The present invention relates to mobile wireless equipment typified by, for example, mobile phones. More particularly, the present invention relates to a mobile phone having higher antenna performance, an analysis device included in the mobile phone, and an analysis method used in the device.
The development of compact embedded antennas has become increasingly desired in recent years as mobile phones have become smaller. Well-known antennas that are in common use include linear antennas, such as monopole antennas, helical antennas, and inverted L antennas. The monopole antenna and the helical antenna are attached to the top of the casing of a mobile phone and protrude from the casing; whereas the inverted L antenna is attached along the casing of a mobile phone, thus being suitable as an embedded antenna.
Foldable mobile phones whose operation panel and display are protected from damage in transit are known. Each foldable mobile phone has two casings that are connected by a hinge part for folding. The antenna is attached to one of the casings.
FIG. 1A is a front view of a known foldable mobile phone and FIG. 1B is a cross-sectional view thereof. Referring to FIGS. 1A and 1B, the foldable mobile phone has an upper casing 103 including a display 107 and a speaker 106, a lower casing 104 including a keyboard 109 and a microphone 108, and a hinge part 105 that connects the upper casing 103 and the lower casing 104 for allowing them to be closed. An antenna 110 is usually attached to the top of the upper casing 103.
A printed circuit board (not shown) is provided in the upper casing 103 or the lower casing 104. The printed circuit board has a transmission unit for supplying transmission power, a power transfer unit for transferring the power to the antenna 110, and a power amplifying unit for amplifying the power. The transmission power is usually supplied to the antenna through an output terminal of the power amplifying unit. A matching circuit (now shown) is provided between the power amplifying unit and the antenna. The matching circuit is designed such that the input impedance of the antenna matches the impedance at the output terminal of the power amplifying unit.
As described above, a common mobile phone is designed such that the input impedance of the antenna is in a matching condition.
Generally, a user making a call by using a mobile phone (during connection) holds the body of the mobile phone with his/her hand to hold the speaker over his/her ear. Since the mobile phone including the antenna is close to the user, the input impedance of the antenna during connection varies depending on the influence of the human body.
For example, with a mobile phone having the antenna at the top of the upper casing, the input impedance of the antenna mainly varies in accordance with the influence of the head of the user. In contrast, with a mobile phone having the antenna at the bottom of the lower casing, the input impedance of the antenna mainly varies in accordance with the influence of the hand of the user.
Although the influence of the human body is described above, the impedance characteristics of the antenna generally vary during connection in accordance with the influence of the ambient environment, such as scattering material (including dielectric material, metallic bodies, and so on) around the mobile phone. The amount of variation in impedance of the antenna generally increases as the influence of the ambient environment increases, so that a predetermined matching condition tends to vary. In a mismatched condition, the power transferred from the power amplifying unit to the antenna returns. From the view point of the antenna, the returning power is return loss, which causes the power supplied to the antenna to decrease. As a result, the communication characteristics, such as antenna gain, of the mobile phone are reduced.
In this manner, a large variation in the impedance of the antenna and a large return loss cause the antenna gain to decrease. Accordingly, the influence of the return loss on the mobile phone should normally be reduced as much as possible in order to maintain the antenna gain, by optimizing the matching circuit and so on in view of an estimated variation in impedance of the antenna during connection.
However, since the variation in impedance of the antenna strongly depends on the way the mobile phone is held by the user, which differs from person to person, the actual variation in impedance may exceed the pre-estimated variation in impedance. In particular, a known mobile phone generally has a single transmission antenna, so that the user has no choice other than to use a reduced-gain antenna.