GB2288284A

GB2288284A - Antenna with a radiating element and a shaped resonating element

Info

Publication number: GB2288284A
Application number: GB9506611A
Authority: GB
Inventors: Christian Sabatier
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 1994-04-01
Filing date: 1995-03-31
Publication date: 1995-10-11
Anticipated expiration: 2015-03-31
Also published as: FR2718292A1; GB9506611D0; GB2288284B; FR2718292B1; DE19512003A1; DE19512003B4

Description

2288284 The present invention relates to the f ield of transmission of

electromagnetic waves, in particular UHF waves.

The invention applies in particular to portable transmitting/receiving devices including a small-scale integrated antenna.

Numerous antennae have been proposed f or this application to portable transmitting/receiving devices.

The antennae used for this purpose are mostly of the inverted-F antenna type.

The structure and the operation of such an inverted-F type antenna is described in the document "Small Antennas" by K. Fujimoto, A. Henderson, K. Hirasawa and J.R. James, published by Research Studies Press Ltd. and John Wiley & Sons Inc.

Such an inverted-F type antenna is represented diagrammatically on the attached Figure 1.

As can be seen in this Figure 1, an inverted-F antenna 10 essentially comprises a main rectangular conductor element 11 parallel to an earth plane 20 and an auxiliary conductor element 12 perpendicular to the main element 11 and to the earth plane 20. The auxiliary element 12 performs the function of a short- circuit on the main element 11, by linking one of the ends of it to the earth plane 20.

The second end of the main element 11 is generally open.

The UHF signal is conveyed by a coaxial excitation cable 13 which is connected to the main element 11 at a site referenced 14 in Figure 1. The choice of this site 14 on the main element 11 determines the impedance of the antenna.

If the wavelength of the UHF signal transmitted is denoted by X, the inverted-F antenna 10 generally possesses the following dimensions: length L of the main element 11: X/4, - width 1 of the main element 11: X/8, and - height h of the auxiliary element 12; X/25.

For frequencies of the order of 2 GRz, capable of being used on portable mobile radio terminal sets, the dimensions of the antenna 10 are of a few centimetres.

These inverted-F antennae 10 exhibit the advantage of having a nearomnidirectional radiating pattern.

On the other hand, these inverted-F antennae exhibit a relatively small' passband, typically of the order of 2 to 3%.

Attempts have already been made to enhance the performance of these known irverted-F antennae.

Thus,the French Patent Application filed on 23 December 1992 under No. 92 15813 describes an improvement to inverted-? antennae consisting in producing the main conductor element in the to= of at least two strands which are generally parallel to each other.

The passband of the antennae obtainxed with such an improvment is of the order of 8 to 10%.

Row the object of the present invention is further to improve the Inverted-? type antennae, in particular by enhancing their passband.

This object is achieved in the context of time present Invention by virtue of an ante==& for transmit ting and/o= receiving electromagnetic signals, particu larly WRY signals, of the inverted-? type. comprising a main conductor element generally parallel to an earth plane, an auxiliary conductor element generally perpen dicular to the main element and to the earth plans and which links one end of the main element to the earth plane, and a coaxial excitation cable linked to the main conductor element, characterized in that the main conductor element co=prinea; at least two strands generally parallel to each other, one fo=ing a radiating element and the other forming a resonator, in which the reacnato=-fo=ing strand comprises at least one transition along its length.

According to another advantageous characteristic of the present invention, the transition la fo=ed by at least one stop or change of width produced on an inner or outer edge of the resonato=-úo=ing st=and, or also of a slot which opens out on the end of. this strand.

Xore precisely, according to a preferred embodiment of the invention, the transition in formed by a stay on the inner edge of the resonator-forming strand.

The present invention also relates to devices for transmitting and/or for receiving electromagnetic signals, in particular MF signals, comprising at least one antenna of the abovementioned type.

Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which will follow, and with regard to the attached drawings given by way of non-limiting example, and in which:

- the previously described Figure I represents a diagram15 =atic view in perspective of a conventional inverted-F antenna, - Figure 2 represents a diagrammatic view in perspective of an antenna in accordance with the present invention placed on a metal box, - the attached Figure 3 represents the curve of the Standing Wave Ratio measured on an antenna in accordance with the present invention as a function of the excitation frequency, - Figure 4 represents the Smith chart of an antenna in 25 accordance with the present invention, - Figure 5 represents a view from above of an antenna in accordanaG with a preferred embodiment of the present invention, and - Figures 6 to 12 represent 7 variant embodiments of an antenna in accordance wit): the present invention.

An antenna 100 in accordance with the present invention, of the inverted-F type, placed on a metal box 150, has been represented diagrammatically in the attached Figure 2.

315 The box 150 may be the subject of numerous embodiments. It preferably takes the form of a rec tangular type box. The box 50 preferably houses Lhe electronic cards carrying out the processing of the tmp signals received by the antenna 100 and/or transmitted by them. The &Mte=a 100 is y=eferably placed outside the box 150, against one of the faces 152 of the latter. This face 152 serves as earth plane. The antenna 100 may be placed on any face of the box.

in a way known per se, and as described previously with regard to Figure 1, the antenna loo essentially comprises a maim conductor element 11o parallel to the earth plane 152, an auxiliary conductor element 120 generally perpendicular to the main element 110 and to the earth plane 152, and a coaxial eXa4tation cable 130.

The auxiliary element 120 links one of the ends; of the main element 110 to the earth plans 152.

The coaxial cable 130 forms the link between the processing means placed in the box 150 and the main element 110.

Moreprecisely, according to the invention, the main element 110 is generally U-shaped, and thus aomyrises at least two strands 111, 112 generally parallel to each other, one forming a radiating element and the other a resonator. More precisely yet, according to the invention, the rescmator-forming strand 112 comprises at least one transition 113 along its length.

The auxiliary element 120 advantageously has a rectangular contour. Its linking edge on the earth plane 152 is referenced 121 in Figure 2. Its linking edge on the main element 110 in referenced 122 in the attached Figure 2.

The two, main 110 and auxiliary 120, elements of the antenna 100 are preferably formed by cutting out in a common metal sheet and bending at 9011 about the edge 122. Linking of the auxiliary element 120 in the region of the edge 121 onto the earth plane 152 is achieved by the use of any appropriate coaventi=al means.

The width dimension of the main element 110, considered parallel to the edge 122, is preferably equal to the width di=ensiozi of the auxiliary element 120. That in to say that the outer edges, respectively 1110 and 1120 of the radiating strand III and of the resonator J strand 112 preferably respectively extend the edges 123 and 124 of the auxiliary element 120 orthogonal to the edges 121 and 122.

The radiating-element forming strand 111 and the resonator- forming strand 112 are connected to a em" n core 114 with rectangular contour adjacent to the edge 122.

The radiating- element forming atrand 111 preferably has a rectangular contour. That is to say that:Lts Inner edge 1111 Is straight and parallel to the abovamentioned outer edge 1110.

on the other band, as indicated previoualy, there is provision according to the invention for a transition along the length of the resonatorfo=4=g strand 112.

According to the preferred embodiment represented in the attached Figure 2, this transition 113 in advantageously formed by a stop on the inner longitudinal edge 1121 of the ren=ator-fa==ing strand 112.

Thus U resonatc)r-fo=-,,,g strand 112 exhibits the chap of two juxtaposed rectangles, referenced respectively 1122 and 1124 in the attached Figure 2.

The rectangle 1122 in adjacent to the core 114.

The second rectangle 1124 forms the free and of the strand 112 opposite the core 114. The first rectangle 1122 has a width, considered parallel to the edge 122.

which In constant along its length, and greater tha- the width of the second rectangle 1124, also constant along its length.

The transition betweezi the two rectangles 1122 and 1124 forms the abovementioned step 113.

According to the invention, the transition or stop 113 ia formed at a distance from tile auxiliary ele=ent 120 of the order of 16, the wavelength used being known as X. Moreover, according to the invention, the depth of the step 113, that is to say the difference in width between the two elements 1122 and 1124 of the resonator strand 112 is of the order of 3/8th. of the width of the base of this radiating element 112 considered in the region of its junction point with the core 114.

The inventor has carried out tests on a system comprising a metal box (simulating a telephone handset) of dimensions: 160 x 55 x 20 mm and with an antenna of the type represented in the attached Figure 2 answering to the following geometry, given with regard to Figure 5 (for a central frequency of the passband f = 1.9165 GHz, i.e. X = 0.156 m):

- length L1 of the radiatingelement forming strand 111, measured from the auxiliary element 120: 36 mm, i.e.

0.23X, - length L2 of the resonator- forming strand 112, measured from the auxiliary element 120: 38 mm, i.e. 0.24X, - length L3 of the core 114: 4.5 mm, i.e. 0.03X, is - distance L4 separating the step 113 from the auxiliary element 120: 24.5 mm, i.e. 0.16X, - width 11 of the auxiliary element 120 and of the main element 110 (distance separating the longitudinal edges 1110 and 1120): 20 mm, i.e. 0.13X, - width 12 of the radiating- element forming strand 111:

3.25 mm, i.e. 0.02X, of the resonator- forming strand 112, at its base: 8 mm, i.e. 0.05X, - width 14 of the resonator- forming strand 112, at its free end: 5 mm, i.e. 0.03X, - width 15 of the step 113: 3 mm, i.e. 0.02X, - distance 16 separating the two strands Ill, 112:

8.75 mm, i.e. 0.06X, - distance L5 separating the point 132 of contact of the coaxial cable 130 on the radiating element 111, from the auxiliary element 120: 5 mm, i.e. 0.03X, - distance 17 separating this point of contact 132 from the outer longitudinal free edge 1110 of the radiating element forming strand 111: 1.6 mm, i.e. 0.01X.

Moreover, on the system tested, the height h of the auxiliary element 120 separating the main element 110 from the earth plane 152 formed on the box 150 was 5 mm.

The curve of the Standing Wave Ratio or SWR measured on the abovementioned antenna is represented in - width 13 i i 7 - the attached Figure 3. By adopting, as passband of the antenna, the frequency band for which the SM is below 2, which corresponds to the definition generally acknowledged by specialists, the curve represented in Figure 3 leads to a passband from 1.787 GHz to 2.046 GHz. i.e. about 15%. Hence the presence of the step 113 on the resonator strand 112 makes it possibly substantially to augment the passband with respect to the previously known' inverted-F antennae.

In Figure 3, the markers 1, 2 and 3 correspond respectively to frequencies of 1.885 GEz, 2.025 GHz and 1.787 GHz, and SWRs respectively of 1.4349, 1.3201 and 1.9998.

The corresponding Smith chart illustrated in the is attached Figure 4, and for which the markers 1, 2 and 3 correspond to the same frequencies as those previously indicated with regard to Figure 3, portrays a loop corresponding to the perfect matching range. The curve illustrated on the Smith chart of Figure 4 shows that the radiating element in not perfectly optimized. A better centring with respect to the centre of the Smith chart would make it possible further to increase performance.

The free ends of the strands 111 and 112, opposite the auxiliary element 120, can be open as has been represented in the attached Figure 2, or also linked by a short-circuit to the earth plane 152, at least in the case of one of these strands, or it is further possible to make provision to link at least one of the ends of these two strands 111, 112 to the earth plane 152, via a capacitor, for example via an adjustable capacitor.

Such an adjustable capacitor provided on at least one of the ends of the strands 111 and 112 can be controlled, for example, by circuits placed in the box 150 so as to modify the characteristics of the antenna.

The antennae in accordance with the present invention are particularly well adapted to meet the functional and ergonomic constraints of portable mobile radio terminals capable of communicating with a fixed station, for example a pylon, a satellite or any ecrulvalent facility.

The large passband, of the order of 15%, obtained in the context of the inventlon makes it possible to use a single antenna operating in transmission and in recap s tion, respectively on two separate frequency bands.

Obviously the preaent InVentiOn, J.8 not limited the particular embodiment which has just been described, but extends to any variant in accordance with the spirit thereof.

in particular, the present invention Is not limited to the use of a main element 110 consisting solely of two stranda 111. 112, but may be extended to main elements 110 comprising a higher number of strands, generally parallel to each other, at least one of then is being provided with a transition along its length.

Moreover, the present invention is not limited to the use of a transition of the step type on the resonator- clamant f=ing strand, but extends to the use of any type of transition equivalent to such a step, on at least one of the strands of the main element.

in Figure 6, for example, a first wabodiment variant has been represented accord.;&.=g to which the step 113, while still being formed on the inner edge 1121 and turned towards the free and of the resonator strand 112, an previously described, covers substantially half of the width of this rean=atc= strand 112.

According to the second embodiment variant represented in Figure 7, the stop 113, formed on the inner edge 1121 of the resonator strand 112, is turned towards the core 114 and not towards the tree end of this strand 112. The end part 1124 of the resonator strand 112 is, for this reao=, wider than the part 1122 adjacent to the care 114.

According to the third embodiment variant repre sented in Figure 8, the step 12.3 is formed on, the outer edge 1120 of the resonator strand 112 and turned towards the free end 0.10 the lazte=.

According to the tourth embodi=ent variant represented in Figure 9, the step 113 in formed on the outer edge 1120 of the resonator strand 112 and turned towards the core 114.

According to the fifth embodiment variant represented in Figure 10, two steps 1130, 1131 are provided, turned towards the free end of the resonator strand 112, respectively on the inner edge 1121 and on the outer edge 1120 of the latter.

According to the sixth embodiment variant represented in Figure 11, two steps 1130, 1131 are provided 10 turned towards the core 114, respectively on the inner edge 1121 and on the outer edge 1120 of the latter.

According to the seventh embodiment variant represented in Figure 12, the transition 113 is formed by a slot which opens out, f or example, on the end of the is resonator strand 112. The two branches 1132, 1134 situ- ated on each side of the slot 113 may be of identical lengths as represented in Figure 12, or of different lengths.

Obviously, the transition can also be formed by 20 a combination of the abovementioned means.

It will of course be understood that the present invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the invention.

Claims

CLAILKS

1. Antenna f 0= transmitting and/or receiving electromagnetic signals, particularly UHF signals, of the inverted-F type, comprising a main conductor element (110) generally parallel to an earth plane (152), an auxiliary conductor element (120) generally perpendicular to the main element (110) and to the earth plane (152) and which links one and of the main element (110) to the earth plane (152), and a coaxial excitation cable (130) linked to the main conductor element (110), characterized in that the main conductor element (11o) comprises at least two strands (111o 112) generally parallel to each other, one (111) forming a radiating element and the other (112) forming a resonator, in which the resonatorforming strand (112) comp=-joes at least one transition (113) along its length.

2. Antenna according to Claim 1, characterized In that the transition in formed by a change of width (112) of the resonator st=and (112).

3. Antenna according to onc of Clalian 1 c= 2, characterized in that the transition in formed by at least onis step (113).

4. Antenna according to one of Claims 1 to 3, characterized in that the transition (113) is formed by at least =c step on the inner longitudinal edge (1121) of the resonator strand (112).

5. ikntez=a according to one of Claims 1 to 4, characterized in that the transition (113) is f ormed by at least one step on the cute= longitudinal edge (1120) of the resonator strand (112).

6. Antenna according to one of Claims 1 to 5, characterized In that the transition (113) in formed by two steps (1130, 1131) produced respectively on the inner edge (1121) and on the outer edge (1120) of the resonator strand (112).

7. Antenna according to One Of Claims 1 to 6, characterized in that the transition (113) comprises at least one stop (113) turned towards the tree end of the resonator strand (112).

8. Antenna according to one of Claims 1 to 6, characterized in that the transition (112) comprises at least one step turned away from the free end of the resonator strand (112).

9. Antenna according to one of Claims 1 or 2, characterized in that the transition is formed by a slot (113).

10. Antenna according to Claim 9, characterized in that the slot (113) opens out on the f ree end of the resonator strand (112).

11. Antenna according to one of Claims 9 or 10, characterized in that the two branches (1132, 1134) situated on each side of the slot (113) are of the same length.

12. Antenna according to one of Claims 9 or 10, characterized in that the two branches (1132, 1134) situated on each side of the slot (113) are of different lengths.

13. Antenna according to one of Claims 1 to 12, characterized in that the resonator strand (112) has a width (13, 14), which is constant respectively on either side of the transition (113).

14. Antenna according to one of Claims 1 to 13, characterized in that the transition (113) delimits an end portion (1124) on the resonator strand (112) which portion is of narrower width (14) than the portion (1122) of the same strand (112) connected to the auxiliary element (120).

15. Antenna according to one of Claims 1 to 14, characterized in that the transition (113) delimits two rectangular portions (1124, 1122) on the resonator strand (112).

16. Antenna according to one of Claims 1 to 15, characterized in that the transition (113) is f ormed at a distance from the auxiliary element (120) of the order of X/6.

17. Antenna according to one of Claims 1 to 16, characterized in that the depth (15) of the step (113) forming the transition in of the order of 3/8th of the width (13) of the resonator strand (112) at its base.

18. Antenna according to one of Claims 1 to 17, characterized in that the length (L2) of the resonator strand (112) is different to X/4.

19. Antenna according to one of Claims 1 to 18, characterized in that the radiating strand (111) and the resonator strand (112) have free ends opposite the auxiliary element (12), in open circuit.

20. Antenna according to one of Claims 1 to 18, characterized in that at least one of the radiating (111) or resonator (112) strands has its free end opposite the auxiliary element (120) linked to the earth plane (152) by a short-circuit.

21. Antenna according to one of Claims 1 to 20, is characterized in that at least one of the radiating strand (111) and the resonator strand (112) has its free end opposite the auxiliary element (120) linked to the earth plane (152) by a capacitor.

22. Antenna according to Claim 21, characterized in that the capacitance is adjustable.

23. Antenna according to one of Claims 1 to 22, characterized in that it is produced from a common metal sheet, by cutting out and f olding in the region of a linking edge (122) between the main element (110) and the auxiliary element (120)

24. Antenna according to one of Claims 1 to 23, characterized in that the main conductor element (110) comprises a common core (114) adjacent to the auxiliary conductor element (120), on which are connected the strand (111) forming the radiating element and the strand (112) forming the resonator.

25. Antenna according to one of Claims 1 to 24, characterized in that the auxiliary conductor element (120) consists of an element with rectangular contour, adjacent to the main conductor element (110) and having a width dimension, considered parallel to the linking edge between the main conductor element (110) and the auxiliary conductor element (120) equal to the width dimension of the main element (110).

J - 13

26. Antenna according to one of Claims I to 25, characterized in that the strand (111) forming the radiating element and the strand (112) f orming the resonator are of different lengths.

27. Device for transmitting and/or receiving electromagnetic signals, in particular UHF signals, characterized in that it comprises at least one antenna in accordance with one of Claims I to 26.

28. Antenna for transmitting and/or receiving electromagnetic signals, substantially as hereinbefore described with reference to and as shown in the accompanying diagrams.