Not Applicable
The present invention relates generally to antennas for handheld, wireless communication devices, and more particularly to multiple-input, multiple-output antennas.
Different types of wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication equipment are available. Many of these devices are intended to be easily carried on the person of a user, often compact enough to fit in a shirt or coat pocket.
As the use of wireless communication equipment continues to increase dramatically, a need exists provide increased system capacity. One technique for improving the capacity is to provide uncorrelated propagation paths using Multiple Input, Multiple Output (MIMO) systems. MIMO employs a number of separate independent signal paths, for example by means of several transmitting and receiving antennas.
MIMO systems, employing multiple antennas at both the transmitter and receiver offer increased capacity and enhanced performance for communication systems without the need for increased transmission power or bandwidth. The limited space in the enclosure of the mobile communication device, however presents several challenges when designing such antennas. An antenna should be compact to occupy minimal space and its location is critical to minimize performance degradation due to electromagnetic interference. Bandwidth is another consideration that the antenna designers face in multiple antenna systems.
Furthermore, since the multiple antennas are located close to each other, strong mutual coupling occurs between their elements, which distorts the radiation patterns of the antennas and degrades system performance, often causing an antenna element to radiate an unwanted signal. Therefore, minimal coupling between antennas in MIMO antenna arrays is preferred to increase system efficiency and battery life, and improve received signal quality.
Therefore, is it desirable to develop a MIMO antenna arrangement which has a compact size to fit within a device housing that is small enough to be attractive to consumers and which has improved performance.
The present multiple port antenna assembly for use in multiple antenna systems, such as MIMO communication devices, provide isolation between two ports in a wide bandwidth, for example covering 2.25-2.8 GHz and supporting multiple communication standards. The exemplary antenna assembly has a pair of radiating elements, which, in the illustrated embodiments, comprise slot antennas, inverted F antennas, and patch antennas. It should be understood, however, that alternative radiating element types may be used, such as patch, planar inverted F (PIFA), monopole and other antenna types. The illustrated slot antennas are formed by creating two straight, open-ended slots at two opposing side edges of a conducting layer etched at one side of a printed circuit board (PCB), to form a pair of quarter wavelength slot antennas. The slots are located along one edge of the PCB opposing each other, and symmetrically with respect to the center line of the PCB. The other side of the PCB is available for mounting other components of the communication device. Each slot antenna in this configuration operates as a quarter wavelength resonant structure, with a relatively wide bandwidth. It should be understood, however, that alternative orientations, dimensions, and shapes may be used. The dimensions of the slots, their shape and their location with respect to the any edge of the PCB can be adjusted to optimize the resonant frequency, bandwidth, impedance matching, directivity, and other antenna performance parameters. It should also be understood that a slot may penetrate through the substrate of a board, in addition to the conducting layer. In addition, loaded slots may be used, with resistive material either at an end or within a slot. Furthermore the slots may be designed as a reconfigurable antenna element, with the frequency of operation being dynamically controlled by a controlling unit. The controlling unit with switches can be used to effectively change the electrical length of the slots and consequently change the frequency of operation for different frequency bands of interest. In one implementation, controllable switches are used, for example, a microelectromechanical system (MEMS), which enables different operating frequencies to be obtained by opening or closing conductive bridges across the slot. Other types of switches such as a PIN diode switch, FET, NEMS, varactor diodes, among others can be used for this purpose.
Each slot has a port to which a signal is applied to excite the slot which causes the respective slot to act as a radiating element of the antenna.
A patterned slot is formed in the conducting layer of the PCB between the pair of slot antennas to provide isolation between the radiators, thereby minimizing electromagnetic propagation from one antenna element to the other antenna element. This is specifically achieved by isolating the currents from the antennas that are induced on the ground plane. The isolation element pattern may be symmetrical with respect to a center line between the two antenna elements, or may be non-symmetrical. The isolating slot of a preferred embodiment has a meandering pattern. In some embodiments, the meandering shape is a serpentine slot that winds alternately toward and away from each antenna. In some embodiments, the electrical length of the isolation element slot is about quarter of the wavelength of the operating frequency.
A third port is provided across the isolating slot so that the isolating slot can be excited and act as yet another radiating element.
Referring initially to
The housing 21 contains a main printed circuit board (PCB) 22 on which the primary circuitry 24 for communication device 20 is mounted. That primary circuitry 24, typically includes a microprocessor, one or more memory devices, along with a display and a keyboard that provide a user interface for controlling the communication device.
An audio input device, such as a microphone 25, and an audio output device, such as a speaker 26, function as an audio interface to the user and are connected to the primary circuitry 24.
Communication functions are performed through a radio frequency circuit 28 which includes a wireless signal receiver and a wireless signal transmitter that are connected to a multiple antenna assembly 30. The antenna assembly 30 may be carried within the lower portion of the housing 21 and will be described in greater detail herein.
The mobile wireless communication device 20 also may comprise one or auxiliary input/output devices 27, such as, for example, a WLAN (e.g., Bluetooth®, IEEE. 802.11) antenna and circuits for WLAN communication capabilities, and/or a satellite positioning system (e.g., GPS, Galileo, etc.) receiver and antenna to provide position location capabilities, as will be appreciated by those skilled in the art. Other examples of auxiliary I/O devices 27 include a second audio output transducer (e.g., a speaker for speakerphone operation), and a camera lens for providing digital camera capabilities, an electrical device connector (e.g., USB, headphone, secure digital (SD) or memory card, etc.).
With reference to
The length of each of the slots 101 and 107, respectively forming the first and second slot antennas 100 and 106, is close to a quarter of a wavelength of the operating frequency. However, it should be understood that each antenna may have a different size than the other, in some embodiments. The width of the two conducting strips 102 and 108 affects the impedance bandwidth and the resonant frequency of the antennas. Those widths can be chosen so that a quarter wavelength resonance mode is excited on each of the first and second slot antennas 100 and 106. In some embodiments, the first and second antenna slots 101 and 107 lie on a common line. The two inner ends 104 and 109 of the first and second slots 101 and 107 are spaced apart by at least one-tenth of a smallest wavelength of a resonant frequency of the first and second radiating element, and are inward from the respective second and third edges 97 and 98 of the ground plane 95.
The ground plane 95 extends along three sides of the first and second slots 101 and 107. A first conducting strip 102 and a second conducting strip 108 are formed between the first edge 96 and the open-ended slots 101 and 107 respectively. The width of the conducting strips 102 and 108 can be adjusted to optimize antenna resonant frequency and bandwidth.
A first signal port 118 is provided by contacts on the ground plane 95 on opposite sides of the first slot antenna 100 near the inner end 104. A second signal port 119 is provided by other contacts on the ground plane 95 on opposite sides of the second slot 107 near its inner end 109. The first and second signal ports 118 and 119 are connected to the radio frequency circuit 28, which uses the first and second radiating elements to transmit and receive signals. That operation can have different modes in which only one of the two radiating elements, i.e. slots 101 and 107, is used to send or receive a signal. Alternatively, two separate excitation signals can be applied simultaneously, one signal to each of the slot antennas 100 and 106. At other times, different signals can be received simultaneously by each of the slot antennas 100 and 106.
The first and second slot antennas 100 and 106 are isolated from each other by a patterned slot cut in the conductive layer 94, between the radiating elements formed by slots 101 and 107. Specifically, an isolation slot 110 is located through the ground plane 95 between the first and second slot antennas 100 and 106 and specifically equidistantly between the inner ends 104 and 109 of the antennas. The isolation element 110 is in the form of an isolating slot that has a serpentine pattern which meanders winding back and forth as a serpentine between the two slot antennas 100 and 106 as the isolating slot progresses inward from the first edge 96. Specifically, the slot of isolation element 110 has a first leg 111 that extends orthogonally inward from the first edge 96, and has an inner end from which a second leg 112 extends parallel to the first edge and toward the first slot antenna 100. The second leg 112 terminates a distance from the first slot antenna 100 and a third leg 113 projects at a right angle from that end of the second leg 112 away from the first edge 96. The third leg 113 terminates at a point from which a fourth leg 114 extends parallel to the first edge 96 and toward the second slot antenna 106, terminating at a remote end. A fifth leg 115 extends at a right angle from that remote end of the fourth leg 114 orthogonally away from the first edge 96. The fifth leg 115 terminates at a point at which a sixth leg 116 extends parallel to the first edge 96 and toward the second edge 97 of the ground plane 95. The six legs 111-116 of the isolation slot 110 provide a meandering slot that winds back and forth between the two antenna slots 101 and 107. The electrical length of this isolation slot 110 can be approximately a quarter of a wavelength at the operating frequency.
This isolation slot 110 provides electrical separation between the two slot antennas 100 and 106. The width and length of each leg and the number of legs of the serpentine isolation slot 110 can be varied to optimize the isolation (i.e., minimize mutual coupling) between the two radiating elements of first antenna assembly 90, as well as the operating bandwidth. The antenna slots 101 and 107 and the isolation slot 110 extend entirely through the thickness of the conductive layer exposing portions of the first major surface 93 of the printed circuit board substrate. In addition, the meandering isolating slot increases the bandwidth of each radiating element by at least three times. By adjusting the length of the legs 111-116, the bandwidth and resonance frequency can be changed. More particularly, the bandwidth can be tuned by changing the length of the sixth leg 116.
An isolation slot pattern 73 comprises first and second L-shaped isolation slots 74 and 76 each forming a meandering pattern. The first isolation slot 74 has a first leg 78 that extends inwardly from the first edge 69 of the ground plane 65. The first leg 78 extends inwardly beyond the first slot 66 terminating at an end from which a second leg 79 projects toward and parallel to the first slot. The second isolation slot 76 has a first leg 80 similarly extending inwardly through the conductive layer from the first edge 69. That first leg 80 extends beyond the second slot 68 terminating at an end from which a fourth leg projects toward and parallel to the second slot 68.
The ground plane 125 extends around each of the first and second slots 130 and 136. A first signal port 142 has contacts on opposite sides of the first slot 130 near the end that is spaced from the ground plane's first edge 96. A second signal port 144 is similarly located with respect to the second slot 136.
The first and second antennas 134 and 140 are isolated from each other by a T-shaped isolation slot 145 which has a first leg 146 extending inwardly through the ground plane 125, perpendicular to the first edge 126 and terminating at an inner end. A second leg 148 extends orthogonally to the first leg 146 and is centered at the remote end of that first leg. Thus, the top of the T shaped isolation slot 145 is spaced inward from the first edge 126. The isolation slot 145 serves the same functions as the previous isolation slots in minimizing electromagnetic propagation from one radiating element to another.
All the previously described slot antennas are coplanar with the ground plane on the printed circuit board and are formed by slots through that ground plane, such as by a conventional photolithographic etching process or by machining.
The fourth antenna assembly 150 includes a first and second inverted F antennas (IFA) 160 and 164 spaced apart at the first edge 158 of the ground plane. A short conductive first support 161 is mechanically and electrically connected to the conductive layer 156 at the first edge 158 of the ground plane and projects away from the substrate, and forms a ground pin for the first inverted F antenna 160. A straight first arm 162 extends from an upper portion of the first support 161 parallel to and spaced from the first edge 158. A first signal pin 163 is spaced from the grounded first support 161 and is connected to the first arm 162 at one end and has a signal contact at the other end. The grounded first support 161, first signal pin 163, and the first arm 162 for the first inverted F antenna 160.
A short conductive second support 165 is mechanically and electrically connected to the conductive layer 156 at the first edge 158 of the ground plane and projecting away from the substrate and forming a ground pin for the second inverted F antenna 164. A straight second arm 166 extends from an upper portion of the second support 165 parallel to and spaced from the first edge 158 and terminates adjacent the third edge 157 of the ground plane. A second signal pin 167 is spaced from the ground pin 165 and is connected to arm 166 at one end and has a signal contact at the other end. The second ground pin support 165, second signal pin 167, and the second arm 166 form the second inverted F antenna 164. The first and second inverted F antennas 160 and 164 oppose each other across a width of the ground plane 159.
It should be understood that the two antennas on the same printed circuit board need not be of the same type. For example, one antenna may be a slot type, while the other may be an inverted F antenna.
The fourth antenna assembly 150 includes a pair of L-shaped isolation slots 168 and 169 in the conductive layer 156 forming the ground plane, which slots are similar to the isolation slots 74 and 76 described with respect to the third embodiment in
With references to
The ground plane 208 extends along three sides of the first and second slot antennas 210 and 216. A first conducting strip 220 and a second conducting strip 222 are formed between the first edge 211 and the open-ended slots of antennas 210 and 216 respectively. The width of the conducting strips 220 and 222 can be adjusted to optimize antenna resonant frequency and bandwidth.
A first signal port 224 is provided by two contacts on the ground plane 208 on opposite sides of the first slot antenna 210 near the inner end 214. A second signal port 226 is provided by other pair of contacts on the ground plane 208 on opposite sides of the second slot 217 near its inner end 218.
Alternatively the first and second slot antennas in
A meandering slot 202 is located through the ground plane 208 between the first and second slot antennas 210 and 216 and preferably equidistantly between the inner ends 214 and 218 of the antennas. The meandering slot 202 is in the form of an isolating slot that has a serpentine pattern which meanders winding back and forth as a serpentine between the two slot antennas 210 and 216 as the meandering slot progresses inward from the first edge 211. The meandering slot is formed by a series of contiguous legs 231-238. Specifically, the meandering slot 202 has a first leg 231 that extends orthogonally inward from the substrate's first edge 211, and has an inner end from which a second leg 232 extends parallel to the first edge and toward the first slot antenna 210. The second leg 232 terminates at a first remote end that is away from the second slot antenna 216 and at a distance from the first slot antenna 210 and a third leg 233 projects at a right angle from the first remote end away from the first edge 211. The third leg 233 terminates at second remote end from which a fourth leg 234 extends parallel to the first edge 211 and toward the second slot antenna 216, terminating at a third remote end. A fifth leg 235 extends at a right angle from the third remote end of the fourth leg 234 and orthogonally away from the first edge 211. The fifth leg 235 terminates at a fourth remote end from which a sixth leg 236 extends parallel to and for the entire length of the fourth leg 234. The sixth leg 236 has a fifth remote end adjacent the inner end 214 of the first slot antenna 210. From the fifth remote end of the sixth leg 236, a seventh leg 237 projects farther inward orthogonally to the first edge 211 and terminates at a sixth remote end. An eighth leg 238 extends, from the sixth remote end, parallel to the first edge 211 and toward the second slot antenna 216. The eight legs 231-238 of the meandering slot 202 provide slot pattern that winds back and forth as a serpentine between the two antenna slots 209 and 217.
A third signal port 230 is provided by two contacts on the ground plane 208 on opposite sides of the eighth leg 238 of the meandering slot 202. A signal applied to the third signal port 230 may be in a different frequency band from the signals applied to the first and second signal ports 224 and 226. Alternatively, the signal applied to the third signal port 230 may be in the same frequency band of the signals applied to any of the first and second signal ports 224 and 226. The electrical length of the meandering slot 202, when acting as a radiating element, is approximately a quarter of a wavelength at the applied signal frequency. The meandering slot 202 can function as an independent antenna. In another application, the signal feed for the first and second slot antennas 210 and 216 can be turned on and off by the radio frequency circuit 28, so that any of those antennas can work as a two element MIMO antenna system along with the meandering slot 202.
The resonant frequency of the fifth antenna assembly 200 can be dynamically tuned by changing the effective electrical length of the meandering slot 202. This may be accomplished, as depicted in
Using a meandering slot radiator has the advantage of occupying less space on the printed circuit board 204 and also improves the bandwidth of the MIMO system.
When not excited, this meandering slot 202 provides electrical separation between the two slot antennas 210 and 216. The width and length of each leg and the number of legs of the serpentine meandering slot 202 can be varied to optimize the isolation (i.e., minimize mutual coupling) between the first and second slot antennas 210 and 216, as well as the operating bandwidth. For example, the seventh and eighth legs 237 and 238 can be omitted and the length of the sixth leg 236 shortened to be approximately equal to the length of the second leg 232, as in the embodiment shown in
With reference to
The primary difference with respect to the sixth antenna assembly 300 is that the meandering slot 302 is symmetrical about a line that is perpendicular to the first edge 211 of the ground plane 208. Specifically, the meandering slot 302 has a first leg 304 that extends orthogonally inward from that first edge 211, and has an inner end from which a second leg 305 extends parallel to the first edge and toward the first slot antenna 210. The second leg 305 terminates at a first remote end away from the second slot antenna 216 and at a distance from the first slot antenna 210, and a third leg 306 projects at a right angle from the first remote end away from the first edge 211. The third leg 306 terminates at second remote end from which a fourth leg 307 extends parallel to the first edge 211 and toward the second slot antenna 216, terminating at a third remote end. A fifth leg 308 extends at a right angle from the third remote end of the fourth leg 307 and orthogonally away from the first edge 211. The fifth leg 308 terminates at a fourth remote end from which a sixth leg 309 extends parallel to the fourth leg 307. The length of the sixth leg 309 is equal to the length of the second leg 305, thus the sixth leg extends parallel along half the length of the fourth leg 307. Thus the meandering slot 302 is symmetrical about a longitudinal center line of the first leg 304.
A third signal port 310 is provided by two contacts on the ground plane 208 on opposite sides of the sixth leg 309 of the meandering slot 302. A signal applied to the third signal port 310 may be in a different frequency band from the signals applied to the first and second signal ports 224 and 226. Alternatively, the signal applied to the third signal port 310 may be in the same frequency band of the signals applied to any of the first and second signal ports 224 and 226. The electrical length of the meandering slot 302, when acting as a radiating element, is approximately a quarter of a wavelength at the applied signal frequency. The meandering slot 302 can function as an independent antenna. One or more conductive bridges 240 in the version in
In
A first meandering slot 416, having the same symmetrical configuration as the meandering slot 302 described in
A similar second meandering slot 420 is located in the ground plane 408 between the second antenna 414 and an edge 422 that is contiguous with and transverse to the first edge 410. The second meandering slot 420 extends inwardly from the first edge 410 and is symmetrical with respect to a line that is perpendicular to that edge and parallel to the second edge 422. A second signal port 424 is provided by two contacts on the ground plane 408 on opposite sides near the innermost end of the second meandering slot 420.
Although the first and second antennas 412 and 414 are depicted as inverted F antennas, they may comprise any other type of antennas commonly used in portable communication devices, such as a patch, a planer inverted F, or a monopole antenna.
Each of the four radiating elements 412, 414, 416, and 420 can be used at the same time or the signals applied to them can be independently disabled by switches operated by a controlling unit. The controlling and switching of the signals applied to these radiating elements can be performed based on the needs of the communication system thereby making that system reconfigurable. For example, any two of the four radiating elements 412, 414, 416, and 420 can be used together as a two element MIMO antenna system. Alternatively, the first and second antennas 412 and 414 may be excited at the same time or the two meandering slots 416 and 420 can be excited together. The again, the first antenna 412 and the first meandering slot 416 can be excited together or the second antenna 414 and the second meandering slot 420 can be used together. As a further variation, the effective length of the meandering slots can be varied to alter their operating frequency by conductive bridges or switches connected across the slot at different positions.
As a further alternative design, the L-shaped meandering slots 74 and 76 in the embodiment of
The foregoing description was primarily directed to a certain embodiments of the antenna. Although some attention was given to various alternatives, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from the disclosure of these embodiments. Accordingly, the scope of the coverage should be determined from the following claims and not limited by the above disclosure.
This application is a continuation in part of U.S. patent application Ser. No. 12/405,955 filed on Mar. 17, 2009.
Number | Date | Country | |
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Parent | 12405955 | Mar 2009 | US |
Child | 12776678 | US |