Patent Application
20110128199
Not Applicable
1. Technical Field
The present disclosure relates generally to radio frequency (RF) communications and antennas, and more particularly to a field-confined wideband antenna for use with RF integrated circuits.
2. Related Art
Wireless communications systems find application in numerous contexts involving information transfer over long and short distances alike, and there exists a wide range of modalities suited to meet the particular needs of each. These systems include cellular telephones and two-way radios for distant voice communications, as well as shorter-range data networks for computer systems, among many others. Generally, wireless communications involve a radio frequency (RF) carrier signal that is variously modulated to represent data, and the modulation, transmission, receipt, and demodulation of the signal conform to a set of standards for coordination of the same.
One fundamental component of any wireless communications system is the transceiver, i.e., the transmitter circuitry and the receiver circuitry. The transceiver encodes information (whether it be digital or analog) to a baseband signal and modules the baseband signal with an RF carrier signal. Upon receipt, the transceiver down-converts the RF signal, demodulates the baseband signal, and decodes the information represented by the baseband signal. The transceiver itself typically does not generate sufficient power or have sufficient sensitivity for reliable communications. The wireless communication system therefore includes a front end module (FEM) with a power amplifier for boosting the transmitted signal, and a low noise amplifier for increasing reception sensitivity.
Another fundamental component of a wireless communications system is the antenna, which is a device that allow for the transfer of the generated RF signal from the transceiver/front end module to electromagnetic waves that propagate through space. The receiving antenna, in turn, performs the reciprocal process of turning the electromagnetic waves into an electrical signal or voltage at its terminals that is to be processed by the transceiver/front end module.
In earlier mobile communication devices such as cellular phones, a conventional antenna was typically mounted on the case of the phone. These antennas were physically large and of various structures, including balanced fed dipoles, monopoles, and loops. Recent marketplace demand, however, has driven the miniaturization of mobile communication devices, concurrently with the incorporation of ever-increasing levels of functionality. Indeed, current smart phones have e-mail features, web browsing features, global positioning system (GPS)/mapping features, gaming features, video streaming features, music playback features, and so forth, in addition to the basic telephone and text messaging capabilities. In order to enable these data-intensive applications, mobile devices, and by extension, the transceivers, the front end modules, and the antennas thereof, must be improved to greater levels of performance. In particular, these components must have increased bandwidth; current high-speed data transfer rates may require a bandwidth of 100 MHz or more depending upon specific applications and operating frequency bands.
With respect to antenna design, the aforementioned goals of high performance/increased bandwidth and reduced physical size tend to be mutually exclusive, and a final configuration is typically a carefully balanced compromise between these two considerations. For antennas utilized in mobile and other portable communication devices, several other factors must be considered as well. In addition to wide bandwidth, the antennas must meet high gain and efficiency requirements because of the limited power source inherent in those devices while also meeting the minimum communication link requirements for the entire system. Furthermore, there must be an adequately low return loss, so that satisfactory performance of the transceiver and the front end module are maintained even when the operating point has drifted beyond a normal range. As the various electrical components of mobile and portable communications devices are densely packed, interference between the antenna and such nearby components is also a source of performance degradation. With current antenna designs, the return loss (S11) at the edges of the operating frequency band is typically around −5 dB, leading to a reduced performance of the front end module. This, in turn, reduces the total radiated power and the total integrated sensitivity of the transceiver. Aside from performance considerations, modern communications devices must be manufactured and sold at a sufficiently low price point for market acceptance. Therefore, the reduction of costs associated with the materials and construction of antennas, as well as the other components, is an important design objective.
Accordingly, there is a need in the art for an improved, ultra wide-band antenna with excellent return loss characteristics across a typical operating bandwidth. There is also a need in the art for an antenna capable of stable performance under various environmental conditions such that the likelihood of de-tuning resulting from nearby components and other objects placed in close proximity to the antenna is reduced.
The present disclosure generally contemplates an antenna assembly that is mountable to a printed circuit board with a radio frequency (RF) transceiver front end module mounted thereto. The antenna assembly may have an ultra-wide operating frequency bandwidth, that is, a greater than 100 MHz bandwidth depending on the frequency band, and has a return loss of −15 dB in the operating bandwidth. Additionally, the antenna assembly may have weak coupling with surrounding circuit components and other objects. Accordingly, a high degree of isolation can be achieved. Along these lines, high gain and high radiation efficiency is possible, and the overall dimensions of the antenna assembly may be kept small.
Several embodiments of the antenna assembly may have various features. One may be a radiating element that has a planar body defining a first confining slot. The dimensions of the first confining slot may correspond to a first set of resonance frequencies of the radiating element. Additionally, there may be a feeding line that extends from the radiating element in an angularly offset relationship to the planar body. The feeding line may be mountable to the printed circuit board and electrically connectible to the RF front end module. The antenna assembly may also include a first grounding line extending from the radiating element in an angularly offset relationship to the planar body. The first grounding line may also be mountable to the printed circuit board. Another feature of the antenna assembly may be a dielectric assembly that supports the planar body of the radiating element and is effective to reduce the dimensions of the radiating element. A first high frequency current loop may be formed from the feeding line to the radiating element about the first confining slot and to the first grounding line. This first high frequency current loop may confine current and electric fields on the radiating element. The present invention will be best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.
These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which:
Common reference numerals are used throughout the drawings and the detailed description to indicate the same elements.
Various embodiments of the present disclosure contemplate an antenna assembly having field-confined, ultra wide-band performance features. In particular, the antenna bandwidth is contemplated to be greater than 100 MHz for the Wireless Local Area Network (WLAN) frequency band of 2.4 GHz to 2.485 GHz. Across the typical operating bandwidth, the return loss is contemplated to be better than −15 dB. Additionally, the antenna assembly has stable performance and not prone to degradation or detuning resulting from nearby components and from objects placed in its vicinity. The detailed description set forth below in connection with the appended drawings is intended as a description of the several presently contemplated embodiments of the antenna assembly, and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and structural features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second, top and bottom, and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.
Since the antenna assembly 10 is mounted to the printed circuit board 12, the orientation in which the various features of the antenna assembly 10 are described, will be in relation to the printed circuit board 12. The printed circuit board 12 has a planar, quadrilateral configuration having a top surface 15, a length 16 and a width 18, as well as a lengthwise axis y, a widthwise axis x, and a vertical axis z. By way of example, the printed circuit board 12 may have dimensions of 80 mm×40 mm. With further particularity, the printed circuit board 12 may be a conventional glass-reinforced epoxy substrate of 60 mil thickness laminated with 1 oz. copper foil, also designated as FR4.Again, the specifics of the printed circuit board 12 are presented by way of example only, and it may take any shape that conforms to the structural constraints of the overall device. Extending vertically from the planar surface of the printed circuit board 12 along the axis z is the antenna assembly 10, and a height 20 is defined thereby.
The first embodiment of the antenna assembly 10 shown in
Extending from the planar body 26 is a feeding line 36 and a grounding line 38. Typical of conventional wireless communication devices, a single antenna is employed for both reception and transmission functions. Accordingly, the RF front end module 14 has a single antenna port 48 that is electrically connectible to the one feeding line 36 over a microstrip line 50. In one embodiment, the microstrip line 50 has an impedance of 50 Ohms for matching to the conventional input and output impedance of the RF front end module 14.
It is contemplated that the feeding line 36 and the grounding line 38 are in an angularly offset relationship to the planar body 26, but are structurally contiguous with the same. As best illustrated in
The feeding line 36, grounding line 38, and the radiating element are understood to be constructed of a single sheet of conductive material such as copper, which in one contemplated embodiment, may have a thickness of 0.008 inches, or 0.203 mm. From the single sheet, material may be selectively removed to define such features. The feeding line 36 and the grounding line 38 are bent at the longitudinal second edge 30 and the lateral third edge 32, respectively, to be in the aforementioned angularly offset/perpendicular relationship to the planar body 26. In its unbent form shown in
It will be recognized by those having ordinary skill in the art that for a given conductor, the electric field line is perpendicular to its surface, while the magnetic field is tangential to its surface and forms a circular closed loop. Accordingly, a magnetic field antenna is understood to have less coupling with surrounding circuit components, and be resistant to detuning. In accordance with various embodiments of the present disclosure, the planar body 26 defines a first confining slot 52. With the antenna being fed by an external source, a high frequency loop 54 is formed from the feeding line 36 to the radiating element 22, about the first confining slot 52 and to the grounding line 38. The feeding line 36 is thus the origin of the high frequency loop 54, while the grounding line 38 is its terminus. The impedance of the high frequency loop 54, and hence the return loss, is dependent upon the dimensions between the feeding line 36 and the grounding line 38. Furthermore, the length of the high frequency loop 54, and by definition, the dimensions of the first confining slot 52, correspond to a first set of resonant frequencies of the radiating element 22.
The high frequency loop 54 is understood to confine the current and electric fields on the radiating element 22 or the antenna volume to result in the aforementioned magnetic field antenna. In operation, coupling between the antenna assembly 10 and the surrounding circuit components can be reduced. Moreover, coupling with other objects that come into close proximity to the antenna assembly 10 during use, such as a human hand or head, can also be reduced. The first confining slot 52 is also understood to reduce the dimensions of the antenna assembly 10 while still achieving the aforementioned performance objectives of wide bandwidth, acceptable return loss, high gain, and high radiation efficiency.
Having discussed the general functional features of the radiating element 22, additional structural details will now be considered. As shown in
As indicated above, the dielectric assembly 24 supports the radiating element 22, and is itself mounted to the printed circuit board 12. It is understood that the dielectric assembly 24 facilitates size reductions with respect to the radiating element 22. It will be recognized by those having ordinary skill in the art that the free space wavelength (λ0) of an electromagnetic wave in a dielectric material is reduced by εr1/2 where εr is the dielectric constant. Thus, it is possible to reduce the dimensions of the radiating element 22 with the introduction of the dielectric material. Referring to
Additional details of the dielectric assembly 24 will now be discussed with reference to
Each of the legs 80 is understood to extend vertically from under the platform 70, and have the same length. As indicated above, the height of the feeding line 36 and the grounding line 38 is contemplated to be 10 mm, and accordingly, the length of the legs 80 is likewise understood to be 10 mm. In order for each of the legs 80 to be secured to the printed circuit board 12, there are via pins 82 extending from the bottom thereof. It is understood that the printed circuit board 12 include via holes through which the pins 82 are inserted.
A portion of the first leg 80a and the second leg 80b that defines the lateral third edge 76 also defines a channel 84 having a depth that corresponds to the thickness of the copper plate (or other metallic material) for the grounding line 38, as well as a width that corresponds to the width of the same. The channel 84 extends along the entire vertical length of the first and second legs 80a, 80b, and is understood to receive the grounding line 38 such that it is flush or substantially flush with the vertical surface of the lateral third edge 76. As indicated above, the width of the grounding line 38 is 2.5 mm, hence the channel 84 is understood to be about 2.5 mm. Along these lines, a portion of the second leg 80b that partially defines the longitudinal second edge 74 defines a channel 86 that receives the feeding line 36. The channel 86 extends along the entire vertical length of the second leg 80b, and has a depth and width corresponding to the thickness and width of the feeding line 36. Similar to the grounding line 38, the feeding line 36 is understood to be flush or substantially flush with the vertical surface of the longitudinal second edge 74.
Referring to
It was previously noted that the dielectric assembly 24, including the carrier 66 and the radome 68, are constructed of plastic. According to one embodiment of the present disclosure, the carrier 66 and the radome 68 have different dielectric properties. Specifically, the carrier is constructed of acrylonitrile butadiene styrene (ABS) plastic, while the radome is constructed of polyvinyl chloride (PVC) plastic.
The above-described first embodiment of the antenna assembly 10 is envisioned to have comparatively small dimensions, wide bandwidth, adequate return loss, and reduced coupling with nearby objects. The performance of the antenna assembly 10 has been simulated and tested for WLAN operation in a 2.45 GHz operating frequency and an ISM operating frequency band of 2.4 to 2.485 GHz. For purposes of this analysis, losses from the RF cable, the connector, and the microstrip lines were de-embedded. The graph of
Referring now to
The second embodiment of the antenna assembly 110 includes a radiating element 112 supported by a dielectric assembly 114. Further details of the radiating element 112 are shown in
The second embodiment of the antenna assembly 110, particularly configured with the structural features described in greater detail below, is contemplated for use in a WLAN communication system with an operating frequency of 2.45 GHz and an ISM frequency band of 2.4 to 2.485 GHz. However, it will be appreciated that the specific configuration may be modified to accommodate other operating frequencies and operating frequency bands. In accordance with the second embodiment of the antenna assembly 110, the longitudinal first edge 118 and the longitudinal second edge 120 have a dimension of 15.5 mm, while the lateral third edge 122 and the lateral fourth edge 124 have a dimension of 8 mm. The radiating element 112 is contemplated to have a thickness 0.008 inches or 0.203 mm, and constructed of copper, though any other material may be substituted.
Extending from the radiating element 112 is a feeding line 126, a first grounding line 128, and a second grounding line 130. With the radiating element 112 mounted to the dielectric assembly 114 as shown in
As previously indicated, the feeding line 126, the first grounding line 128, and the second grounding line 130 are in a spaced relationship. In this regard, one embodiment envisions the spacing to be approximately 1 mm. The first and second grounding lines 128, 130 are understood to be narrower in width at approximately 1.6 mm, while the feeding line 126 is understood be wider in width at approximately 2.8 mm. In accordance with various embodiments, the vertical height of the radiating element 112 is contemplated to be 10 mm; accordingly, the length of the feeding line 126, the first grounding line 128, and the second grounding line 130 is also 10 mm.
Opposite the feeding line 126 and the first and second grounding lines 128, 130, there is a bent section 144, which is bent along the lateral fourth edge 124. The bent section 144 is contemplated to be perpendicular to the planar body 116, and, by way of example only, may be 3.2 mm. Accordingly, the length of the radiating element 112 can be reduced.
Similar to the first embodiment of the antenna assembly 10, the second embodiment of the antenna assembly 110 includes a first confining slot 146 that is understood to reduce coupling between the radiating element 112 and nearby components or objects. With the antenna fed by an external source, a first high frequency loop 148 is formed from the feeding line 126 to the radiating element 112, about the first confining slot 146, to the first grounding line 128. The feeding line 126 is understood to be the origin of the first high frequency loop 148, and the first grounding line 128 is understood to be its terminus. The impedance of the first high frequency loop 148 and the return loss is dependent upon the dimensions between the feeding line 126 and the first grounding line 128. The length of the first high frequency loop 148 and thus the dimensions of the first confining slot 146 correspond to a first set of resonant frequencies of the radiating element 112.
In addition to the first confining slot 146, the second embodiment of the antenna assembly 110 includes a second confining slot 150. A second high frequency loop 152 is formed from the feeding line 126 to the radiating element 112, about the second confining slot 150, to the second grounding line 130. In this regard, the feeding line 126 is also the origin of the second high frequency loop 152. The terminus of the second high frequency loop 152 is the second grounding line 130. The second high frequency loop 152 is understood to confine the current and electric fields for resisting de-tuning and improving performance stability. The impedance of the second high frequency loop 152 and the return loss is similarly dependent on the dimensions between the feeding line 126 and the second grounding line 130. Additionally, the length of the second high frequency loop 152 and the dimensions of the second confining slot 150 correspond to a second set of resonant frequencies of the radiating element 112.
The length of the first high frequency loop 148 is configured differently from the length of the second high frequency loop 152, hence there are different resonant frequencies. Different lengths with respect to the first high frequency loop 148 and the second high frequency loop 152 are achieved by varying the dimensions of the first confining slot 146 and the second confining slot 150, as will be described in greater detail below. In accordance with various embodiments of the present disclosure, superposition of multiple resonant frequencies is contemplated to form a radiating element with different resonant peaks in a given frequency range and define an aggregate operating frequency bandwidth. With these features, an antenna with ultra-wide bandwidth is envisioned.
As best illustrated in
Similarly, the longitudinal second edge 120 defines a second open end 160 of the second confining slot 150. Like the first confining slot 146, the second confining slot 150 is defined by a first section 162 extending laterally from the second open end 160, along the same axial direction as the lateral third and fourth edges 122, 124 of the planar body 116. The dimensions of the first section 162 of the second confining slot 150 is understood to be the same as the dimensions of the first section 156 of the first confining slot 146, i.e., 2.6 mm. Additionally, the second confining slot 150 is defined by a second section 164 that extends longitudinally from the first section 162 and is contiguous therewith, along the same axial direction as the longitudinal first and second edges 118, 120 of the planar body 116. The dimensions of the second section 164 of the second confining slot 150 is understood to be different from the dimensions of the second section 158 of the first confining slot 146, being 2 mm. The second confining slot 150 is also contemplated to have an L-shaped configuration. The length of the first section 156 of the first confining slot 146 may differ from the first section 162 if the lengths of the respective second sections 158, 164 are modified such that the relationship between the total length of the first confining slot 146 and the second confining slot 159 is maintained.
With reference to
The various features noted above in relation to the first embodiment of the dielectric assembly 24 including the carrier 66 and the radome 68 thereof are understood to be the same in the second embodiment of the dielectric assembly 114. For instance, the corresponding carrier 166 includes a platform 170 of similar or identical dimensions as the planar body 116 of the radiating element 112. Extending from the corners of the platform 170 are legs 172 that define a vertical height and elevate the platform 170 from the surface of the printed circuit board 12. The legs 172 are understood to include a modality for securing the same to the printed circuit board 12. Mounted to the platform 170 is the planar body 116 of the radiating element 112. Specifically, the platform 170 includes a set of mounting pins 174 that are received in series of mounting holes 176 defined by the planar body 116. The radome 168 is attached on to the planar body 116 and the carrier 166. In this regard, the radome 168 defines a series of coaxial mounting holes 178 that receives and frictionally retains the mounting pins 174.
Typically, antennas are designed to be match to a 50 Ohm characteristic impedance, as RF circuits, and front end modules in particular, have input and output impedances of 50 Ohm for the sake of impedance matching. It is recognized, however, that the free space that bounds the antenna has an impedance of 377 Ohm. This impedance is treated as a load during transmission, or a source during reception. Conventional antenna designs apply a radiation boundary condition that matches the 377 Ohm free space impedance to the 50 Ohm impedance of the connected RF circuit. As such, the antenna serves as a basic impedance matching network. When the impedance is directly matched from 377 Ohm to 50 Ohm, it is understood that the operating frequency bandwidth may be narrow depending on the antenna structure and the operating frequency band. On the other hand, if the impedance is matched in multiple steps, the operating frequency bandwidth could be increased. Thus, in accordance with one embodiment of the present disclosure, a primary impedance of the antenna assembly 110 is matched to an impedance of the RF front end module 14 in a plurality of steps.
The second embodiment of the antenna assembly 110 described above is understood to have an impedance of more than 50 Ohm, but less than 377 Ohm. By way of example, this impedance may be 200 Ohm. As shown in the Smith chart of
The above-described second embodiment of the antenna assembly 110 is envisioned to have comparatively small dimensions, wide bandwidth, excellent return loss, and reduced coupling with nearby objects. The performance of the antenna assembly 110 has been simulated and tested for WLAN operation in a 2.45 GHz operating frequency and an ISM operating frequency band of 2.4 to 2.485 GHz. For purposes of this analysis, losses from the RF cable, the connector, and the microstrip lines were de-embedded. The graph of
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects. In this regard, no attempt is made to show details of the present invention with more particularity than is necessary for the fundamental understanding of the antenna assembly, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
This application relates to and claims the benefit of U.S. Provisional Application No. 61/256,172 filed Oct. 29, 2009 and entitled “FIELD-CONFINED WIDEBAND ANTENNA TECHNOLOGY FOR RF FRONT-END IC APPLICATIONS”, which is wholly incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61256172 | Oct 2009 | US |
