Patent Application
20100231461
The present disclosure relates generally to radio frequency (RF) antennas, and more specifically to multi-band RF antennas.
The number of radios and supported frequency bands for wireless communication devices continues to increase as there are increasing demands for new features and higher data throughput. Some examples of new features include multiple voice/data communication links—GSM, CDMA, WCDMA, LTE, EVDO—each in multiple frequency bands (CDMA450, US cellular CDMA/GSM, US PCS CDMA/GSM/WCDMA/LTE/EVDO, IMT CDMA/WCDMA/LTE, GSM900, DCS), short range communication links (Bluetooth, UWB), broadcast media reception (MediaFLO, DVB-H), high speed internet access (UMB, HSPA, 802.11a/b/g/n, EVDO), and position location technologies (GPS, Galileo). With each of these new features in a wireless communication device, the number of radios and frequency bands is incrementally increased and the complexity and design challenges for a multi-band antenna supporting each frequency band as well as potentially multiple antennas (for receive and/or transmit diversity) may increase significantly.
One traditional solution for a multi-band antenna is to design a structure that resonates in multiple (a plurality of) frequency bands. Controlling the multi-band antenna input impedance as well as enhancing the antenna radiation efficiency (across a wide range of operative frequency bands) is restricted by the geometry of the multi-band antenna structure and the matching circuit between the multi-band antenna and the radio(s) within the wireless communication device. Often when this design approach is taken, the geometry of the antenna structure is very complex and the physical area/volume of the antenna increases.
With the limitations on designing multi-band antennas with high antenna radiation efficiency and associated matching circuits, another solution is utilizing multiple antenna elements to cover multiple operative frequency bands. In a particular application, a cellular phone with US cellular, US PCS, and GPS radios may utilize one antenna for each operative frequency band (each antenna operates in a single radio frequency band). The drawbacks to this approach are additional area/volume and the additional cost of multiple single-band antenna elements.
In certain applications of multi-band antennas, the multi-band antenna match is adjusted electronically (with a single-pole multi-throw switch) to select an optimal match for the multi-band antenna (with 50 ohms) at a particular operative frequency band; i.e., between US cellular, US PCS, and GPS is but one example. This multi-band antenna performance may degrade as more frequency bands are added, as the multi-band antenna structure is not changed for different operative frequency bands.
There is a need for a multi-band antenna with improved radiation efficiency across a broad range of operative frequencies for wireless communication devices without the size penalty of traditional designs.
To facilitate understanding, identical reference numerals have been used where possible to designate identical elements that are common to the figures, except that suffixes may be added, when appropriate, to differentiate such elements. The images in the drawings are simplified for illustrative purposes and are not necessarily depicted to scale.
The appended drawings illustrate exemplary configurations of the disclosure and, as such, should not be considered as limiting the scope of the disclosure that may admit to other equally effective configurations. Correspondingly, it has been contemplated that features of some configurations may be beneficially incorporated in other configurations without further recitation.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention can be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary embodiments of the invention. It will be apparent to those skilled in the art that the exemplary embodiments of the invention may be practiced without these specific details. In some instances, well known structures and devices are shown in block diagram form in order to avoid obscuring the novelty of the exemplary embodiments presented herein.
The device described therein may be used for various multi-band antenna designs including, but not limited to wireless communication devices for cellular, PCS, and IMT frequency bands and air-interfaces such as CDMA, TDMA, FDMA, OFDMA, and SC-FDMA. In addition to cellular, PCS or IMT network standards and frequency bands, this device may be used for local-area or personal-area network standards, WLAN, Bluetooth, & ultra-wideband (UWB).
Modern wireless communication devices require antennas to transmit and receive radio frequency signals for a variety of applications. In many designs, the wireless communication device antennas include one or more monopole elements placed above the wireless communication device ground plane. Monopole antenna elements provide sufficient antenna gain if the electrical length of the antenna structure resonates at the desired operating frequency. The wireless communication device and antennas may be incorporated in handheld devices (cellular phones for voice applications, portable video phones, smart phones, tracking GPS+WAN devices, and the like) and portable computing devices (laptops, notebooks, tablet personal computers, netbooks and the like).
Monopole antenna system 10 will have a directive gain of 3 dBi in the ideal case at the resonant frequency defined by the electrical length L of monopole antenna element 12. Monopole antenna 10 will also have a lower input resistance as measured between antenna port 14 and ground plane 22 (measured at RF port 20) than RF I/O source 24, resulting in overall lower antenna efficiency.
The input impedance of monopole antenna element 12 may be transformed to match RF I/O source 24 to improve antenna efficiency, as measured at antenna port 18, utilizing an inductor-capacitor matching network (LC 16). However, LC 16 will only provide an optimal impedance match at one operating radio frequency and LC 16 will introduce losses (in terms of insertion loss) associated with the quality (Q) of both inductor and capacitors in real circuits.
The electrical length can be realized with a wire length L. The wire length L is typically a quarter wavelength (or greater) of the operating frequency in free space depending on the ground plane dimensions of the wireless communication device. In one design example, if wire length L is equal to a quarter wavelength of the operating frequency, the input impedance of monopole antenna element 12 as measured at antenna port 18 will be approximately 50 ohms and is matched to RF I/O source 24.
Multi-band antenna 100 is formed on a flexible printed circuit board 104 which includes a modified monopole element 110a with indents 112a, 112b, 114a, and 114b to fold the modified monopole antenna element 110a with the correct dimensions for a specific wireless communication device application.
In one exemplary embodiment, the length L of modified monopole element 110a is 25 mm, the height H is 11 mm and when folded, the overall dimensions of the multi-band antenna 100 are 25 mm×7 mm×5 mm. Other physical dimensions may be required for different operative band configurations. Other physical shapes may be required for different or physical constraints of the wireless communication device and may be physically represented by metallized structures formed (e.g., stamped) in either two or three dimensions as shown in
The multi-band antenna 100 include antenna matching components 116 and 118 to transform modified monopole element 110a impedance, measured at a first radio frequency input 142, across a range of frequencies, to match RF I/O port 136 impedance as measured at an external radio frequency (RF) port 122. In the exemplary embodiment, antenna matching component 116 is connected along the lower right edge of the modified monopole element 110a to external radio frequency (RF) port 122 and to ground plane 134. Ground plane 134 is connected to or shares in whole or in part the ground plane of a wireless communication device (as shown in
As shown in
The second radio frequency input 138—where DC blocking capacitor 126 along with switch 128 connect to the modified monopole element 110a and antenna loading capacitors 132a-132e connect to ground plane 134—may be shifted left to right to optimize the bandwidth and center frequency of multi-band antenna 100. The bandwidth of a selected operative frequency band is defined by the physical dimensions of multi-band antenna 100 and to some extent the reference ground plane of the wireless communication device connected to ground plane 134.
Switch control for switch 128 is not shown, but is usually a set of digital signals for enabling individual ones of the antenna loading capacitors 132a-132e to connect to the second radio frequency input 138 through series DC blocking capacitor 126. Control signals originate from the wireless communication device (312 in
Switch 128 may be replaced with discrete switch circuits (SPST, SP2T, SP3T, etc and combinations thereof) and the number of RF common input and RF loading output ports may be changed based on the number of operative frequency bands, required bandwidth and radiation efficiency of multi-band antenna 100.
In alternate exemplary embodiments, multiple switch positions change simultaneously to subtract or add multiple antenna loading capacitors, thereby increasing the number of possible operative frequency bands. DC blocking capacitor 126 is only required if there is a DC current path from each common switch port to ground.
Additionally, antenna loading capacitors 132a-132e may be replaced with a different number of lumped or distributed loading elements (depending on the number of operative frequency bands for switch 128). In particular, antenna loading capacitors may be replaced with voltage variable capacitors, inductors or a series or parallel combination of inductors and capacitors (LC circuits and integrated LC circuits) or equivalent antenna loading elements. The physical position of individual antenna loading capacitors, inductors or LC circuits (antenna loading elements) may be anywhere between the gap between modified monopole element 110a, switch 128, and ground plane 134. In an exemplary embodiment, the individual antenna loading capacitors are connected between ground plane 134 and switch 128 individual RF loading ports.
The multi-band antenna 100 of
Multi-band antenna 200b is a mirror image of multi-band antenna 200a. The mirrored multi-band antenna 200b is functionally identical to multi-band antenna 200a and may reduce the cable or electrical routing lengths between the multi-band antennas and the wireless communication device(s) embedded within the portable computer. Multi-band antennas 200a (two of each) and 200b (two of each) may be located along the top edge of the portable computer upper housing 302 and connected to ground plane 304 behind the portable computer 300 display. Alternately, the multi-band antennas 200a (two of each) and 200b (two of each) may be located on the sides of the portable computer upper housing 302 and connected to ground plane 304 behind the portable computer 300 display. Other multi-band antenna configurations are possible; i.e.; multi-band antennas may be split between the side and top edges of the portable upper housing 302, split between the portable upper housing 302 and the portable lower housing 308, or located only along the edges of the portable lower housing 308.
A wireless communication device 312 may be behind portable computer display on ground plane 304 (within upper housing 302, not shown) or may be placed on a portable computer motherboard (on motherboard 310) within main housing 308 (as shown). Typically in portable computers, the main housing 308 is connected to the upper housing 302 via a hinge or a swivel for tablet computers. In a typical portable computer 300, the wireless communication devices are located on motherboard 310 while the antennas are usually located within upper housing 302, and RF signals are routed through hinge/swivel 306 with RF cables. One of the benefits of the multi-band antennas 200a (two of each) and 200b (two of each) is that only four RF cables are needed regardless of the number of operative frequency bands per antenna as opposed to implementing separate antennas for individual operative frequency bands. Four RF multi-band antennas are sufficient for 802.11n (MIMO using all four multi-band antennas), as well as combinations of wide-area, local-area, and personal-area networking simultaneously. However, it's conceivable in the future that more than four multi-band antennas may be utilized for new applications of wireless communication devices.
Handheld wireless communication device 400 includes a housing 402 with a main circuit board (MCB 404). Multi-band antennas 200a and 200b connect to an upper edge of MCB 404 (RF signal path and ground plane connections). Multi-band antenna 200b is a mirror image of multi-band antenna 200a. Mirrored (in one dimension) multi-band antenna 200b is functionally identical to multi-band antenna 200a and the RF I/O ports are in close proximity on handheld wireless communication device main circuit board (MCB 404). Multi-band antennas 200a and 200b are typically located along the top edge of MCB 404 and connected to a ground plane within MCB 404. Alternately, multi-band antennas 200a and 200b may be located on one or both sides of MCB 404 and connected to a ground plane within MCB 404.
Alternative exemplary embodiments may include one multi-band antenna 200 or more multi-band antennas (not shown) depending on the number of simultaneous operative frequency bands within handheld wireless communication device 400. Multi-band antenna 200, 200a, 200b provide compact size and improved antenna efficiency over a broad range of operative frequency bands verses traditional antenna designs.
Wireless communication device 406 is embedded on MCB 404 within a main housing 402 as shown in
Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the exemplary embodiments of the invention.
The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
The previous description of the disclosed exemplary embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these exemplary embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
