Adjustable antenna apparatus and methods

Abstract

An adjustable monopole antenna apparatus and methods. In one embodiment, the antenna apparatus is intended for mobile terminals. In an exemplary implementation, there is an adjusting point is provided from which a conductor is branched to an adjusting circuit. The adjusting circuit comprises a switch and alternative reactive elements connected to ground, selectable by the switch. When a reactive element is changed, the electric length and resonance frequency of the radiator change, and the corresponding operating band shifts. If the antenna is configured as a dual-band antenna, the above-mentioned operating band is the lower band. One or more higher operating bands are based e.g. on radiating slots implemented by the same radiator conductor. The operating band of the exemplary embodiment of the antenna below the frequency 1 GHz can be shifted in a wider range than in the corresponding known antennas.

Claims

1. An adjustable antenna, comprising: a ground plane; a monopole type radiator with a feed point and first and second slots; an adjusting circuit configured to enable adjustment of at least one operating frequency of the adjustable antenna; an adjusting point in communication with the monopole type radiator and the adjusting circuit; a short-circuit point disposed on the ground plane; and a feed point disposed between the short-circuit point and the adjusting point; wherein the adjusting point is disposed substantially between the first and second slots.

2. The adjustable antenna of claim 1, further comprising a substantially rectangular dielectric support element having first and second distal ends, the feed point disposed towards the first distal end of the substantially rectangular dielectric support element, and the adjusting point disposed substantially central along a longitudinal axis of the substantially rectangular dielectric support element.

3. The adjustable antenna of claim 1, wherein the first and second slots are configured to each individually radiate and receive electromagnetic energy in a first frequency band, and the monopole type radiator is configured to radiate and receive electromagnetic energy in a second frequency band, the second frequency band being lower in frequency than the first frequency band.

4. The adjustable antenna of claim 3, further comprising a parasitic radiator element, at least a portion of the parasitic radiator element disposed proximate the feed point so as to induce substantial electromagnetic coupling therebetween.

5. The adjustable antenna of claim 4, wherein the parasitic radiator element is configured to operate substantially within the first frequency band.

6. The adjustable antenna of claim 1, further comprising a parasitic radiator element, at least a portion of the parasitic radiator element disposed proximate the feed point so as to induce substantial electromagnetic coupling therebetween.

7. The adjustable antenna of claim 1, further comprising a conductor connecting the adjusting point to the adjusting circuit, the conductor being configured to function as a reactance having a certain value, the certain value selected to optimize shifting of at least one operating band of the adjustable antenna.

8. The adjustable antenna of claim 1, wherein the adjusting circuit comprises: at least two reactive elements; and a multi-way switch in switchable communication with the at least two reactive elements; wherein the multi-way switch is configured to selectively place one of the at least two reactive elements in electrical communication with the adjusting point and the ground plane so as to set an operating band of the adjustable antenna to a desired value or range.

9. The adjustable antenna of claim 8, wherein the operating band is below a frequency of 1 GHz.

10. The adjustable antenna of claim 6, wherein the parasitic radiator element is configured to parasitically couple to at least a portion of the monopole type radiator so as to widen an operating frequency of the adjustable antenna.

11. The adjustable antenna of claim 1, wherein the first and second slots are configured to cause respective first and second portions of the monopole type radiator to radiate in an operating frequency.

12. The adjustable antenna of claim 11, wherein: the first and second slots are configured to implement a higher operating band for the adjustable antenna; and the adjusting point is located substantially between an area of the monopole type radiator where the first slot is disposed and an area where the second slot is disposed.

13. The adjustable antenna of claim 1, wherein the adjusting point is located in the monopole type radiator at a distance/from the feed point measured along a middle line of a conductor of the monopole type radiator, the distance/being a length of the middle line.

14. The adjustable antenna of claim 1, wherein a distance of the adjusting point from the feed point is in the range of 0.1 l to 0.9 l measured along a middle line of the monopole type radiator, l being a total length of the middle line.

15. The adjustable antenna of claim 2, further comprising a parasitic element disposed on at least one surface of the substantially rectangular dielectric support element and configured to parasitically couple to at least a portion of the monopole radiator so as to widen an operating band of the adjustable antenna.

16. The adjustable antenna of claim 15, wherein the monopole type radiator is disposed on at least one surface of the substantially rectangular dielectric support element.

17. The adjustable antenna of claim 16, wherein the monopole type radiator is disposed on at least three surfaces of the substantially rectangular dielectric support element.

18. The adjustable antenna of claim 2, wherein the adjusting point is disposed between the feed point and the second distal end of the substantially rectangular dielectric support element.

19. The adjustable antenna of claim 1, further comprising an intermediate conductor configured to connect the adjusting point to the adjusting circuit and function as an inductance having a certain value selected to optimize shifts of the at least one operating frequency of the adjustable antenna.

Description

(1) These and other features, objectives, and advantages of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein:

(2) FIG. 1 presents an example of the adjustable antenna according to the prior art,

(3) FIG. 2 presents a second example of the adjustable antenna according to the prior art,

(4) FIG. 3 presents an example of the adjustable antenna according to the invention,

(5) FIG. 4 presents an example of the adjusting circuit of an antenna according to the invention,

(6) FIG. 5 presents a second example of the adjustable antenna according to the invention, and

(7) FIG. 6 presents an example of the band characteristics of an antenna according to the invention.

(8) FIGS. 1 and 2 were already described in conjunction with the description of the prior art.

(9) In FIG. 3 there is an example of the antenna according to the invention. The antenna is located at one end of the circuit board PCB of a radio device. The radiating conductors are of conductive coating of the dielectric antenna frame FRM, which is here a box with relatively thin walls. The frame FRM and the radiating conductors constitute an antenna component 300, which is attached on the surface of the circuit board, where the ground plane GND is located. In the figure the antenna component has been drawn apart from the circuit board for the sake of clarity.

(10) In the example the antenna has two operating bands, the lower one of which is based on the resonance of the conductor of the monopole radiator 310. The feed point FP of the antenna is at one end of the monopole radiator 310, which end is here called the first end. An intermediate conductor 315 branches from the monopole radiator to the adjusting circuit 340 of the antenna. In this description and claims the branching point is called the adjusting point AP of the antenna. The adjusting circuit is located on the circuit board PCB in the inner space of the antenna frame FRM. A part of the intermediate conductor 315 is thus on the circuit board. The adjusting point divides the radiating conductor in question in two parts, the first part 311 between the first end and the adjusting point and the second part 312 between the adjusting point and the tail end.

(11) The edge of the ground plane is aside the antenna component 300. Alternatively, the ground plane can extend at least to some extent under the antenna component.

(12) The adjusting circuit 340 is in principle similar to the one in FIG. 2. Thus it comprises a multiple-way switch SW and a reactive element X1-XN between its each change-over terminal and the ground plane, or ground GND. The common terminal of the switch is connected to said adjusting point AP through an LC circuit, which functions as an ESD protector. Therefore, one reactive element at a time is a part of the circuit between the adjusting point and ground, depending on the state of the switch. Changing the reactive element by controlling the switch changes the antenna's resonance frequency, which correspond to the lower operating band, and thus the place of this operating band.

(13) It is substantial in the invention that the adjusting point AP is not located right at the first end nor at the tail end of the radiating conductor. In FIG. 3 the adjusting point is located about halfway along the radiator conductor. More generally it can be said that the distance of the adjusting point from the feed point FP, measured along the middle line of the radiating conductor, is 0.1 l . . . 0.9 l, in which l is the length of this middle line. In this case the effect of the adjustment is made good, that is the shift range of the operating band is made wide enough. The optimal point naturally depends on the case, in other words, what kind of device the antenna is made for and what kind the structure itself is made. When designing the shifting steps of the operating band, the parameters are, besides the location of the adjusting point, the reactances of the reactive elements, the length and width of the intermediate conductor 315 and the place of the adjusting circuit. Also the inductance of the coil in said LC circuit can be utilized as a design parameter.

(14) For implementing the higher operating band of the antenna the monopole radiator 310 has been shaped so that there are two slot radiators in it. The first part 311 of the monopole radiator rises from the feed point FP, which is near the first end of the antenna component 300, through the side surface of the frame FRM to its upper surface, makes there a pattern, returns back to the side surface and then again to the upper surface towards the adjusting point AP. A first slot SL1 with a U-shape remains between the successive portions of the first part. The second part 312 of the monopole radiator runs from the adjusting point along an edge of the upper surface of the frame to the second end of the antenna component, turns there to the direction of the head, continues then on the side of the head surface and further on said side surface next to its starting point, or the adjusting point AP. A second slot SL2 remains between the successive portions of the second part 312. The first and second slot are designed so that oscillation with different frequencies is excited in them, which both frequencies nevertheless are located in the range of the higher operating band. In accordance with the explanation afore, in the example of FIG. 3 the adjusting point AP is located between the radiator area, where the first slot SL1 is, and the area, where the second slot SL2 is.

(15) The antenna shown in FIG. 3 includes also a parasitic element 320 which is a conductor strip at the first end of the antenna component. The parasitic element is connected to the ground plane GND from the short-circuit point SP which is located next to the feed point FP on the circuit board PCB. The starting end of the parasitic element and the starting end of the first part of the monopole radiator are close to each other so that there is a significant electromagnetic coupling between them. By a suitable design an oscillation can be excited in the parasitic element e.g. at a frequency in the higher operating band.

(16) FIG. 4 shows an example of the adjusting circuit in the antenna according to the invention. The number of the alternative reactive elements in the adjusting circuit 440 is four. The first reactive element is a capacitor C41, which is then between the first change-over terminal of the multiple-way switch SW and the signal ground, or ground plane GND. Correspondingly, the second ‘reactive element’ is an open circuit, thus representing a very high reactance, the third reactive element is a coil L41 and the fourth reactive element is a coil L42. In series with these coils there are blocking capacitors CB to break the direct current circuit from the control of the switch. The capacitance of the blocking capacitors is so high, e.g. 100 pF, that they constitute almost a short-circuit at the antenna's use frequencies.

(17) Between the common terminal of the switch SW and the intermediate conductor 415 leading to the adjusting point AP there is a capacitor C42, and between this capacitor's end on the side of the adjusting point and the ground plane there is a coil L43. The LC circuit C42-L43 functions as an ESD protector of the switch. In addition, the capacitor C42 functions as a blocking capacitor preventing the forming of a direct current circuit from the control of switch to the ground through the coil L43 or the radiator. The state of the switch is set by the control signal CTR.

(18) FIG. 5 shows another example of the antenna according to the invention. The antenna comprises a monopole radiator 510, a parasitic element 520, an intermediate conductor 515, an adjusting circuit 540 and ground plane GND as in the example of FIG. 3. The intermediate conductor branches from the monopole radiator at the adjusting point AP, which is located relatively far from both the first and the tail end of the radiating conductor. In this case the monopole radiator, intermediate conductor and parasitic element are of conductive coating of a thin dielectric plate, and they all together constitute a flexible antenna circuit board ACB. The antenna circuit board is attached on the inner surface of the outer cover COV of a radio device, and it follows the cover's shape. The contact pads on the antenna circuit board are connected to the circuit board PCB of the radio device by contacts, like the contact CT functioning as a part of the intermediate conductor 515. In the example the adjusting circuit 540 is located on the opposite side of the circuit board PCB. The ground plane GND is a part of the conductive upper surface of the circuit board PCB.

(19) FIG. 6 shows an example of the band characteristics of the antenna according to invention. The measured prototype is like the one in FIG. 3 and the adjusting circuit is like the one in FIG. 4. In the adjusting circuit the first reactive element C41=0.3 pF, the third reactive element L41=15 nH and the fourth reactive element L42=3.9 nH. Curve 61 shows the fluctuation of the reflection coefficient S11 of the antenna as a function of frequency, when the switch is in state 1, or its common terminal is connected to the first reactive element, curve 62 shows the fluctuation of the reflection coefficient, when the switch is in state 2, curve 63 shows the fluctuation of the reflection coefficient, when the switch is in state 3, and curve 64 shows the fluctuation of the reflection coefficient, when the switch is in state 4.

(20) It is seen from the curves that the total shift of the lower operating band of the antenna is about 200 MHz and the total bandwidth is more than 280 MHz, if the value −5 dB of the reflection coefficient is regarded as criterion for the boundary frequencies of the band. By this criterion the lower operating band is about 690-760 MHz when the switch is in state 1, about 735-825 MHz when the switch is in state 2, about 800-894 MHz when the switch is in state 3 and about 875-975 MHz when the switch is in state 4. In switch's state 3 the operating band well covers the frequency range 824-894 MHz of the GSM850 system, and in state 4 it well covers the frequency range 890-960 MHz of the GSM900 system.

(21) The higher operating band of the antenna in the example is very wide, about 1.7-2.7 GHz, from which the range 2.3-2.4 GHz is a bit poor. The higher operating band is based on three resonances: the resonance r1 of the parasitic element, the frequency of which is about 1.8 GHz, the resonance r2 of the second slot radiator formed by the monopole radiator, the frequency of which is about 2.2 GHz, and the resonance r3 of the first slot radiator, the frequency of which is about 2.6 GHz. The state of the switch in the adjusting circuit naturally affects a little also the higher operating band, but this effect is non-essential.

(22) The adjustable antenna according to the invention has been described above. Naturally, its structure can in details vary from that presented. The shapes of the radiating elements of the antennas can vary widely. Also the implementation of the reactive elements in the adjusting circuit can vary. At least a part of them can be also short planar transmission lines on the surface of the circuit board. The invention does not limit the manufacturing method of the antenna. For example, said antenna frame can be a part of the outer cover of the radio device or the radiators can be on the surface of a chip type substrate. The inventive idea can be applied in different ways within the scope defined herein.

(23) While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the invention. The foregoing description is of the best mode presently contemplated of carrying out the invention. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the invention. The scope of the invention should be determined with reference to the claims.