MXPA98001325A - Structure for multiple band antenna for a portable radio - Google Patents

Abstract

The present invention relates to a first coil (110) resonant at a first frequency, and a second coil (120) resonant to a second frequency, coupled to a direct conductor portion (140) of an antenna element (130) to form a structure for multiple bands antenna. The first and second coils (110) and (120) are preferably in different axial lengths and circumferences, wound in opposite directions and located coaxially around the element (130) of the antenna. Additional coils can be added to accommodate additional bands and upper coils (150) can be used to achieve a multiple position structure

Description

STRUCTURE FOR ANTENNA OF MULTIPLE BANDS FOR A PORTABLE RADIO FIELD OF THE INVENTION l_j_ Technical Field The present invention relates to antennas and, more particularly, refers to coils for feeding structures for multiple band antennas.

BACKGROUND OF THE INVENTION A helical coil is known for coupling to a straight wire antenna that can be extended, for example, in U.S. Pat. No. 4,121,218 of Irwin et al. The helical coil and the straight wire that can be extended have the dimensions necessary for resonance in a particular frequency band of a portable radio, such as a cellular phone. As different digital and analog cell phone systems are promulgated around the world, the antennas that correspond to each of the different cellular systems are known. Users who subscribe to cell phones who travel through different systems or who use a cell phone in a geographical area with more than one system, want a unique cell phone that can be used in more than one P103J / r'RMX system. Therefore, communication between the different frequency bands in the same radius is desirable. Because antennas of different bands for the same cell phone could also be inconvenient for a user, a unique antenna structure capable of operating in more than one band is desirable. New cell phone designs have been developed to satisfy the convenience of the user. Most users appreciate small packages that are convenient to carry and use. A multi-band antenna structure of a compact design and having low manufacturing costs is desirable. It has been difficult to come up with a compact multi-band antenna structure that is capable of performing at a high gain like single-band antenna structures. The best known antenna structures for maximizing gain in a band have design features that produce a lower optimal gain in other bands. An antenna gain performance equal to or better than existing single-band antennas is desired for all bands in a single and compact antenna structure. This has not been possible before the present invention which will be explained below with reference to the accompanying drawings.

P1033 / 98MX BRIEF DESCRIPTION OF THE DRAWINGS OR FIGURES Fig. 1 illustrates a sectional side view of an embodiment of an antenna structure in an elevated position. Fig. 2 shows a sectional side view of an embodiment of the antenna structure of FIG. 1 in a lowered position; Fig. 3 illustrates a side view in section and detail of two helical coils alone; Fig. 4 illustrates a sectional view of another embodiment of a structure in an elevated position; and Fig. 5 illustrates a multiple band radiotelephone.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention provides a compact and unique antenna structure capable of producing resonance in more than one frequency band. A first coil corresponding to a first band and a second coil corresponding to a second band are arranged adjacent to a straight portion of an antenna element in a resonance configuration in their respective first and second frequency bands. By placing these first and second coils both coaxial with the straight portion of the antenna element, one more structure is achieved P1033 / 9TMX compact. It has been found that more efficient gain performance in the band can be obtained by reducing the coupling between the coils. It is preferred to wind the two coaxial coils in opposite directions, to reduce the coupling interference. Additionally, making a coaxial coil larger in diameter than the other coaxial coil reduces the coupling interference and gives the coil a shorter linear length on the outside, further reduce this interference. A first coil 110 and a second coil 120 are illustrated arranged coaxially around an antenna element 130 having a straight portion 140. The first coil 110 and the second coil 120 are preferably helical coils. The antenna element 130 preferably has an upper coil 150, at an upper end thereof, and is encapsulated by dielectric material. The first coil 110 and the second coil 120 are preferably contained in a base 160 made of a dielectric material. Coupling interference between the coils reduces the effectiveness of the gain of the antenna structure because the energy that should be coupled between the straight portion and the coil of interest is, this time, coupled to another coil. When the P1033 / 9BMX energy from the antenna structure, preferably all the energy radiates from the straight portion. For example, when the antenna structure is used at a radius to transmit radiation energy to a first frequency band by the first coil 110, it is desired that all the radiation energy radiate from the straight portion 140 of the antenna element 130 . However, some energy will radiate from the first coil 110 itself and, additionally, will be coupled from the first coil 110 to the second coil 120 and, thus, is absorbed by the circuitry of the radio connected to the second coil 120. The The energy radiated by the coil 110 and absorbed by the additional coil 120 dissipates power, resulting in an inefficient operation of the antenna structure. By making the first coil 110 be of a larger circumference and, therefore, be outside of the second coil 120, the coupling interference will be reduced. In addition, placing the coil having a shorter axial length on the outside also reduces coupling interference. The linear length is the total length of the coil if it is unrolled and stretched out linearly. The axial length is the axial length along the line formed by the straight portion 140 of the antenna element 130. Therefore, in FIG. 1, the first coil 110 has P1033 / 98MX approximately half of the second coil 120 but, very generally, the same linear length as the second coil 120. However, when stretched, the linear length of the first coil 110 is preferably smaller than that of the second coil 120, because the first coil preferably causes resonance in a first frequency band higher than the second coil that causes resonance in a second frequency band. Also, it has been found that by winding the first and second coils 110 and 120 in opposite directions, the coupling is further reduced when they are coaxial with each other, as shown in FIG. 1. The direction of the turns of the helical coils in relation to each other is preferably opposite to cause subtraction of the electric and magnetic field vectors and, thus, minimize the coupling. When the turns are in opposite directions, the magnetic field of one coil is negative with respect to that of the other coil. The first coil 110 has an axial length of approximately 3.5 millimeters (approximately 0.138 inches), and a linear length of approximately 22.5 millimeters (approximately 0.886 inches). These preferred dimensions for the first coil 110 are coupled to the antenna element 130 having a length P1033 / 98MX total of approximately 76 millimeters (approximately 2.99 inches) and a straight driving portion 140 of approximately 48.5 millimeters (approximately 1.91 inches) and an upper coil 150 having an axial length of approximately 27.5 millimeters (approximately 1.08 inches), a circumference of approximately 14.2 millimeters (approximately 0.559 inches) and a linear length of approximately 163 millimeters (approximately 6.42 inches). The first coil 110 operates with the antenna element 130 which, in this way, resonates at approximately 1800 megahertz. The second coil 120 preferably has an axial length of about 6.0 millimeters (about 0.236 inches), a circumference of about 23 millimeters (about 0.906 inches) and a linear length of about 66 millimeters (about 2.6 inches). The second coil 120, when operating with the preferred antenna element described above, resonates at a frequency band of approximately 920 megahertz. The distance between the lower end of the conductive straight portion 140 of the antenna element 130 is preferably spaced approximately 1.0 millimeters (approximately 0.039 inches) from the upper end of the second coil 120, when the antenna element 130 is in the raised position as shown in FIG. illustrated in the P1033 / 98MX FIG. 1. The first coil 110 is connected to the transmitter and receiver of a radio by the feeder 115 and the second coil 120 is supplied to the transmitter and receiver of a radio by the feeder 125. The relative dielectric constant of the base 160 is preferably about 2.3 and the relative dielectric constant of the antenna element 130 should be approximately the same, in the preferred embodiment. The straight wire 140 of the antenna element forms a dipole. When the straight wire 140 is placed near the helical coils in an elevated position, the antenna element is simultaneously resonant at an integer multiple of 1/2 of a wavelength at the lowest frequency of one of the bands and at the same integer multiple or an integer multiple greater than 1/2 of a wavelength at the highest frequency of one of the bands. When the upper coil is positioned near the helical coils, in a low position, the upper coil of the element is simultaneously resonant to a multiple integer of 1/4 of a wavelength, at a higher frequency of one of the bands. FIG. 2 illustrates a sectional side view of the structure of the antenna of the embodiment of FIG. 1 in a low position. The upper coil 150 is located P1033 / 98MX is coaxial between the first coil 110 and the second coil 120, when it is in the low position of FIG. 2. By providing the upper coil 150, the axial lengths of the first and second coils 110 and 120 can be reduced for effective operation in the low position. If the effectiveness in the low position is not important, then the upper coil 150 can be reduced. However, to improve the efficiency in the low position, the upper coil 150 can be eliminated anyway, if the lengths of the first and second coils 110 and 120 are increased to compensate for the loss of the radiator in the upper coil 150. Therefore, the upper coil 150 is optional and is preferred in certain circumstances. FIG. 3 illustrates a sectional view, in detail, of the two helical coils. The first coil 110 and the second coil 120 are wound on the base 160. The coils 110 and 120 are preferably not embedded in a thick plastic cartridge of dielectric material of the base 160. Instead, it is preferred that the material dielectric of the base is as thin as possible while maintaining the integrity of the structure of the base and the coils. The additional dielectric material near the coils affects the performance of the antenna. In addition, it adds unnecessary weight and size to the antenna structure. Base 160 contains a flange 170 P1U33 / 9RMX annular in the lower portion of it. This annular shoulder 170 serves to ensure the assembly of the antenna with the top part of a portable radio, such as a radiotelephone. The first feeder 115 and the second feeder 125 then internally connect the radiotelephone to separate the transmitters - one transmitter for each of the different bands. FIG. 4 illustrates a sectional side view of another embodiment of an antenna structure in an elevated position. A third coil 280 is located adjacent the first coil 210 and a second coil 220. The antenna element 230 'has a conductive straight portion 240 and an upper helix 250 is disposed with the first and second coils 210 and 220. The first, second and third coils 210, 220 and 230 provide resonance in the different first, second and third frequency bands. The third coil 280 is located along, rather than coaxially, with respect to the first and second coils 210 and 220, to reduce the coupling interference between them. It has been found that the distance between the third coil 280 and the second coil 210 and 220 affects the amount of coupling interference between them. The third coil 280 is spaced from the coils 210 and 220 by a distance to avoid coupling interference. The third coil PIU33 / "HMX 280 is preferably next to the first and second coils 210 and 220, spaced apart from each other by a sufficient amount to reduce the coupling to the first and second coils 210 and 220, while still maintaining a suitable coupling with the conductive straight portion 240 of the antenna element 230. The base 260 preferably has a minimum amount of dielectric material to reduce the probability of affecting the first, second and third coils 210, 220 and 230. In this way, an air gap is preferred over the distance between coil 280 and first and second coils 210 and 220. In the preferred embodiment of FIG 4, base 260 has separate annular recesses 270 and 271 to be mounted in the portion of a portable radio and openings for their respective first, second and third feeders 215, 225 and 285. The coupling achieved by an electric field is related to a capacitive coupling and correctly described as such. The coupling that is achieved through a magnetic field is related to an inductive coupling and is correctly described as such. The magnetic and electric field coupling are vector quantities and occur simultaneously. In this way, their vector quantities can be added or subtracted and as such can be reinforced with each other P1033 / 98MX or can cancel each other. It has been found that by geometrically arranging the helical multiple coils side by side, the vector quantities (capacitive and inductive) can be added or subtracted to reduce the electromagnetic coupling with the other helical coils and improve the electromagnetic coupling with the conductive straight portion. The combination of magnetic and electric fields is an electromagnetic field. Each of the coils is spaced at a pole distance from the bottom of the straight portion 240. The coupling of the electric field decreases inversely as the distance between the coils increases. The coupling of the magnetic field also decreases as the distance between the coils increases. But the coupling of the magnetic field decreases faster than the coupling of the electric field with respect to the distance between the coils. The magnetic field decreases according to the square of the distance of the coil, assuming that the mathematical approximations are valid in the small distances that appear in the sizes used in the portable devices. In this way, coil 280 is preferably spaced from coils 210 and 220, where the magnitude of the magnetic and electric field is equal. P1033 / 98MX The lower end of the conductive straight portion 140 is positioned near the upper ends of the coils. The spacing post distance between the lower end of the conductive straight portion and the upper ends of the helical coils determines the magnitude of the coupling of the electric field. The greater the separation, the smaller the coupling of the electric field. Preferably, this antenna structure is first approximated by an electromagnetic simulation in a computer using computer programs such as the Numerical Electromagnetic Code (NEC 4.0) and then perfected by means of a fine tuning of a physical model in the laboratory. The correct coupling is indicated both in the antenna gain performance and in the average antenna input impedance, as a function of frequency. The best coupling condition occurs when a smaller cusp appears in the normally circular impedance terrain in a Smith sheet, as the post distance between the conductive straight portion 240 and the coils varies. This post distance can be found by moving the lower end of the straight conductive portion towards the top of the helical coil, until its lower cusp appears. FIG. 5 illustrates a band radiotelephone P1033 / 9TMX multiple 391 which has a multi-band capability. The base 360 is mounted on an upper portion of a radiotelephone 391. The antenna element 330 is slidably located on the base 360. The multiple band radiotelephone 391 has multiple transmitters 393 and 395, one transmitter for each band. A heat output from a first transmitter 393 is connected to a first coil in the base 360. Preferably, an earth output from this first transmitter is connected to a flat ground portion 397 of the radiotelephone 391. A heat output from a second transmitter 395 is preferably connected to a second coil of base 360. The ground output of second transmitter 395 is preferably also carried to ground, such as the same ground plane 397 or a different one of a radiotelephone 391. therefore, each coil of the antenna structure corresponds to a different frequency of a transmitter. It should be understood that the transmitters 393 and 395 may alternatively be receivers and / or transceivers. In addition, a single radio circuit capable of executing a multiple band operation can be employed and, therefore, the separate transmitters 393 and 395 would be unnecessary. Although the invention was described and illustrated in the foregoing description and drawings, it should be understood that this description is only by way of example and that P1033 / 9T X can make numerous changes and modifications by someone skilled in technology, without departing from the true spirit and panorama of the invention. For example, the different configurations of the upper coils can be used based on the packing requirements. U.S. Pat. Serial No., Lawyer Reference Number CE01938R, entitled Side-By-Side Coil-Fed Antenna For a Portable Radio to Phillips et al. and presented on February 19, 1996 is specifically incorporated here as a reference.

P1033 / 98MX

Claims (19)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property:.,. A structure for multiple band antenna, CHARACTERIZED BY: a first coil configured for resonance in a first frequency band by using a first number of turns of a first circumference, wherein the first circumference is less than a wavelength of the first frequency band; a second resonant coil for resonance in a second frequency band different to the first frequency band, by using a second number of turns of a second circumference, wherein the second circumference is smaller than a wavelength of the second frequency band; an antenna element having a straight portion (140) located adjacent to both the first coil and the second coil, for the electromagnetic coupling of both the first coil and the second coil.
2. 2. A structure for multiple band antenna according to claim 1, wherein the first coil and the second coil are coaxial with the

   P1033 / 98MX other.
3. 3. A multi-band antenna structure according to claim 2, wherein the first circumference of the first coil is larger than the second circumference of the second coil.
4. 4. A multi-band antenna structure according to claim 3, wherein the first coil has a shorter axial length than the second coil.
5. 5. A multi-band antenna structure according to claim 4, wherein the first coil has a shorter linear length than the second coil.
6. 6. A multi-band antenna structure according to claim 4, wherein the first coil has a linear length equal to or greater than the second coil.
7. 7. A multi-band antenna structure according to claim 3, wherein the first coil and the second coil have a different number of turns. A multi-band antenna structure according to claim 1, wherein the turns of the first coil and the turns of the second coil are wound in opposite directions to each other.
8. P1033 / 98MX
9. 9. A structure for multiple band antenna according to claim 8, wherein the first coil and the second coil have a different number of turns.
10. A structure for multiple band antenna according to claim 8, wherein the first coil and the second coil have different linear lengths.
11. 11. A structure for multiple band antenna according to claim 1, further comprising a third coil configured for resonance to a third band "of different frequency to the first and second bands, when using wire turns of a circumference less than a wavelength of a third frequency band, wherein the third coil is located next to the antenna element having a straight portion and which is remote from the first and second coils to reduce the electromagnetic coupling with the first and second coils
12. 12. A multi-band antenna structure according to claim 11, wherein the first coil and the second coil are coaxial with each other
13. 13. A multi-band antenna structure according to the invention. claim 1, where the portion

    P1033 / 98 X straight of the antenna element consists of a straight wire electromagnetically coupled to the first coil and to the second coil.
14. 14. A multi-band antenna structure according to claim 13, wherein the straight wire is positioned near the first coil and the second coil is in an elevated position, the antenna element is simultaneously resonant to a multiple. integer of 1/2 of a wavelength at the lowest frequency of one of the bands and to the same integer multiple or an integer multiple greater than 1/2 of a wavelength at the highest frequency of a'a of the bands
15. 15. A structure for multiple band antenna according to claim 13, wherein the antenna element consists of an upper helical coil operatively coupled to the straight wire at an upper end.
16. 16. A structure for multiple band antenna according to claim 15, wherein when the upper helical coil is positioned near the first coil and the second coil, in a low position, the upper coil of the antenna element is simultaneously resonant to an integer multiple of 1/4 of a wavelength at the lowest frequency of one of the bands and to an integer multiple of 1/4 of a length of

    P1033 / 98MX wave at the highest frequency of one of the bands.
17. 17. A structure for multiple band antenna according to claim 15, wherein in a low position, the upper helical coil is axially positioned both within the first coil and the second coil.
18. 18. A structure for multiple band antenna according to claim 13, wherein in an elevated position, the straight wire is preferably close to an upper part of the first and second coils
19. 19. A structure for multiple band antenna according to claim 1, further comprising a circuit operatively coupled to the first coil and to the second coil for amplifying the respective radio frequency signals to a first band and a second band.

    P1033 / 98MX