EP1538696A1 - Dualband cell phone with omnidirectional radiation pattern - Google Patents

Abstract

The telephone has an antenna, and an earth plane of length (L). The earth plane is divided into two parts (4, 5) with preset lengths (L1, L2), where the parts are connected through anti-resonant circuits (6, 6`) that are placed in an articulation hinge of two container parts (1, 2). The circuits have resonance centered on one of frequencies of a frequency band. The parts (4, 5) are disposed on respective parts (1, 2).

Description

Field of the invention

The invention relates to a dual-band mobile telephone in which the radiofrequency (RF) radiation pattern is omnidirectional for each of the frequency bands. This mobile phone has a antenna, internal or external, as well as a ground plane divided into two parts connected by a plug circuit.

The invention finds applications in the field of telephones dual-band mobile phones and, in particular, in the area of electrical dimensions of a dual-band mobile phone.

State of the art

In the field of mobile telephony and, in particular, dual-band mobile phones, tests are done on the phones to know, in particular, the radiated performance of the phone. These tests consist of measuring the emission / reception radiation of the antenna the phone for each frequency band on the phone. A diagram corresponding to this radiation is then plotted.

Generally, the measurement of this radiation is done by placing the mobile phone at a certain location compared to an antenna of measuring and moving the measurement antenna around the mobile phone, in an XYZ space, in order to perceive the radiation emitted or received while around the mobile phone. The minimum distance between the phone and the measuring antenna is usually λ / 2, where λ is the wavelength of the signal transmitted or received by the mobile phone antenna. The measurement of perceived radiation, point by point, by the measuring antenna allows draw a radiation diagram. This diagram is part of a plan YZ.

An example of a mobile phone, placed in a measurement space XYZ, is shown in Figure 1. This phone has a housing 1 including the length is approximately the length of the ground plane. It comprises also an antenna 3 which we want to measure the radiation in space X Y Z.

An antenna usually has a radiating element, such as a solenoid or radiating plane, and a ground plane. This mass plan has a length L. The ground plane can be constituted by the circuit board mobile phone. As a result, we often approximate the length of the ground plane by the length of the phone itself.

The length of the ground plane can be compared to the length waveform λ of the signal transmitted or received by the antenna of the mobile phone. When the length L of the ground plane is less than or equal to λ / 4, then the radiation pattern obtained for the mobile phone is omnidirectional. On the contrary, when the length L of the ground plane is equal to or greater than λ / 2, then the radiation pattern of the telephone mobile no longer has this omnidirectional feature.

In the particular case of a dual-band telephone, the diagram of radiation is established for each frequency band. We can get a diagram very different for one frequency band and the other. In In particular, a much higher power is obtained for a band low frequency than for a high frequency band. In other words, we obtain a more omnidirectional diagram for a frequency band low only for a high frequency band.

In the case of a dual-band telephone operating in the bands GSM (ie around 900 MHz) and DCS (ie around 1800 MHz), the radiated power measured with conventional tests for the GSM band is much larger than that obtained for the band DCS frequency. Indeed, at 900 MHz, if the length L of the ground plane is less than or equal to λ / 4, we obtain the radiating diagram of the figure 2. This diagram has two lobes, substantially round, placed side by side coast and centered on the Y axis Z. We understand, according to diagram, that the radiation is omnidirectional, in the Y direction. Thus, if we measure the power of radiation in one direction, by example the direction Y, we have a high power since directed totally in that direction.

As the wavelength is inversely proportional to the frequency, at a frequency of twice 900 MHz, that is to say 1800 MHz, the wavelength λ is divided by 2. The length L is no longer inferior or equal to λ / 4. We then obtain a radiation pattern of the type of the one shown in Figure 3. This radiation pattern has four lobes substantially symmetrical with respect to the point of origin O. Each lobe is located between the Y and Z directions. It is thus seen that the radiation is not omnidirectional. So, if we measure the power of radiation emitted in one of the directions, for example the direction Y, this power is relatively low since the radiation is distributed according to several directions.

The measured radiation power is therefore clearly higher in the GSM band than in the DCS band, with the technique previously described.

In addition, mobile phone manufacturers are seeking to integrate more and more functions in the housing of the phone. For that, and so to keep a small housing, manufacturers have more and more use of mobile phones having two articulated parts. These phones are usually called "clam". Examples of articulated two-part phones are described in EP-A-1 258,943 and US-A-5,561,437.

Presentation of the invention

In the invention, it is considered that, in practice, the antenna works both in the DCS band and in the GSM band, that is to say that the radiated power of the antenna is also good for the band DCS only for the GSM band. It is only the measurement technique that gives very different radiation power values for the GSM band and for the DCS band.

To overcome the disadvantages inherent in the measurement technique, the invention proposes to adapt the electrical dimensions of the telephones the operating frequencies used for the transmission of signals. In other words, the invention proposes to divide the ground plane of the mobile phone in a first and a second parts and, depending of the frequency band considered, take into account the length of a single part of the ground plane or the total length of the two parts of the mass plan. For this, the two parts of the ground plane are connected electrically by a plug circuit.

More specifically, the invention relates to a mobile phone type dual band comprising an antenna and a ground plane of length L, and characterized by the fact that the ground plane is divided into a first part of length L1 and a second portion of length L2, with L1 + L2 = L, the first and second parts being connected via at least one plug circuit.

• la premier partie du plan de masse est placée dans la première partie du boítier,
• la seconde partie du plan de masse est placée dans la seconde partie du boítier, et
• le circuit bouchon est placé dans une charnière d'articulation des première et seconde parties du boítier.

The invention relates, in particular, to a mobile phone of the clam type, comprising a first housing part and a second housing part hinged to each other. This mobile phone is characterized by the fact that:

• the first part of the ground plane is placed in the first part of the housing,
• the second part of the ground plane is placed in the second part of the housing, and
• the plug circuit is placed in a hinge hinge of the first and second parts of the housing.

Brief description of the drawings

Figure 1, already described, represents an example of a mobile phone in an XYZ measurement space.

Figure 2, already described, represents an example of a diagram of radiation conventionally obtained for the GSM frequency band.

FIG. 3, already described, represents an example of a diagram of radiation conventionally obtained for the DCS frequency band.

FIG. 4 represents a mobile phone of the clam type, in accordance with FIG. the invention.

FIGS. 5A and 5B show examples of diagrams of radiation obtained, respectively, for the GSM frequency bands and DCS, with the mobile phone of Figure 4.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As explained previously, the electrical dimensions of a mobile phone condition the phone radiation pattern, by the existence of a high-frequency current flow, due to the mass, electrical connections, etc. The invention proposes to adapt these electrical dimensions at the operating frequencies used by the mobile telephone for transmitting and / or receiving signals. In In particular, it proposes to adapt electrical dimensions to GSM and DCS frequencies.

This adaptation of the electrical dimensions is achieved by dividing the mobile phone's ground plane in a first part and a second part, which may be considered independently of one another or additionally one and the other. For that, the first and second parts of the ground plane are connected electrically via a circuit plug.

The mobile phone of the invention may be a monoblock telephone, that is to say formed of a single housing, in which the ground plane, by example made by the circuit board of the phone, is deliberately divided in two parts. The two parts of the mass plan are then located one to following each other, in the case of the phone, and connected by a circuit plug also located in the housing of the phone.

In a preferred embodiment of the invention, the telephone mobile is a clam-type telephone, that is to say with two parts articulated with each other. When both parties are substantially aligned, then the phone is in communication mode, that is, can make or receive calls. When both parties are substantially one above the other, so the phone is in non-communication, that is, it is off and can not receive or transmit calls.

The operation of a monoblock telephone of the invention is substantially identical to that of a phone type clam. It's the latter embodiment which will now be described.

Figure 4 shows an example of a mobile phone type clam, according to the invention. This mobile phone has a first part of housing 1 and a second housing part 2.

Generally, the first housing part 1 comprises an antenna transmission / reception 3. This antenna 3 can be an internal antenna, for example of patch type (that is to say a plane antenna located above a ground plane) or an external antenna, for example of the solenoid type.

The ground plane is usually formed by the circuit board of the mobile phone. In the invention, the ground plane is divided into two ground plane parts.

The first housing part 1 comprises a first part of the plan 4. This first ground plane part is formed by example, by the printed circuit located in the first housing part and with many components such as a screen display, a speaker, etc. The components of this printed circuit are classics in a clam-type mobile phone and are, by therefore, not described here.

The second housing part 2 has a second plan part 5. This second ground plane part is formed by example, by the printed circuit located in the second housing part 2 and with many components such as the keyboard.

The first ground plane portion 4 has a length L1. This length L1 is approximately the length of the first part of housing. The second ground plane portion 5 has a length L2, which is approximately the length of the second housing part. The lengths L1 and L2 may be the same or different. Whatever the values from L1 and L2, we consider that L1 + L2 = L, L being the total length of the plane mass of the phone, which is approximately the total length of the phone in communication mode.

As shown in FIG. 4, the first and second parts of the plane 4 and 5 are electrically connected by two plug circuits 6 and 6 '. Preferably, these plug circuits are placed at the edges of the parts of the ground plane, that is, as close as possible to the lateral extremities of these parts. Indeed, in practice, we see that the current flows, between the two parts, essentially by the side edges of the printed. We note that if we connect the first and second parts of the ground plane 4 and 5 by two wires of connections, so we get a radiation pattern identical to that obtained for a telephone the mass plan would be unique, that is to say, not divided, and length L.

The invention therefore proposes to place at least one plug circuit between the two parts of the ground plane. Preferably two plug circuits are placed between the two ground plane parts, near the edges both sides. These two plug circuits are centered on the resonance value of one of the frequencies of the bands transmission / reception of the mobile phone, called the tuning frequency.

More specifically, a plug circuit is a circuit composed of a capacitance and inductance in parallel and arranged to present a relatively high impedance for the tuning frequency and a relatively low impedance for all other frequencies. In particular, in the invention, we will choose to center the circuit stopper on a tuning frequency that corresponds to the frequency of the most band high, especially the DCS band.

In one embodiment of the invention, each circuit is realized plug using a subminiature inductor of type 0201 (from dimensions 0.6 x 0.3 mm) manufactured by Murata Manufacturing Co., Ltd.

These plug circuits keep the nominal dimension the mobile phone's ground plane for one of the frequency bands, in particular the GSM band, and to limit the size of the ground plane of the mobile phone to the first part of the case for the other band of frequency, in particular the DCS band.

In other words, the connection of the first and second parts of the housing plug circuits allows to have, at the frequency of 900 MHz, a plan of mass length L = L1 + L2 and, at the frequency of 1800 MHz, a plan of mass length L1. The second part of the ground plane 5, length L2, is then cut off and not taken into account for the measurement of radiation at 1800 MHz frequency. In other words, only the first part of the ground plane 4, of length L1 is taken into account for measurement of radiation in the DCS band. This is explained by the fact that at the low frequency, ie 900 MHz, the HF current flows throughout the length L1 + L2 of the ground plane and that at the high frequency, ie 1800 MHz, the current does not flow in the second part of the ground plane.

Thus, for operation in the GSM band, the length considered for comparison with the wavelength λ is the length total of the ground plane, ie L. We always have L ≤ λ / 4. The measurement of radiation thus provides an omnidirectional diagram, as shown in Figure 5A. For operation in the DCS band, the length considered for comparison with the wavelength λ is the length of the first part of the ground plane, L1. We then have L1 ≤ λ / 4. Measurement radiation then provides an omnidirectional diagram, as shown in FIG. 5B A radiation diagram is thus obtained omnidirectional for the high frequency, the DCS band, while keeping an omnidirectional diagram for the low frequency, ie the GSM band.

In other words, a mobile phone whose initial mass plan is of length L is divided into a first part of ground plane 4 of length L1 and a second ground plane portion 5 of length L2. We have therefore L1 + L2 = L. This division, or separation, of the ground plane can be implemented in any mobile phone. The phones However, mobile clam-type devices have the advantage of presenting a mass separated mechanically, by the very fact of the existence of two parts housing.

In such a clam-type telephone, there are generally electrical connections between the first and second housing parts. These electrical connections ensure the passage of digital signals or analog. These electrical links can be provided by a network wired, called FLEX. In the invention, to ensure that the entire HF current goes through the plug circuits, we propose to isolate electrically the electrical connections other than the plug circuits. This insulation can be achieved, for example, by means of a ferrite for all the electrical connections or a shock choke mounted on each electrical connection or by an electronic assembly comprising a filter network mounted on a bus. This insulation can be placed by example, in the hinge hinge of the two parts of the housing or in a specific cage, near the hinge.

Claims (6)

A dual-band mobile telephone comprising an antenna (3) and a ground plane of length L, characterized in that the ground plane is divided into a first portion (4) of length L1 and a second portion (5) of length L2, with L1 + L2 = L, the first and second parts being connected via at least one plug circuit (6). Mobile telephone according to claim 1, characterized in that the plug circuit is positioned on the edges of the first and second parts of the ground plane. Mobile telephone according to claim 1 or 2, characterized in that the plug circuit has a resonance centered on the frequency of one of the frequency bands. Mobile telephone according to claim 3, characterized in that the resonance of the plug circuit is centered on the highest band frequency. Mobile telephone according to any one of claims 1 to 4, comprising a first housing part (1) and a second housing part (2) articulated with each other, characterized in that : the first part of the ground plane (4) is placed in the first part of the housing, the second part of the ground plane (5) is placed in the second part of the housing, and the plug circuit (6) is placed in a hinge hinge of the first and second parts of the housing. Mobile telephone according to claim 5, characterized in that it comprises electrical connections placed between the first and the second housing parts, these connections being electrically isolated from the plug circuit.

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