Title of Invention

A SMALL ANTENNA FOR PORTABLE RADIO EQUIPMENT DEVICE

Abstract

The present invention relates to a small antenna (20) for a portable radio equipment device (10) comprising a loaded monopoly radiator (12) comprising a first conductor (23) having a given length horizontal to a printed circuit substrate (11,21) and a second conductor (22) having a meander line shape and installed vertical to said first conductor (23); and a ground radiator (13) comprising separately a first ground (24) and a second ground (25) at a lower portion of said printed circuit substrate (21) , said first and second grounds (24,25) being symmetrical to said second conductor (22) .

Full Text

1. Field of the Invention The present invention relates to small antenna for a portable radio equipment device and more specifically, to a flat top-loaded monopole antenna with high gain for a two-way pager having a ground radiator of special meander line shape.. 2. Description of the Related Art As a portable radio equipment becomes mixtured and light-weigh in recent times, there has also been significant development in a small antenna which are suitable to be used for such equipment. In consideration of characteristic of the small antenna, it should be convenient and simple for a user to utilize the small antenna for use in the portable radio equipment as well as the small antenna has to have high gain and indirection characteristic. In addition, when a terminal is placed near a human body, it is required to minimize the basic characteristic of the antenna, that is, input impedance and variation of the gain. Solution to meet the above requirements has been disclosed in the United States Patent No. 4,700,194 which was invented by Ogawa et al, filed by Matsushita Electric Industrial Co., Ltd. and allowed on October 13, 1987. According to the above patent, if the antenna current flows on a ground circuit and a case of the equipment, the current flowing on the antenna is varied in case that the terminal case is placed in the vicinity of the human body, so that the input impedance and the gain of the antenna may be further varied. For this reason, even without using a quarter-wave trap or a balance to unbalance transformer (hereinafter, referred to as Balun) used in a prior art sleeve antenna technique, good electrical isolation between the antenna and the ground circuit of a coaxial transmission line or the electric circuit may be resulted provided in the antenna not to flow the antenna current on the ground circuit and the case of the equipment. The construction of a prior art quarter-wavelength microstrip antenna (hereinafter, referred to as QMSA) which is explained in the above U.S. Patent No. 4,700,194. centers around a dielectric, the antenna is included with a radiation element on one surface of the dielectric and a ground element on other surface thereof. Here, a first feed radiation element as first feeding means is electrically connected a signal line of the transmission line. Further, a second feed radiation element is constructed on the ground element so as to electrically connect the ground line of the transmission line and the ground element, which is located at a position where the voltage of the standing Voltage wave induced on the ground element becomes minimum. Additionally describing, in a conventional microstrip antenna, the ground plane no longer acts as the ground in the case when the dimensions of the ground plane is relatively small compared to a wavelength of the frequency to be used. In this case, a sinusoidal variation of a voltage distribution, or a standing voltage wave is induced on the ground plane. As a result, a parasitic current is induced on the outer conductor of the coaxial transmission line. In this time, for the sake of minimumly reducing the generation of the parasitic current, - 2 - the outer conductor of the transmission line is connected to the ground element at a second feed point where the voltage of the standing voltage wave induced on the ground element becomes minimum. With this structure, the parasitic current on the transmission line can be reduced or eliminated without any quarter—wave trap which is used in the conventional sleeve antenna configuration. Accordingly, the variations of the characteristics of the antenna can be considerably reduced in the event that the antenna is placed in the vicinity of the human body or an electric circuit. The gain characteristic depending upon lengths of a quarter-wavelength microstrip antenna varies according to embodiments of the prior art. The gain characteristic further varies depending upon width of a quarter-wavelength microstrip antenna according to an embodiment of the prior art. However, the quarter-wavelength microstrip antenna is disadvantageous in that variation of the efficiency characteristic of the antenna considerably relies on the thickness of the printed circuit substrate (hereinafter,referred to as PCB). That is, in consideration of the gain of the antenna, upon the thickness of the PCB is thick, the antenna is large in size and light in weight; thereby causing inconvenience in that the user can not easily port in. To the contrary, upon the thickness of the PCB is thin, while the user can port the antenna, the gain of the antenna may be deteriorated resultedly. SUMMARY OF THE INVENTION 3. It is an object of the present invention to provide a small antenna which is small in size, light in weight, and high in gain so as to be simple to be ported to a user and suitable to be used for a portable radio equipment, thereby minimizing the characteristic variation of the antenna in the case that the antenna is provided near the human body. In order to achieve the above object, the present invention is provided with a small antenna for a portable radio equipment, comprising: a loaded monopole radiator including a first conductor having a given length horizontal to a printed circuit substrate and a second conductor having a meander line shape and installed vertical to the first conductor; and a ground radiator including separately a first ground and a second ground at a lower portion of the printed circuit substrate, the first and second grounds being symmetrical to the second conductor. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: FIG. 1 is a diagram showing the construction of a prior art quarter-wavelength microstrip antenna; FIG. 2 is a diagram showing variation of the gain characteristic depending upon total length of a quarter-wavelength microstrip antenna according an - 4 - embodiment of the prior art; FIG. 3 is a diagram showing variation of the gain characteristic depending upon width of a quarter-wavelength microstrip antenna according an embodiment of the prior art; FIG. 4 is a diagram showing variation of the gain characteristic depending upon not metallized length Gz of a quarter-wavelength microstrip antenna according an embodiment of the prior art; FIG. 5 is a diagram showing the construction of a dipole antenna according to an embodiment of the present invention; FIG. 6 is a detailed circuit diagram of FIG. 5; FIG. 7 is a diagram showing current distribution of a loaded monopole and an equivalent monopole; FIG. 8 is a graph showing gain versus length of a dipole antenna; and FIG. 9 is a graph showing gain versus width of a dipole antenna. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Hereinafter, a preferred embodiment of the present invention will be concretely explained with reference with accompanying drawings. Most of all, throughout the drawings, it is noted that the same reference numerals of letter will be used to designate like or equivalent elements having the same function. Further, in the following description, numeral specific details such as concrete components composing the circuit and the frequency, are set forth to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. The detailed description on known function and - 5 - constructions unnecessarily obscuring the subject matter of the present invention will be avoided in the present invention. FIG. 5 is a diagram showing the construction of a monopole antenna according to an embodiment of the present invention, which is applied to a two-way pager. With respect to FIG. 5, an antenna system 20 is comprised of a conductor radiator 12. of the loaded monopole shape, a ground radiator 13 embodied with the meander line shape, and a coaxial transmission line 27 for connecting the conductor radiator 12 and the ground radiator 13 to the PCB 11 installed with a radio frequency power amplifier. The conductor radiator 12 and the ground radiator 13 are deposited at one major surface of the PCB 21 as one of planes and can be installed in an antenna case 28 of the flip shape. The antenna system 20 moves in directions of Z and Y centering around X-axis of the two-way pager 10. Therefore, in operation, the antenna system 20 is in a vertical position, namely, moves in the direction of Z while being in a horizontal position, moves in the direction of Y. FIG. 6 is a detailed circuit diagram of FIG. 5, which shows specifically the PCB 21 of the antenna, system 20 in detail. The conductor radiator 12 of the loaded monopole shape is composed of a horizonal conductor 23 and a vertical conductor 22, the conductor 22 has the meander line shape. Here, an upper end of the vertical conductor 22 is loaded on the horizontal conductor 23. An electric length of the vertical conductor 22 is 0.49 wavelength and that of the horizontal conductor 23 is 0.3 wavelength. This is designed in consideration that the length of the antenna having highest gain among equivalent vertical monopole antennas is 0.625 wavelength. Further, while a flip-shape antenna case 28 is installed in best using the above lengths, the antenna system 20 uses a loading unit and a the - 6 - meander line shape in order to obtain the maximum gain. The ground radiator 13 is positioned in the lower portion of the PCB 21 of the antenna system 20 parallel to the horizontal conductor 23. At this moment, the ground radiator 13 is placed in a reflective position on the vertical conductor 22. The around radiator 13 is divided into first and second radiators 24 and 25 connected with a ground of the coaxial transmission line 27 at a ground position 26 of the feed point and the first and second ground radiators 24, 25 are symmetrical with respect to a vertical portion 22 of the conductor radiator 12 i.e a vertical conductor. Then to enhance the efficiency of the ground radiator 13, each electric length of the first and second ground radiators 24 and 25 is required to be made as a quarter wavelength . The quality of the PCB 21 of the antenna system 20 for use in a preferred embodiment of the present invention is FR-4, and the thickness thereof is 0.25mm . The PCB 21 thereof can be inserted into the flip-shape antenna case 28 whose quality is polycarbonate. and uses a capacitor 34 and an inductor 35 for impedance matching. 7. When explaining in detail operation of the antenna according to the preferred embodiment of the present invention, it is as follow. The antenna efficiency is determined by the radiation efficiency and further, the radiation efficiency can be shown with following expression 1. C Expression wherein, ?= is the radiation efficiency ,Rr is a radiation resistance (O ), and RL is a loss resistance ( O ). 7A. In the above expression 1, as the length of the radiator decreases, the radiation resistance Rr decreases. To heighten the radiation efficiency related closely to the antenna efficiency, it is necessary to increase the length of the radiator having the high radiation resistance Rr as well as to use the loss resistance RL having low loss quality. Thus, the embodiment of the present invention is applied with a method for making the conductor to have meander line shape to reduce the physical length of the antenna radiator whereas heightening the radiation efficiency with increases of the length of the radiator depending on the wavelength. Finally, the gain of the antenna can be heightened without increasing the physical length of the radiator. As K. Harchenko pointed out in the paper entitled with "antenna conductor with meander line shape"(Radio, No.8, 1979, P21), the higher the meander line rate of the antenna becomes, the narrower the passband of the antenna becomes. Therefore, as depicted in FIG. 6, the horizontal radiator 23 loaded on the radiator 22 is used in the embodiment of the present invention, so that the electric equivalent length can increase by value required without making the bandwidth of the antenna to be narrow. Accordingly, it results in effects in that the antenna operates in like manner when increasing the physical length of the radiator, thereby enhancing the antenna gain. FIG. 7 is a diagram showing current distribution of a loaded monopole and an equivalent monopole, wherein FIG. 7a illustrates the loaded monopole radiator and current distribution thereof, and FIG. 7b illustrates the current - 8 - distribution of the equivalent monopole antenna upon the loaded monopole antenna really operates. This is to obtain further good current distribution in the vertical conductor of the antenna. Thus, the antenna operates in like manner when increasing as much as ? lv by the horizontal conductor (loaded radiator) used, which will be shown by following expression 2. [ Expression 2 ] wherein ? lv is increased length of the equivalent vertical conductor. In the case of the loaded monopole antenna, unless the current value at an end point of the vertical conductor 22 as shown by A of FIG. 7a becomes 0, the value is determined by reactive impedance of the horizontal conductor 23 of the loaded monopole antenna. At this moment, only when the input reactive impedance of the loaded radiator at point A as shown by A of FIG. 7a is equal to that thereof as shown by B of FIG. 7b, the vertical conductor of the antenna can increase as much as ? resultedly. In this situation, the input reactive impedances XA and XB of the loaded radiator at positions A and B are shown in following expressions 3 and 4. [ Expression 3 ] - 9 - wherein, lH is length of arm of the horizontal conductor of the loaded monopole and ZOH is intrinsic impedance of the horizontal conductor of the loaded monopole. [ Expression 4 ] wherein ZOV is intrinsic impedance of the vertical conductor of the loaded monopole. As well, upon two input reactive impedance XA and XB are equal to each other, ? v will be obtained by following expression 5. [ Expression 5 ] As a result, lveqv is a sum of lv and ? lv, that is, lveqv = lv + ? lv. In other words, it can be seen that the physical length of the monopole antenna is extended as much as ? lv then to be operated. Furthermore, the terminal case coated with the metal film or the ground of the installed PCB has been served as the ground of the general monopole antenna. Due to this, when the user grasps the terminal by hands, the radiation efficiency can be still reduced even though the ground thereof serves as the ground radiator. The above state is well disclosed in "Mobile Antenna Systems Handbook" made by K. Fujimoto -10 - and J. R. James, Artech House, Boston-London, 1994, P217-243. The first and second ground radiators 24 and 25 are adapted in the preferred embodiment of the present invention for minimizing the effects influenced on the radiation of the monopole antenna when the terminal is placed near the human body. And then, since the antenna current is separated from the ground of the two-way pager 10, the reduction of the radiation efficiency can be minimized in a user's hands. As well,' when the user actually utilizes the terminal, the first and second ground radiators 24 and 25 are included on the PCB 21 of the antenna installed at an upper surface of the two-way pager 10 to be apart at maximum from the human body. The first and second ground radiators 24 and 25 are varied depending on signal voltage law and the varied signal voltage generates the parasitic current flowing along the surface (ground) of the coaxial transmission line 27, thereby easily changing the antenna characteristic such as the direction pattern of the antenna, the input impedance thereof, and the gain thereof. Thus, to prevent the variation of such characteristic, the first and second radiators 24 and 25 are designed as follows. That is, the first an second radiators 24 and 25 are opposed to each other centering around the Z-axis of the antenna on the PCB 21 thereof and each electric length thereof is designed as L = (2n-1) ? /4 (herein, n = positive constant). What is to say, the electric length of the first and second ground radiators 24 and 25 is designed as an odd multiple of one-quarter wavelength. If the electric length of the first and second ground radiators 24 and 25 are equal to each other, the parasitic current flowing from the surface of the ground radiator 26 to the ground thereof can be minimized to thereby generate - 11 - little degradation of the antenna characteristic variation and the radiation efficiency due to the body contact even if the ground of the two-way pager 10 is positioned adjacent to the human body. It can be understood from FIGs. 2 to 4 that the gain characteristic of the QMSA is varied depending to the lengths L and Gz and the width W of the antenna and that gain characteristic thereof is not good in comparison with the graph showing gain versus length of a dipole antenna in FIG. 8. To recognize the above fact more actually, the specification of the antenna used in the embodiment according to the present invention (L = 47.3mm, ?y = 4.5, f = 916MHz) is adapted in the prior art antenna. The comparison of the gain between the antenna according to the present invention and the prior art antenna is as below. In FIG 1, when assuming that b = ? s/4 , L = 47.3mm, ?Y = 4.5, f = 916MHz, and d = 1.2mm, ? s , b, and Gz are shown in following expressions 6 to 8. [ Expression 6 ] [ Expression 7 ] - 12 - [ Expression 8 ] Gz = L - b = 8.7mm Regarding FIGs. 2 and 4, in the case that L is 47.3mm and Gz is 8.7mm, each gain is approximately -12.5dBd (-10.35dBi). The antenna used in the present embodiment has it electric length of 0.625 ? . In this event, the gain is about 3dBd (5.15dBi) with reference to FIG. 8. Thus, the prior art has a problem in that the gain can be degraded as much as about 15 dB. Another problem of the prior art is that the antenna efficiency characteristic ? of the QMSA has the difference as the thickness d of the PCB upon operation. When the specification of the antenna used in the present embodiment is adapted in the prior art antenna ( L = 47.3mm, ?y = 4.5, f = 916MHz, d = 0.25mm), the gain according to the variation of the thickness d thereof with reference to FIG. 9 is as below. The gain of the aforesaid antenna specification has characteristic of about -12.5dBd. Here, the thickness d is 1.2mm and then, as shown in FIG. 9, the antenna efficiency is determined by following factors of expression 9. [ Expression 9 ] F =d/? o Xo =c/f =3X10/916X10 =327.5 mm F = 1.2/327.5=0.003664 - 13 - Referring to FIG. 9, when F=d/? is 0.003664,the antenna efficiency is about 50%. When the thickness d of the PCB is 0.25mm, F is 0.000736 and the antenna efficiency falls on approximately 4.5%. Consequently, when d is 1.2mm, ? is about ( = )50%. When d is 0.25mm, ? is about 4.5%. The case that the thickness is thick (that is, d is 1.2mm) has about 11 times value of gain as the value of the case that the thickness is thin (that is, d is 0.25mm). When calculating the gain by using the above result, the gain of the antenna will be given in following expression 10. [ Expression 10 ] G = -12;5dBd - 10 log11 = -22.9dBd Lastly, it can be seen from the above expression 10 that the gain is reduced by about 10dB in comparison with the case that d is 1.2mm. In addition, the gain is reduced by about 25dB in comparison with the gain of the dipole antenna. Since the antenna system according to the present invention is capable of being embodied on the thin PCB, it has effects on enhancing the convenience for usage and the simplicity for portability because of being simply installed at the upper surface of the terminal. Further, because the vertical radiator placed on the PCB is designed to be the meander line shape, the physical length is advantageously reduced to obtain the best electric characteristic in the limited size of the antenna. Furthermore, since the upper end of the vertical radiator - 14 - uses another horizontal radiator and the vertical radiator is equivalently increased, it results in enhancing the gain of the antenna. Moreover, now that the vertical and horizontal radiators and the ground radiator are embodied with one thin PCB, it is convenient to manufacture such antenna. As well, the ground radiator prevents the antenna current from being flown on the terminal ground, the variation of the characteristic of the antenna can be minimized depending upon the variation of the state of the terminal ground, for example, factor such as body contact. Therefore, the present invention is advantageous in that the antenna having more stable and good characteristic can be embodied. Therefore, it should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present invention, but rather that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims. - 15 - WE CLAIM: 1. A small antenna (20) for a portable radio equipment device (10) comprising: a loaded monopole radiator (12) comprising a first conductor (23) having a given length horizontal to a printed circuit substrate (11,21) and a second conductor (22) having a meander line shape and installed vertical to said first conductor (23); and a ground radiator (13) comprising separately a first ground radiator (24) and a second ground radiator (25) at a lower portion of said printed circuit substrate (21), said first and second grounds (24,25) being symmetrical to said second conductor (22). 2. The antenna as claimed in claim 1, wherein said loaded monopole radiator (12) comprises a vertical conductor (22) of a meander 1ine shape and a loading 1ine (27) of a horizontal conductor extended right and left at an upper end of said vertical conductor (22). 3. The antenna as claimed in claim 1 or 2, wherein said ground radiator (13) is deposited symmetrical to said vertical conductor (22) of said loaded monopole radiator (12) so that a right portion of a second ground radiator (25) and a left portion of a first ground radiator (24) can be connected to each other because said ground radiator (13) has a meander line shape, whereby each electrical length of said first and second ground radiators (24,25) is an odd multiple of one quarter wavelength. 16. 4. The antenna as claimed in claim 3, wherein said printed circuit substrate (11,21) is installed at a body of said equipment (10) provided with a radio frequency amplifier, and connected to a coaxial cable (27). 9. The antenna as claimed in claim 4, wherein said coaxial cable (27) has a signal line of one end connected at a lower portion of ©aid vertical conductor (23) of said loaded monopole radiator (12) and a ground line thereof connected to said first and second ground radiators (24,25), a signal line of other end connected at a signal line of said device (10) and a ground 1ine thereof connected to a ground portion (26) of said device whereby said antenna (20) and said device (10) can be reciprocally connected to each other electrically. 6. The antenna as claimed in claim 1, wherein said printed circuit substrate (11,21) is installed in a flip antenna case (28). 17. 7, The antenna as claimed in claim 6,wherein said antenna case (28) is composed of polycarbonate. The present invention relates to a small antenna (20) for a portable radio equipment device (10) comprising a loaded monopoly radiator (12) comprising a first conductor (23) having a given length horizontal to a printed circuit substrate (11,21) and a second conductor (22) having a meander line shape and installed vertical to said first conductor (23); and a ground radiator (13) comprising separately a first ground (24) and a second ground (25) at a lower portion of said printed circuit substrate (21) , said first and second grounds (24,25) being symmetrical to said second conductor (22) .

Documents:

01155-cal-1997 abstract.pdf

01155-cal-1997 claims.pdf

01155-cal-1997 correspondence.pdf

01155-cal-1997 description(complete).pdf

01155-cal-1997 drawings.pdf

01155-cal-1997 form-1.pdf

01155-cal-1997 form-2.pdf

01155-cal-1997 form-3.pdf

01155-cal-1997 form-5.pdf

01155-cal-1997 gpa.pdf

01155-cal-1997 priority document other.pdf

01155-cal-1997 priority document.pdf

1155-cal-1997-granted-abstract_.pdf

1155-cal-1997-granted-acceptance publication_.pdf

1155-cal-1997-granted-claims_.pdf

1155-cal-1997-granted-correspondence_.pdf

1155-cal-1997-granted-description (complete)_.pdf

1155-cal-1997-granted-drawings_.pdf

1155-cal-1997-granted-form 1_.pdf

1155-cal-1997-granted-form 2_.pdf

1155-cal-1997-granted-form 3_.pdf

1155-cal-1997-granted-form 5_.pdf

1155-cal-1997-granted-gpa_.pdf

1155-cal-1997-granted-letter patent_.pdf

1155-cal-1997-granted-priority document_.pdf

1155-cal-1997-granted-reply to examination report_.pdf

1155-cal-1997-granted-specification_.pdf

1155-cal-1997-granted-translated copy of priority document_.pdf