Patent Grant
7808433
The present invention relates generally to antenna devices and more particularly to a controllable internal multi-band antenna device for use in portable radio communication devices, such as in mobile phones. The invention also relates to a portable radio communication device comprising such an antenna device.
Internal antennas have been used for some time in portable radio communication devices. There are a number of advantages connected with using internal antennas, of which can be mentioned that they are small and light, making them suitable for applications wherein size and weight are of importance, such as in mobile phones. A type of internal antenna that is often used in portable radio communication devices is the so-called Planar Inverted F Antenna (PIFA).
However, the application of internal antennas in a mobile phone puts some constraints on the configuration of the antenna, such as the dimensions of the radiating element or elements, the exact location of feeding and grounding portions etc. These constraints may make it difficult to find a configuration of the antenna that provides a wide operating band. This is particularly important for antennas intended for multi-band operation, wherein the antenna is adapted to operate in two or more spaced apart frequency bands. In a typical dual band phone, the lower frequency band is centered on 900 MHz, the so-called GSM 900 band, whereas the upper frequency band is centered around 1800 or 1900 MHz, the DCS and PCS band, respectively. If the upper frequency band of the antenna device is made wide enough, covering both the 1800 and 1900 MHz bands, a phone operating in three different standard bands is obtained. In the near future, antenna devices operating four or even more different frequency bands are envisaged.
The number of frequency bands in passive antennas is limited by the size of the antenna. To be able to further increase the number of frequency bands and/or decrease the antenna size, active frequency control can be used. An example of active frequency control is disclosed in the Patent Abstracts of Japan 10190347, which discloses a patch antenna device capable of coping with plural frequencies. To this end there are provided a basic patch part and an additional patch part which are interconnected by means of PIN diodes arranged to selectively interconnect and disconnect the patch parts. Although this provides for a frequency control, the antenna device still has a large size and is not well adapted for switching between two or more relatively spaced apart frequency bands, such as between the GSM and DAMSP and/or DCS and PCS bands.
Instead, this example of prior art devices is typical in that switching in and out of additional patches has been used for tuning instead of creating additional frequency band at a distance from a first frequency band.
The Patents Abstracts of Japan publication number JP2000-236209 discloses a monopole antenna comprising a linear conductor or on a dielectric substrate, see
A problem in prior art antenna devices is thus to provide a multi-band antenna of the PIFA type with a small size and volume and broad frequency bands which retains good performance.
It is a main object of the present invention to provide such apparatus and method that at least alleviate the above problems.
An object of the present invention is to provide an antenna device of the kind initially mentioned wherein the frequency characteristics provides for at least two comparatively wide frequency bands while the overall size of the antenna device is small.
Another object is to provide an antenna device having better multi-band performance than prior art devices.
The invention is based on the realization that several frequency bands can be provided in a physically very small antenna by arranging the antenna so that the effective frequency band for the radiating elements can be controlled by controlling a switch. That is, the radiating elements may be tuned to a first frequency band, or a first set of frequency bands, in a first mode and a second frequency band, or set of frequency bands, in a second mode by operating said switch.
Patent applications SE0301200-2, SE0302979-0, SE0400203-6 filed in Sweden by the same applicant as the present application concerns similar matters as the present invention and are hereby incorporated by this reference. A concurrent application filed Sweden on the same date as the present application by the same applicant also concerns the same area and is hereby also incorporated by this reference.
It has been suggested that the radiating elements should be divided in two parts and connected with a switch to thereby achieve the above purpose. On such switch element may be a diode. Since, however, diodes are not ideal components it has been discovered that they may cause sharp harmonics which may not be tolerated in some standards. The present inventors have discovered that by providing the diode, or switch, on the ground plane, where the currents in the diode are much smaller compared to currents in the diode if provided on the radiating element, these harmonics are not at all as disturbing, and it is easier to design an antenna keeping within limits defined by different standards.
By placing the diode on the ground plane the harmonics created by the currents in the diode are not transmitted because they are trapped by the ground near the excitation.
Thus, there is provided a multi-band antenna device having an antenna volume as small as about 2 cm3 which means that the size of the antenna is remarkably reduced compared to standard multi-band patch antennas but still with maintained or improved RF performance. Also, the bandwidths of the antenna device according to the invention can be improved compared to corresponding prior art devices but without any increase in size, which is believed to be a result of the use of the basic frequency mode of the antenna structure. As an example thereof, bandwidths of as much as 15% of the centre frequency of the higher frequency band have been obtained as compared to 9-10% in conventional prior art antenna devices.
These objects among others are, according to a first aspect of the present invention, attained by an antenna device for a portable radio communication device operable in at least a first and a second frequency band, the antenna device comprises: a first electrically conductive radiating element having a feeding portion connectable to a feed device (RF) of the radio communication device for feeding and receiving radio frequency signals, a first ground plane portion arranged at a distance from the first radiating element, a second ground plane portion, and a controllable switch arranged between the first and second ground plane portion for selectively interconnecting or disconnecting the first and second ground plane portion.
The above objects among others are, according to a second aspect of the present invention, attained by a method for achieving multi-band characteristics for a antenna having at least one radiating element provided above a first and a second ground plane portion, and wherein the radiating element is connected to the first ground plane portion, comprising the steps of:—feeding a radio frequency signal to the radiating element, and—operating a switch provided between the first and second ground plane portions, wherein the switch is open to radio frequency signals in a first mode and closed to radio frequency signals in a second mode, to alter the effective operating frequency band of the antenna.
The above objects among others are, according to a third aspect of the present invention, attained by a portable radio communication device, comprising such an antenna device.
By dividing the ground plane in two parts and connecting these two parts with a switch it is possible to control the configuration of the ground plane and thereby the resonance frequency of the antenna.
According to a variant of the present invention the switch comprises a PIN diode.
According to a variant of the present invention the state of the switch is controlled by means of a control voltage input (VSwitch).
By using a PIN diode as a switch to state of the switch is easily controllable by providing a voltage input.
According to a variant of the present invention a high pass filter is connected between the first and second ground plane portions, which high pass filter allows the radio frequency signals to pass. This provides for the possibility to have a slit with a controllable length in the ground plane.
According to a variant of the present invention the radiating element is generally planar.
According to a variant of the present invention the first and second ground plane portion are arranged in the same plane having parallel normals. That is, the two ground plane parts are arranged side by side under the radiating element.
According to a variant of the present invention the first and second ground plane means are arranged in a substantially orthogonal relationship with substantial orthogonal normals. That is, the first ground plane portion is provided under substantially the complete radiating element and the second ground plane portion is provided at the side of the first ground plane portion and radiating element.
According to a variant of the present invention the second ground plane means comprises a feeding portion for feeding the control voltage to the switch. The feeding portion is connectable control logic in a radio communication device so that the radio communication device can select which operating mode the antenna should take.
According to a variant of the present invention a filter is provided between the feeding portion for feeding a control voltage to the switch and the second ground plane means. According to a variant of the present invention the filter is a low pass filter blocking signals at frequencies equal to and higher than the lower frequency band of the at least a first and a second frequency bands. This prevents high frequency signals from reaching the control logic connected to the feeding portion.
According to a variant of the present invention the antenna comprises a second radiating element. The radiating element is open for different designs to achieve resonance at the desired frequency.
According to a variant of the present invention the first and/or second radiating element has a configuration that provides for more than one resonance frequency. According to common knowledge it is possible to design a PIFA antenna to be resonant in two different frequency bands. By operating the switch it is therefore possible to achieve an antenna which is working in four different frequency bands.
According to a variant of the present invention the first radiating element comprises a connection to the first ground plane portion.
Further characteristics of the invention and advantages thereof will be evident from the following detailed description of embodiments of the invention.
The present invention will become more fully understood from the detailed description of embodiments of the present invention given herein below and the accompanying
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular techniques and applications in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and apparatuses are omitted so as not to obscure the description of the present invention with unnecessary details.
The radiating element 101 is connected 108 to a first ground plane portion 104. The first ground plane portion 104 is commonly connected to the ground of the portable radio telecommunication device, through a ground connection 105. The first ground plane portion is further connected to a second ground plane portion 106 through a switch 107. The antenna is basically a planar inverted F antenna with an adjustable ground plane configuration. When the switch 107 is open the radiating element 101 sees the first ground plane portion 104 as the complete ground plane, but when the switch 107 is closed the radiating element 101 sees the combined first and second ground plane portions 104 and 106 as the complete ground plane. This will affect the position of the resonance frequency or frequencies for the antenna.
Thus by operating the switch 107, the antenna can be switched between two different operating modes. For instance may the antenna be tuned to have two resonance frequencies when the switch is off, such as 850 Mhz and 1800 Mhz, corresponding to the DAMPS and DCS standards, and two other resonance frequencies when the switch is on, such as 900 Mhz and 1900 Mhz, corresponding to GSM and PCS. Thus an antenna is achieved which is capable of communication in four different frequency bands.
When Vswitch is applied to the second ground plane portion 106 the diode 201 will open, and basically provide a short-circuit between the first ground plane portion 104 and the second ground plane portion 106. Thus both the first and second ground plane portion will be connected to the radiating element 101 through the connection 108 and the diode 201.
Consequently, it is possible to control the configuration of the ground plane by applying a voltage to the second ground plane means 106, to thereby control the resonance frequency of the antenna.
By having the second ground plane portion 401 orthogonally to the first ground plane portion 104, the first ground plane portion can be provided to cover substantially the complete area of the radiating element 101. This is beneficial in that it reduces radiation in the direction of the first ground plane portion 104, which is often in the direction of a human head when the antenna is implemented in a portable radio telecommunication device. Thus this arrangement reduces SAR.
It will be obvious that the invention may be varied in a plurality of ways. The second ground plane portion may for instance be positioned side-by-side with the radiating element, or may have a U-shape so that a first part is parallel with the first ground plane portion and a second part is parallel with the radiating element. Such variations are not to be regarded as a departure from the scope of the invention. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0402182 | Sep 2004 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2005/001270 | 9/2/2005 | WO | 00 | 1/11/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/031170 | 3/23/2006 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20080246674 A1 | Oct 2008 | US |
