Patent Application
20090073055
This invention relates in general to wireless devices, and more particularly, to an internal multi-element multi-band antenna for use in hand-held devices.
Wireless communication is the transfer of information over a distance without the use of electrical conductors or “wires.” This transfer is actually the communication of electromagnetic waves between a transmitting entity and remote receiving entity. The communication distance can be anywhere from a few inches to thousands of miles.
Wireless communication is made possible by antennas that radiate and receive the electromagnetic waves to and from the air, respectively. The function of the antenna is to “match” the impedance of the propagating medium, which is usually air or free space, to the source that supplies the signals sent or interprets the signals received.
Antenna designers are constantly balancing antenna size against antenna performance. Unfortunately, these two characteristics are generally inversely proportional. To make matters more difficult, consumers are now favoring cellular phones with internal antennas. The ever-shrinking size of cellular phones leaves little space inside the phone for these antennas. To add even more complexity to this communication problem, phones are needed that offer communication in multiple modes and in multiple frequency ranges, requiring multiple and differening antenna elements within the phone. With the reduction in antenna element real estate, communication performance suffers.
Therefore, a need exists to overcome the problems with the prior art as discussed above.
A loop antenna, in accordance with an embodiment of the present invention includes a ground plane and a conductive element with a first C-shaped element portion having an open end and a closed end, with only the open end extending directly above a first portion of the ground plane, a second C-shaped element portion having an open end and a closed end, with only the open end extending directly above a second portion of the ground plane, and a transmission line element disposed between the first C-shaped element portion and the second C-shaped element portion and positioned directly above a third portion of the ground plane.
In accordance with another feature of the present invention, the first C-shaped element portion has a first end, the second C-shaped element portion has a second end and the transmission line element is in a series connection between the first end of the first C-shaped element portion and the second end of the second C-shaped element portion.
In accordance with a further feature of the present invention, the first C-shaped element portion is symmetrical with the second C-shaped element portion.
In accordance with a yet another feature, the present invention includes a stub element coupled to the conductive element at a feedpoint of the conductive element and one of generally follows the shape of one of the C-shaped element portions and meanders in a proximity of one of the C-shaped element portions.
In accordance with a yet another feature, the present invention includes a handset supporting and containing the element and the ground plane, the handset having a first side to face a user's head during use and a second side to face a user's hand during use, wherein the ground plane is disposed between the first side and the second side and the element is disposed between the first side and the ground plane.
The present invention, according to an embodiment, is a wireless communication device that includes a first side with user-interactable components, a second side to be supported by a user's hand, a ground plane disposed between the first side and the second side and having outer edges, and a conductive element located between the first side and the ground plane. The conductive element includes a first element portion forming a C-shape with an open end directly above a first portion of the ground plane and a closed end extending beyond at least one edge of the ground plane, a second element portion forming a C-shape with an open end directly above a second portion of the ground plane and a closed end extending beyond at least one edge of the ground plane, and a transmission line element connecting the first element portion to the second element portion and positioned directly above a third portion of the ground plane.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention.
The terms “a” or “an”, as used herein, are defined as one or more than one. The term “plurality”, as used herein, is defined as two or more than two. The term “another”, as used herein, is defined as at least a second or more. The terms “including” and/or “having”, as used herein, are defined as comprising (i.e., open language). The term “coupled”, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
The present invention provides a novel and efficient multi-band antenna structure that includes an asymmetrical λ/2 (half wavelength) folded dipole element and a λ/4 (quarter wavelength) resonant stub element. The elements share a common feeding point and utilize a common grounding plane. The invention is advantageous in that it allows for a reduction of the area normally needed for a λ/2 antenna element, without interfering with Radio Frequency (RF) performance.
An antenna is a transducer designed to transmit or receive radio waves, which are a class of electromagnetic waves. In other words, antennas convert radio frequency electrical currents into electromagnetic waves, and vice versa. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, radar, and space exploration.
Physically, an antenna is a conductor that generates a radiating electromagnetic field in response to an applied alternating voltage and the associated alternating electric current. Alternatively, an antenna can be placed in an electromagnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals. It is through these antennas that electronic wireless communication is made possible.
The electromagnetic (EM) “spectrum” is the range of all possible electromagnetic radiation. This spectrum is divided into frequency “bands,” or ranges of frequencies, that are designated for specific types of communication. Many radio devices operate within a specified frequency range, which limits the frequencies on which the device is allowed to transmit. The lower and upper-bound frequencies are the points at which signal strength of the device falls off by 3 dB.
EM energy at a particular frequency (f) has an associated wavelength (k). The relationship between wavelength and frequency is expressed by:
λ=c/f
where c is the speed of light (299,792,458 m/s). It therefore follows that high-frequency EM waves have a short wavelength and low-frequency waves have a longer wavelength.
The Integrated Digital Enhanced Network (iDEN) is a mobile telecommunications technology, developed by Motorola, Inc., of Schaumberg, Ill., which provides its users the benefits of a trunked radio and a cellular telephone. iDEN places more users in a given spectral space, as compared to analog cellular and two-way radio systems, by using speech compression and Time Division Multiple Access (TDMA). iDEN is designed and licensed to operate in the frequency band starting at 806 MHz up to and including 941 MHz. In addition to the iDEN band there are other bands in the 825-960 MHz frequency range that are used by cellular systems. For purposes of lexography the combined range of frequencies from 806-960 MHz will be designated as the “cellular band.” The present invention provides a λ/2 antenna element that efficiently operates in the cellular band frequency range.
The Global Positioning System (GPS) is currently the only fully-functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 Earth orbiting satellites that transmit precise microwave signals, the GNSS enables a GPS receiver to determine its location, speed, and direction. The present invention includes a GPS element that that is tuned to receive GPS signals at the frequency of 1575.42 MHz and can also be tuned (if desired) to the 1800-1990 MHz Personal Communications System (PCS) frequency bands.
The particular cellular phone 100 is a well-known “clamshell” device, where the term “clamshell” refers to the way the phone 100 folds 114 and places the display screen 106 directly above the keypad 102 when closed. This folding feature not only makes the device smaller and easily transportable, it also protects the display screen from damage. The present invention, however, is not limited to clamshell designs or to any particular type or configuration of cellular phone.
The element 204 can be of any suitable radiating material. The cellular band element 204 includes two generally C-shaped element portions 206 and 208, which, together, efficiently operate in frequency ranges covering the cellular band. A C-shaped portion, as defined herein, is any shape where two points along the length of the element cross a single plane, with a curved portion being disposed between the two points. In addition to the curved portion, the length between the two points that cross the plane can also include one or more line segments or other curves.
Each of the generally C-shaped portions 206 and 208 is oriented so that the open end of the C-shape 218 is positioned directly above a portion of the ground plane 202 and the closed, or curving, part of the C-shape 220 extends away from the ground plane 202. In this configuration, only part of the cellular band element 200 feels the full effect of the ground plane 202. The cellular band element 200 has a feed point 212, where the element 200 is energized, and a ground point 214, where the element 200 is shorted to the ground plane 202. The ground point 214 is the only place where the element 220 makes direct electrical contact with the ground plane 202.
The ground plane 202 is defined as “partial” because it is smaller than the element 204 to which it is coupled in the region where the antenna element portions reside. The ground plane 202 is further defined as having a connecting end 222 where the antenna 200 connects to the ground plane 202 and an opposite end 224 that extends over a region beyond the antenna element 204. In the region 224 beyond the antenna elements 204, the ground plane 202 can take on any arbitrary shape and can be larger than the antenna element.
A transmission line element 210 is provided between the first C-shaped portion 206 and the second C-shaped portion 208 and is positioned so that the entire transmission line element 210 is directly above the ground plane 202. As can be seen in
The transmission line element 210 is a reactive distributive element that provides length to the overall element 200 as well as electromagnetic coupling to the ground plane 202. The added length provided by the transmission line element 210 extends the overall element length closer to the desirable λ/2 dimension. The electromagnetic coupling provided by the transmission line element 210 also makes the element electrically appear taller than it is, which helps “match” the antenna element 200 to the impedance of air. In this particular embodiment, the transmission line element 210 is rectangular in shape, although the invention is not so limited and can be, for example, square or curved.
In the particular embodiment shown in
Table 1 below presents the results of a simulation that compares radiation and system efficiency between the folded dipole antenna of the present invention and a prior-art internal λ/4 wire antenna. The comparison is performed, as is shown in
There are two metrics that quantify antenna performance for cellular phones. One metric is Radiation efficiency defined as the radiated efficiency of the antenna excluding mismatch loss. The radiation efficiency metric indicates mainly the effect of detuning and dissipation from a user's hand. The second metric is System efficiency which is the radiation efficiency including mismatch loss. System efficiency indicates the effect of mismatch loss to the antenna. The simulation comparison in the Dispatch Position shows that the folded dipole of the present invention provides an increased radiation efficiency of 1.7 dB (10*LOG (31.77/21.46)) over the prior art internal λ/4 wire antenna design. The folded dipole of the present invention also provides an increased system efficiency of 3.1 dB (10*LOG(30.92/15.12)) over the prior art internal λ/4 wire antenna design.
Referring now back to
The second element 216 is connected to element 204 at the feed point 212 and is electromagnetically coupled to element 204 along its length to match the impedance of element 216 to the desired feed point impedance (typically 50 Ohm). Element 216 can also be a constructed with a meandering conductor in the region of an outer edge of area 208, which is electromagnetically coupled to element 204 and whose overall electrical length is λ/4 at the GPS frequency. The term “meandering,” as user herein, means a winding path or course. Element 216 can also be disposed above element 204.
An element 506 is positioned directly above the ground plane 504 and is spaced away from the ground plane 504, but extends beyond the ground plane 504 on both sides. The element 506 can be made of any suitable radiating material. The element 506 includes two generally C-shaped portions 508 and 510 substantially defining operation in frequency ranges covering the cellular band. In this embodiment, there is no discontinuity between the two generally C-shaped portions 508 and 510. The dotted lines in
Each of the generally C-shaped portions 508 and 510 is oriented so that the open end of the C-shape is positioned directly above the ground plane 504 and the closed, or curving, part of the C-shape extends away from the ground plane 504. In this configuration, only part of the element 506 feels the affect of the ground plane 504. The antenna 500 also has a ground point 512, where the element 506 is shorted to the ground plane 504.
A transmission line element 514 is provided between the first general “C” shape portion 508 and the second general “C” shape portion 510 and is positioned so that the entire transmission line element 514 is directly above the ground plane 504. In the embodiment illustrated, the transmission line element 514 is rectangular, but the invention is not so limited and can be, for example, square or curved. As can be seen in
The transmission line element 514 is a reactive distributive element that provides length to the overall element 506 as well as electromagnetic coupling to the ground plane 504. The added length provided by the transmission line element 514 extends the overall element length closer to the desirable λ/2. The electromagnetic coupling provided by the transmission line element 514 also makes the element electrically appear taller than it is, which helps “match” the antenna element 506 to the impedance of air.
One noticeable difference from the embodiment of
In the particular embodiment shown in
The embodiment of
Conclusion
As should now be clear, embodiments of the present invention provide a multi-band antenna that exceeds cellular band and UPS antenna performance specifications, as well as the performance of traditional antennas, such as the prior art internal λ/4 wire antenna. The inventive antenna advantageously provides a half wavelength cellular band element that is fits within the interior of a phone and is minimally impacted by the user's hand during operation. In addition, the shape of the antenna does not interfere with existing component located within several models of cellular phones.
Non-Limiting Examples
Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.
