees to another. Signals feeding feed line  220  are transmitted with a vertical polarization, and signals feeding feed line  820  are transmitted with a horizontal polarization. Further, four sets of coupling apertures are shown in  FIG. 8 , two sets of coupling apertures are oriented between the feed lines and concentric slots, and two sets of apertures are oriented as dummy apertures.  FIG. 8  presents the architecture of a compact slot resonating ring antenna with aperture coupling and dummy aperture for multi-band and dual polarization operation. 
     FIG. 9  shows a circuit board cross section. Circuit board  900  includes conductive layers  902  and  106 , and also includes dielectric  905  separating the conductive layers. Conductive layer  106  includes concentric slots as described above. Conductive layer  902  forms a plane, and may be used as a voltage or ground plane as described above. Circuit board  900  also includes probes  914 ,  916 , and  918 . Probes are insulated from conductive layer  902 , and are oriented beneath each of the concentric slots. 
   In operation, each of probes  914 ,  916 , and  918  are driven with electrical signals, and the probes emit signal energy to be coupled with the concentric slots. In some embodiments, one or more signal traces exists between conductive layers  902  and  106  to provide electrical signal(s) to the probes. In other embodiments probes  914 ,  916 , and  918  are fed from below conductive layer  902 . The probes may be fed separately, or in common. 
     FIG. 10  shows an exploded view of the conductive layers of a multi-band slot resonating ring antenna formed in circuit board  900  ( FIG. 9 ). Conductive layer  106  is shown having concentric slots  204 ,  206 , and  208 , and is described with reference to previous figures. Conductive layer  902  is shown having probes  914 ,  916 , and  918  with major axes substantially perpendicular to conductive layer  902 . In some embodiments, the probes are aligned with an associated slot. For example, probe  914  may be aligned with slot  204 ; probe  916  may be aligned with slot  206 , and probe  918  may be aligned with slot  208 . In the probe feeding scheme, the impedance matching is realized by the appropriate probe height to increase the coupling and associated power transfer. 
     FIG. 11  shows a plan view of each layer of the multi-band slot resonating ring antenna of  FIG. 10 . Probes  914 ,  916 , and  918  can be seen insulated from conductive layer  902 . The probes are oriented beneath the corresponding concentric slot. 
     FIGS. 12-14  show plan views of conductive layers and feeding probes for various multi-band slot resonating ring antenna embodiments.  FIG. 12  shows two sets of feeding probes oriented substantially 180 degrees from each other. In some embodiments, one set of probes is driven, and the second set of probes are dummy probes. Dummy feeding probes may enhance the symmetry of the electromagnetic field distribution in the radiating elements, and improve polarization purity. In the dummy probe feeding scheme, each of the slot resonating rings is fed by two symmetrical probes—where only one probe is physically connected to the radio signal and the dummy probe is not connected to the radio signal. In other embodiments, both sets of probes are driven, and the SRRA is a “multiple feed line” antenna. 
     FIG. 13  shows two sets of feeding probes oriented substantially 90 degrees from each other. In some embodiments, both sets of probes are driven to provide dual polarization.  FIG. 14  shows four sets of feeding probes. Any combination of feeding probes may be driven with signals. For example, in some embodiments, the probes on the left and top may be driven for dual polarization, while the probes on the right and bottom may be dummy probes. In other embodiments, the probes on the left and right may be driven with one set of signals, while the probes on the top and bottom may be driven with a set of out of phase signals for polarization diversity. This balanced feeding scheme and the associated isolation among the feeding probes may result in reducing the cost of the overall wireless devices by eliminating or relaxing the specifications of key components of radio front ends, including switches, diplexers, baluns, and band pass filters. 
     FIG. 15  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  1500  may be used by a wireless device or a slot resonating ring antenna to couple signal energy. Method  1500  is not limited by the particular type of apparatus, or system performing the method. The various actions in method  1500  may be performed in the order presented, or may be performed in a different order. Further, in some embodiments, some actions listed in  FIG. 15  are omitted from method  1500 . 
   Method  1500  is shown beginning at block  1510  in which signal energy is emitted from a microstrip trace on a conductive plane. This may correspond to feed line  220  ( FIG. 2 ) emitting signal energy. At  1520 , the signal energy is passed through one of a plurality of apertures in a different conductive plane. This may correspond to signal energy passing through any of the apertures shown in the various figures. For example, signal energy may pass through any of the apertures shown in  FIGS. 2 ,  3 ,  6 ,  7 , or  8 . In some embodiments, signal energy is passed through a first set of apertures to provide a signal at a first polarization, and signal energy is passed through a second set of apertures oriented substantially 90 degrees from the first set of apertures to provide a signal at a second polarization. 
   At  1530 , the signal energy is coupled to one of a plurality of concentric slots in another conductive plane. In various embodiments of the present invention, this corresponds to coupling signal energy to concentric slots  214 ,  216 , and  218  in conductive plane  106 . 
     FIG. 16  shows a system diagram in accordance with various embodiments of the present invention. Electronic system  1600  includes antenna  1654 , physical layer (PHY)  1640 , media access control (MAC) layer  1630 , processor  1610 , and memory  1620 . In operation, system  1600  sends and receives signals using antenna  1654 , and the signals are processed by the various elements shown in  FIG. 16 . 
   Antenna  1654  may be any of the slot resonating ring antenna embodiments described herein. For example, antenna  1654  may include coupling apertures or feed probes. Further, antenna  1654  may include dummy apertures or dummy feed probes. Still further, antenna  1654  may include a single feed line or multiple feed lines. In addition, antenna  1654  may have any polarization, including dual polarization. 
   Physical layer (PHY)  1640  is coupled to antenna  1654  to interact with other wireless devices. PHY  1640  may include circuitry to support the transmission and reception of radio frequency (RF) signals. For example, as shown in  FIG. 16 , PHY  1640  includes multi-band radio, frequency (RF) subsystem  1646  and baseband circuits  1642 . In some embodiments, RF circuits  1646  include additional functional blocks to perform analog-to-digital conversion, digital-to-analog conversion, filtering, frequency conversion or the like. 
   Multi-band RF subsystem  1646  receives signals from antenna  1654  and performs additional processing. For example, in some embodiments, multi-band RF subsystem  1646  performs low noise amplification (LNA), frequency down-conversion, demodulation, or other functions. Further, in some embodiments, multi-band RF subsystem  1646  also includes a transmitter, and performs modulation, filtering, frequency up-conversion, power amplification, or the like. Examples of multi-band RF subsystem configurations are described with reference to  FIGS. 17-19 , below. 
   Baseband circuit  1642  may be any type of circuit to provide digital baseband processing in a communications system. In some embodiments, baseband circuit  1642  includes a processor such as a digital signal processor (DSP), and in other embodiments, baseband circuit  1642  is implemented as a system on a chip (SOC) that includes many functional blocks. 
   PHY  1640  may be adapted to transmit/receive and modulate/demodulate signals of various formats and at various frequencies. For example, PHY  1640  may be adapted to receive ultra-wideband (UWB) signals, time domain multiple access (TDMA) signals, code domain multiple access (CDMA) signals, global system for mobile communications (GSM) signals, orthogonal frequency division multiplexing (OFDM) signals, multiple-input-multiple-output (MIMO) signals, spatial-division multiple access (SDMA) signals, or any other type of communications signals. The various embodiments of the present invention are not limited in this regard. 
   Media access control (MAC) layer  1630  may be any suitable media access control layer implementation. For example, MAC  1630  may be implemented in software, or hardware or any combination thereof. In some embodiments, a portion of MAC  1630  may be implemented in hardware, and a portion may be implemented in software that is executed by processor  1610 . Further, MAC  1630  may include a processor separate from processor  1610 . 
   Processor  1610  may be any type of processor capable of communicating with memory  1620 , MAC  1630 , and other functional blocks (not shown). For example, processor  1610  may be a microprocessor, digital signal processor (DSP), microcontroller, or the like. 
   Memory  1620  represents an article that includes a machine readable medium. For example, memory  1620  represents a random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), read only memory (ROM), flash memory, or any other type of article that includes a medium readable by processor  1610 . Memory  1620  may store instructions for performing software driven tasks. Memory  1620  may also store data associated with the operation of system  1600 . 
   Example systems represented by  FIG. 16  include cellular phones, personal digital assistants, wireless local area network interfaces, wireless wide area network stations and subscriber units, and the like. For example, system  1600  may be a multi-band multi-standard mobile wireless devices using multiple antennas: one for cellular application, one for GPS application, and one for wireless LAN and/or Bluetooth application. Further, in some embodiments, additional antennas are utilized for mobile TV operation (e.g., DVB-H, T-DMB, ISDB) and/or wide wireless area network (WWAN) operation (e.g., WiMAX). The multi-band SRRA embodiments may be used to replace multiple antennas with a single, highly integrated and compact antenna design. Many other systems uses for multi-band slot resonating ring antennas exist. For example, antenna  1654  may be used in any system without a processor. 
     FIGS. 17-19  show various antenna/amplifier coupling schemes in accordance with various embodiments of the present invention. The antennas of  FIGS. 17-19  may be implemented as any of the antenna embodiments disclosed herein. 
     FIG. 17  shows antenna  1710 , TDD switch or FDD duplexer  1720 , multi-band power amplifier  1730 , and multi-band low noise amplifier  1740 . Antenna  1710  has a single feed line that is switched between transmit and receive operations. Further, the multi-band amplifiers are frequency multiplexed between the various operating frequencies supported by the antenna. 
     FIG. 18  includes antenna  1710 , TDD switch  1820 , three single band power amplifiers in parallel, and three low noise amplifiers in parallel. In operation, the coupling scheme of  FIG. 18  provides for simultaneous multi-band operation for either transmit or receive operations. 
     FIG. 19  shows a single antenna with multiple feed lines, with each feed line coupled to a TDD switch or FDD duplexer. Each TDD switch or FDD duplexer is coupled to a single-band power amplifier for transmission, and a single-band low noise amplifier for reception. 
   Although the present invention has been described in conjunction with certain embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the invention and the appended claims.