The present invention relates to the field of communications systems, and, more particularly, to antennas for mobile wireless communications devices and related methods.
Mobile devices are being required to support multiple applications, such as GSM, PSC, UMTS, WLAN, Wibro (Wireless broadband), and Bluetooth, and LTE, which in turn require multiple antennas, since one antenna cannot typically cover the bandwidth requirements of the multiple applications due to the physical limitations of an antenna described in “Physical Limitations of Antennas,” IEEE Transactions on Antennas and Propagation, vol. 51, no. 8, pgs. 2116-2123, 2003. As a result, multiple antennas must now share the already limited space within the mobile device.
Furthermore, techniques such as multiple-input multiple-out (MIMO) have emerged, which significantly increase the performance of HSPA (high speed packet access) and LTE (long term evaluation) networks. This is usually accomplished by using multiple antennas arranged to have low correlation between two or more unique radio signals. In large devices, where space is less limited, this is easily accomplished by using spatial diversity (distance between antennas), or somehow by pattern diversity (difference between antenna aiming directions), and polarization diversity together. Unfortunately, the size of mobile wireless communications devices (e.g., cellular devices) continue to decrease and so too does the allowable space for the device antenna. As a result, having multiple antennas in a close proximity poses significant coupling and mode isolation problems; furthermore, the signals received by each of the antennas may be undesirably correlated. This noticeably disrupts MIMO performance.
Thus it can be seen that designers of antennas for mobile devices face significant challenges, particularly wherein the antennas may be capable of covering as many bands as possible while being small in size and still having a high performance.
One form of antenna commonly used in mobile devices is the monopole antenna. Compared to PIFA or IFA, a monopole can easier achieve large bandwidth because they may be arranged to radiate at two or more resonant frequencies (from its fundamental mode, second order and higher modes) Since a monopoles inherent dual mode characteristic makes it easy to achieve a frequency ratio of two-to-one of its upper and lower frequency band.
However using a single radiator for multi-order modes poses a difficulty, particularly if specific frequency bands are to be adjusted independently. Additionally, in a single radiator if one of the operating bands is required to be relatively wide the monopole may not cover all bands, such as GSM 900 (880 to 960 MHz) at a lower band and GSM1880/1900 and UMTS2100 (1710 to 2170 MHz) together at an upper band, unless additional parasitic branches are used to enhance the bandwidth and adjust the frequency ratio. However this introduces additional volume and potential higher-mode coupling among radiation elements.
Another disadvantage is that since a monopole is typically a quarter-wavelength of the fundamental mode, the size of the antenna is increased when it is designed to operate at lower resonant frequency bands.
Accordingly, it is desirable to have a monopole that may be arranged in a limited space.
The present disclosure will be better understood with reference to drawings in which:
a-e show schematic diagrams of various aspects of an implementation of a multi-band three-dimensional (3D) folded monopole antenna assembly, according to an embodiment of the present matter;
a-7d shows graphs of measured far-field radiation patterns at respective resonant frequencies of 900 MHz, 1800 MHz, 2.5 GHz and 5.5 GHz for the antenna of
a-b show schematic diagrams of respective top and bottom perspective views of an antenna according to another embodiment of the present matter;
a-c show schematic diagrams of multi-port antenna configurations according to further embodiments of the present matter;
a-b show schematic diagrams of various ground plane stub sizes for the two-port antenna of
a-c show plots of measured S parameters, for the antenna configuration of
a-c show plots of measured S parameters, for the antenna configuration of
a-c show plots of measured S parameters, for the antenna configuration of
In the following description like numerals refer to like structures illustrated in the drawings. For clarity a set of orthogonal axes x-y-z are shown in the drawings, where appropriate, to provide a frame of reference for describing the relative arrangement of the structures in the various drawings. The terms horizontal and vertical where used are for convenience of describing structures oriented with respect to the x-y plane and the y-z plane respectively, and are not meant to be limiting.
The present matter describes multi-band three-dimensional (3D) folded monopole antennas for use in mobile devices. More particularly the present matter describes a small compact multi-radiation element antenna that exhibits high mode isolation allowing it to cover several communication application frequency bands such as GSM 1900, UMTS2100, GPS, WALN in the 2 GHz and higher range and the lower bands such as 1 GHz and wherein the operational frequency bands of antenna elements can be adjusted independently i.e. the upper bands can be adjusted independently of the lower bands. In other words the high mode isolation allows the antenna to function at different operation frequencies.
Furthermore, the multi-radiation element antenna also exhibits high isolation between the radiation elements. In other words there are low couplings (or power transferred from one element to another) at the operation frequencies of the antenna.
Furthermore the present matter describes a multi antenna array comprised of two or more of the multi-radiation element antennas, wherein the antennas of the array also exhibit high isolation.
In accordance with a first aspect of the present matter there is provided a multi-band antenna comprising a dielectric substrate, a ground plane formed on a first area of the dielectric substrate, a radiation part arranged on a second area of the dielectric substrate where the ground surface is not formed, a feed section formed of a metallic trace and having one end connected to the radiation part and an opposite end disposed near an edge of the ground plane for forming a feed point. The radiation part having a pair of monopole antenna elements formed of conductive metallic traces; a first monopole for radiating at a first resonant frequency, and a second monopole for radiating at a second resonant frequency and the conductive metallic traces being folded to form a three dimensional structure, with at least a portion of the first monopole spaced from a plane of the substrate and the second monopole.
There is further provided a patch element coupled to the second monopole and arranged in a spaced relationship to the first monopole, a width of the patch element for determining the resonant frequency of the second monopole antenna element, independently of the resonant frequency of the first monopole.
There is further provided a dielectric shell defining a generally rectangular shape having opposing top and bottom faces, opposing first and second end faces and opposing first and second side faces, the bottom face of the dielectric shell positioned in the second area of the substrate and the three dimensional structure of the metallic trace being formed around the dielectric shell.
In accordance with a further aspect there is provided a mobile wireless communication device comprising a housing, a dielectric substrate carried within the housing, wireless communication circuitry carried by the substrate within said housing, and a multi-band antenna coupled to the wireless communication circuitry and comprising a ground plane formed on a first area of the dielectric substrate, a radiation part arranged in a second area of the dielectric substrate where the ground surface is not formed, a feed section formed of a metallic trace and having one end connected to the radiation part and an opposite end disposed near an edge of the ground plane for forming a feed point; and the radiation part formed of conductive metallic traces; a first monopole for radiating at a first resonant frequency, and a second monopole for radiating at a second resonant frequency and the conductive metallic traces being folded to form a three dimensional structure, with at least a portion of the first monopole spaced from a plane of the substrate and the second monopole.
In accordance with a still further aspect there is provided a mobile wireless communication device comprising a housing, a dielectric substrate carried within said housing, wireless communication circuitry carried by the substrate, a ground plane formed on a first area of the dielectric substrate, a plurality multi-band antennas arranged in a second area of the dielectric substrate where the ground surface is not formed and coupled to said wireless communication circuitry, each of the multi-band antennas having a pair of monopole radiating elements including a patch element associated with respective ones of the multi-band antennas, a width of the patch element for determining a resonant frequency of its associated antenna.
There is further provided in the still further aspect a stub section coupled to the ground plane and extending into the second area, a stub size being selected for determining an operating frequency and isolation of the multi-band antennas.
In accordance with a still further aspect there is provided a method for implementing a multi-band antenna for use in a mobile device, the method comprising forming a ground plane in a first area of a dielectric substrate, the dielectric substrate for positioning within a housing of the mobile device; arranging a plurality of multi-band antennas in a second area of the dielectric substrate where the ground surface is not formed, the antennas for coupling to wireless communication circuitry, each of the multi-band antennas having a pair of monopole radiating elements including a patch element associated with respective ones of the multi-band antennas; and determining resonant frequency of respective antennas by adjusting a width of the patch element associated with that antenna.
In accordance with a still further aspect the method includes selecting a size of a stub section for extending the ground plane into the second area, for determining an operating frequency and isolation of the multi-band antennas.
Referring to
Referring to
The 3D geometrical configuration of the pair of folded monopoles is shown more clearly in
As shown in
As the total length and layout of each monopole antenna element determines the antenna's performance, the total length may be optimized taking into account the constraints on the volume for the antenna and the desired resonant frequency. The total length controls the fundamental resonating mode of the monopole elements, as will be appreciated by those skilled in the art. The modes at higher frequencies are generated at various portions of this length.
The 3D wrapping of the antenna controls the current distribution along the monopole length, and thus controls the electrical length(s) for the higher resonant frequency band(s) as well as antenna bandwidth, as will also be appreciated by those skilled in the art.
The initial electrical length of the first and second monopoles is set to a quarter of the wavelength of respective first and second resonant frequencies for the chosen fundamental modes. In an implementation the fundamental mode is set at 1 GHz for the first monopole and 2 GHz for the second monopole. The geometric parameters may be optimized by using electromagnetic simulators such as those based on Finite-difference time-domain (FDTD) computational electrodynamics modeling techniques, as is known in the art. An example of which is a commercially available program by CST.
The width d of the patch 120 varies the bandwidth and performance of the antenna. In an exemplary implementation the width d of the patch 120 is set to 2 mm, identical to the width of the other strips. The dielectric shell has dimensions of 14 mm in length (l1), 7 mm in width (w2) and 7.5 mm in height (h). It is to be noted that the dielectric shell is mounted to the top surface of the substrate and thus the height of the dielectric shell is increased by 1.5 mm, the thickness of the substrate 104. The lengths of the sections of metallic strips for the first monopole are as follows: S0=3 mm, S1h=7 mm, S2=[s21=4 mm, s22=2.5 mm, s23=10 mm, s24=2.5 mm, s25=4 mm], S3=7 mm, S4=[s41=40 mm, s42=2.5 mm, s43=12m, s44=6 mm], S5=[s51=5.5 mm, s52=11 mm]. The lengths of the sections of metallic strips for the second monopole are as follows: S0=3 mm, S1v=7.5 mm (the vertical section) and P=14 mm. The above dimensions are for an exemplary embodiment; however, it will be appreciated by those skilled in the art that other dimensions and/or materials may be used in different embodiments.
Referring to
Furthermore, by simulating surface current distributions (not shown) for the antenna, having dimensions as above, it was demonstrated that the first monopole monopole-1202 operates at its fundamental mode and the total length of the first monopole monopole-1202 is approximately a quarter wavelength. As operation frequency is increased to 2 GHz, it was verified that the first monopole monopole-1202 operates at the second-order mode of 2 GHz. At this frequency, the electrical length of the first monopole monopole-1202 is a half wavelength. Furthermore, as the operation frequency is increased to 5.2 GHz, multiple nil points appear for the current distributions on the first monopole monopole-1202. Hence, the antenna works at the higher order mode and its electrical length is more than one wavelength. In the case of the second monopole monopole-2 when it is excited alone at 2 GHz the currents also flow in a continuous direction, which means that the second monopole monopole-2 operates at the fundamental mode and its length is a quarter wavelength. Finally, when the two monopoles were simultaneously excited at several frequencies the frequency bands of 1 GHz, 2 GHz and 5.5 GHz, the first monopole monopole-1202 had strong surface currents while the second monopole monopole-2204 exhibited weak surface currents. Accordingly, it can be inferred that the two monopoles have high-mode isolation, and that the first monopole monopole-1202 primarily determines these resonant frequencies. However, when the antenna operates at the 2.5 GHz band, the two monopoles exhibit strong surface currents, so they both have an influence in this band.
As mentioned earlier, the width d of the patch 120 changes the resonant frequency and bandwidth of the antenna. Accordingly, referring now to
Another characteristic shown in
In applications requiring frequency agility RF-switches, such as RF-MEMS (Radio-Frequency Micro-Electro-Mechanical System), may be used to dynamically increase or decrease the patch P width d so that the antenna provides greater flexibility.
Referring to
Referring, additionally to
Referring now to
The antenna 808 also comprises two monopole antenna elements, 810 and 812 formed on the dielectric shell illustrated in
It may be seen from the above that there is described herein a compact 3D folded multi-band high mode-isolation, monopole antenna for handheld devices. The antenna has a simple structure and a small size combined with high-efficiency. As shown in the exemplary implementations, in addition to the two bands at 900 MHz and 5.5 GHz, the exemplary antennas provide a number of resonant frequencies within a desirable bandwidth in the frequency range of 2 GHz to 4 GHz by adjusting the patch width. This is useful when finalizing antenna designs because antenna adjustments are generally required at a late stage of product development. Typically large adjustments in the antennas dimensions are not feasible since the antenna's overall size has been fixed at the production stage.
Furthermore the antenna of the present matter can be easily adapted for used in mobile devices for reception of two or more unique radio signals, which require relatively low correlation between each of the received signals.
Accordingly, referring now to
In
Referring to
The isolation may be attributed to the two antennas having well implemented antenna diversities such as spatial, polarization and pattern diversity. Thus it may be seen that the diversity techniques applied to the pair of antennas result in high isolation (low coupling) between the two ports. For example, whereas the two monopole antenna elements of each antenna are arranged vertically with respect to each other for polarization and pattern diversities, each of the dual antennas are separated for spatial diversity.
Varying a size and arrangement of stub sections, such as stub section 903, may change the response of the two-port antenna arrangement shown in
Similarly,
Still further, in
It may be seen from the S parameter plots in
Exemplary components of a hand-held mobile wireless communications device 2200 in which one or more of the above-described folded monopole antennas 108 may be used are now described with reference to
The mobile device of
Mobile device 2200 is preferably a two-way wireless communication device having at least voice and data communication capabilities. Mobile device 2200 preferably has the capability to communicate with other computer systems on the Internet. Depending on the exact functionality provided, the mobile device may be referred to as a data messaging device, a two-way pager, a wireless e-mail device, a cellular telephone with data messaging capabilities, a wireless Internet appliance, or a data communication device, as examples.
Where mobile device 2200 is enabled for two-way communication, it will incorporate a communication subsystem 2211, including a receiver 2212 and a transmitter 2214, as well as associated components such as one or more, preferably embedded or internal, antenna elements 2216 and 2218, local oscillators (LOs) 2213, and a processing module such as a digital signal processor (DSP) 2220. As will be apparent to those skilled in the field of communications, the particular design of the communication subsystem 2211 will be dependent upon the communication network in which the device is intended to operate.
Network access requirements will also vary depending upon the type of network 2219. A GSM/UMTS device typically has a subscriber identity module (SIM) in order to get full service from the network. A cdma2000 device typically has such access credentials stored in it non-volatile memory or may use a removable user identity module (RUIM) in order to operate on a CDMA network. The SIM/RUIM interface 2244 is normally similar to a card-slot into which a SIM/RUIM card can be inserted and ejected like a diskette or PCMCIA card. The SIM/RUIM card can have approximately 64K of memory and hold many key configurations 2251, and other information 2253 such as identification, and subscriber related information.
When required network registration or activation procedures have been completed, mobile device 2200 may send and receive communication signals over the network 2219. As illustrated in
Signals received by antenna 2216 through communication network 2219 are input to receiver 2212, which may perform such common receiver functions as signal amplification, frequency down conversion, filtering, channel selection and the like, and in the example system shown in
Mobile device 2200 preferably includes a microprocessor 2238 which controls the overall operation of the device. Communication functions, including at least data and voice communications, are performed through communication subsystem 2211. Microprocessor 2238 also interacts with further device subsystems such as the display 2222, flash memory 2224, random access memory (RAM) 2226, auxiliary input/output (I/O) subsystems 2228, serial port 2230, two or more keyboards or keypads 2232, speaker 2234, microphone 2236, other communication subsystem 2240 such as a short-range communications subsystem and any other device subsystems generally designated as 2242. Serial port 2230 could include a USB port or other port known to those in the art.
Some of the subsystems shown in
Operating system software used by the microprocessor 2238 is preferably stored in a persistent store such as flash memory 2224, which may instead be a read-only memory (ROM) or similar storage element (not shown). Those skilled in the art will appreciate that the operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile memory such as RAM 2226. Received communication signals may also be stored in RAM 2226.
As shown, flash memory 2224 can be segregated into different areas for both computer programs 2258 and program data storage 2250, 2252, 2254 and 2256. These different storage types indicate that each program can allocate a portion of flash memory 2224 for their own data storage requirements. Microprocessor 2238, in addition to its operating system functions, preferably enables execution of software applications on the mobile device. A predetermined set of applications that control basic operations, including at least data and voice communication applications for example, will normally be installed on mobile device 2200 during manufacturing. Other applications could be installed subsequently or dynamically.
A preferred software application may be a personal information manager (PIM) application having the ability to organize and manage data items relating to the user of the mobile device such as, but not limited to, e-mail, calendar events, voice mails, appointments, and task items. Naturally, one or more memory stores would be available on the mobile device to facilitate storage of PIM data items. Such PIM application would preferably have the ability to send and receive data items, via the wireless network 2219. In a preferred embodiment, the PIM data items are seamlessly integrated, synchronized and updated, via the wireless network 2219, with the mobile device user's corresponding data items stored or associated with a host computer system. Further applications may also be loaded onto the mobile device 2200 through the network 2219, an auxiliary I/O subsystem 2228, serial port 2230, short-range communications subsystem 2240 or any other suitable subsystem 2242, and installed by a user in the RAM 2226 or preferably a non-volatile store (not shown) for execution by the microprocessor 2238. Such flexibility in application installation increases the functionality of the device and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications may enable electronic commerce functions and other such financial transactions to be performed using the mobile device 2200.
In a data communication mode, a received signal such as a text message or web page download will be processed by the communication subsystem 2211 and input to the microprocessor 2238, which preferably further processes the received signal for output to the display 2222, or alternatively to an auxiliary I/O device 2228.
A user of mobile device 2200 may also compose data items such as email messages for example, using the keyboard 2232, which is preferably a complete alphanumeric keyboard or telephone-type keypad, in conjunction with the display 2222 and possibly an auxiliary I/O device 2228. Such composed items may then be transmitted over a communication network through the communication subsystem 2211.
For voice communications, overall operation of mobile device 2200 is similar, except that received signals would preferably be output to a speaker 2234 and a microphone 2236 would generate signals for transmission. Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on mobile device 2200. Although voice or audio signal output is preferably accomplished primarily through the speaker 2234, display 2222 may also be used to provide an indication of the identity of a calling party, the duration of a voice call, or other voice call related information for example.
Serial port 2230 in
Other communications subsystems 2240, such as a short-range communications subsystem, is a further optional component which may provide for communication between mobile device 2200 and different systems or devices, which need not necessarily be similar devices. For example, the subsystem 2240 may include an infrared device and associated circuits and components or a Bluetooth™ communication module to provide for communication with similarly enabled systems and devices.
The embodiments described herein are examples of structures, systems or methods having elements corresponding to elements of the techniques of this application. This written description may enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the techniques of this application. The intended scope of the techniques of this application thus includes other structures, systems or methods that do not differ from the techniques of this application as described herein, and further includes other structures, systems or methods with insubstantial differences from the techniques of this application as described herein.