Shared antenna and portable radio device using the same

Abstract: A shared antenna is provided comprising a linear antenna (8) electrically connected to the upper end of a power pin (1a) of a microstrip plane antenna (1) via a capacitive element (7). The shared antenna is used in both satellite communications and ground communications and can be used without a need for mechanical switching of the antenna. Further, crimped radiating elements (9, 10) having spatial expansion are electrically connected to the vicinity of the upper end of a feed pin (1a) of a microstrip plane antenna (1) via a capacitive element (7), thereby realizing superior impedance matching and radiation patterns of the shared antenna.

Description: BACKGROUND OF THE INVENTION The present invention relates to the field of communications, and more particularly, to an antenna for use in portable radio communications utilizing a satellite and in portable radio communications established between ground radio stations. Further, the present invention relates to a portable radio using the antenna. In recent years, the conception of a portable telephone using a satellite has been proposed. A frequency band of 1.6 GHz is assigned to communications from a ground portable telephone to a satellite, and a frequency band of 2.4 GHz is assigned to communications from a satellite to a ground portable telephone. The frequency band of 1.6 GHz is also assigned to bidirectional communications between the ground and a satellite. Frequency bands of 800 MHz, 1.5 GHz, and 1.9 GHz have already been assigned to ground communications. With regard to a shared antenna used for both satellite communications and ground communications, it has been proposed a method of feeding power to the upper end of a two-wire helical antenna which uses a coaxial line and lead wires (Unexamined Japanese Patent Publication 9-219621). SUMMARY OF THE INVENTION The object of the present invention is to provide an antenna which can be used for both satellite communications and ground communications and a portable radio (or portable telephone) which enables both satellite communications and ground communications. According to the present invention, a shared antenna is provided comprising the features of claim 1. Further developments thereof are specified in the subclaims. Such an antenna is used in both satellite communications and ground communications without the need of mechanical action, by attaching a linear radiating element via a capacitive element to the front end of a feed pin which supplies a high-frequency current to a microstrip plane antenna. A shared antenna according to the present invention comprises a microstrip plane antenna 1 (hereinafter simply referred to as an MSA), a capacitive element 7, and a linear radiating element 8. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a shared antenna according to an embodiment of the present invention; Fig. 2 is a schematic view showing a composite antenna formed by connection of a helical antenna to the lower end of the shared antenna; Fig. 3 is a general view showing an example of a portable radio which has the composite antenna shown in Fig. 2 formed into a rod shape; Fig. 4 is a plot showing the result of measurement of patterns radiated from the antenna shown in Fig. 3 at a satellite communications frequency and a frequency band of ground portable telecommunications; and Fig. 5 is a block diagram showing the circuitry of the antenna of the portable radio shown in Fig. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a schematic representation showing the configuration of a shared antenna according to the present invention. In the drawing, reference numeral 1 designates a microstrip plane antenna (MSA); 1a a feed pin; 1b a patch-shaped radiating element; 1c a dielectric substrate; 4 a ground conductor (conductor plate); 7 a capacitive element; and 8 a linear radiating element. The MSA 1 operates as a circularly-polarized antenna at the first frequency by appropriate designing of the dielectric constant or dimension of a dielectric substrate 1c; a parameter of the dielectric substance such as thickness; the dimension of the patch-shaped radiating element 1b labeled to the dielectric substrate 1c; or the position of the feed pin 1a. As shown in Fig. 2, the linear radiating element 8 operates at the second frequency as a grounded quarter-wave linearly-polarized antenna by means of a helical antenna positioned below the ground conductor 4. An explanation will now be given of a case where the MSA 1 operates as a circularly-polarized antenna. For example, a patch-shaped radiating element 1b is attached to the dielectric substrate 1c, thereby constituting a single-point back feed MSA 1. Taking a longer side of the MSA 1 as A and a shorter side of the same as B , the MSA 1 is formed so as to obtain 100 x A/B = 102 to 103 % or thereabouts. At this time, the longer side A oscillates at a comparatively low frequency, to thereby exhibit elliptically polarized characteristics. The shorter side B oscillates at a comparatively high frequency, to thereby exhibit elliptically polarized characteristics orthogonal to the foregoing elliptically polarized characteristics. The MSA 1 operates at a frequency between these elliptically polarized characteristics as a circularly-polarized antenna. To connect a feed line 6 to the feed pin 1a, impedance matching is ensured by adjusting the position of the feed pin 1a. More specifically, it is essential that the feed pin 1a be positioned at an intersection of diagonal lines of the MSA 1 in such a way as to obtain 100 x (A - B) /A = 30% or thereabouts. Next, an explanation will be given of the coupling between the MSA 1 and the linear radiating element 8. The capacitive element 7, such as a capacitor, is connected to the upper end of the power feed pin 1a of the MSA 1. The linear radiating element 8, such as a helical antenna, is connected to the top of the capacitive element 7. By means of the capacitive element 7, there is reduced interference between the circularly-polarized antenna which operates at the first frequency and the linearly-polarized antenna which operates at the second frequency. Particularly, a radiation pattern of the circularly-polarized wave is improved. Fig. 2 shows an example of a composite antenna 12 which is formed by combination of a composite antenna proposed by the applicant of the present patent application (Japanese Patent Application 8-196038) and the shared antenna shown in Fig. 1. A helical antenna 2 positioned below the MSA 1 comprises linear radiating elements 2b which are electrically connected to the ground conductor 4 of the MSA 1 and receive power. The helical antenna 2 of the present example is formed into a four-wire helical antenna as a representative example of the helical antenna. In Fig. 2, the elements which are the same as those shown in Fig. 1 are assigned the same reference numerals. Reference numeral 2a designates a dielectric column (a dielectric columnar support) around which the linear radiating elements 2b are wrapped. Reference numeral 2c is an insulating substance which is interposed between the linear radiating elements 2b so as to prevent direct contact at an intersection of the linear radiating elements 2b at the lower end of the helical antenna 2. Reference numeral 2d is an intersection where the linear radiating elements 2b cross each other without a physical contact by means of the presence of the insulating substance 2c. Reference numeral 3 designates a feed point common to the MSA 1 and the helical antenna 2. The feed pin 1a is connected to a feed line (a coaxial line) 6 which passes through the dielectric substrate 1c and keeps out of contact with holes formed in the ground conductor 4. The linear antenna 8 is electrically connected to the upper end of the feed line 6 via the capacitive element 7. Fig. 3 shows an example of the composite antenna 12 shown in Fig. 2 which is formed into a rod and is attached to a portable radio 11. Fig. 4 shows the result of measurement of radiation patterns of the composite antenna 12 which are formed over the longitudinal cross-section of the composite antenna 12 at the frequency bands of 1.6 GHz and 800 MHz with a configuration equivalent to that shown in Fig. 2. Patterns radiated in lower right and left directions are radiated at a frequency band of 800 MHz. The pattern principally radiated in an upward direction is radiated at a frequency band of 1.6 GHz. In Fig. 3, the elements which are the same as those shown in Fig. 2 are assigned the same reference numerals. The composite antenna 12 is sheathed with an antenna holding cylinder 13 and is configured so as to rotate around a rotary shaft A. When the portable radio 11 is waiting for an incoming call, the composite antenna 12 can be collapsed toward a casing of the portable radio 11. A built-in microstrip plane antenna (MSA) 30 is provided on the inside of an upper surface of the casing of the portable radio 11. A diversity antenna is formed by means of the MSA 30 and the composite antenna 12 in combination. The MSA 30 has a gain in a right-bank (or left-bank) circularly-polarized mode which is the same as that of the composite antenna 12 primarily in the zenith. The diversity antenna comprises the composite antenna 12 shown in Fig. 5, the MSA 30, a radio section 31, and signal composition means (or signal selection means) 32 including the composite antenna 12 and the MSA 30. In Fig. 3, the composite antenna 12 is retained by the antenna retaining cylinder 13 and is positioned in an elevated position spaced from the casing of the portable radio 11 by only the length of the connection section 13a, thereby preventing a gain loss of the radio at a low elevation angle which would otherwise caused by the head of the user during a call. A call is made while the composite antenna 12 is in an upright position as shown in Fig. 3, and communications is established by means of a given right-bank (or left-bank) circularly-polarized wave. When the radio 11 is in a wait state, the composite antenna 12 is rotated to and is brought into close contact with the side surface of the casing of the portable radio 11. A rotary connector 33 rotates the composite antenna 12 with regard to the casing of the portable radio 11. A dotted line shown in Fig. 5 indicates a collapsed state of the composite antenna 12 as a result of rotation. In the collapsed state, the composite antenna 12 is oriented in the direction opposite to the direction of the same when the radio 11 is used, so that the direction of rotation of the circularly-polarized wave becomes reversed. Accordingly, the sensitivity of the composite antenna 12 is considerably deteriorated, and the MSA 30 principally operates while the radio 11 is in a wait state. Fig. 4 is a diagram showing the result of measurement of patterns radiated from the antenna shown in Fig. 3 at a satellite communications frequency and a frequency band of ground portable telecommunications; According to the embodiment of the present invention, a portable radio can cope with a plurality of radio communications services without mechanical switching action, by addition of a linear radiating element via a capacitive element to the front end of a feed pin which supplies a high-frequency current to a microstrip plane antenna. Since there is not required a need of mechanical switching action, the reliability of the antenna and the radio main body is improved.

Claims: A shared antenna for use in a portable radio communication device, comprising a back-feed microstrip plane antenna (1), the microstrip antenna having a patch-shaped conductor (1b) provided on one surface of a plate-like dielectric substance (1c), a ground conductor plate (4) provided on the other surface of the dielectric substance (1c), characterized in that a single feed pin (1a) is connected with the patch-shaped conductor (1b), of the microstrip plane antenna (1) and a linear radiating element (8) is electrically connected to the upper end of the feed pin (1a) via a capacitive element (7). The shared antenna according to claim 1, wherein the microstrip plane antenna (1) is a circularly-polarized antenna, and the linear radiating element (8) is a linearly-polarized antenna. The shared antenna according to claim 1 or 2, wherein a helical antenna (2) is electrically connected to a lower surface of the ground conductor (4) of the microstrip plane antenna (1) constituting the shared antenna. The shared antenna according to any of claims 1 to 3, wherein the microstrip plane antenna (1) operates at a first frequency, and the linear radiating element (8) operates at a second frequency which differs from the first frequency.

Inventors: NAKADA SHINICHI, OBATA TOORU, SUGURO AKIHIRO, NAKADA, SHINICHI, OBATA, TOORU, SUGURO, AKIHIRO, Nakada, Shinichi, c/o Kyocera Corporation, Obata, Tooru, c/o Kyocera Corporation, Suguro, Akihiro, c/o Kyocera Corporation
Applicants: KYOCERA CORP, KYOCERA CORPORATION
Application year: 1997
Main classification: H01Q21
IPC codes: H01Q21, H01Q11, H04Q7, H01Q9, H01Q13, H01Q5, H01Q3, H01Q1