High gain portable radio selective call receiver using a microstrip construction for inter-board connections

Abstract: A radio selective call receiver capable of improving an antenna property by connecting a first circuit board (21) on a high frequency side and a second circuit board (22) on a low frequency side by using a microstrip line (9). On the first circuit board (21), a component mounting part (23) including an antenna (1) an antenna tuning circuit and a high frequency circuit part operated by a frequency resonant with an antenna tuning frequency is mounted, and on the second circuit board (22) another component mounting part (24) including a low frequency circuit part operated by a lower frequency than the antenna tuning frequency is mounted. The first and second circuit boards are connected by a flexible circuit board (31) provided with the microstrip line (9) having a high impedance with the antenna tuning circuit.

Description: The present invention relates to a portable radio selective call receiver known as a pocket bell (trade name), and more particularly to a UHF band portable radio selective call receiver having a construction with an antenna and receiving electric parts positioned closely together. Description of the Related Arts Fig. 1 shows a conventional UHF band radio selective call receiver. In Fig. 1, a UHF band radio signal received by an antenna 1 is amplified in a radio part 2 and is then demodulated in a waveform shaping part 3. In a control part 4, the demodulated signal output from the waveform shaping part 3 is compared with its own read number previously written in a readable individual number memory part 5, and, when both are coincident with each other, a sound signal is output to a speaker drive circuit 7 and a light signal is also output to an LED drive circuit 10 via a terminal 16c of a jack 16 and a terminal 17c of a plug 17. The speaker drive circuit 7 amplifies the input sound signal to drive a speaker 8 to output a call sound, and the LED drive circuit 10 amplifies the light signal to flash an LED 11. Further, when the received signal includes a display information signal, the control part 4 picks up this display information signal to output it to a display drive circuit 13 via a terminal 16d of the jack 16 and a terminal 17d of the plug 17. The display drive circuit 13 processes the display information signal to display it on a display 14. In this case, the display information signal is a signal having a sufficiently low frequency component compared with a UHF band frequency in a similar manner to the sound signal and the light signal. The display information for the display information signal is stored in a display information memory part 12. The control part 4 can be constructed by a micro-processor and a ROM (read only memory) storing a control program or by a logic circuit composed of a random logic. A battery 15 is a power source of the radio selective call receiver and supplies the necessary power for the operation of the radio part 2, the LED drive circuit 10 and the like. A step-up circuit 6 steps up the voltage of the battery 15 to apply a raised voltage for operation to the control part 4, the display drive circuit 13 and the like. The power is supplied to the LED drive circuit 10 via a terminal 16b of the jack 16 and a terminal 17b of the plug 17, and the raised voltage is applied to the display drive circuit 13 via a terminal 16a of the jack 16 and a terminal 17a of the plug 17. Fig. 2 shows an exploded view of the conventional radio selective call receiver assembled on boards. In Fig. 2, on a printed circuit board 21, a component mounting part 23 including the antenna 1, the radio part 2 and the like and the jack 16 are mounted and a pair of positive and negative terminals 26 and 25 for connecting the battery 15 is also mounted. Also, on another printed circuit board 22 to be overlapped with the printed circuit board 21, the plug 17 to be connected with the jack 16 mounted on the printed circuit board 21 and a component mounting part 24 including the display drive circuit 13 and the like are mounted, and on the surface part of the printed circuit board 22, the display 14 is mounted. Fig. 3 illustrates an overlapped state of the printed circuit boards 21 and 22 while the jack 16 is coupled with the plug 17. In this connection state, the printed circuit boards 21 and 22 are assembled so that the concavoconvex surfaces of the component mounting parts 23 and 24 may be mutually engaged with each other. A power source pattern 51 formed on the printed circuit board 21 supplies the power of the battery 15 to the opposite printed circuit board 22 side via the jack 16 and the plug 17. The impedance of the power source pattern 51 is the same as an earth pattern. In a conventional 150 MHz band radio selective call receiver, as disclosed in the U.S.P. 4,491,978 (Japanese Patent Publication No. 62-42534), by inserting a choke coil in series between a power source pattern and an earth pattern for connecting a high frequency part operated at a frequency tuned with an antenna circuit and a low frequency part operated at a lower frequency than the frequency for the high frequency part, an earth line of the low frequency part can possess a high impedance with respect to an antenna, and an open area of the antenna can be substantially increased to reduce an antenna loss and to obtain a high gain. That is, the gain reduction of the antenna under the influence of the low frequency part can be prevented. In the conventional UHF band radio selective call receiver, when there exists an unnegligible conductor such as a power source pattern against a waveform of a frequency tuned with an antenna circuit located near or within an opening of an antenna, due to a magnetic field generated by a current flowing in the conductor, an electromagnetic field near the antenna is disturbed to deteriorate the antenna properties. That is, by the influence of the conductor pattern, the antenna gain can be reduced. In this UHF band radio selective call receiver, since a concentrated constant can not be used, it can be hard to improve the antenna properties by using the choke coil different from the 150 MHz band radio selective call receiver. It is therefore an object of the present invention to provide a radio selective call receiver in view of the aforementioned problems of the prior art, which is capable of improving an antenna property such as an antenna loss, preventing a generation of an unnecessary magnetic field, preventing a reduction of an antenna gain to achieve a high antenna gain and achieving a high density mounting of components on boards. In accordance with one aspect of the present invention, there is provided a radio selective call receiver with a built-in antenna, comprising: a first circuit board provided with an antenna, an antenna tuning circuit connected to the antenna, and a high frequency circuit part connecting to the antenna tuning circuit and operating at a first frequency resonant with an antenna tuning frequency; a second circuit board provided with a low frequency circuit part operating at a second frequency lower than the antenna tuning frequency; and connection means including a micro-strip line for connecting the first and second circuit boards, the microstrip line having a high impedance with respect to the antenna tuning frequency. In an embodiment of the radio selective call receiver of the present invention, the first and second circuit boards are connected by a flexible circuit board and the microstrip line is formed on the flexible circuit board. In an embodiment of the radio selective call receiver of the present invention, the microstrip line is shaped in zigzag, and magnetic fields generated by a current flowing in the microstrip line are mutually nullified. According to the present invention, since the first circuit board on the high frequency side and the second circuit board on the low frequency side are connected by the connection means including the microstrip line having a high impedance with respect to the antenna tuning frequency, the loss at the antenna mounted on the first circuit board can be reduced. That is, an antenna gain reduction due to the current flow within a conductor for connecting the first and second circuit boards can be prevented. Further, according to an other embodiment of the present invention, since the first and second circuit boards are connected by the flexible circuit board provided with the microstrip line, the antenna gain can be improved, and there is no need to form the microstrip line on the first circuit board to enable a high density mounting of the first circuit board. Furthermore, since the microstrip line is formed in zigzag so as to mutually nullify the magnetic fields generated by the current flowing in the zigzag pattern, a generation of an unnecessary magnetic field influencing to the antenna properties can be prevented. The objects, features and advantages of the present invention will become more apparent from the consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram of a conventional radio selective call receiver; Fig. 2 is an exploded perspective view of the conventional radio selective call receiver shown in Fig. 1, mounted on printed circuit boards; Fig. 3 is a side view of the conventional radio selective call receiver shown in Fig. 2, wherein two printed circuit boards are overlapped with each other; Fig. 4 is a block diagram of one embodiment of a radio selective call receiver according to the present invention; Fig. 5 is an exploded perspective view of the radio selective call receiver shown in Fig. 4, mounted on printed circuit boards; Fig. 6 is a side view of the radio selective call receiver shown in Fig. 5, wherein two printed circuit boards are overlapped with each other; Fig. 7 is an exploded perspective view of another embodiment of a radio selective call receiver according to the present invention, mounted on printed circuit boards; and Fig. 8 is a side view of the radio selective call receiver shown in Fig. 7, wherein two printed circuit boards are overlapped with each other. Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the views and thus the repeated description thereof can be omitted for brevity, there is shown in Fig. 4 one embodiment of a UHF band radio selective call receiver according to the present invention. In Fig. 4, a UHF band radio signal received by an antenna 1 is amplified in a radio part 2 including an antenna tuning circuit and a high frequency circuit part and is then demodulated in a waveform shaping part 3. In a control part 4, the demodulated signal output from the waveform shaping part 3 is compared with its own read number previously written in a readable individual number memory part 5, and, when both are coincident with each other, a sound signal is output to a speaker drive circuit 7 and a light signal is also output to an LED drive circuit 10 via a microstrip line (ML) 9C, a terminal 16c of a jack 16 and a terminal 17c of a plug 17. The speaker drive circuit 7 amplifies the input sound signal to drive a speaker 8 to output a call sound, and the LED drive circuit 10 amplifies the light signal to flash an LED 11. Further, when the received signal includes a display information signal, the control part 4 picks up this display information signal to output it to a display drive circuit 13 via a microstrip line 9D, a terminal 16d of the jack 16 and a terminal 17d of the plug 17. The display drive circuit 13 processes a conversion of the display information signal into a signal required for a code conversion and a display to display it on a display 14. The display information for the display information signal is stored in a display information memory part 12. A battery 15 supplies electric power to the circuit parts such as the radio part 2 and the like and to the LED drive circuit 10 via a microstrip line 9B, a terminal 16b of the jack 16 and a terminal 17b of the plug 17. Also, the voltage of the battery 15 is raised to a necessary voltage in a step-up circuit 6, and the step-up circuit 6 supplies the raised voltage to the control part 4 and the like and to the display drive circuit 13 via a microstrip line 9A, a terminal 16a of the jack 16 and a terminal 17a of the plug 17. An earth line of a printed circuit board 21 side is connected to an earth line of a printed circuit board 22 side via a microstrip line 9E, a terminal 16e of the jack 16 and a terminal 17e of the plug 17. Fig. 5 shows an exploded structure of the UHF band radio selective call receiver mounted on the printed circuit boards 21 and 22, and Fig. 6 shows the overlapped printed circuit boards 21 and 22 connected with each other. In Figs. 5 and 6, on the printed circuit board 21 on the high frequency part, a component mounting part 23 including the antenna 1, the radio part 2 and the like and the jack 16 are mounted and a pair of positive and negative terminals 26 and 25 for connecting the battery 15 is also mounted. Also, on the printed circuit board 22 on the low frequency part connected to the printed circuit board 21, the plug 17 to be connected with the jack 16 mounted on the printed circuit board 21 and a component mounting part 24 including the display drive circuit 13 operated at a lower frequency than an antenna tuning frequency and the like are mounted, and on the surface part of the printed circuit board 22, the display 14 is mounted. A part of a power source pattern extending from the positive terminal 26 is constituted by the microstrip line 9B, and the power of the battery 15 is supplied to the printed circuit board 22 side via this microstrip line 9B, the terminal 16b of the jack 16 and the terminal 17b of the plug 17. In this case, the microstrip line 9B is shaped in zigzag so that, when the current is flowing, the generated magnetic fields may be mutually nullified so as to prevent the generation of an unnecessary magnetic field influencing the antenna properties, and by optimizing its line path length, a high impedance with respect to the antenna tuning frequency is obtained to cut high frequency components. Also, the other microstrip lines 9A, 9C, 9D and 9E (not shown) have a similar function as the microstrip line 9B. The microstrip lines 9A, 9B, 9C, 9D and 9E are composed of a wiring pattern formed on the printed circuit board 21, and thus no particular cost is required for formation of the microstrip lines. Further, by using a multi-layer printed circuit board for the printed circuit board 21 and arranging the microstrip lines 9A, 9B, 9C, 9D and 9E in an internal layer, a high density mounting of the printed circuit board 21 can be obtained. The lines including the terminals of the jack 16 and the plug 17 have a high impedance with respect to the antenna tuning frequency and the magnetic fields generated by the lines do not influence the antenna properties. Next, in Figs. 7 and 8, there is shown another embodiment of a UHF band radio selective call receiver according to the present invention. In this embodiment, a flexible circuit board 31 is used for connecting the printed circuit boards 21 and 22 in place of the jack 16 and the plug 17. The flexible circuit board 31 is composed of patterns including a power source line, an earth line and signal lines, and in particular, the power source line is composed of a pattern including the microstrip line 9B. As described above, in this embodiment, the printed circuit boards 21 and 22 are coupled by the flexible circuit board 31 and the microstrip line 9B is formed in the flexible circuit board 31. Hence, there is no need to form the microstrip line 9B on the printed circuit board 21 and it is possible to achieve the high density mounting of the printed circuit board 21. According to the present invention, as described above, since the connection patterns such as the power source pattern for supplying the power of the battery provided on one printed circuit board to another printed circuit board connected to the one printed circuit board are constructed by the microstrip lines, the disturbance of the magnetic field near the antenna due to the current flowing in the connection patterns can be prevented to raise the antenna gain compared with a conventional radio selective call receiver. Further, by using the flexible circuit board for the coupling of the two printed circuit boards, the microstrip lines can be formed on the flexible circuit board, and thus the high density mounting of the printed circuit board can be possible. As a result, a compact radio selective call receiver with a high gain antenna can be constructed. Further, by forming the microstrip line in zigzag, the magnetic field generated by the flowing of the current in the microstrip line can be nullified, and the generation of an unnecessary magnetic field for influencing the antenna properties can be prevented. As a result, the antenna gain can be further raised. While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by those embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope of the present invention as defined in the claims.

Claims: A radio selective call receiver with a built-in antenna, comprising: a first circuit board (21) provided with an antenna (1), an antenna tuning circuit connected to the antenna, and a high frequency circuit part connecting to the antenna tuning circuit and operating at a first frequency resonant with an antenna tuning frequency; a second circuit board (22) provided with a low frequency circuit part operating at a second frequency lower than the antenna tuning frequency; and connection means (16, 17, 31) for connecting the first and second circuit boards, the connection means including a microstrip line (9A, 9B, 9C, 9D, 9E) having a high impedance with respect to the antenna tuning frequency, the microstrip line connecting the first and second circuit boards. The radio selective call receiver as claimed in claim 1, wherein the connection means includes a flexible circuit board (31) and the microstrip line is formed on the flexible circuit board. The radio selective call receiver as claimed in claim 1 or 2, wherein the microstrip line (9A, 9B, 9C, 9D, 9E) is shaped in zigzag, and, when a current flows in the microstrip line, generated magnetic fields are mutually nullified. The radio selective call receiver as claimed in any of claims 1 to 3, wherein wiring patterns formed on the first and second circuit boards (21, 22) are composed of the microstrip lines. The radio selective call receiver as claimed in any of claims 1 to 4, wherein the first circuit board (21) is a multi-layer circuit board, and the microstrip line is arranged in an internal layer.

Inventors: ASAI TAKAYUKI, YAGI MASAHARU, ASAI, TAKAYUKI, YAGI, MASAHARU, ASAI, TAKAYUKI, C/O NEC CORPORATION, Yagi, Masaharu, c/o NEC Shizuoka, Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1993
Main classification: H04B1
IPC codes: H04Q7, H01P3, H04B1