KR20080086322A - Antenna device and portable radio communication device comprising such antenna device - Google Patents

Abstract

An antenna device and a portable radio communication device having the same are provided to supply a proper signal regardless of a gain change by uniformly maintaining a noise figure over the entire operating frequency range through a half-loop antenna. An antenna device for a portable radio communication device receives radio signals in at least a first operating frequency band. The antenna device includes a radiation element(10), a ground plane(312), and an amplifier stage. The radiation element has a feed unit. The amplifier stage is connected to the feed unit of the radiation element and connectable to a receiving device for radio signals. The radiation element is a part of a loop. The loop includes a part of the ground plane.

Description

TECHNICAL DEVICE AND PORTABLE RADIO COMMUNICATION DEVICE COMPRISING SUCH ANTENNA DEVICE

1 is a schematic diagram showing an antenna device according to the invention connected to an FM receiving circuit;

2 shows in detail a first embodiment of an antenna device according to the invention;

3 shows in detail a second embodiment of an antenna device according to the invention;

4 is a schematic diagram of a radiating element structure of an antenna device according to the present invention;

5 is a schematic diagram of a multi-turned radiating element structure of an antenna device according to the present invention.

6 is a partially cutaway perspective view of an antenna device in accordance with the present invention embedded in a portable wireless communication device.

 7 is a partially cutaway perspective view of an antenna device of a variant embodiment in accordance with the present invention embedded in a portable wireless communication device.

The present invention relates generally to an antenna device, and more particularly to an antenna device for use in a wireless communication device, such as a mobile phone, adapted for radio signals having a relatively low frequency, such as radio signals in the FM band. It is about.

Embedded antennas have long been used in portable wireless communication devices. There are many advantages associated with using built-in antennas, one of which is that built-in antennas are small and lightweight, making them suitable for applications where size and weight are important, such as mobile phones.

However, the application of embedded antennas in mobile phones imposes restrictions on the structure of the antenna element. In particular, in portable wireless communication devices, space for an embedded antenna array is limited. These constraints may make it difficult to find the structure of the antenna for a wide range of operating bands. This is especially true for antennas intended for use with radio signals of relatively low frequencies as the given physical length of the antennas becomes longer than antennas operating with relatively high frequencies.

One particular application that operates in a relatively low frequency band is an FM radio application. This FM band is limited as frequencies between 88 and 108 MHz in Europe or between 76 and 110 MHz in the United States. Prior art antenna structures, such as loop antennas or monopole antennas fitted within the case of a portable radio device, indicate that the antenna has either too bad performance over a sufficiently wide frequency band or enough performance over a too narrow frequency band. Will result in unsatisfactory operation.

Instead, a conventional FM antenna for a portable wireless communication device is provided in a headphone wire connected to the portable wireless communication device. The structure with relatively long wires allows sufficient antenna length even for low frequency applications. However, if no external antenna is allowed, this solution is clearly not feasible.

Another problem is that the second antenna interferes with the operation of the FM antenna when a second antenna such as a Global System for Mobile Communications (GSM) antenna is provided to a communication device such as an FM antenna.

It is an object of the present invention to provide a built-in antenna device for use in a portable wireless communication device, so as to operate with sufficient performance over a frequency band having a relatively low frequency, such as an FM radio band.

The present invention is based on an implementation in which an active embedded antenna can be formed as a half loop antenna.

According to the invention, an antenna device is provided in a portable wireless communication device adapted to receive wireless signals in at least a first operating frequency band, the antenna device being connected to a feeder, a ground plane and the feeder and to a radio signal And a radiating element comprising an amplifying stage connectable to a receiving device for the device, wherein the antenna device is characterized in that the radiating element is part of a loop, wherein the loop comprises part of the ground plane.

Also provided is a portable wireless communication device comprising the antenna device.

The antenna device according to the present invention provides operation with sufficient performance over a frequency band with a relatively low frequency, such as the FM radio band. By using a half-loop antenna, it has been found that the noise figure is uniform over the entire operating frequency range, providing an adequate signal for the noise ratio despite the gain variations.

In a preferred embodiment, the antenna device comprises a printed circuit board provided with a ground plane, wherein the feeding portion of the radiating element is provided at or near one end of the printed circuit board and of the radiating element opposite to the feeding portion. An end is grounded at or near the other end of the printed circuit board. In this way, the area of the printed circuit board is used to the maximum.

The capacitor is preferably connected between the radiating element and the ground portion relatively close to the feeding portion of the radiating element. Such a capacitor, preferably having a value of 10-40 pF, increases the source resistance exhibited by the transistor of the amplifier, thereby matching noise and increasing safety. In addition, crosstalk from the first antenna is minimized because the radiating element is grounded at or near the ends of the printed circuit board where the field E field of the first antenna device, such as a GSM antenna, is large.

Still other preferred embodiments are defined in the dependent claims.

The invention will now be described by way of example with reference to the attached drawings.

Detailed description of the invention

In the following, a detailed description will be given of a preferred embodiment of an antenna device and a portable wireless communication device according to the invention.

In the following description and claims, the term radiating element is used. It is apparent that the term is intended to cover electrically conductive elements arranged for transmitting, receiving and transmitting wireless signals.

First, referring to FIG. 1, an overall configuration of an antenna device 1 according to the invention is shown. It comprises a radiating element 10 in the form of a non-resonant piece of electrically conductive material. This radiating element is part of a half-loop antenna, as described in detail below. That the radiating element is part of a loop means a half loop antenna, where the loop comprises part of the ground plane. Thus, the non-resonant pieces of electrically conductive material form a half loop and the loop is completed by the ground plane.

The radiating element has a shunt capacitor 20 arranged to resonate with the radiating element, an amplifier input, and a feed part 11 connected to an optional electrostatic discharge (ESD) protection circuit. The resonant frequency response acts as a bandpass filter for signals in the operating frequency band. For operation in the FM band, the bandpass filter is between 88 and 108 MHz in Europe and between 76 and 110 MHz in the United States.

The function of the resonant frequency response also acts as an ESD protection circuit, effectively blocking most of the ESD pulse spectrum. In addition, the filter can detect interference from signals that may be from other antennas provided to a wireless communication device, such as electromagnetic interference (EMI) signals and cellular GSM antennas that work well at frequencies on the FM antenna. Eliminate or at least reduce.

The amplifier stage 30 is arranged behind the parallel capacitor 20 to amplify the signals received by the radiating element 10.

The signals received and amplified by the antenna device 1 are applied to an FM receiving circuit 40, which may be a conventional circuit manufactured by Philips Semiconductors and sold under the name HVQFN40. The FM receiving circuit comprises an RF input 41 connected to the amplifier 30.

The parallel capacitor 20 and the amplifier stage 30 is preferably provided relatively close to the radiating element 10 to minimize the interference and parasitic effects from an external signal source.

   The implementation of the overall idea represented in FIG. 1 will now be described with reference to FIG. 2.

The amplifier stage 30 includes a field effect transistor (FET) having a gate connected to the parallel capacitor 20, a source directly connected to ground, and a drain connectable to the input 41 of the FM receiver circuit 40. There is also a load resistor 32 connected between the drain of the transistor 31 and the feed voltage Vdd.

For the antenna device 1 to operate, the transistor has a minimum noise figure of 1 dB or less and a gain of 15 dB or more in the operating frequency band. It is also desirable for the transistor to have a noise resistance Rn of less than 10 Ohms to achieve the best possible signal reception for any antenna structures. Another desirable characteristic of transistors is their low input capacitance, preferably less than 3 pF, resulting in high input impedance.

It is obvious that the antenna device described above is an active device. It is preferable to allow the radiating element to be designed directly with the amplifier stage in the above-described structure.

An alternative implementation of the idea of the invention in the form of a second embodiment will now be described with reference to FIG. 3. As in the first embodiment described above, the antenna device comprises a radiating element 10 having a feed section 11, a parallel capacitance and an amplifying stage 30. However, in the second embodiment the parallel capacitance is adjustable, i.e. implemented as a so-called varactor 120 to provide a controllable antenna device. Moreover, the amplifier stage is a so-called cascode amplifier 130. This cascode amplifier includes a field effect transistor 131 with a gate connected to the radiating element and a parallel capacitance, a source directly connected to ground, and a drain connected to the second field effect transistor 133. . The gate of the second transistor 133 is connected to ground via a capacitor 134. The drain of the second transistor 133 is connectable to the input portion 41 of the FM receiver circuit 40. There is also a load resistor 132 connected between the drain of the second transistor 133 and the feed voltage Vdd.

In the second embodiment, the FM transmission circuit 140 is connected to the radiating element via the switch 141. This switch is essential if the input impedance Z _TX of the transmitting circuit is too low, such as 10 times lower than the input impedance Z _RX of the amplifier 130 in front of the receiving circuit 40. However, the switch 141 may be omitted if the input impedance Z _TX of the transmitting circuit is about the same as the input impedance Z _RX of the amplifier 130.

By providing a transmitting circuit connected to the radiating element 10, the radiating element can be shared to function for both transmitting and receiving. This transmitting circuit will preferably be connected to the radiating element at approximately the feed section 11.

The overall layout of the radiating element of the antenna device according to the invention will now be described with reference to FIGS. 4 and 5. The printed circuit board (PCB) 310 is suitably arranged in a portable wireless communication device (not shown in these figures). The ground plane 312 is provided on the printed circuit board. Signal loads corresponding to the amplifiers 30 and 130 described above are provided on the printed circuit board, which is preferably a multilayer printed circuit board. The radiating element 10, which is preferably a wire-shaped electrical conductor, is connected to the amplifier at the feed section 11, preferably at or near one end of the printed circuit board. This conductor continues parallel to the printed circuit board for most of the length of the printed circuit board 310 and at a distance h from the printed circuit board. The end of the conductor 10 opposite to the end connected to the signal source is connected to a ground plane 312 provided on the printed circuit board at or near the other end of the printed circuit board 310. This means that the radiating element forming the half-loop has the advantage of as much space as possible because the loop area is important for antenna performance.

The capacitor 20 is provided between the radiating element and the ground portion relatively close to the feed portion 11. These capacitors, preferably with a value of 10 to 40 pF, increase the source resistance seen by the amplifier's transistors to match noise and increase stability.

In an alternate embodiment, conductor 10 is provided in one or more turns and in the example shown in FIG. 5 in two turns. The conductor of the first half-loop is led to the lower side of the printed circuit board through the hole 314 in the printed circuit board. On its lower side, the conductor extends along the printed circuit board, preferably from one end of the printed circuit board to the other end in the form of a microstrip line 10a. There, the conductor is led along the printed circuit board at a distance from the printed circuit board through the second hole in the printed circuit board at a predetermined distance from the printed circuit board and finally grounded at the second end of the printed circuit board. . In this way, the radiation resistance proportional to the number of loop turns in the rectangle is increased to improve the performance of the antenna.

The ferrite inside the loop, referred to schematically at 14, can be used in both the embodiment of FIG. 4 and the embodiment of FIG. 6 to improve the performance of the antenna device.

A first preferred location of an antenna device according to the invention as described above with reference to FIGS. 1 to 3 will now be described with reference to FIG. 6, where a portable wireless communication device 300 such as a mobile phone The overall outline of the case is described.

 The case is shown partially cut away to clarify the location of the antenna device, which may be any of the devices described with reference to FIGS.

The printed circuit board 310 is provided in a case having a circuit (not shown) conventionally identified in a mobile phone. An FM receiving circuit 40 is also mounted on the printed circuit board. On top of the case there is provided an antenna radiating element 320 for transmitting and receiving RF signals for a cellular mobile phone such as a GSM system.

A battery package (not shown) is also provided towards the back of the case 300.

The FM antenna radiating element 10 is preferably positioned such that the radiating element 10 is connected to the FM circuit at the end of the printed circuit board opposite to the end where the radiating element 320 is provided. The radiating element then extends along the long side of the printed circuit board until it reaches the other end of the printed circuit board, where it is grounded to the ground plane 312 provided on the printed circuit board 310.

To make the antenna device less sensitive to orientation, the radiating element 10 may be provided to extend along a short side of the printed circuit board before being grounded to the ground plane 312 provided on the printed circuit board (FIG. 6).

Preferred embodiments of the antenna device according to the invention have been described. However, it will be apparent to those skilled in the art that embodiments may be varied within the scope of the appended claims without departing from the idea of the invention.

It is apparent that the shape and size of the antenna device according to the invention can be modified within the scope defined by the appended range. Thus, accurate antenna structures can be modified to correspond to the shape, desirable performance, and the like of the wireless communication device. The above described embodiments of the antenna device according to the invention have been described with antenna devices which are adapted for the reception of radio signals in the FM frequency band. However, other applications are also possible as used for digital video broadcast (DVC) signals in the frequency range of about 400-800 MHz.

Although portable wireless communication devices have been described with reference to use in mobile phones, it is evident that the idea of the present invention is also applicable to other portable wireless communication devices, devices that are portable but intended primarily for fixed use. Examples may be a small clock such as a travel alarm clock, a TV receiver or a game console. Applications of the antenna device according to the invention which may be present exist in personal digital assistants (PDAs), MP3 and CD players, FM radio receivers, and portable computers. Another application is in a vehicle. Thus, the term portable wireless communication device should be interpreted in a broad sense.

The embodiments described above with reference to FIGS. 6 and 7 include a GSM antenna. It is obvious that the operating frequency can be replaced by another antenna as long as it is on a low frequency band, such as the FM band. The second antenna can also be omitted.

Field effect transistors (FETs) have been described as preferred transistor types. It is apparent that other types of transistors may be used, such as heterojunction bipolar transistors (HBTs).

It is obvious that the transmitting circuit Tx portion can also be implemented in the first embodiment shown in FIG. It is also apparent that the capacitor 20 of the first embodiment can be replaced with a varactor.

According to the present invention, it is possible to provide a built-in antenna device for use in a portable wireless communication device so that it can operate with sufficient performance over a frequency band having a relatively low frequency, such as an FM antenna.

Claims (14)

An antenna device for a portable wireless communication device adapted to receive wireless signals in at least a first operating frequency band, Radiating element 10 comprising a feed unit (11; 111), Ground plane 312, In the antenna device comprising an amplifying stage 30 connected to a feeder of the radiating element and connectable to a receiving device for radio signals. The radiating element is part of a loop, wherein the loop comprises a part of a ground plane. The method of claim 1, The feeding portion 11 of the radiating element is provided at or near one end of the ground plane, and the end of the radiating element opposite to the feeding part is grounded at or near the other end of the ground plane. device. The method of claim 2, And a capacitor (20; 120) connected between the ground plane (312) and the radiating element relatively close to the feed section (11). The method of claim 3, wherein And the capacitor (20; 120) has a value of 10-40 pF. The method of claim 3, wherein The capacitor (120) has an adjustable capacitance value. The method of claim 1, The ground plane (312) is provided on a printed circuit board (310) and the radiating element (10) extends along a long side of the printed circuit board. The method of claim 6, The radiating element (10) is an antenna device, characterized in that additionally extends along the short side of the printed circuit board (310). The method of claim 1, The radiating element (10) is an antenna device, characterized in that it comprises a plurality of turns. The method of claim 8, A portion of the radiating element (10) is characterized in that it is provided in part as a micro strip line (10a). The method of claim 1, And said radiating element is designed directly with said amplifier stage. The method of claim 1, An antenna device, characterized in that it comprises a ferrite (14) inside the half-loop of the radiating element. The method of claim 1, And the radiating element (10) is connectable to a transmitting circuit (40). The method of claim 1, And the first operating frequency band is an FM band. A portable wireless communication device (300) comprising an antenna device according to claim 1.

Images