US3623161A

US3623161A - Fractional wavelength folded antenna mounted on portable radio

Info

Publication number: US3623161A
Application number: US60507A
Authority: US
Inventors: Kyohei Fujimoto; Toshio Tatsuzawa
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1967-09-26
Filing date: 1970-08-03
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23

Abstract

A portable radio device provided with an antenna small sized and not projected from the device for the convenience of handling, which antenna has two polarizations to be made operable almost free from disadvantages in operation due to change in electromagnetic field which are brought about with influences of ambient geographical features or houses.

Description

United States Patent Appl. No. Filed Patented Assignee Priorities FRACTIONAL WAVELENGTH FOLDED ANTENNA MOUNTED ON PORTABLE RADIO 10 Claims, 11 Drawing Figs.

u.s. Cl 3431702, 343/829, 343/862, 343/873 51 int. Cl H0lq 1/24 [50] Field of Search 343/702,

[56] References Cited UNITED STATES PATENTS 2,417,793 3/ l 947 Wehner 343/708 3,426,352 2/1969 Fenwick 343/750 3,427,624 2/1969 Waneslow et al 343/750 Primary ExaminerEli Lieberman AnomeyStevens, Davis, Miller & Mosher ABSTRACT: A portable radio device provided with an antenna small sized and not projected from the device for the convenience of handling, which antenna has two polarizations to be made operable almost free from disadvantages in operation due to change in electromagnetic field which are brought about with influences of ambient geographical features or houses,

Ill/ll,

PATENTEDuuv 23 I971 3,623,161

SHEET 3 or 3 FIG. /0

- [/WE/WED L TYPE WH/P FRACTIONAL WAVELENGTH FOLDED ANTENNA MOUNTED ON PORTABLE RADIO BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to small-sized portable radio devices with a transmitter and/or a receiver incorporated therein such as radio communication device, radio receiver, television receiver and the like.

2. Description of the Prior Art In the conventional portable-type radio devices, it is the usual practice to use a whip antenna. With a device having an antenna projected therefrom, inconvenience is encountered in handling the same, and there has been a fact that such a projected antenna is apt to be broken and consequently the MTBF of the portable device is significantly decreased. On the other hand, with a device provided with an extensible antenna, the antenna must be extended so as to project from the device every time the device is to be used, so that inconvenience is experienced in that not only the handling thereof is troublesome but also the characteristics thereof tend to be varied due to its directivity.

SUMMARY OF THE INVENTION The present invention intends to eliminate the foregoing drawbacks of the antenna systems of the conventional portable radio device.

Accordingly, it is a primary object of the present invention to provide a radio device wherein inconvenience in handling the device is eliminated by making the antenna so that it does not project from the radio device as in the conventional case.

1 A further object of the invention is to provide a radio device wherein the space occupied by the antenna is minimized for the convenience of handling the device.

Another object of the present invention is to provide a radio device with improved antenna matching and efficiency, even though the space for the antenna is minimized.

A still further object of the invention is to provide a radio device which has a long MTBF by the use of an antenna which does not project from the radio device.

Still another object of the present invention is to provide a radio device wherein the space in the body thereof can be effectively utilized.

Still another object of the present invention is to provide a portable radio device with an antenna having two polarizations to thereby be made operable almost free from disadvantages in operation due to changes in electric field which are brought about with influences of ambient geographical features or houses or buildings.

Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view showing a radio device according to one embodiment of the present invention;

FIG. 2 is an enlarged view showing the main portion of the device shown in FIG. 1;

FIG. 3 is an equivalent circuit diagram of the main portion of the device shown in FIG. 1;

FIGS. 4aand 4bare the equivalent circuits decomposed into the balanced and unbalanced modes derived from FIG. 3;

FIGS. 5 and 6 show views of further embodiments of the antenna according to the present invention;

FIG. 7 shows on the Smith Chart an admittance characteristic diagram of the antenna of the present invention;

FIG. 8 is an equivalent expression of the antenna shown in FIG. 4a;

FIG. 9 shows the coordinate system of the antenna; and

FIG. 10 is a radiation characteristic diagram of the present inventive antenna used within the UI-IF band.

DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of the present invention will be described with reference to FIGS. I and 2, wherein the reference numeral 1 represents a portable radio device body, and 2 an antenna with an element 2 parallel to the radio device body I disposed in close relationship thereto and a feeding point 3 provided on the other element 2" thereof. The radio device body 1 serves as a part of an infinite conductive plate with respect to the antenna 2.

As described above, in this embodiment, the antenna 2 is mounted with the parallel element 2' with a structure of relatively low profile on the radio device body I which serves as part of an infinite conductor plate.

Thus, since the antenna 2 is not projected from the radio device body as in the case with a whip antenna but is disposed in parallel with a surface of the body so that the entire space occupied thereby is reduced and no particular cautions may be required against the damages to the antenna, the device according to the present invention can be conveniently handled and used. Furthermore, since the radio device body 1 itself serves as part of an infinite conductor plate, not only a short antenna can be efficiently utilized through suitable feeding thereto but also the matching thereof can be conveniently achieved. Still further, since there is no need to incorporate the antenna within the body I, the space defined within the body can be efiectively utilized. In the case where the casing for the radio device body is molded of a plastic material, a metal plate serving as a part of the infinite conductor plate may be provided at the position where the antenna is mounted.

FIG. 2 illustrates details of the antenna 2 which is a type of inverted L. The antenna 2 having a feeding point 3 provided on the element 2" is mounted in such a manner that the'element 2 thereof is disposed in closed relationship to the radio device body I, the body 1 per se is adapted to serve as a part of an infinite conductor plate.

The antenna 2 may be completely embedded in the dielectric material 5 to thereby protect the antenna 2 and make it possible to reduce the length of the antenna. In this case, the effective length of the antenna can effectively be increased in accordance with the dielectric material 5 in which the antenna is embedded so that the actual length of the antenna is can be correspondingly reduced, provided that the dielectric loss of the dielectric material 5 is very small.

The reference numeral 4 represents a matching element attached to the antenna element 2" of the antenna 2. That is, in this embodiment, the antenna 2 is provided with the matching element 4 by which the matching of the antenna can be facilitated without any other component.

Provided that the antenna 2 is located on the infinite conductor plate 1 as shown in FIG. 2, this antenna portion is represented by the equivalent diagram as shown in FIG. 3 when taking into consideration the image of the antenna.

In FIG. 3 the dotted line shows the position of the surface of the indefinite conductor plate 1 of FIG. 2 and the antenna system of the invention is represented in the symmetrical form with respect to the dotted line; in this Figure mark V, indicates a feeding voltage and L, indicates an electric current at the feeding terminal. This antenna system is separated into two modes of balance and unbalance components which are shown in FIGS. 4b and 4arespectively. More specifically, the matching element 4 is equivalently represented by the balance component comprising two parallel lines which have thicknesses pl and p2 respectively and are spaced apart from each other at a distance S and whose length is I as shown in FIG. 4b and the unbalance component as shown in FIG. 4 a of the type which feeds by short circuiting the input terminal portions of each parallel line. Either component contributes to the radiation, however, in the event that the distance S is greatly decreased only the unbalance component contributes to'the radiation.

Let us assume that mark i represents the input voltage and l b the input terminal current for the balance mode. while mark V represents the feeding voltage and I ,,the feeding terminal current for the unbalance mode. Although these values are determined by the voltage or current distribution factors dependent upon the geometrical dimension of the antenna such as the foregoing thickness, spacing or distance thereof. etc., the method of determining the same will not be described in detail herein. The feeding terminal impedance Z ,,,of this antenna system is given by the formula:

that the magnitude of the dimension (I+S+L) is taken as approximately equal to -r/4 and a relationship Sl2 50 but a relationship (I S+L) is maintained and the dimensions of the body of the usual portable radio device are arranged to lie 5 within a range extending from h/lOO to M (this may be derived from the relationship (I S+L). In particular the present invention defines the height of the cutaway portion less than the magnitude of M30, so that the dimensions of the antenna element 2" is made in the range of A/ 100 to M50. 0 With the above relationship (I S+L), the following equations (3) to (7) can be derived and the radiation pattern of the Z in 7' T' a// b antenna of the invention is obtainable as almost nondirectional, a b l. in regard to the elements aand b: component on the x-y where Z and Z indicate the feeding terminal impedance and plane the input impedance respectively of the unbalance mode ane-r'kR tenna system and the balance mode antenna system, the ex- Eli: 60I R ks cos (3) pression 42 /122,, the calculation value of 2Z,,'4Z,,/4Z,,+2Z,, and Z, is given by the following equation with the characteristic impedance Z, of the equivalently represented two parallel lines:

Z,,=jZ tan k! (2) where k=(21r/)\) (it represents a wavelength). Accordingly, the feeding terminal impedance Z of this antenna system depends upon the length l of its matching element, the spacing S between the two parallel lines and the thickness pl and p2 of the antenna elements. it is possible to make the feeding terminal impedance Z ,match the load impedance, for example, 500, by adjusting the foregoing parameters. in a case where the impedance of the antenna of length L is capacitive the matching is made very easily, since the impedance of the balance mode of the matching element is inductive, one way for obtaining this matching condition is to adjust the height I of the position of the matching element. in practice, this is achieved by providing a short-circuiting element T at the position corresponding to the height I with a resultant change of 2,, as shown in FIG. 5. I

in a case where the impedance of the antenna of length L is inductive, the impedance matching is achieved by disconnecting the matching element 4 from the element 2' of the antenna, which results in rendering the input impedance Z capacitive.

An example of the admittance characteristics of the antenna for practical use is shown in FIG. 7. As a consequence the antenna of the present invention has a merit such that it does not require additional device other than the antenna element itself for achievingimpedance matching with the result of a simplified matching mechanism. in particular, it is noted as a feature that the matching is easily made, for example, by connecting the matching element 2" with the element 2 of the antenna and by adjusting the length of the element in accordance with the impedance characteristic of the antenna. in a practical case, this feeding terminal impedance characteristics may differ from that of the equation (I) since the dimension of the body is not infinite and the equivalent expression of the antenna of FIG. 4 may not be explicitly assumed to be correct. When taking into consideration the capacity inherent to the body, however, the antenna of the invention may be substantially treated by the equivalent circuit shown in FIG. 4. In the case of a conventional antenna, it is very difl'icult to achieve impedance matching with the presence of appreciable amount of capacity due to the body of the device. in the case of the present antenna, the matching is very simply and easily performed, so that an antenna having a high efficiency can be obtained.

in the next place, the radiation characteristic of the present antenna is specified, by taking the equivalent expression of this antenna as shown in FIG. 8, to be as follows.

For the sake of explanation, supposing that the antenna elements are provided in parallel relationship with the Z axis of the coordinate system as shown in FIG. 9, in this case the electric field intensity E at a distant point P is derived as follows. Herein the following derivation has been obtained assuming component on the xzplane e- 1r E =60 R kS [Cos cos a) The radiation characteristic of this antenna system with respect to the x-y plane becomes almost nondirectional with the selection of an appropriate polarization on account of the fact that the radiation field generated by the elements aand band the radiation field generated by the element care respectively determined to define the phase difference of 90 therebetween and drawing a locus shaped in figure eight. Both the radiation pattern due to the elements aand band the radiation pattern due to the element cwith respect to the x-z plane draw a shape of figure eight and they are also 90 out of phase with each other, so that the total radiation pattern in this case becomes almost nondirectional. Thus, in the case of using the antenna of this invention oriented in the lateral direction, its nondirectivity can be favorably utilized in a portable-type device. Further, in the event that this antenna is used in the vertical plane, it is used as a nondirectional antenna by selecting its plane of polarization in accordance with that of an opposite station which may use either vertical or horizontal polarization. I

in practice, the frame of the body 1 is not in an indefinite 6O plane, which does not result in obtaining a perfect radiation pattern of figure eight, and reflection due to neighboring material objects or ground cause variations in the plane of polarization, which permits the use of the present antenna without great difference in handling with either plane of polarization, e.g., a vertical or a horizontal one depending on that of the opposite station. Therefore the present antenna overcomes an inconvenience inherent in the conventional devices employing a whip antenna and which must be used in only one plane of polarization. The practical example of the field radiation pattern of the present antenna used in the UHF band is shown in FIG. 10, in which the radiation pattern of the whip antenna is also shown as a reference. As apparent from this Figure, the antenna of the present invention can be used without bringing about any remarkable difference in performance from the whip antenna.

As mentioned above, by providing at one comer portion of a portable radiodevice a low profile antenna of a height which does not exceed the edge line of the portion and forming this antenna into a shape such that the matching is easily effected as stated in the foregoing, it is possible to provide a radio device comparable in performance to a conventional radio device which uses a whip antenna, but which are easily broken and inconvenient in handling, and which provides an improved MTBF.

What we claim is:

l. A portable radio device comprising a metal casing enclosing a radio set and having one comer portion cutaway and an antenna mounted on said casing at the cutaway area, said antenna comprising a first antenna element erected from a feeding portion of said cutaway area and a second antenna element extending from and at the right angle to said first element to transmit and receive radio waves of two components from polarization, the height of said antenna to the casing being made lower than the peripheral edge level of said casing, said device further comprising a third element provided in the vicinity of said feeding portion and in alignment with said antenna for producing matching effect as well as radiation.

2. A portable radio device according to claim 1, wherein the height of the said cutaway portion is determined not greater than the length of one-thirtieth wavelength.

3. A portable radio device according to claim 1, wherein the height of said antenna is determined equal to or less than onefittieth wavelength and equal to or greater than one-hundredth wavelength.

4. A portable radio device according to claim 1, wherein the entire length of said antenna is made approximately equal to one-fourth wavelength.

5. A portable device according to claim 1. wherein the thickness, length of said elements and the distance. between the second and third elements relate to the matching condition.

6. A portable radio device according to claim I, wherein said matching effect is achievable depending upon the impedance of the matching element composed of said first and third elements e.g., the impedance of the equivalent parallel line composed of said first and third elements and the capacity of said metal casing, said matching element per se contributing to the radiation.

7. A portable radio device according to claim 6, wherein the impedance of said matching element represents an inductive impedance and matches the capacitive impedance of the antenna composed of said first and second elements when said third element connects with said antenna elements, and the impedance of said matching element represents a capacitive impedance and matches an inductive impedance of the antenna composed of said first and second elements when said third element does not connect with said first element.

8. A portable radio device according to claim 1, wherein the radiation pattern of the antenna becomes nondirectional when the antenna is oriented in the vertical plane and the polarization is varied in a plane in parallel with the earth.

9 A portable radio device according to claim 1 wherein the radiation patterns of the antenna become nondirectional when the antenna is oriented in the lateral direction.

10. A portable radio device according to claim 1, wherein the antenna provided at said corner of said casing is mounted by the use of a dielectric element which fits in said cutaway portion of the casing.

t I! i i l

Claims

1. A portable radio device comprising a metal casing enclosing a radio set and having one corner portion cut away and an antenna mounted on said casing at the cutaway area, said antenna comprising a first antenna element erected from a feeding portion of said cutaway area and a second antenna element extending from and at the right angle to said first element to transmit and receive radio waves of two components of polarization, the height of said antenna to the casing being made lower than the peripheral edge level of said casing, said device further comprising a third element provided in the vicinity of said feeding portion and in alignment with said antenna for producing matching effect as well as radiation.

2. A portable radio device according to claim 1, wherein the height of said cutaway portion is determined not greater than the length of one-thirtieth wavelength.

3. A portable radio device according to claim 1, wherein the height of said antenna is determined equal to or less than one-fiftieth wavelength and equal to or greater than one-hundredth wavelength.

5. A portable device according to claim 1, wherein the thickness, length of said elements and the distance between the second and third elements relate to the matching condition.

6. A portable radio device according to claim 1, wherein said matching effect is achievable depending upon the impedance of the matching element composed of said first and third elements, e.g., the impedance of the equivalent parallel line composed of said first and third elements and the capacity of said metal casing, said matching element per se contributing to the radiation.

9. A portable radio device according to claim 1, wherein the radiation patterns of the antenna become nondirectional when the antenna is oriented in the lateral direction.