BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a transmitting and receiving apparatus and more specifically to a portable compact transmitting and receiving apparatus having a casing accommodating an antenna and a battery.
2. Description of the Related Art
Recently, a positioning system based on an Ultra Wide Band (UWB) radio technology using wide band radio waves has been investigated. The positioning system includes a system for determining the position of a customer who is in a shop, for example. In the system, a transmitting and receiving apparatus (UWB tag) is provided to be carried by a customer or mounted on a shopping cart used by the customer in the shop. Further, plural communication devices (base stations) separated from each other are provided in predetermined areas in the shop. The position of the customer is detected by the signal communications between the transmitting and receiving apparatus and the communication devices.
In this case, the transmitting and receiving apparatus is desired to be thin and compact because it is assumed that the customers wear straps of the transmitting and receiving apparatuses around their neck in practical cases.
The applicant et al. of the present invention have applied a plane antenna including a home-plate shaped element pattern and a substantially square-shaped ground pattern disposed in the vicinity of the element pattern as a UWB antenna. The UWB antenna is preferably used for a thin transmitting and receiving apparatus. In addition, preferably, a button cell battery may be used to reduce the thickness of the transmitting and receiving apparatus.
Unfortunately, in the technical field of the UWB antenna for such a portable apparatus, no remarkable research focusing on how a layout of the element pattern and the button cell battery influences the antenna characteristics has been made.
SUMMARY OF THE INVENTION
The present invention is made in light of the above circumstances and may provide a transmitting and receiving apparatus having a UWB antenna with improved antenna characteristics.
According to an aspect of the present invention, there is provided a transmitting and receiving apparatus including a UWB antenna including a home-plate shaped element pattern having a triangular shaped part at one end side in the height direction, and a ground pattern on an apex side of the triangular shaped part of the element pattern; and a battery disposed on one side of the element pattern and separated from the element pattern by a prescribed distance so that the influence of the element pattern on the characteristics of the UWB antenna is within an allowable range.
According to an embodiment of the present invention, the transmitting and receiving apparatus is capable of having satisfactory antenna characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features, and advantages of the present invention will become more apparent from the following descriptions when read in conjunction with the accompanying drawings, in which:
FIG. 1 is an exploded perspective view showing a transmitting and receiving apparatus according to an embodiment of the present invention;
FIG. 2 is an oblique perspective view schematically showing the inside of the transmitting and receiving apparatus;
FIGS. 3A and 3B are plan and front perspective views, respectively, of the transmitting and receiving apparatus;
FIGS. 4A and 4B show a UWB antenna of the transmitting and receiving apparatus and typical antenna characteristics of the UWB antenna;
FIG. 5 is a view schematically showing the UWB antenna in the transmitting and receiving apparatus in FIG. 1;
FIG. 6 is a drawing showing an analysis model resembling the UWB antenna for simulation;
FIG. 7 is a graph showing the antenna characteristics obtained by the simulation using the analysis model in FIG. 6;
FIG. 8 is a graph showing the relationship between the distance between an element pattern and a ground pattern part in the 90 degree direction and the gain obtained by the simulation using the analysis model in FIG. 6;
FIG. 9A is a drawing showing the transmitting and receiving apparatus without a battery;
FIGS. 9B through 9E are graphs showing measured antenna characteristics of the transmitting and receiving apparatus in FIG. 9A (without battery);
FIG. 10A is a drawing showing the transmitting and receiving apparatus including a battery;
FIGS. 10B through 10E are graphs showing measured antenna characteristics of the transmitting and receiving apparatus in FIG. 10A (with battery).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Next, an embodiment of the present invention is described with reference to the accompanying drawings.
FIG. 1 is an exploded perspective view showing a portable transmitting and receiving apparatus (UWB tag) 10 according to an embodiment of the present invention. FIG.2 is a perspective view showing the inside of the transmitting and receiving apparatus 10. FIG. 3A is a plan view showing the inside of the transmitting and receiving apparatus 10. FIG. 3B is a front view from the Y2 side of the transmitting and receiving apparatus 10. In the figures, the X1-X2, Y1-Y2, and Z1-Z2 directions denote the width, the longitudinal (height), and the thickness directions, respectively.
As shown in FIGS. 1 through 3B, the transmitting and receiving apparatus 10 includes a flat casing 11, a transmitting and receiving module 50, a button cell battery accommodating section 70, and a button cell battery 80. The flat casing 11 includes an upper half case 20 and a lower half case 30, both made of synthetic resin. The transmitting and receiving apparatus module 50 is accommodated in the casing 11 and has transmitting and receiving functions. The button cell battery 80 is accommodated in the button cell battery accommodating section 70 in the casing 11. As shown in FIG. 3A, the transmitting and receiving apparatus 10 has a substantially square shape and has the sizes of approximately 40 mm width “L10”, approximately 45 mm height “L11”, and approximately 8 mm thickness “T10”.
When the transmitting and receiving apparatus 10 is put to practical use in a manner where a user wears a strap of the transmitting and receiving apparatus 10 around the neck, the Y1-Y2 direction becomes the vertical (height) direction.
The transmitting and receiving module 50 includes a circuit substrate 51 having a built-in UWB antenna 60, IC parts (not shown) mounted on the circuit substrate 51, and a negative electrode terminal member 55 and a positive electrode terminal member 56, each fixed in the vicinity of a fringe of the circuit substrate 51.
The circuit board 51 has a square shape, and includes a cutout part 52 at the corner between the X1 side and the Y1 side for accommodating the button cell battery 80.
As shown in FIG. 4 as well, the UWB antenna 60 includes a home-plate shaped element pattern 61 having a triangle shape part 61b on the Y2 side of the UWB antenna 60, a substantially L-shaped ground pattern 62, and a ground pattern part 64 formed by the button cell battery 80 described below. The combination of the ground pattern 62 and the ground pattern part 64 is herein referred to as a practical ground pattern 63. The element pattern 61 has a symmetric shape with respect to a center line “61CL”. The element pattern 61 and the ground pattern 62 are disposed on the Y1 side and the Y2 side, respectively, with respect to each other. As shown in FIG. 3A, there is a triangle part 61b on the Y2 side the element pattern 62, and there is an apex 61a on the Y2 side of the triangle part 61b. The apex 61a is close to an edge on the Y1 side of the ground pattern 62. The position of the edge on the X2 side of the element pattern 61 corresponds to the position of the edge on the X2 side of the circuit substrate 51 in the x axis direction, so that the distance between the element pattern 61 and the cutout part 52 in the x axis direction is maximized. Further, the element pattern 61 and the ground pattern 62 are formed on the upper surface of the circuit substrate 51 by an etching process. Still further, the surfaces of the element pattern 61 and the ground pattern 62 are covered with an insulation film. Still further, there is provided a coaxial connector 65 surface-mounted on the upper surface of the circuit substrate 51 and is positioned above both a part of the element pattern 61 and a part of the ground pattern 62.
The center frequency of the UWB antenna 60 is, for example, 4.5 GHz. The element pattern 61 has sizes of approximately 16 mm width “W” and approximately 15 mm height “H”.
Both the negative electrode terminal member 55 and the positive electrode terminal member 56 protrude into the cutout part 52.
The button cell battery accommodating section 70 includes a space 71 defined by the cutout part 52 inside the casing 11. The space 71 accommodates the protruding negative electrode terminal member 55 and the protruding positive electrode terminal member 56.
As shown in FIG. 1, when the button cell battery 80 having a button-shape is installed in the button cell battery accommodating section 70, the negative electrode surface 81 and the positive electrode surface of the button cell battery 80 are on the Z1 and Z2 sides and are in contact with the negative electrode terminal member 55 and the positive electrode terminal member 56, respectively.
In the transmitting and receiving apparatus 10 according to the embodiment of the present invention, the UWB antenna 60 and the button cell battery accommodating section 70 (the button. cell battery 80) are arranged so that the button cell battery accommodating section 70 (the button cell battery 80) is on the X1 side of the element pattern 61 of the UWB antenna 60. Because of this arrangement, the transmitting and receiving apparatus 10 becomes reasonably compact. Furthermore, advantageously, it is considered that from a high frequency point of view, both the negative electrode surface 81 and the positive electrode surface 82 of the button cell battery 80 installed in the button cell battery accommodating section 70 serve as ground patterns.
In FIG. 3, the distance “A” between the end on the X1 side of the element pattern 61 and the end on the X2 side of the end of the button cell battery 80 (the end on the X2 side of the circumference of the button cell battery 80) is 7 mm. That is, the circumferential surface of the button cell battery 80 installed in the button cell battery accommodating section 70 faces and is separated from an end 61X1 on the X1 side of the element pattern 61 by 7 mm so as to be side by side. Further, the element electrode surface 81 of the button cell battery 80 is in substantially the same plane as the extended plane of the element pattern 61. Because of the distance “A” of 7 mm, the UWB antenna 60 is capable of having acceptable antenna characteristics. More particularly, the reduction of the gain due to the characteristics of the button cell battery 80 is within an allowable range, thereby realizing satisfactory antenna characteristics.
It should be noted that the UWB antenna 60 transmits and receives impulses having a very short pulse width approximately 5 ns.
Next, the antenna characteristics (direction pattern) of the UWB antenna 60 is described.
[Simulation]
FIGS. 4A and 4B show the antenna characteristics of a typical UWB antenna 60B having a home-plate shaped element pattern 61 and a substantially square-shaped ground pattern 62B. The antenna characteristics of the UWB antenna 60B are formed in three dimensions and the shape of the antenna characteristics is like an apple. The solid line 100 in FIG. 4B shows the directional pattern in the X-Y plane including the UWB antenna 60B, that is an X-Y plane directional pattern. On the other hand, the solid line 110 in FIG. 4A shows the directional pattern cut in a X-Z plane “S” including the apex 61a of the element pattern 61 and has a substantially circular shape.
FIG. 5 schematically shows a configuration of the UWB antenna 60. As shown in FIG. 5, the UWB antenna 60 includes the element pattern 61 and a practical ground pattern 63 (hatching area in FIG. 5). The practical ground pattern 63 includes a patterned ground pattern 62 and a ground pattern part 64 formed by the button cell battery 80.
First, an analysis is performed by simulation. FIG. 6 shows an analysis model 200 resembling the UWB antenna 60 for the simulation. The parts same as those in FIG. 5 are denoted by the same reference numerals having a suffix “A”.
In the simulation, an edge on the X2 side of the ground pattern part 64A is moved in the X axis direction. As shown in FIG. 6, a symbol “A” denotes the distance between the edge of on the X2 side of the ground pattern part 64A and an edge on the X1 side of the element pattern 61A. In the simulation, the distance “A” is gradually increased from 3 mm to 26 mm, namely a gap between the ground pattern part 64A and the element part 61A is gradually broadened. Then, the antenna characteristics in the X-Z plane at the frequency of 4.5 GHz is obtained by calculation.
FIG. 7 shows antenna characteristics simulated while the distance “A” is changed. In FIG. 7, the lines 110A, 110B, and 110C show the antenna characteristics in the X-Z plane when the distance “A” is 3 mm, 7 mm, and infinity (∞), respectively. The solid line 110D shows substantially circular-shaped antenna characteristics in the X-Z plane when the distance “A” is 23 mm.
In the vicinity of 90 degrees in the graph of FIG. 7, the antenna characteristics are degraded due to the ground pattern part 64 reducing the gain on the X1 side of the element pattern 61A.
The solid line “I” in FIG. 8 shows the antenna characteristics on the X1 side (90-degree direction) of the element pattern 61A. In FIG. 8, the horizontal axis denotes the distance “A”, and the vertical axis denotes the gain in the 90-degree direction. As shown in FIG. 8, the gain is 0 dBi when the distance “A” is 23 mm, the gain is −1 dBi when the distance “A” is 7 mm, and the gain is −4 dBi when the distance “A” is 3 mm.
Further, the solid line “I” in FIG. 8 shows that as the distance “A” decreases, the gain tends to be decreased. Particularly, as the distance “A” decreases in an area where the distance “A” is 7 mm or less, the gain decreased abruptly.
In antenna characteristics it is generally assumed that the minimum allowable gain after reduction is 70% of a ideal gain. Namely, gain reduction down to −3 dBi is the allowable maximum.
Referring back to the graph in FIG. 8, the distance “A” where the gain reduction is −3 dBi is approximately 4 mm.
The above simulation result suggests that in the UWB antenna, the distance “A” should be 4 mm or more, namely the distance “A” should not be less than 4 mm.
[Measurements]
FIGS. 9B through 9E show the antenna characteristics in the X-Z plane of the UWB antenna 60 of the transmitting and receiving apparatus 10 in FIG. 1 when the button cell battery 80 is not installed. On the other hand, FIGS. 10B through 10E show the antenna characteristics in the X-Z plane of the UWB antenna 60 when the button cell battery 80 is installed.
More specifically, FIG. 9A shows the transmitting and receiving apparatus 10 in which no button cell battery 80 is installed. FIGS. 9B through 9E show the antenna characteristics in the X-Z plane of the UWB antenna 60 in the frequencies of 3 GHz, 4 GHz, 4.5 GHz, and 5 GHz, respectively.
FIG. 10A shows the transmitting and receiving apparatus 10 in which the button cell battery 80 is installed. FIGS. 10B through 10E show the antenna characteristics in the X-Z plane of the UWB antenna 60 at the frequencies of 3 GHz, 4 GHz, 4.5 GHz, and 5 GHz, respectively.
When the gains in the X1 (90 degree) direction at the frequency of 4.5 GHz are compared based on FIGS. 9D and 10D, the gain “G2” in FIG. 10D is almost the same as the gain “G1” in FIG. 9D.
This result indicates that the result obtained by the above simulation is correct.
Similarly, when the gains in the X1 (90 degree) direction in the frequency of 3 GHz are compared based on FIGS. 9B and 10B, the gain “E2” in FIG. 10B is almost the same as the gain “E1” in FIG. 9B; when the gains in the X1 (90 degree) direction in the frequency of 4 GHz are compared based on FIGS. 9C and 10C, the gain “F2” in FIG. 10C is almost the same as the gain “F1” in FIG. 9C; and when the gains in the X1 (90 degree) direction in the frequency of 5 GHz are compared based on FIGS. 9E and 10E, the gain “H2” in FIG. 10E is almost the same as the gain “H1” in FIG. 9E.
[Modified Embodiment]
In a modified embodiment of the present invention, the distance “A” in the transmitting and receiving apparatus 10 may be 4 mm as the minimum distance.
Further, in another modified embodiment of the present invention, the transmitting and receiving apparatus 10 may include a battery having a different shape from that of the button cell battery 80.
The present invention is not limited to the embodiments described above, and may be applicable to, for example, a thermal printing apparatus having no cutting device, namely, a thermal printing apparatus including a thermal head, a platen roller, a motor for driving the platen roller, and a mechanism reducing and transmitting the rotation of the motor for driving the platen roller to the platen roller.
The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2007-308621, filed on Nov. 29, 2007, the entire contents of which are hereby incorporated by reference.
Patent Grant
8253632
