KR20030020407A - Radio communication device with slot antenna - Google Patents

Abstract

A wireless communication device, such as a mobile phone or a Bluetooth device, includes a ground conductor 302 comprising a slot 304 and means 308 coupling a transceiver to the slot to make the ground conductor act as an antenna. Such a device can allow for efficient broadcast performance to be obtained with a significantly smaller volume than known antenna arrangements. In one embodiment, ground conductor 302, slot 304 and transceiver are integrated into module 206, which is adapted to connect to other ground conductors that provide most of the antenna area. Other conductors will generally be a printed circuit board ground plane or mobile phone handset. Matching and wide band circuits will conveniently be included in the module. By changing the connection area between the module and the other ground conductor, the resonant frequency of the slot 304 can be modified.

Description

Radio communication device with slot antenna

Wireless terminals, such as mobile phone handsets, are generally included in an external antenna, such as a regular mode spiral or zigzag line antenna, or a planar inverted-F antenna (PIFA) or similar internal antenna.

These antennas are small (proportional in wavelength) and, therefore, narrowband due to the fundamental limitations of small antennas. However, cellular wireless communication systems generally have a fractional bandwidth of 10% or more. For example, to achieve this bandwidth from PIFA, there is a direct relationship between the bandwidth of the patch antenna and its volume, which requires considerable volume, but this volume is not readily available due to the current tendency to miniaturize the handset. Thus, due to the above mentioned limitations, efficient broadband radiation cannot be achieved from the small antennas of today's wireless terminals.

Another problem with known antenna arrangements for wireless terminals is that they are generally uncomfortable, and thus are strongly coupled to the terminal case. As a result, a significant amount of radiation is emitted from the terminal itself rather than from the antenna. An antenna supply is directly coupled to the terminal case, and a wireless terminal having the advantage of its direct coupling is disclosed in the currently pending international patent application WO 02/13306 (application reference number PHGB010056). When the antenna is supplied through a suitable matching network, the terminal case or other ground conductor acts as an efficient broadband radiator.

The present invention relates to a wireless communication device comprising a ground conductor and a transceiver, and also to a wireless communication device including such a device.

1 shows a model of an asymmetric dipole antenna, showing a combination of an antenna and a wireless terminal.

2 is a plan view of a radio frequency (RF) module installed on a ground conductor.

3 is a plan view of an RF module including a slotted ground plane;

4 is a graph of the efficiency E measured against the frequency f of MHz for a configuration similar to that shown in FIGS. 2 and 3.

5 is a plan view of a test piece including a slotted PCB ground surface supplied by a microstrip line.

FIG. 6 is a graph of return loss (S ₁₁ ) of dB measured against frequency f of MHz for the test piece shown in FIG. 5 without matching.

FIG. 7 is a Smith chart showing impedance measured in the test piece shown in FIG. 5 over a frequency range of 800-3000 MHz without matching. FIG.

FIG. 8 is a graph of return loss (S ₁₁ ) of dB measured against frequency f of MHz for the test piece shown in FIG. 5, supplied through a series LC matching circuit. FIG.

FIG. 9 is a Smith chart showing the impedance measured at the test piece shown in FIG. 5, supplied through a series LC matching circuit, over a frequency range of 800-3000 MHz. FIG.

FIG. 10 is a graph of measured efficiency (E) versus frequency f of MHz for the test piece shown in FIG. 5 without matching. FIG.

11 is a plan view of a particular embodiment of an RF module.

FIG. 12 is a graph of measured efficiency (E) versus frequency (f) of MHz for the RF module shown in FIG.

FIG. 13 is a graph of return loss (S ₁₁ ) of dB measured against frequency f of MHz for the RF module shown in FIG.

It is an object of the present invention to provide a compact antenna device for a wireless terminal.

According to a first aspect of the invention there is provided a wireless communication device comprising a ground conductor comprising a slot and means for coupling a transceiver to the slot, whereby the ground conductor can function as an antenna.

Slots can efficiently couple transceivers to ground conductors, and the dimensions of ground conductors typical of wireless terminals, such as mobile telephone handsets, provide wide radiation bandwidth. In the device manufactured according to the invention, the area to be separated from the components in order to avoid interference with or from the antenna is much smaller than known antenna devices.

The ground conductor and associated slots can be included in a module that installs on another ground conductor, such as a printed circuit board ground plane. Such devices have the advantage that the supply is precisely controlled within the module and that other ground conductors provide a larger radiation area. Such a module can also be made significantly smaller than known antenna solutions and can additionally include transceiver circuitry in the same volume.

Matching circuitry may also be included in the module. The device manufactured according to the invention is particularly suitable for driving through a broadband matching circuit. Dual and multi-band matching circuits may also be included.

By adding PIFA to the device manufactured according to the invention, polarization diversity can be achieved from very small volumes.

According to a second aspect of the present invention there is provided a wireless communication device comprising an apparatus manufactured according to the first aspect of the invention.

The present invention is similar to those of an asymmetric dipole that can separate the impedances of the antenna and the wireless handset, which are not proposed in the prior art, and are based on the recognition that the antenna impedance can be replaced with a non-radiative coupling element. .

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

Like reference numerals in the drawings are used to indicate like components.

Common pending international patent application WO 02/13306 (Application No. PHGB010056) discloses an antenna device in a case of a wireless terminal or other ground conductor which forms part of a terminal which is supplied via a suitable matching network and which acts as an efficient broadband radiator. . All content of these applications is incorporated herein by reference.

In summary, the combination of an antenna and a wireless terminal (eg mobile telephone handset) may be considered an asymmetric dipole. 1 shows this model of impedance seen by a transceiver in transmission mode at the antenna supply point of a wireless handset. The first arm 102 of the asymmetric dipole represents the impedance of the antenna, the second arm 104 represents the impedance of the handset, and both arms are driven by the source 106. As shown in the figure, the impedance of such a device is substantially equal to the sum of the impedances of each arm 102, 104 driven separately with respect to the virtual ground 108. The model is equally valid for the receiving side when the source 106 is replaced by an impedance representing the impedance of the transceiver.

It is disclosed in WO 02/13306 that the antenna impedance can be replaced by a physically small capacitor that couples the antenna supply to the handset. In one embodiment the capacitor was a parallel planar capacitor having a size of 2x10x10 mm on a handset with a size of 10x40x100 mm. The careful design of the handset allows the bandwidth to be much larger than conventional antenna and handset combinations. The reason is that while the handset operates as a low Q radiating element (simulations show that typical Q is about 1), conventional antennas generally have a Q of about 50.

The problem with using parallel planar capacitors to couple the transceiver to the ground plane is that it requires significant volume (although this volume is much less than that required by PIFA). As part of the current trend towards ever-smaller wireless terminals, low profile modules are being developed that include the RF circuitry needed for a device (such as a mobile phone or a Bluetooth terminal). Such modules are generally shielded by a metal container, although shielding is not always necessary. The addition of a capacitor plate of the size described above doubles its height, thereby increasing the volume occupied by such a module by more than two times, which is undesirable.

In the device manufactured according to the invention, RF power is supplied from the transceiver to the ground plane via a slot in the ground plane. This apparatus is shown with reference to FIGS. 2 and 3, each of which is a plan view of an RF module including an RF module mounted on a ground conductor and a slotted ground plane. The RF module 206 is mounted on a printed circuit board (PCB) having a rectangular ground surface 202 with a rectangular cutout 204 (shown in dashed). Module 206 electrically connects two ground surfaces 202 and 302, including ground surface 302 having a size slightly larger than cutout 204. The ground plane 302 of the module has a slot 304 about 1/4 wavelength longer than the operating frequency of the module 206. The module includes an RF circuit 306 (not shown in detail) and a connection 308 to the side of the slot 304 away from the RF circuit.

In operation as a transmitter, power from RF circuit 306 is supplied to ground planes 302, 302 across a slot. In operation as a receiver, RF signals received by ground surfaces 302 and 202 are extracted by slot 304 and supplied to RF circuit 306. Such a supply does not provide optical bandwidth like the capacitor coupling described in WO 02/13306, but the device provides a wider bandwidth compared to conventional antennas, and there is a lot of trade-off between volume and bandwidth. Will be appropriate for the application.

The slot 304 shown is wrapped around the RF circuit 306. The resonant frequency of a slot can be designed primarily by quarter wavelength slot resonance, and its bandwidth determined by the combination of slot 304 and ground planes 302, 202. Incorporating the slot 304 into the module 206 enables tuning its resonant frequency by changing the connections between the module's ground plane 302 and the PCB ground plane 202. Although the cutout 204 of the PCB ground surface 202 is rectangular and shown to be of similar size as the module 206, this is not important. The cutout 204 needs to be free of metallisation on the PCB directly below the slot 304 (actually the cutout 204 is larger than the slot 304 by at least product tolerances and alignment errors). The effective slot sizes are determined by the sizes of the slots 304 in the module 206, not by the sizes of the cutouts 204). The module is relatively distant from the circuitry remaining on the PCB, but since it remains accessible for direct access to the module, the module 206 location of the PCB edge is appropriate as shown.

Measurements were made for an embodiment for use in a Bluetooth application, similar to that shown in FIGS. 2 and 3. In this embodiment, the module 206, which must include the RF circuit and the slot 304, was provided at the PCB ground plane 202 (without the cutout 204). The module 206 is housed in a metal container connected to the PCB ground plane 202, which ensures that the reference ground is shared between RF and other elements. The dimensions of the PCB ground plane 202 are 100x40 mm, and their volume to accommodate the module 206 and the slot 304 (and thus correspond to the volume of the module as shown in Figure 3) is 15x13x2 mm. The folded slot 304 has a width of 1 mm and a total length of 17 mm.

The efficiency E of this embodiment is measured and the result is shown in FIG. 4 for frequencies between 2300 and 2760 MHz. It can be seen that the efficiency is greater than 50% over a bandwidth above 350 MHz. This occupies less than half the volume, which is about twice the bandwidth that could be obtained from a 15x10x5 mm PIFA. Another advantage is that unlike other planar antenna solutions, no significant volume is required to space other circuits to avoid interference with antenna operation.

Test pieces were made to investigate other applications of the present invention. FIG. 5 is a plan view of a test piece including a copper ground plane 202 having a size of 40 × 100 mm on a 0.8 mm thick FR4 circuit board (measured insulation constant of 4.1). A slot 304 of 3x26.5 mm is provided in the ground plane, which is on the back side of the PCB and through the via hole 508 spaced 3 mm from the closed end of the slot 304 at the edge of the slot. It is supplied via a 2.5 mm wide microstrip line 506 (shown in dashed lines) to be connected.

The return loss (S ₁₁ ) of the test piece is measured and the results are shown in FIG. 6 for frequencies between 800 and 3000 MHz. A Smith chart illustrating the impedance measured in this embodiment over the same frequency range as the frequency is shown in FIG. 7. It can be seen that the 10db bandwidth of this embodiment is about 175MHz. The low operating frequency compared with the first embodiment is a result of the non-bandwidth being kept similar and the slot length being longer.

Because of the inherent wideband performance of this embodiment, the bandwidth can be wider by the use of wideband matching circuits without significant loss of efficiency. The frequency response corresponding to that predicted from this device is inductive at low frequencies and capacitive at high frequencies. Therefore, a series LC resonant circuit is suitable. 8 (loss of reflection) and 9 (Smith chart) show the simulated response when an inductance of 5 nH and a capacity of 1.3 pF are arranged in series with the slot feed 508. The 10dB bandwidth increases to about 200MHz, and the tuning component losses are less than 0.2dB at the center of the band (assuming Q of the component is 50). It is clear that the response can be further optimized, for example, by supplying slot 304 at a slightly higher impedance level or by providing a second parallel resonant circuit. As a useful side effect, the bandwidth extension circuit performs a useful band filtering function to reduce the filtering requirements of the RF circuit 306. This is beneficial if there is another system separated in frequency present in the device and an increase in isolation is required.

The efficiency E of the test piece is measured and the result is shown in FIG. 10 for frequencies between 1500 and 2200 MHz. It can be seen that the efficiency is more than 50% over a bandwidth of about 400 MHz.

11 shows a top view of an embodiment of an RF module 206 made in accordance with the present invention having an overall size of about 15x13 mm. This embodiment was manufactured by Philips Semiconductors, product number BGBA100, and is intended for use in Bluetooth applications. L-type ground conductor 302 includes an L-shaped slot 304. The slot is supplied through a 1.5 nH inductor connected to junctions 1102 and 308 and a 3 pF series capacitor connected to junctions 1104 and 1106. Another matching circuit, including a 1.3nH series inductor and a 1.8pF shunt capacitor, is connected between the series capacitor and the 50µs feed. Other RF circuits 306, not shown, are included in the area surrounded by the dotted lines. This circuit includes a plurality of ground connections, so that when mounted on a PCB, the entire area enclosed by the dashed lines can be considered substantially the ground conductor.

In this embodiment, the PCB ground plane is closer to half the wavelength length than the test piece of FIG. 5, significantly improving bandwidth. For each of the frequencies between 1500 and 3500 MHz, FIG. 12 is a graph of the measured efficiency E of the module of FIG. 11, and FIG. 13 is a graph of the measured return loss S ₁₁ of the module of FIG. ₁₁ . The module 206 was mounted with a slot 304 opening on the long edge of the PCB with dimensions of 100 × 40 mm, the module being spaced 25 mm from the short edge of the PCB. Efficiency is greater than 80% and return loss is greater than 10dB over 1GHz bandwidth from 1900 to 2900MHz. The link test measurement shows sufficient performance over a length of more than 10m, thus meeting the requirements of the Bluetooth specification.

The present invention is also suitable for use in multiband applications, where a multiband matching circuit will be included in module 206 for multiband use. In such applications, the wideband nature of the present invention provides multiband performance much simpler than narrowband antennas.

The present invention may be used to provide polarization diversity from a wireless terminal. Desirable polarization diversity is difficult to achieve in practice because in small antennas, the antenna and PCB interact with each other and the PCB emits more frequently than the antenna itself. Thus, polarization is not of the antenna but of the PCB. This means that even if two small antennas are oriented at right angles, the composite radiation has substantially the same polarization.

Polarization diversity can be achieved by using slot 304 (as described above) in combination with conventional PIFA. The antennas can be located in the same volume (very small RF module) but have substantially different polarizations. This is because the slot 304 is inserted into the PCB rather than supplied corresponding to the PCB. The polarization of the slot 304 depends on its orientation in the PCB, and the PIFA will have the polarization of the PCB. This may be arranged to provide orthogonality and will be at least partially achieved without modification of the PIFA or notch. If the two antennas are very tightly coupled, a switch may also be provided across the notch when the PIFA receives.

As described above, the slot 304 may be included in the ground plane 302 or the PCB ground plane 202 of the RF module 206. RF components may or may not be provided in the form of module 206 when included in PCB ground plane 202. The advantage of including the slot 304 in the module 206 is that the supply can be more accurately controlled while matching, bandwidth expansion, and multi-band operation can be performed in a well controlled manner. It can be seen that there are significant advantages in the manufacture of integrated modules that can be connected to the PCB ground plane for improved radiation performance.

The above references to the RF module 206 do not exclude the inclusion of other non-RF components such as, for example, baseband circuitry and device control circuitry within the module. In the embodiments shown above, the slot 304 is open at one end. However, when supplied in a planar manner, slots shielded at both ends may equally well be used.

By reading this specification, other changes will be apparent to those skilled in the art. Such modifications will include other features already known in the design, manufacture, and use of some of the wireless communications devices and components, which may be used instead or in addition to the features already described herein. The word "a" or "an" preceding an element in this specification and claims does not exclude the presence of a plurality of such elements. In addition, the word "comprising" does not exclude the presence of elements or steps other than those listed here.

Claims (11)

12. A wireless communications apparatus, comprising: a ground conductor comprising a slot and means for coupling a transceiver to the slot, thereby making the ground conductor function as an antenna. 10. The wireless communications device of claim 1, wherein the ground conductor, transceiver, and slot are integrated into a module adapted for connecting to another ground conductor. 3. The wireless communications device of claim 2, wherein the module is housed in a conducting container. 4. The wireless communications apparatus of claim 2 or 3, wherein the module further comprises a matching circuit. 5. The wireless communications apparatus of claim 4, wherein the matching circuit is adapted for dual band matching. Device according to one of the claims 2 to 5, characterized in that a means for changing the connection area between the ground conductor and the other ground conductor is provided, thereby changing the operating frequency of the device. Device. 7. A wireless communication device according to any one of the preceding claims, wherein the slot is folded or zigzag. 8. The radio communication device according to any one of claims 1 to 7, wherein the other ground conductor is a printed circuit board ground plane. 9. A wireless communications device as claimed in any preceding claim, wherein said other ground conductor is a handset case. 10. The wireless communications device of any one of the preceding claims, further comprising a planar inverted-F antenna, wherein polarizations of the ground conductor and the planar antenna are significantly different. A wireless communication instrument comprising the device of claim 1.