EP1250724A1

EP1250724A1 - Antenna for mobile terminal

Info

Publication number: EP1250724A1
Application number: EP00987895A
Authority: EP
Inventors: Stig- Ke Larsson
Original assignee: Telia AB
Current assignee: Telia Co AB
Priority date: 1999-12-13
Filing date: 2000-12-12
Publication date: 2002-10-23
Also published as: SE9904541D0; SE9904541L; NO20022489L; NO326242B1; NO20022489D0; WO2001043225A1; EE200200320A; SE517911C2

Abstract

The invention relates to one at a mobile terminal arranged antenna element, which at use of said terminal makes possible a reduction of the from the mobile terminal transmitted radio frequency radiation towards the user's head and hand. Said reduction results in that the attenuation of the radio waves is reduced, which in its turn means that the range of the mobile terminal increases at given radiated transmitting power. By the invention, the by the user experienced quality in the communication will be improved in areas with poorer communication conditions. At good communication conditions the power consumption will be reduced, which means that the battery will last for a longer conversation time. The invention is characterized in an antenna (1), preferably an antenna of type helix antenna, which is angled out from the mobile terminal at conversation state, and which at watching mode is arranged to be foldable towards, alternatively foldable into, the upper part of the terminal.

Description

ANTENNA FOR MOBILE TERMINAL

TECHNICAL FIELD The invention relates to an antenna device at a mobile terminal, in the first place a hand portable terminal arranged to be connected to a telecommunication network for mobile telecommunication, for instance a cellular mobile telephone network. At use of said terminal with said antenna element an improved antenna efficiency is made possible at the mobile terminal, which results in improved communication possibilities and that the battery consumption in transmission mode is reduced.

PRIOR ART

It is known to, by different means, reduce influence of the towards the user's head directed radio waves at use of mobile terminals with the aim to reduce the risk that the human body is injured.

Accordingly there are solutions where the mobile terminal is placed in a case which screens off and by that limits the radio frequency radiation. There also are antenna solutions with directional antenna where the antenna is articulated arranged in a hinge device to make it possible to direct the antenna optimally.

In patent application JP 730 7607 is described a telescopic antenna (rod antenna) to a mobile terminal where the antenna can be bent in a joint. By this maneuver the radiation effect of the antenna at use can be directed away from the head in order to by that reduce the injure which the radiation might cause to close located parts of the head. Further has in the patent application EP 806 809A1 been described a mobile terminal which is equipped with a rod antenna which is articulated mounted in the upper side of the mobile terminal. A screening covering covers the point of attachment and the joint. The antenna can at use of the mobile terminal be angled from the head in order to by that reduce the radiation which is directed towards the head. By the antenna being angled from the head, the radiation levels directed towards the head are expected to fall below the threshold values which have been set by the health department of the Peoples Republic of China.

BACKGROUND OF THE INVENTION

An embarrassing dilemma for the telecommunication operators is that about one third of the experienced quality in a mobile telecommunication network is determined by the performance of the mobile terminal. Therefore the operator is directly afflicted if a terminal has poorer communication qualities, because the consequence of the experienced poor quality often is annoying to subscribers. In addition to that the experienced poorer quality results in bad reputation for the operator, these annoyed subscribers will call the operator's customer service and complain about poor coverage, though the problem actually is in the terminal. Helix antennas, also called stub antennas, which are common on mobile terminals, by that cause considerable problems since these have poorer communication qualities than the longer, usually extensible, rod antennas. This is especially noticeable at the outer fringe of the coverage area of base stations, in houses and in cars without external antenna.

The main reason for the voice quality of a mobile terminal having a stub antenna (helix antenna) being so much poorer than if the same terminal was equipped with an antenna with a longer rod (half wave antenna) is that the stub antenna is influenced considerably more by the user' s head than the rod antenna is. It is important that the impedance in the radio part of the terminal and antenna match each other because the signal from the radio part shall meet a constant load to achieve best effect at the transmission. Antennas therefore are designed to function as a 50 Ω-load for the radio part. But usually existing antennas are designed to operate without interfering objects in the surroundings, which does not correspond to reality because a mobile terminal is held close to the ear and often is used in an environment with a lot of interfering objects in the surroundings, for instance in a car or in a building.

If the terminal, when used, is held to the ear, there is a coupling between the antenna of the terminal and the tissue of the user's head and hand. In that way a part of the signal is reflected back into the antenna, at which the load, and by that the output power, starts varying. The smaller the distance between antenna and the head, the stronger the coupling between the antenna and the head. If said distance is of the size cm, the coupling is considerably changed if the terminal is moved some mm, at which the transmitted power from the terminal is noticeably influenced. This also means that said coupling becomes larger at smaller antennas, such as stub antennas, which, during conversation, have all their extent in the surroundings of the user's head.

When the transmitted power decreases, the sensibility of the receiving part is also reduced, at which the user experience a deteriorated quality.

TECHNICAL PROBLEM

The antenna function at a mobile terminal which is held at the ear, is influenced by the user's head and hand. This influence on the antenna results in that a large portion of the to the antenna fed output power is lost as heating power in head, hand and in the terminal. By a large portion of the power being lost, the efficiency of the antenna is reduced, at which more transmission power must be used. At use within areas where the transmitting power of the terminal is limiting, for instance at the fringe area of the coverage area of a base station, or within an area with a screening effect, as in a car or in a building, the communication possibilities will instead be influenced, which is experienced by the user as deteriorated quality. Measurements have shown that the transmitted power can be reduced by up to 10 dB at 900 MHz when a stub antenna is used close to the head, compared with use of a dipole antenna in free space. This big power loss is due to that the surroundings of the antenna is very important for the efficiency of the antenna. At use of mobile terminals, the power capacity of the battery is a limiting factor. By this power limitation also conversation time and voice quality will be limited. An improved antenna efficiency of the mobile terminal would imply that the battery consumption in transmission mode is reduced, and by that longer conversation time can be achieved, and an improved voice quality can be obtained. The mobile telecommunication operator must by big investments build an infrastructure with base stations which arranges for mobile telecommunication to the terminals. The location of base stations is to a large extent influenced by the range of the mobile terminals. A limited range by that means that the operator has to make a big investment in infrastructure. If, on the other hand, the range can be increased, said investment can be limited. An improved antenna efficiency of the mobile terminal consequently implies that it is possible for an operator to reduce the costs for network extension, since the need for density of base stations will be reduced. The easiness to handle a mobile terminal is to a great extent influenced by the on the terminal existing antenna. A protruding antenna often results in that the terminal will be too big to carry in a pocket and the antenna can protrude if the terminal is placed in a case and by that cause big trouble for the user when the terminal is not used. By the antenna being possible to fold into, or towards, the terminal, the mobile terminal will be more practical to carry since there is no protruding antenna.

TECHNICAL SOLUTION

The antenna of one by hand carried mobile telecommunication terminal is influenced during operation by the user's head and hand. This influence means that a part of the to the antenna fed output power is lost as heating power in the user's head and hand. A reduction of said influence from the tissue of the user' s body consequently should increase the efficiency of the antenna. The invention relates to one at a mobile terminal arranged antenna element, which at use of said terminal makes possible a reduction of the from the antenna element transmitted high frequency radio waves towards the user' s head and hand. Said reduction results in that the attenuation of the radio waves are reduced, which in its turn results in that the range of the mobile terminal will increase without need to increase the transmission power. The invention is characterized in an antenna, preferably an antenna of type helix antenna, which is angled out from the mobile terminal at conversation state, and which at watching mode is arranged to be manually or automatically foldable towards, alternatively foldable into, the upper side of the terminal.

ADVANTAGES

An improved antenna efficiency, especially under more difficult circumstances as in a car or in a building or at the fringe of the coverage area of the terminal, results in an improved voice quality. If the antenna efficiency of the mobile terminal is improved, the battery consumption in transmission state will be reduced and the conversation time will be prolonged. Alternatively there is possibility to benefit from the improved antenna efficiency by providing the mobile terminal with a smaller and by that cheaper and lighter battery.

An improved antenna efficiency of the mobile terminal means that it is possible for an operator to reduce the costs for network extension since the mobile terminal can be used under poorer communication conditions, for instance at larger distance from the opposite station. By that, distances between base stations in a mobile telecommunication network can be greater, which can result in a reduction of the investment in infrastructure for the mobile telecommunication network. In a cellular network the cells at that can be made larger.

With the antenna foldable into, or towards, the terminal, the mobile terminal will be more practical to carry, since there is no protruding antenna.

LIST OF FIGURES

Figure 1 shows the mobile terminal from the side with the antenna (1) in unfolded conversation state.

Figure 2 shows the mobile terminal from the side with the antenna (1) in folded watching mode.

Figure 3 shows the mobile terminal from above with the antenna (1) in folded watching mode. Figure 4 shows the mobile terminal from above with the antenna (1) in unfolded conversation state.

Figure 5 shows the mobile terminal during call/conversation.

Figure 6 shows the measurement environment with phantom hand (4) and phantom head (5) . DETAILED DESCRIPTION

The description below refers to the figures of the appendix.

PREFERRED EMBODIMENT

Terminals which are used in telecommunication networks for mobile communication are equipped with antennas of different types. The antennas often are of a type which protrudes from the terminal, usually an extensible rod antenna or a fixed stub antenna. When the terminal is used held by hand against the head, the from the antenna transmitted useful power is limited by losses in form of radiation which is attenuated by objects in the surroundings. The transmitted antenna power is especially influenced by very close, nearby objects - objects at a centimeter distance from the antenna element. In order to reduce these losses, the antenna is arranged according to the invention so that the radiation towards head and hand when the terminal is used held in hand against the head becomes smaller than it is at the today normal arrangement of antenna. By the arrangement, which reduces the losses, a higher antenna efficiency is achieved, which in its turn i.a. makes longer conversation time at unchanged battery, or the use of a smaller battery, possible. According to the invention an antenna (1) of type helix antenna or stub antenna is utilized, mounted on one short side of the terminal (6), see Figure 1-4. The antenna is mounted so that it can be angled out from the terminal in conversation state. For best effect, the antenna should protrude at the back (8) of the terminal so that the angle between the antenna and the side of the user's head during use of the terminal for conversation is about 90°. At watching mode, and when the terminal is not used, the antenna can be located parallel with an above the short side (6) of the terminal, see Figure 2 and 3. By the antenna being mounted in a joint, the user can easily turn out the antenna element fit conversation and fold it back when the conversation s finished. Alternatively, the turning is made by an automatic device. The antenna arrangement according to the invention makes an antenna function primarily consisting of the stub antenna which protrudes from the terminal and articulated parts at the back (8) of the terminal. By these functional antenna elements, the radiation will be transmitted from parts of the terminal in connection with the back of the terminal. The transmitting parts by that will be at a relative great distance, several cm, form the user's head. By that, the losses caused by effects from the head will be limited so that a considerably better antenna efficiency is achieved. The antenna arrangement according to the invention has, compared with other solutions that are available, low losses and a neat design. Other antenna arrangements with corresponding efficiency are usually equipped with a big extensible/telescopic antenna.

VERIFICATION

There are not yet any established measuring methods for the loss in an antenna device on a mobile terminal. Especially there is lacking a measuring method which shows the losses in a faded environment. By the in this patent application described measuring method is obtained a relation between the antenna losses in a real environment, such as where a mobile terminal normally is used, and a dipole antenna in free space. The used measuring method is based on that measuring is made in a reflecting environment. That means that the measuring can be made in an ordinary office room and that the telephone at the same time is influenced by a simulated head and a simulated hand. The performed measurements have been made by utilizing a phantom hand (4) and a phantom head (5), see Figure 6. The measurements have been arranged so that both measure object and measure antenna have been turned in a number of directions at the same time as a lot of measuring values have been registered.

For measuring of transmitted radiation power an equipment has been used which can measure how much microwave energy that is absorbed in the head of a person during a telephone conversation. From the measuring it has also been possible to estimate the peak value of the absorbed power during the conversation. The measurements have shown that the closer to the head the antenna is located, the higher the peak value.

Measurement results from the use of the in this invention described antenna device have been compared with other measuring results from use of usually existing stub antennas. The measurements show that a reduction of "Body Loss" of 3-4dB is possible to achieve by an antenna design according to the invention.

The invention is not limited to the above described embodiments but can in addition to that be subject to modifications within the frame of the following patent claims and the idea of invention.

Claims

PATENT CLAIMS

1. An antenna device (1) for use in connection with a mobile terminal to be held in hand, which is intended to, at use, be held against the ear, and which is used connected to a mobile telecommunication network, for instance a cellular mobile telephone network, c h a r a c t e r i z e d in that said antenna device is orientated in relation to the terminal so that antenna losses caused by mutual influence between said antenna device and the user's head and hand is reduced.

2. An antenna device as claimed in patent claim 1, c h a r a c t e r i z e d in that said antenna device is of type stub antenna.

3. An antenna device as claimed in patent claim 1 or 2, c h a r a c t e r i z e d in that said antenna device provides an improved antenna efficiency.

4. An antenna device as claimed in patent claim 3, c h a r a c t e r i z e d in that said antenna device makes use of lower power amplification for transmission of radio frequency radiation from the terminal possible.

5. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that said antenna device results in lower power consumption which makes possible longer conversation time at unchanged battery, or possibility to use a smaller battery.

6. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that said antenna device provides an improvement of the voice quality.

7. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that said antenna device provides an improvement of the reception of radio signals in the terminal.

8. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that said antenna device at conversation state is directed out from and, in its entire extent, on the opposite side in relation to the side of the terminal which is intended to at use be held against the ear.

9. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that said antenna device at conversation state is directed outwards from the user's head.

10. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that the main extent of said antenna device forms about a right angle to the side of the user' s head at use of the terminal for conversation.

11. An antenna device as claimed in any of the patent claims l to 9, c h a r a c t e r i z e d in that the main extent of said antenna device forms about a right angle (2) to the plane which the front (7) or back (8) of the terminal forms.

12. An antenna device as claimed in any of the previous patent claims, c h a r a c t e r i z e d in that said antenna is arranged, at watching mode, to be manually or automatically foldable towards, alternatively foldable into, the upper side of the terminal.