Portable Radio Communication Apparatus Having Diversity Reception Function

The present invention relates to a portable radio communication apparatus and, more particularly, to such an apparatus having a diversity reception function.

An example of portable radio communication apparatus of the foregoing type is disclosed in "No. 2455: Study on a Diversity Antenna for Portable Radio Unit" by Taga et al, National Convention (Record) of the Institute of Electronics and Communication Engineers of Japan, pp. 10-155, 1984. The communication apparatus disclosed in this paper includes two folded, inverted F-type antennas which are built in a housing, so that diversity reception may be performed through those antennas. Although such construction is suitable for portable apparatus design, it fails to achieve a requisite degree of antenna gain.

A portable radio communication apparatus capable of attaining sufficient gain is disclosed in a Japanese unexamined laid-open patent application entitled "Portable Radio," No. Sho No. 62-49729, namely, 49729 of 1987 by Hashiomoto et al. which is assigned to the assignee of the instant application (Corresponding patent applications are: U.S. Ser. No. 897,989; European Ser. No. 86306575.1; Canadian, Ser. No. 516,870-8; and Australian, Ser. No. 61837/86.). As will be described in detail later, the apparatus of the foregoing Japanese application is provided with a single sleeve or whip antenna and a single built-in antenna for effecting diversity reception. The sleeve or whip antenna is connected to both a transmitter and a diversity receiver while the built-in antenna is connected to the diversity receiver. The sleeve or whip antenna may be tucked away in a housing to enhance portability. So long as the apparatus is used with the sleeve or whip antenna pulled out of the housing, sufficiently high reception and transmission gains are assured due to the high antenna gain and diversity gain of the sleeve or whip antenna. However, once the sleeve or whip antenna is retracted into the housing, the transmitter becomes substantially inoperable and makes bidirectional communication impractical.

It is, therefore, an object of the present invention to provide an improved portable radio communication apparatus having a diversity reception function.

It is another object of the present invention to provide a portable radio communication apparatus having a diversity reception function which achieves a sufficiently high reception gain.

It is yet another object of the present invention to provide a portable radio communication apparatus having a diversity reception function which is capable of transmitting even when a sleeve or whip antenna is retracted into a housing or folded adjacent the housing.

In accordance with the present invention, there is provided a portable radio communication apparatus comprising transmitter means, diversity receiver means, transmission filter means connected to the transmitter means, and first and second reception filter means connected to the diversity receiver means. The apparatus further comprises first antenna means capable of being retracted towards a housing of the apparatus, second antenna means mounted inside of or on an outer periphery of the housing, and switch means for connecting the second antenna means to a node between the transmission filter means and first reception filter means in a first condition in which the first antenna means is retracted towards the housing, and for connecting the first antenna means to such node and the second antenna means to the second reception filter means in a second condition in which the first antenna means is extended away from the housing.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:

FIG. 1 is a schematic block diagram showing a prior art portable radio communication apparatus having a diversity reception function, for facilitating an understanding of the present invention;

FIGS. 2A and 2B are schematic block diagrams of a portable radio communication apparatus having a diversity reception function embodying the present invention, respectively showing two different conditions;

FIGS. 3A and 3B are schematic block diagrams of an essential part of a portable radio communication apparatus according to another embodiment of the present invention; and

FIG. 4 is a schematic view of a specific construction of a switch driving mechanism which may be included in the apparatus shown in FIGS. 2A and 2B or 3A and 3B; and

FIGS. 5 to 7 are schematic views showing exemplary structures for receiving and folding a sleeve and a whip antenna.

To better understand the present invention, brief reference is first made to a prior art radio communication apparatus, shown in FIG. 1. As shown, the apparatus includes an antenna 14, which is connected to a transmitter 12 and a diversity receiver 11 through, respectively, a transmission filter 81 and a reception filter 82. Filters 81 and 82 are contained in a duplexer 8. An antenna 15 is connected to the diversity receiver 11 through a reception filter 10. The antenna 14 is implemented with a sleeve antenna or a .lambda./2 whip antenna which has a high radiation gain and allows a minimum of high-frequency current to flow through a housing. Here, .lambda. is representative of the wavelength of a signal used. On the other hand, the antenna 14 15 is implemented with an antenna which, although lower in gain than a sleeve or whip antenna, can be built in a housing as is typical for a flat antenna.

So far as gain is concerned, both of the antennas 14 and 15 should preferably comprise a sleeve antenna or a .lambda./2 whip antenna. However, when it comes to portability and design, mounting two such antenna on a housing is difficult. For example, a .lambda./2 whip antenna has an element length of substantially 16 cm for a 900 MHz frequency band. Mounting two such antennas each having the foregoing length on a housing would be impractical. On the other hand, the antenna 15 exclusively for reception preserves the diversity effect even if the gain is lowered by about several dB compared to the transmit/receive antenna 14; therefore, antenna 15 can be implemented with a flat antenna. Further, not only the space diversity effect but also the polarization diversity effect can be expected if a flat antenna is used in combination with a vertical polarization antenna; such as a sleeve antenna or a .lambda./2 whip antenna.

For the above reason, using a built-in antenna in a portable radio communication apparatus in combination with the sleeve or whip antenna of FIG. 1 is advantageous, and actually this combination is used in the present invention. However, the construction shown in FIG. 1 has the drawback that when the sleeve or whip antenna is retracted, the apparatus becomes unable to transmit, as previously stated. Specifically, when the antenna 14 is retracted in the housing, the gain is lowered to a value which is even far smaller than that of the built-in antenna 15; in the worst case, the antenna 14 is electrically isolated and makes transmission impossible. Hence, the prior art apparatus shown in FIG. 1 cannot be used in a system in which a transmission should begin automatically in response to a reception.

Referring to FIG. 2A, a portable radio communication apparatus embodying the present invention is shown in block diagram form. In the figure, a first antenna 1 is implemented with a sleeve or whip antenna which may be retracted into a housing 13 of the apparatus or folded adjacent the housing as described in detail later. The antenna 1 protrudes from the housing 13 unless retracted or folded. In this particular embodiment, the antenna 1 is assumed to be bodily retracted into the housing 13. A second antenna 2 is implemented with a microstrip or like flat antenna which is built in the housing 13 or mounted on the outer periphery of the housing 13 so as not to protrude from the housing 13.

When the first antenna 1 is retracted into the housing 13 as shown in FIG. 2A, it is electrically disconnected from a first switch 5. By the movement of the first antenna 1 into the housing 13, the first switch 5 is automatically caused to shift the connection of an antenna terminal 9 of a duplexer 8 from the first antenna 1 to the second antenna 2. When terminal 9 is connected to antenna 2, a second switch 6, interlocked with the first switch 5, disconnects a reception filter 10, having the receive frequency band as its pass band, from the second antenna 2, the receive frequency band being the pass band of the filter 10. Specifically, the first antenna 1 is retracted into the housing 13, the switches 5 and 6 are actuated such that the second or built-in antenna 2 becomes connected to a transmitter 12 via a transmission filter 81 and also to a diversity receiver 11 via a reception filter 82.

In FIG. 2B, the apparatus of FIG. 2A is shown in a condition wherein the first antenna 1 is pulled out of the housing 13 to its outermost position. As shown, since contacts 3 and 4 are brought into connection, the first antenna 1 is connected to the switch 5. The switch 5 is operated to connect the first antenna 1 to the antenna terminal 9 of the duplexer 8 while disconnecting the second or built-in antenna 2. The second switch 6, on the other hand, is actuated to connect the built-in antenna 2 to the diversity receiver 11 via the reception filter 10. In short, when the first antenna 1 is held in the outermost position, the antenna 1 is shared for transmission and diversity reception while, at the same time, the second or built-in antenna 2 is exclusively assigned to diversity reception.

In the condition shown in FIG. 2B, a line 7 extending between the first and second switches 5 and 6 is connected to the antenna 2 and, therefore, apt to disturb high-frequency matching. Such an occurrence can be eliminated by dimensioning the line 7 sufficiently shorter than .lambda./4 or equal to an integral multiple of .lambda./2 of the receive frequency band.

Referring to FIGS. 3A and 3B, an essential portion of a second exemplary embodiment of the present invention is shown. The second embodiment has the same structure as the first one of FIGS. 2A and 2B except that a switch 106 having three contacts is used in the second embodiment in place of the switch 6 having two contacts. The conditions shown in FIGS. 3A and 3B correspond to those of FIGS. 2A and 2B, respectively. In FIG. 3A, the first antenna 1 is disconnected from the terminal 9 of duplexer 8 while the second or built-in antenna 2 is connected via terminal 9 to the transmitter 12 and the diversity receiver 11 through the duplexer 8. On the other hand, in FIG. 3B, the first antenna 1 is connected via terminal 9 to the transmitter 12 and the diversity receiver 11 through the duplexer 8 while the second antenna 2 is connected to the diversity receiver 11 through the reception filter 10.

Unlike the connecting line 7 of FIG. 2B, a connecting line 107 is disconnected from the second antenna 2 in the condition shown in FIG. 3B. Accordingly, the line 107 has no adverse effect on the high-frequency matching, described above. In other words, the length of line 107 can be freely selected.

Referring to FIG. 4, there is shown an illustrative and not limitative mechanism for automatically actuating the switches 5 and 6 (or 106) in response to the movement of the first antenna 1 into and out of the housing 13. As shown, while the first antenna 1 is fully or partly received in the housing 13, a lever 16 is urged by a spring 20 to the position shown in the figure. As the antenna 1 is pulled out to the outermost position, the conductor 3 fixed to the bottom of the antenna 1 with the contact 4 and rotates the lever 16 about a pin 17 against the action of the spring 20. Then, the lever 16 presses against actuators 18 and 19 which are respectively associated with the switches 5 and 6 (or 106), whereby the switches 5 and 6 or 106 are actuated as explained above with reference to FIGS. 2A and 2B or 3A and 3B.

FIGS. 5 to 7 show exemplary configurations of the first antenna 1. In FIG. 5, a sleeve antenna 41 serves as the first antenna 1 and may be fully received in the housing 13. In FIG. 6, a whip antenna 51 serves as the first antenna 1 and may be fully retracted in the housing 13. In FIG. 7, a whip antenna 61 implements the first antenna 1 and is foldable along the outer periphery of the housing 13.

In summary, the foregoing describes a portable radio communication apparatus in which, when a sleeve or whip antenna is extended away from a housing of the apparatus, a sufficient gain is achieved due to the gain of that antenna and diversity reception by that antenna and by a built-in antenna. Another advantage of the present invention is that even when the sleeve or whip antenna is retracted towards the housing, the built-in antenna is automatically switched from a receive-only condition, to a transmit and receive condition thereby allowing transmission and reception to be performed as needed. Hence, user can conveniently wait for a reception while carrying the apparatus in a bag or the like with the antenna retracted, and confirm the reception, especially if needed to enable reception of a message. The user may find that the built-in antenna suffices for communication; if so, the sleeve or whip antenna may conveniently be left retracted.

Although the present invention has been described in connection with a plurality of preferred embodiments thereof, many other variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.