MXPA99004946A - A dielectric-loaded antenna - Google Patents

Abstract

A dielectric-loaded loop antenna for operation at frequencies above 200 MHz has an elongate cylindrical core with a relative dielectric constant greater than 5, a pair of co-extensive helical antenna elements, a coaxial feeder structure extending through the core from a proximal end to a distal end where it is coupled to the antenna elements, and a balum formed on the core cylindrical surface and connected to the feeder structure at the proximal end of the core. Each helical antenna element is bifurcated at an intermediate position so that proximally, it is formed of two generally parallel branches each of which is coupled to a respective linking path around the core to meet a corresponding branch of the other elongate element therefore forming a conductive loop between the two conductors of the feeder structure. The two conductive loops have different electrical lengths as a result of, for example, the branches being of differents lengths. In a preferred embodiment, the linking paths around the core are formed by the rim of a split conductive sleeve constituting the balum. The sleeve is formed in two parts separated by a pair of longitudinally extending diametrically opposed quarter wave slits each of which extends from the space between the branches of a respective helical antenna element to a short circuited end adjacent the proximal end of the core.

Description

DIELECTRIC LOADED ANTENNA DESCRIPTION OF THE INVENTION This invention relates to a dielectric charged antenna for operating at frequencies in an excess of 200 MHz, and having a three-dimensional antenna element structure on or adjacent to the surface of an elongate dielectric core, which is formed of a solid material having a relative dielectric constant greater than 5. Such antenna is known from published UK Patent Application No. GB 2292638A, which discloses a quadrifilar antenna having an antenna element structure with four helical antenna elements formed as metallic conductor rails on the cylindrical outer surface of a cylindrical ceramic core. The core has an axial passage with an inner metallic lining and the passage houses an axial feeder conductor, the inner conductor and the liner forming a coaxial feeder structure for connecting a feeder line to the helical antenna elements via radial conductors formed on the end of the nucleus opposite the feeder line. The other ends of the antenna elements are connected to a virtual, common ground conductor, in the form of a coated sleeve surrounding a near end portion of the core and connected to the external conductor of the coaxial feeder formed by the lining of the axial passage. The sleeve, together with the feeder structure forms a trap, isolating the helical elements from the ground, still providing conductive paths around its ring interconnecting the helical elements. This antenna is mainly intended to be an omnidirectional antenna for circularly receiving polarized signals from sources that may be directly above the antenna, ie on its axis, or at smaller angles of elevation below a few degrees above a plane perpendicular to the axis. It is continued that this antenna is particularly suitable for receiving signals from global positioning system (GPS) satellites. Since the antenna is also capable of receiving polarized signals vertically or horizontally, it can be used in other radio communication devices such as manual or mobile cordless telephones. A dielectric charged antenna, which is particularly suitable for use as a portable telephone, is a helical, bifiliar antenna, in which two half-turn, diametrically opposed helical elements form, together with a conductive sleeve as described above, a twisted loop producing a radiation pattern, which omnidirectional except for two null points centered on an axis perpendicular to the plane formed by the four ends of the two helical elements. This antenna is described in co-pending British Patent Application No. 91610581.2, the contents of which are part of the description of the present application by the lining of the axial passage. The sleeve, together with the feeder structure forms a trap, isolating the helical elements from the ground, still providing conductive paths around its ring interconnecting the helical elements. This antenna is mainly intended to be an omnidirectional antenna for circularly receiving polarized signals from sources that may be directly above the antenna, ie on its axis, or at smaller angles of elevation below a few degrees above a plane perpendicular to the axis. It is continued that this antenna is particularly suitable for receiving signals from global positioning system (GPS) satellites. Since the antenna is also capable of receiving polarized signals vertically or horizontally, it can be used in other radio communication devices such as manual or mobile cordless telephones. A dielectric charged antenna, which is particularly suitable for portable telephone use is a helical box antenna, bifiliar, where two helical elements of half turn, diametrically opposed form, together with a conductive sleeve as described above, a twisted loop producing a radiation pattern, which omnidirectional except two null points centered on an axis perpendicular to the plane formed by the four ends of the two helical elements. This antenna is described in co-pending British Patent Application No. 91610581.2, the contents of which are part of the description of the present application by reference. When this box antenna is properly mounted to a mobile telephone device, the presence of the null points reduces the level of radiation directed towards the user's head during signal transmission. Since the gain of the antenna is greater than many mobile telephone antennae, it is significantly less than the maximum value above and below a central resonant frequency. It is an object of this invention to provide a relatively wide bandwidth antenna or capable of operating in two different frequency bands. According to a first aspect of this invention, a dielectric charged frame antenna is provided to operate at frequencies above 200 MHz, comprising an elongate dielectric core formed of a solid material having a dielectric constant greater than 5 and, on or adjacent to the surface of the core, a three-dimensional antenna element structure including at least one pair of opposed laterally elongated antenna elements, which extend between longitudinally spaced positions on the core, and link conductors extending around the core to interconnect the elongated elements of said pair, the elongated elements of said pair having first respective ends coupled to a power connection and second ends coupled to the link conductors, wherein said elongated elements and the bonding conductors together form at least two looping trajectories, each extended ndose from the power connection to a site separated over the length of the core from the power connection, then around the core, and back to the power connection, the electrical length of one of the two paths being greater than that of the other path at an operating frequency of the antenna. Since the loop conductor paths have different electrical lengths, their resonant frequencies are different and can be selected to coincide, for example, with the center frequencies of the transmission and reception bands of a mobile telephone system. The link conductors can be formed by a balun (symmetric-asymmetric) quarter wave on the outer surface of the core adjacent to the opposite end of the power connection, the latter being provided by a feeder structure extending longitudinally through the core . In a preferred embodiment, the link conductors are formed through mutually insulated portions of a balun sleeve, so that each of the two loop conductor paths includes the ring of a respective sleeve portion. The parts of the sleeve are insulated from each other through slots longitudinally in extension in the conductive material forming the sleeve, the electrical length of each slot from one short-circuited end towards the relevant sleeve ring being at least about equal to a quarter-wave length at the operating frequency, so that the insulation between the two Cuff parts are provided at their junctions with the elongated antenna elements. Alternatively, each link conductor may be formed by a conductive strip extending around a respective side of the core from one elongated antenna element towards the other. In another alternative, a link conductor can be formed in this manner, and the other can be formed through the ring of a quarter-wave balun sleeve, with or without the slots described above. The advantage of incorporating a balun sleeve is that the antenna can then operate in a balanced mode from an individual end feed coupled to the feeder structure. Alternatively, each link conductor may be formed through a conductive strip extending around a respective side of the core from one elongated antenna element to another. In another alternative, one link conductor may be formed in this manner, and the other may be formed by a ring of a quarter-wave balun sleeve, with or without the slots described above. The advantage of incorporating a balun sleeve is that the antenna can then operate in a balanced mode from an individual end feed to the feeder structure. Advantageously, the antenna element structure has an individual pair of elongated antenna elements, laterally opposite, each of which is bifurcated in order to have a divided portion, which extends from a site between the first and second ends of the element away from each of the respective link conductors. The difference in electrical length between the two loop conductor paths can be achieved by forming one or both of the divided portions as branches of different lengths. Each branch can then be connected to respective connecting conductors around opposite sides of the core, which, at least in the region of the elongated elements, are isolated from each other. It will be appreciated that the difference in path lengths can be achieved not only by making the branches with different lengths, but also by forming the link conductors differently on opposite sides of the core. Particularly satisfactory operation can be achieved by arranging the electrical length of each branch to be approximately 90 ° (or (2n + 1)? / 4, where n = 0, 1, 2 ..) at the resonant frequency of its trajectory respective driver,? being the corresponding wavelength. The link conductors represent a site of low impedance at the operating frequency, and each length of 90 ° acts as a current-to-voltage transformer, so that the impedance at the branch of each bifurcated element is relatively high. Therefore, at the resonant frequency of one of the conductor paths, excitation occurs in that path simultaneously with the isolation of the other path or trajectories. It continues in that two or more different resonances can be obtained at different frequencies due to the fact that each branch charges the conductive path of the other only minimally when the other is in resonance. In effect, two or more isolated low impedance paths are formed around the core. In the preferred antenna, according to the invention, the advantageous low impedance connection point for the antenna elements at their junctions with the connecting conductor or conductors is provided through annular bonding conductors in the form of a conductive sleeve divided, cylindrical, which operates together with a feeder structure extending longitudinally through the core to form an isolation trap, which causes the circulation of currents around the conductive loop paths that will be confined to the ring of the sleeve. By connecting the near end of the sleeve to the feeder structure and arranging the longitudinal electrical length of the sleeve to be approximately nx90 ° within the operating frequency band of the antenna (where n is an odd number), the Cuff provides a virtual connection to the ground for elongated suede elements. The sleeve is divided in the sense that longitudinally extended grooves are formed as ruptures in the conductive material of the sleeve. In this way, in the case of each elongated antenna element having branches, as described above, which are connected to the sleeve ring, there are two slots, each of which which extends from the space between the branches of one of the respective elongated antenna elements towards a respective short circuit end, thus forming two-part cylindrical sleeve parts. Since the slots each have an electrical length of approximately one quarter wavelength (? / 4) in the operating frequency band, the zero impedance of the shorted end is transformed to a high impedance between the parts of sleeve in its joints with the branches of the elongated antenna elements. In order to adapt the electrical length of? / 4 for each slot, each one can have the L-shape, having a first part that runs longitudinally and a second part adjacent to the adjacent short-circuit end, which runs perpendicular to the longitudinal part. By arranging one of the second end portions to be directed in one direction around the core and the other second part to be directed in the opposite direction around the core, the electrical length of one of the parts of the sleeve may be increased with respect to to the other (by virtue of an oppression of the longitudinal conductive path). The importance of this becomes evident when the ring of a part of the sleeve is at a different longitudinal site from the ring of the other part of the sleeve, since if the compression is arranged in one of the shorter sleeve portions, its Electrical length can be increased so that the frequency at which the action of the balun occurs most effectively is conducted closer to the resonant frequency of the longest of the two loop conductor paths. In this way, with the ends of the elongated antenna elements lying generally in a common plane, the ring of the complete sleeve is effectively staggered since the connection providing around one side of the antenna is in a different longitudinal position on the core from the connection it provides around the opposite side. This means that each bifurcated antenna element has two branches, one shorter than the other, the shorter one can be connected to that portion of the sleeve ring that is closer to the distant end of the core, while the other longer branches are connected to that part of the ring that is furthest from the far end, thus creating conductive loops at different lengths and with different resonant frequencies. The branched portions of each element advantageously run parallel and close to one another, terminating on the ring of the sleeve at the bottom and upper part of the respective passage in the ring, ie at the ends of high impedance of the groove. The extension of the bandwidth of the antenna and a reduction in the physical length can be achieved, in the case of a cylindrical bar-shaped core, by forming each elongated antenna element as a half-turn helix. Preferably, the propeller is bifurcated approximately midway between the end of the bar and the link conductor.

According to another aspect of the invention, a dielectric charged frame antenna for operating at a frequency above 500 MHz comprises an elongated cylindrical core having a relative dielectric constant greater than 5, and an antenna element structure on the surface external core comprising a pair of diametrically opposed elongated antenna elements and annularly arranged link conductors. The elongate elements extend from a feed connection at one end of the core to the linking conductors, with the ends of the elongated elements preferably lying substantially in a common plane containing the axis of the core, in terms of the angular differences between the lines formed by radii joining the ends of the elongated elements to the axis of the core are no greater than 20 °. To achieve resonances at separate frequencies, the elongated elements are bifurcated to define two loop conductor paths of different electrical lengths, each coupled to the power connection. The invention also includes, in accordance with yet another aspect, a portable radio communication unit having a radio transceiver, an integral headset for directing the sound energy from an internal face of the unit, which, during use , is positioned against the user's ear, and an antenna as described above. The antenna is mounted so that the common plane lies parallel to the inner face of the unit. so there is a null point in the radiation pattern of the antenna in the direction of the user's head. According to a fourth aspect of the invention, a dielectric charged frame antenna for operating at frequencies of about 200 MHz comprises an elongate dielectric core formed of a solid material having a relative dielectric constant greater than 5 and, on or adjacent to the core surface, a three-dimensional element structure including at least one pair of opposed laterally elongated antenna elements, which extend between longitudinally spaced positions on the core, and at least one link conductor extending around the core to interconnect said elements of the pair, the elongate elements having first respective ends coupled to a power connection and second ends coupled to at least one link conductor, wherein said elongated elements and the connecting conductor or conductors together form at least two loop paths, each extending from the feed connection to a site longitudinally separated from the core from the feed connection, then around the core, and back to the power connection, the electrical length of one of the two paths being greater than that of the other path and extending around the core on its opposite side from the other path, where the link conductor comprises a conductive sleeve surrounding to the core, the elements elongate of said pair being connected at their respective second ends to a ring of the sleeve to provide first and second conductor bond paths between the elongated elements around the respective opposite sides of the core, and wherein the ring is stepped so that the first link path extends around one side of the core substantially at a first longitudinal location and the second link path extends around the other side of the core substantially at a second, different longitudinal location. The invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a perspective view of an antenna according to the invention; Figure 2 is an equivalent circuit diagram of part of the antenna of Figure 1; Figures 3A, 3B and 3C are graphs showing the reflected energy as a frequency function; Figure 4 is a diagram illustrating the radiation pattern of the antenna of Figure 1; Figure 5 is a perspective view of a telephone apparatus, incorporating an antenna according to the invention; Figure 6 is a perspective view of a first alternative antenna according to the invention; Figure 7 is a perspective view of a second alternative antenna according to the invention; Figure 8 is a perspective view of a third alternative antenna according to the invention; and Figure 9 is a perspective view of a fourth alternative antenna according to the invention. Referring to Figure 1, a preferred antenna 10 according to the invention has an antenna element structure with two longitudinally extended metal antenna elements, 10A, 10B, on the cylindrical outer surface of a ceramic core 12. core 12 has an axial passage 14 with an internal metallic lining 16, and the passage accommodates an internal, axial feeder conductor 18 surrounded by a dielectric insulation envelope 19. The internal conductor 18 and liner 16 in this case, form a feeder structure for coupling a feed line to the antenna elements 10A, 10B in a feeding position on the distal end face 12D of the core. The antenna element structure also includes corresponding radial antenna elements 10AR, 10BR, formed as metallic conductors on the distal end face 12D diametrically connecting the opposite ends 10AE, 10BE of the longitudinally extended elements 10A, 10B to the feeder structure. In this embodiment, the longitudinally extended elements 10A, 10B are of equal average length, each being in the shape of a helix running half a turn about the axis 12A of the core 12, each propeller laterally opposite to the other and being longitudinally co-operative. extensive It is also possible that each propeller Execute multiple half turns, for example one full turn or 1 2 turns. The antenna elements 10A, 10B are respectively connected to the internal conductor 18 and the outer lining 16 of the feeder structure by their respective radial elements 10AR, 10BR. Each of the longitudinally extended elements 10A, 10B has a closely divided portion formed by respective pairs of substantially quarter wave, parallel branches, 10AA, 10AB and 10BA, 10BB. These branches generally extend in the same direction as the undivided portion 10AU, 10BU, of each element 10A, 10B, the junction between the undivided and divided portions being, in this mode, approximately halfway between the distant and near ends. of elements 10A, 10B. To form complete conductor loops, each branch of antenna element 10AA, 10AB, 10BA, 10BB is connected to the ring (20RA, 20RB) of a common virtual ground conductor 20, in the form of a conductive sleeve surrounding a near end portion of the cable. core 12. This sleeve 20 in turn is connected to the liner 16 of the axial passage 14 by a coating 22 on the near end face 12P of the core 12. In this way, each conductive loop formed by the helical elements 10A, 10B (including the respective branches), the radial elements 10AR, 10BR, and the ring of the respective portion 20AR, 20RB of the sleeve 20 is fed at the end remote from the core by a feeder structure, which extends through the core from the near end, and lies between the antenna elements 10A, 10B. The antenna consequently has a bifiliar helical structure of extreme feeding. On at least its upper or distant portion, the cuff is divided into two opposite portions 20A, 20B, each subtending an angle approaching 180 ° on the core axis 12A, and separated one from the other through longitudinal slots 20S, which are breaks in the conductive material of the sleeve 20 extending from the spaces between the near ends 10AAE, 10ABE, 10BAE, 10BBE of the branches of the antenna element towards the short-circuited ends 20SE. In this embodiment, each of the slots 20S has a longitudinal portion parallel to the core axis and a tail portion, which extends around the core, the two portions forming an "L". The lower tail portions are directed in opposite directions towards each other in order to press the width of one of the shorter parts (20A) of the two sleeve parts 20A, 20B. At any given cross section through the antenna 10, the antenna elements 10A, 10B are substantially diametrically opposed, and the near ends 10AAE, 10ABE, 10BAR, 10BBE of the branches of the antenna element are also substantially and diametrically opposite, where they coincide with the ring of the sleeve 20, as well as the grooves 20A.

It will be noted that the ends 10AE, 10BE, 10AAE, 10ABE, 10BAE, 10BBE of the antenna elements 10A, 10B all lie substantially in a common plane containing the axis 12A of the core 12. The effect of this is explained below. This common plane is indicated by the chain lines 24 in Figure 1. The power connection to the antenna element structure and the feeder structure also lie in the common plane 24. In this preferred antenna as shown in Figure 1 , the conductive sleeve 20 covers a near portion of the antenna core 12, thus surrounding the feeder structure 16, 18, the material of the core 12 filling the entire space between the sleeve 20 and the metal liner 16 of the axial passage 14. The sleeve 20 form a divided cylinder connected to the liner 16 through a coating 22 of the near end face 12P of the core 12, the combination of the sleeve 20 and the covering 22 forming a balun, so that the signals in the transmission line formed by the feeder structure 16, 18, are converted between an unbalanced state at the near end of the antenna and a balanced state at an axial position approximately in the plane of l upper edge 20RA, 20RB of the sleeve 20. To achieve this effect, the axial lengths of the sleeve portions 20A, 20B are such that in the presence of an underlying core material of a relatively high dielectric constant, the balun has an electrical length approximately? / 4 or 90 ° in the band of operating frequency of the antenna. Since the core material of the antenna has a being of a width at least as large as its thickness over its operative length. The rails can be formed by initially coating the surfaces of the core 12 with a metal layer and then selectively removing the layer to expose the core in accordance with the required pattern. Alternatively, the metallic material can be applied through selective deposition or by printing techniques. In all cases, the formation of the rails as an integral element on the outside of a dimensionally stable core leads to an antenna having dimensionally stable antenna elements. It will be understood from the foregoing that the longitudinally extended antenna elements 10A, 10B, together with the ring portions 20RA, 20RB of the sleeve portions 20A, 20B, form two loop conducting paths in the operating frequency scale of the antenna, each loop path being isolated from the ground. In this way, a first loop conductive path starts at the feed connection on the distal face 12D of the core and extends via the radial conductor 10AR, the upper portion of the element 10A, one of the branches 10AA of the lower portion of the element 10A, a first semicircular portion 20RA of the ring of the sleeve 20 extending around one side of the core 12, one of the branches 10BA of the element 10B, the distal portion of the element 10B and, finally, the radial conductor 10BR back to the feeder. The other conductive path also forms a loop starting at the feeder. In this case, the path follows the element 10AR, the distal portion of the element 10A, the other branch 10AB of the element 10A, the other portion 20RB of the ring of the sleeve 20, this time extending around the opposite side of the core 12 from the portion of ring 20RA, then via the other branch 10BB of the antenna element 10B, the distal portion of the element 10B and, finally, back to the feeder via the radial element 10BR. These two conductive paths of different physical and electrical lengths as a result of the branches 10AA, 10BA of the first conductor path being longer than those 10AB, 10BB of the second conductor path, and by virtue of the ring portion 20RA being further away from the power connection on the distal end 12D of the core that of the other ring portion 20RB. This difference in height between the two ring portions 20RA and 20RB results in the ring having a stepped profile with the branches of the antenna element of each element 10A, 10B being attached to the sleeve 20 on the opposite sides of the ring steps , as shown in Figure 1. As a result of the different lengths of the loop conductor paths, they have different resonant frequencies. An equivalent circuit diagram representing the antenna element structure of the antenna of Figure 1 is shown in Figure 2. The undivided distal portion of each antenna element 10A, 10B, together with the respective radial connections 10AR, 10BR can be represented by a transmission line section of an electrical length, which is at least approximately equal to? / 4 or, more generally, (2n + 1)? / 4, where? is the central wavelength of the antenna operation band and n = 0, 1, 2, 3, ... The branches 10AA, 10AB, 10BA, 10BB are represented by similar transmission line sections, i.e. as two pairs of sections connected in parallel, all connected in series between the remote portions of the antenna elements 10A, 10B and the virtual earth represented by the portions of 20RA ring, 20RB of sleeve 20. Branching sections have electric lengths? ^ 4 or? 2/4 as shown, depending on whether they are part of the longest or shortest loop conducting path, the longest having a resonant frequency that corresponds to a wavelength? and the shortest having a resonant frequency that corresponds to a wavelength? 2. Since the insulation effect of the sleeve 20 confines currents mainly to the ring portions 20RA, 20RB when the antenna is resonant in a loop mode, these represent maximum current locations. For signals having a wavelength in the region of? 1 and? 2, the quarter-wave branches of 10AA-10BB act as current-to-voltage transformers, so that in the point where each antenna element is divided there is a maximum voltage and the impedance that looks at each branch tends to be infinite, as shown in Figure 2. Consequently, when a conductive loop is in resonance, the impedance that looks at the branches of the other loop is high (providing that? -iy? 2 are of the same order). This means that the resonance of one loop is not significantly affected by the drivers of the other loop. Therefore, there is a degree of isolation between the two resonant modes modalized in two different trajectories. The individual antenna elements 10A, 10B each being divided into two parallel conductors passing from the balun connection point (ie, the sleeve ring) to the maximum voltage points at intermediate locations along the elements, isolating the two resonant trajectories (the conducting loops) one from the other. This provision, as shown in Figure 2, can be viewed either as a transformation line system or coupled. The stepped sleeve ring 20RA, 20RB not only creates two different loop path lengths around the opposite sides of the core, so that two resonant frequencies are possible, but also divides the reducer transformer balun represented by the sleeve 20 into two parallel resonant lengths. It should be noted that each longitudinal slot 20S in the sleeve 20 is arranged to have an electrical length in the region of a quarter wavelength at the center frequency of the required operating frequency scale, and for this reason they are L-shaped in the modality of Figure 1. It will be appreciated that a sufficient length can be obtained from other configurations, for example, by causing the slots to have an oscillating trajectory or allowing them to extend around the near edge of the antenna towards the coating 22 on the near end face 12P of the core 12. These quarter-wave slots 20S have the effect isolating the upper regions of the two sleeve portions 20A, 20B from one another, so that the currents in the longer of the two conducting loops confine to the ring portion 20RA, and those in the shortest loop to the 20RB ring portion. Isolation is achieved through the transformation of the zero impedance of the short circuit ends 20SE to the high impedance between the sleeve parts 20A, 20B at the level of the two ring parts 20RA, 20RB. The arrangement of the tail portions of the slots 20S which will be directed to each other, as shown in Figure 1, has the effect of introducing a restriction in the current path between the ring portion 20RA of the shortest ( 20A) of the two sleeve parts 20A, 20B and the connection of the sleeve to the feeder structure 16 at the near end of the core. This restriction increases the longitudinal impedance of the sleeve part 20A, in effect by adding an inductance, thus tending to reduce the frequency at which the balun effect due to that Cuff part 20A is very pronounced. In fact, this frequency can be matched to the resonant frequency of the loop conducting path, which includes the ring of this sleeve part 20A, in this case the longest of the loop conducting paths. The length of the slots has an effect on the ability of the antenna to operate efficiently at separate frequencies. With reference to Figures 3A, 3B, and 3C, if the slot is too short to promote effective isolation between the upper regions of the two sleeve portions 20A, 20B, a comparatively weak secondary peak is formed at the highest of the two resonant frequencies, as shown in Figure 3A. At an optimal slot length, strong isolation is obtained and a constructive combination of the two resonances occurs due to the two conducting loops, as shown in Figure 3B, from which it will be seen that strong resonances occur at two separate frequencies, which, however, are closer than the two resonance frequencies shown in Figure 3A. If the length of the slots increases more, the insulation becomes less effective and the antenna has a primary resonance at a higher frequency and a weaker secondary resonance at a lower frequency; the opposite situation to that of Figure 3A. Depending on the tolerance to which the antenna is manufactured, an individual adjustment of each antenna can be provided by initially forming the slots with a comparatively total length. cut and remove the conductive material of the sleeve 20 at the groove ends 20SE according to the test results. This can be done, for example, by grinding or by laser ablation. The arrangement for the ends 10AE, 10BE, 10AAE, 10ABE, 10BAE and 10BBE of the antenna elements 10A, 10B to lie substantially in the common plane (Figure 1) is the preferred basis for configuring the antenna element structure, so that the current integral induced in the elementary segments of this structure by an incident wave in the antenna from a direction 28 normal to the plane 24 and having a flat frontal wave sum zero in the feeding position, ie, wherein the feeder structure 16, 18 is connected to the antenna element structure. In practice, the two elements 10A, 10B are equally arranged and equally loaded on either side of the plane 24, producing a vectorial symmetry around the plane. The antenna element structure with the half-turn helical elements 10A, 10B operates in a shape similar to a simple flat loop, having a null point in its radiation pattern in a direction transverse to the axis 12A and perpendicular to the plane 24. radiation pattern, therefore, is approximately a number eight shape in both vertical and horizontal planes, transverse to axis 12A, as shown in Figure 4. The orientation pattern with respect to the perspective view of the Figure 1 is shown by the axis system comprising the axes x, y, z, shown both in Figure 1 and Figure 4. The radiation pattern has two null points or notches, one on each side of the antenna, and each centered on line 28, shown in Figure 1. The notch in the direction and tends to be slightly more hollow than that in the opposite direction, as shown in Figure 4, due to the masking of the ring portion of sleeve carrying current, 20RA, through the longer sleeve portion 20B when the antenna is viewed from the right-hand side, as seen in Figure 1. The antenna has particular application at frequencies between 200 MHz and 5 GHz. The radiation pattern is such that the antenna conducts itself especially for use in a portable communication unit such as a cellular or wireless telephone apparatus, as shown in Figure 5. To orient one of the points nulls of the orientation pattern in the direction of the user's head, the antenna is mounted so that its central axis 12A (see Figure 5) and plane 24 (see Figure 1) are parallel to the internal face 30I of the apparatus 30, and specifically the inner face 30I in the region of the earpiece 32. The shaft 12A also runs longitudinally in the apparatus 30, as shown. The closest ring portion 20RB of the sleeve 20 (Figure 1) is on the same side of the antenna core as the inner face 30I of the apparatus. Again, the relative orientations of the antenna, its radiation pattern, and the Apparatus 30 are evident by comparing the x-axis system, y, z, as shown in Figure 5, with the representations of the axis system in Figures 1 and 2. With a core material having a substantially higher relative dielectric constant than that of the air, eg, er = 36, an antenna, as described above for the DECT band in the region of 1880 MHz at 1900 MHz typically has a core diameter of approximately 5 mm and the longitudinally extended elements 10A, 10B they have an average longitudinal degree (that is, parallel to the central axis 12A) of approximately 16.25 mm. The width of the elements 10A, 10B and their branches is approximately 0.3 mm. At 1890 MHz, the length of the balun sleeve 20 is typically in the region of 5.6 mm or less. Expressed in terms of the operating wavelength? in the air, these dimensions are, at least approximately, for the longitudinal (axial) degree of the elements 10A, 10B: 0.102 ?, for the core diameter: 0.0315 ?, for the balun sleeve: 0.035? or less, and for lane width: 0.00189 ?. The precise dimensions of the antenna elements 10A, 10B can be determined in the design stage by taking own value delay measurements and iteratively correcting errors on a trial and error basis. The adjustments in the dimensions of the conductive elements during the manufacture of the antenna can be carried out in the manner described in United Kingdom patent application No. 2292638A aforementioned with reference to Figures 3 to 6 thereof. All the subject matter of this previous application is incorporated in the present application by reference. The small size of the antenna adapts its application in portable personal communication devices. The conductive balun sleeve 20 and / or conductive layer 22 on the near end face 12P of the core 12 allow the antenna to be mounted directly on a printed circuit board or other grounded structure in a particularly secure manner. Typically, if the antenna is to be mounted at the end, the near end face 12P can be welded to a ground plane on the upper surface of a printed circuit board with the internal power conductor 18 passing directly through a hole Coated on the board to weld to a conductive rail on the lower surface. Alternatively, the sleeve 20 can be clamped or welded to a ground plane of a printed circuit board extending parallel to the axis 12A, with the distal portion of the antenna, carrying the antenna elements 10A, 10B, extending beyond an edge of the antenna. plane to ground. It is possible to mount the antenna 10 either entirely within the portable unit, or partially projecting as shown in Figure 5. Alternative antennas according to the invention are shown in Figures 6 to 9. First, referring to Figure 6, a comparatively simple antenna stocked with the sleeve balun of the Figure 1, the link conductors formed by the ring portions in Figure 1 being replaced by elongated, annular strip elements, 32A, 32B, one of which is connected to the near ends 10AAE, 10BBE of the branches of longer antenna element 10AA, 10BB, the other being connected to the near ends 10ABE, 10BAE of the shorter branches 10AB, 10BA to form conductive loops of different lengths. As in the embodiment of Figure 1, the ends of the antenna elements lie in a common plane, producing a generally toroidal radiation pattern with null points perpendicular to the plane. This antenna, lacking a balun, works best when coupled to a balanced source or balanced load. A second alternative antenna, as shown in Figure 7, has the same antenna element structure of Figure 6, including semicircular elongated link conductors 32A, 32B extending around the core 12 to different longitudinal positions, but adds a balun of conductor sleeve 20 enclosing a near portion of the core 12 and connected to the external conductor of the feeder structure as in the antenna of Figure 1. This allows conversion between individual end balanced lines, but with insulation between the link conductors 32A, 32B being provided only by their separation from each other and from the sleeve 20. With reference to Figure 8, the third alternative antenna is similarly constructed to the second alternative antenna shown in Figure 7, except that an additional conductive loop is provided under each elongated helical antenna element 10A, 10B having a split portion with three branches 10AA, 10AB, 10AC, 10BA, 10BB and 10BC. As before, each pair of branches is closely connected together through a respective link conductor extending around the core 12, but since there are three pairs of branches, there are now three respective link conductors 32A, 32B, 32C. These are located in different longitudinal positions, so that the three conductive loops formed by the antenna elements and the link conductors are each at a different electrical length, thus defining three resonant frequencies. As in the embodiment of Figure 7, the conductor balun sleeve 20 is a continuous cylinder, the near end of which is connected to the external conductor of the feeder structure. The embodiment of Figure 8 indicates that, depending on the area of the core and the width of the antenna elements, two or more loops can be provided to obtain a required antenna bandwidth. The antenna element ends still lie approximately in a common plane. Referring to Figure 9, in a fourth alternative construction, the continuous conductor balun sleeve 20 is used as the link conductor for one of the two branches of a double conductive antenna. In this way, the pair of longer suede element branches 1 0AA, 10BB is connected to the annular ring 20R of the sleeve 20 in approximately diametrically opposite positions. The shorter branch pair 10AB, 10BB, has an elongated link conductor 32B as in the embodiments of Figures 6 to 8, isolated from the sleeve 20. This combines the advantages of insulation between the link conductors, the presence of a balun and a total length, which is less than the second alternative embodiment described above with reference to Figure 7.

Claims (9)

1. - A dielectric charged frame antenna for operating at frequencies above 200 MHz, comprising an elongate dielectric core formed of a solid material having a relative dielectric constant greater than 5 and, on or adjacent to the surface of the core, a structure of three-dimensional antenna element including at least one pair of opposed laterally elongated antenna elements, which extend between longitudinally spaced positions on the core, and link conductors extending around the core to interconnect the elongated elements of the pair, the elongated elements of said pair having first respective ends coupled to a feed connection and second ends coupled to the link leads, wherein said elongated elements and the link leads together form at least two loop conductor paths, each extending from the link feeding to a location n longitudinally separated from the core from the power connection, then around the core, and back to the power connection, the electrical length of one of the two paths being greater than that of the other path at an operating frequency of the antenna.

2. An antenna according to claim 1, wherein it has an individual pair of elongated antenna elements, laterally opposed, each of the two pairs of elements being bifurcated in order to have a divided portion, which extends from a location between the first and second ends towards the second end.

3. An antenna according to claim 2, wherein the divided portion of at least one of the antenna elements comprises branches of different electrical lengths.

4. An antenna according to claim 3, wherein the electrical length of each branch is in the region of 90 ° to the resonant frequency of the respective loop conductive path.

5. An antenna according to any of claims 2 to 4, wherein, for each loop conducting path at its respective resonant frequency, the total electrical length formed by the divided portions and the respective link conductor is in the region 180 °.

6. An antenna according to any of claims 2 to 5, wherein each element of the pair is bifurcated in a location corresponding to a maximum voltage at an operating frequency of the antenna. An antenna according to any of the preceding claims, characterized in that it has a plurality of annular part link conductors extending around the core, each elongated antenna element extending between the power connection and the conductors of link. 8. An antenna according to claim 7, wherein the first and second ends of the elongated antenna elements lie generally in a common plane, and wherein the link conductors define a first link path extending around a side of the core substantially in a first longitudinal location and a second link path extending around the other side of the core substantially in a different longitudinal location. 9. An antenna according to any of the preceding claims, characterized in that it includes a conductive sleeve, and a feeder structure extending longitudinally through the core from a distant end of the core to its near end, the feeder structure providing the power connection at the distal end of the core and being coupled at the near end of the core to the conductive sleeve to form a ground connection for the sleeve. 10. An antenna according to claim 9, wherein the electrical length of the sleeve is at least approximately equal to n.90 ° at an operating frequency of the antenna, where n is an odd integer. 11. An antenna according to claim 9 or claim 10, wherein the elongated antenna elements are coupled to a ring distant from the sleeve, said ring constitutes at least one of the link drivers. 12. An antenna according to claim 11 and any of claims 2 to 7, wherein each of the divided portions of the antenna elements has branches, one of which is connected to the distal ring of a first part of the antenna. sleeve to form a link path around one side of the core and the other is connected to the distal ring of a second part of the sleeve to form a link path around the other side of the core, the first and second parts of the sleeve being spaced apart. of the other on at least part of its longitudinal degree through a pair of slots longitudinally extended in the conductance material of the sleeve. 13. An antenna according to claim 12, wherein each slot has a short circuit end and thus has an electrical length, which is at least approximately one quarter of a wavelength at said operating frequency. . 14. An antenna according to claim 13, wherein each slot has a generally L-shaped. 15. An antenna according to claim 14, wherein the short-circuited end portions of the slots are directed in directions. opposites around the nucleus. 16. An antenna according to any of claims 12 to 15, wherein the distal ring of the first part of the sleeve extends around the core at a location longitudinal, and the distal ring of the second part of the sleeve extends around the other side of the core at a different longitudinal location. 1

7. An antenna according to claim 15 and claim 16, wherein the short circuit end portions of the slots are directed to each other in order to cause a narrowing of the longitudinal conductive path formed by said sleeve portion. , which has its distant ring closer to the near end of the nucleus. 1

8. An antenna according to any of claims 2 to 17, wherein the core is substantially ndrical and each elongated antenna element is helical, executes p half turns around the core, where p is an integer, and bifurcates so that the respective split portion has two parallel helical branches substantially following the same helical path as the undivided portion of the element. 1

9. An antenna according to claim 18, characterized in that it further comprises a coaxial feeder structure that passes through the core on its central axis from a near end towards a distal end of the core, where the link conductors are formed by a longitudinally divided conductive sleeve connected to the external conductor of the feeder structure at the near end of the core and having a distal ring connected to branches of the elements of elongated antenna, the feeder structure providing the power connection at the remote end of the core, wherein the elongated antenna elements are respectively coupled to the internal and external feeder structure conductors. 20. An antenna according to claim 19, wherein the average axial electrical length of the sleeve is at least approximately equal to 90 ° at the center of the operating frequency scale. 21. A dielectric charged frame antenna for operating at frequencies above 200 MHz comprising an elongated ndrical core having a relative dielectric constant greater than 5, and an antenna element structure on the outer surface of the core comprising a pair of diametrically opposed elongated antenna elements and annularly arranged link conductors, the elongated elements extending from a feed connection at one end of the core to the link conductors, wherein the elongated elements each are bifurcated to define, in combination with the link conductors, two loop conductor paths of different lengths coupled to the power connection and having different electrical resonant frequencies. 22. An antenna according to claim 21, wherein the link conductors are arranged to provide a virtual ground connection, isolated for the bifurcated portions of the elongated elements, and the bifurcation of each elongated element. it is positioned so that the electrical lengths of the bifurcated parts produce a voltage for the current transformation at the respective resonant frequencies of the loop. 23. An antenna according to claim 21 and claim 22, wherein the ends of the elongated elements lie substantially in a common plane containing the core axis. 24.- A portable radio communications unit that has a radio transceiver, an integral receiver to direct sound energy from an internal face of the unit which, during use, is placed against the user's ear, and an antenna in accordance with any of the preceding claims, wherein the first and second ends of the elongated antenna elements lie generally in a common plane and the antenna is mounted on the unit, so that the common plane lies generally parallel to the internal face of the unit so there is a null point in the radiation pattern in the direction of the user's head. 25. A dielectric charged frame antenna for operating at frequencies above 200 MHz comprising an elongate dielectric core formed of a solid material having a relative dielectric constant greater than 5 and, on or adjacent to the surface of the core, a three-dimensional antenna element structure including at least one pair of opposed laterally elongated antenna elements, which extend between longitudinally spaced apart positions on the core, and by at least one link conductor extending around the core to interconnect the elements of the pair, the elongated members having first respective ends coupled to a power connection and second ends coupled to at least one link conductor, wherein the elongated elements and the conductor or link conductors together form at least two loop conductor paths, each extending from the power connection to a location separated in the length of the core from the power connection, then around the core, and back to the power connection. feeding, the electrical length of one of the two trajectories being greater than that of the other path and extending around the nucleus on its opposite side from the other path, wherein the link conductor comprises a conductive sleeve enclosing the core, the elongate elements of said pair being connected in their seconds respective ends to a ring of the sleeve to provide first and second conductive link paths between the elongated elements around respective opposite sides of the core, and wherein the ring is stepped, so that the first link path extends around a side of the core substantially in a first longitudinal location and the second link path extends around the other side of the core substantially in a second, different longitudinal location. 26. An antenna according to claim 25, wherein the first and second ends of the elongated elements generally lie in a common plane. 27. An antenna according to claim 26, characterized in that it includes a feeder structure that extends longitudinally through the core from a distant end of the core towards a near end thereof, the feeder structure providing the power connection in the Distant end of the core and being coupled at the near end of the core to the conductive sleeve to form a ground connection for the sleeve, wherein the electrical length of the sleeve is at least approximately equal to n.90 °, at a frequency of operation of the antenna, where n is an integer of number im par. SUMMARY A dielectric charged frame antenna to operate at frequencies above 200 MHz has an elongated cylindrical core with a relative dielectric constant greater than 5, a pair of co-extensive helical antenna elements, a coaxial feeder structure extending through the core from a near end to a distal end, where it is coupled to the antenna elements, and a balun formed on the cylindrical surface of the core and connected to the feeder structure at the near end of the core. Each helical antenna element is bifurcated at an intermediate position, so that closely, it is formed of two generally parallel branches, each of which is coupled to a respective link path around the core to coincide with a corresponding branch of the other element. elongated, thus forming a conductive loop between the two conductors of the feeder structure. The two conductor loops have different electrical lengths as a result of, for example, that the branches are of different lengths. In a preferred embodiment, the linking paths around the core are formed through the ring of a split conductor sleeve constituting the balun. The sleeve is formed of two parts separated by a pair of quarter-wave grooves, diametrically opposite, longitudinally extended, each of which extends from the space between them. branches of a respective helical antenna element toward a short circuit end adjacent to the near end of the core.