Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/12—Supports; Mounting means
  • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
  • H01Q1/24—Supports; Mounting means by structural association with other equipment or articles with receiving set
  • H01Q1/241—Supports; Mounting means by structural association with other equipment or articles with receiving set used in mobile communications, e.g. GSM
  • H01Q1/242—Supports; Mounting means by structural association with other equipment or articles with receiving set used in mobile communications, e.g. GSM specially adapted for hand-held use
  • H01Q1/243—Supports; Mounting means by structural association with other equipment or articles with receiving set used in mobile communications, e.g. GSM specially adapted for hand-held use with built-in antennas
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
  • H01Q1/38—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith formed by a conductive layer on an insulating support
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q21/00—Antenna arrays or systems
  • H01Q21/28—Combinations of substantially independent non-interacting antenna units or systems
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
  • H01Q9/0428—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave
  • H01Q9/0435—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave using two feed points
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
  • H01Q9/045—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means

Definitions

• the present invention relates to techniques for creating multiple antenna diversity on mobile telephone handsets, PDAs (Personal Digital Assistants) and other electrically small radio platforms.
• Embodiments of the present invention enable a plurality of antennas to be simultaneously mounted in an electrically small space and yet have good diversity, as indicated by measured low cross-correlations between their 3-D antenna patterns. Diversity is required to combat the multipath problem and is particularly needed when high data transmission rates are required.
• Embodiments of the present invention may incorporate various types of antenna devices, including dielectric resonator antennas (DRAs), high dielectric antennas (HDAs), dielectrically loaded antennas (DLAs), dielectrically excited antennas (DEAs) and traditional conductive antennas made out of electrically conductive materials.
• DRAs dielectric resonator antennas
• HDAs high dielectric antennas
• DLAs dielectrically loaded antennas
• DEAs dielectrically excited antennas
• traditional conductive antennas made out of electrically conductive materials.
• DRAs are well known in the prior art, and generally are formed as a pellet of a high permittivity dielectric material, such as a ceramic material, that is excited by a direct microstrip feed, by an aperture or slot feed or by a probe inserted into the dielectric material.
• a DRA generally requires a conductive groundplane or grounded substrate.
• the main radiator is the dielectric pellet, radiation being generated by displacement currents induced in the dielectric material.
• HDAs are similar to DRAs, but instead of having a full ground plane located under the dielectric pellet, HDAs have a smaller ground plane or no ground plane at all.
• DRAs generally have a deep, well-defined resonant frequency, whereas HDAs tend to have a less well-defined response, but operate over a wider range of frequencies.
• a DLA generally has the form of an electrically conductive element that is contacted by a dielectric element, for example a ceramic element of suitable shape.
• the primary radiator in a DLA is the electrically conductive element, but its radiating properties are modified by the dielectric element so as to allow a DLA to have smaller dimensions than a traditional conductive antenna with the same performance.
• a further type of antenna recently developed by the present applicant is the dielectrically excited antenna (DEA).
• DEA comprises a DRA, HDA or DLA used in conjunction with a conductive antenna, for example a planar inverted-L antenna (PILA) or planar inverted-F antenna (PIFA).
• PILA planar inverted-L antenna
• PIFA planar inverted-F antenna
• the dielectric antenna component i.e. the DRA, HDA or DLA
• a conductive antenna located in close proximity to the dielectric antenna is parasitically excited by the dielectric antenna, often radiating at a different frequency so as to provide dual or multi band operation.
• the conductive antenna may be driven so as parasitically to drive the dielectric antenna.
• the different views of the signal can be combined to achieve some optimum or at least improved performance such as maximum or at least improved signal to noise ratio, minimum or at least reduced interference, maximum or at least improved carrier to interference ratio, and so forth.
• Signal diversity using several antennas can be achieved by separating the antennas (spatial diversity), by pointing the antennas in different directions (pattern or directional diversity) or by using different polarisations (polarisation diversity).
• Antenna diversity is also important for overcoming the multi-path problem, where an incoming signal is reflected off buildings and other structures resulting in a plurality of differently phased components of the same signal.
• a significant problem arises when diversity is required from a small space or volume such that the antennas have to be closely spaced.
• An example of this is when a PCMCIA card, inserted into a laptop computer, is used to connect to the external world by radio.
• Most high data rate radio links require diversity to obtain the necessary level of performance, but the space available on a PCMCIA card is generally of the order of about 1/3 of a wavelength. At such a close spacing, most antennas will couple closely together and will therefore tend to behave like a single antenna.
• isolation there is little isolation between the antennas and, consequently, there is little diversity or difference in performance between the antennas.
• about -20dB coupling (isolation) is the target specification between antennas operating on the same band for a PCMCIA card.
• access points in WLAN and the like applications
• -40dB Such high isolation is extremely hard to achieve with conventional antennas when the access points are the size of domestic smoke alarms and less than a wavelength across.
• isolation between WLAN and Bluetooth® antennas of - ⁇ 4-OdB or more is seen as desirable.
• Kumar & K. P. Ray, Artech House, 2003] describes how the fat dipole concepts can be extended to printed microstrip antennas (MSAs).
• Figure 2 shows the general design of an MSA and Kumar & Ray show that rectangular, triangular, hexagonal and circular printed microstrip antennas all have broadband properties.
• an antenna device including a dielectric substrate having a first, upper surface and a second, lower surface, a conductive groundplane on the second surface or located between the first and second surfaces, and at least two conductive feedlines formed on the first surface and extending from feed points to predetermined radiating points at edge or corner parts of the first surface, wherein the groundplane does not extend under the radiating points, characterised in that the groundplane is configured as to extend between the radiating points and in that the feedlines are widened at the radiating points and/or are provided with discrete dielectric elements at the radiating points.
• an antenna device including a dielectric substrate having a first, upper surface and a second, lower surface, a conductive groundplane on the second surface or located between the first and second surfaces, and four conductive feedlines formed on the first surface and extending from feed points to predetermined radiating points at edge or corner parts of the first surface, wherein the groundplane does not extend under the radiating points, characterised in that the groundplane is configured as to extend between the radiating points and in that two of the radiating points are located at adjacent corner parts of the first surface and two of the radiating points are located at opposed edge parts of the first surface.
• the conductive feedlines are supplied with energy at the feed points by way of electrical connections that pass through the dielectric substrate and through gaps or holes in the conductive groundplane.
• the electrical connections can be joined to signal lines on the underside of the substrate without shorting to the conductive groundplane. It is preferred to locate the signal lines underneath the groundplane so as to shield the radiating points and thus to reduce possible interference with the radiating characteristics of the antenna device.
• Other feeding arrangements may be used and will be well known to those of ordinary skill in the art.
• the conductive feedlines may be configured as microstrip feedlines printed on the dielectric substrate in a known manner.
• the dielectric substrate may be generally rectangular in shape with four comer regions and four edges, with the conductive feedlines extending into the four comer regions from a region or regions of the first surface above the conductive groundplane.
• the conductive groundplane is configured so as not to extend into the four comer regions of the substrate, but to extend to all four edges of the substrate.
• Four radiating points are thus defined on the first surface at the four corner regions.
• the radiating points may be brought closer together by locating a first pair of radiating points in two adjacent comer regions of the first surface as before, and locating the other two radiating points at opposed edge regions of the first surface of the substrate between the two adjacent comer regions bearing the first pair of radiating points and the remaining two comer regions.
• the conductive groundplane is then configured so as not to extend underneath the two radiating points on the opposed edge regions, but may extend into the two comer regions not bearing radiating points.
• the substrate maybe triangular in shape, preferably being an equilateral triangle.
• the conductive groundplane does not extend into comer regions of the second surface, and three conductive feedlines are provided on the first surface and respectively extend into the three comer regions thereof to define three radiating points.
• similar configurations may be provided on any polygonal substrate, for example pentagonal, hexagonal, heptagonal, octagonal and so forth. Indeed, it is not so much the shape of the substrate that is important, but more the relative arrangement of the radiating points and the groundplane.
• the substrate it is generally desirable for the substrate to have as small an area as possible so that it can easily be contained within a small device such as a mobile telephone handset or a WLAN access point.
• the radiating points are advantageously located at comer or edge regions of the first surface of the substrate.
• the feedlines may be printed on the first surface by conventional techniques, and may be made of copper or other suitable conductive materials. Any other suitable techniques may be used to form the feedlines.
• the feedlines may be wider or thicker at the radiating points than they are along their lengths. This makes use of the 'fat' monopole technique outlined in the introduction to the present application.
• the radiating points may accordingly be configured as rectangles, cones, disks, ellipses, annuli, triangles, hexagons, polygons or other regular or irregular shapes.
• the feedlines are provided with discrete dielectric elements at the radiating points so as to operate as DRAs, HDAs, DLAs or DEAs.
• the dielectric elements are preferably in the form of ceramic elements have a high relative permittivity, for example S r > 5, particularly preferably > 10.
• S r > 5 particularly preferably > 10.
• the precise configuration of the dielectric elements in relation to the ends of the feedlines determines whether the radiating points act as DRAs, HDAs, DLAs or DEAs, as will be explained in more detail in the examples given hereinafter.
• the dielectric elements may have any appropriate shape depending on the operating requirements of the antenna device.
• the elements may have a wedge shape or be configured as a sector of a cylinder with a pointed end and a curved side.
• the pointed end may face outwardly from the comer region, or may face inwardly.
• the elements may have a generally oblong shape.
• triangular prisms triangular prisms with rounded comers
• elongate thin curved elements bridge-shaped elements
• elements shaped as sections cut along a chord of a cylinder and all of the shapes described here but having a top surface that curves down towards the edge of the dielectric substrate on which the elements are mounted rather than having a flat fop surface generally parallel to the substrate.
• the dielectric elements are soldered or otherwise attached on top of the feedlines in the comer or edge regions of the first surface of the substrate.
• the ends of the feedlines may be attached to a vertical side surface of the dielectric elements, or even extend on to top surfaces of the dielectric elements.
• the surfaces of the dielectric elements that contact the ends of the feedlines may be metallised, and in some embodiments at least inwardly facing side surfaces of the dielectric elements may also be metallised so as to improve isolation between the radiating points.
• the dielectric elements are positioned on the first surface so that they do not overlap the groundplane, otherwise the antenna device will not function correctly. This is generally the case when the dielectric elements are configured to operate as DLAs or dielectrically loaded monopoles. In other embodiments, however, it is permissible for the dielectric elements to overlap the groundplane, for example when the elements are configured to operate in particular HDA modes.
• FIGURE 1 shows a prior art WLAN antenna device
• FIGURE 2 shows a prior art printed 'fat' monopole antenna device
• FIGURE 3 shows a first embodiment of the present invention
• FIGURE 4 shows an Sn return loss plot for the embodiment of Figure 3
• FIGURE 5 shows an alternative dielectric element orientation for the embodiment of Figure 3
• FIGURE 6 shows the embodiment of Figure 3 in relation to a coordinate system used for antenna performance measurements of Figures 7 to 12;
• FIGURES 7 to 12 show various experimentally measured radiation patterns for the antenna device of Figure 3;
• FIGURE 13 shows the embodiment of Figure 3 with reference to 3-D cross- correlation coefficients
• FIGURE 14 shows a radiation pattern formed by a particularly preferred embodiment of the present invention.
• FIGURE 15 shows a second, compact embodiment of the present invention
• FIGURE 16 shows an alternative compact embodiment of the present invention
• FIGURE 17 shows a further variation of the compact embodiment of Figures 15 and 16;
• FIGURES 18 to 21 show reflection and transmission plots and a radiation pattern for each of the radiating points of the embodiment of Figure 17;
• FIGURE 22 shows further variation of the compact embodiment, without any dielectric elements at the radiating points
• FIGURE 23 shows reflection and transmission plots and a radiation pattern for one of the radiating points of the embodiment of Figure 22.
• FIGURES 24 to 26 show various geometries for an antenna device of the present invention.
• Figure 1 shows a prior art printed microstrip dual monopole antenna device, including a dielectric substrate 1 in the form of an FR4 PCB, a main conductive groundplane 2 on the underside of the substrate 1, two printed microstrip lines 3 on the upper side of the substrate 1, the lines 3 terminating in two radiating sections 4, and a small 'T'-shaped section of groundplane 5 on the underside of the substrate 1 in a location between the two radiating points 4.
• Figure 1 also shows the device in cross-section, where it can be seen how the two microstrip lines 3 pass from the upper side of the substrate 1 to its lower side through a pair of gaps or holes 6 in the groundplane 2, and terminate in a pair of SMA connectors 7 which are electrically isolated from the groundplane 2 by insulating washers 8.
• the two microstrip lines 3 are configured such that the radiating sections 4 point towards comers 9 of the substrate 1 and are disposed at 90 degrees to each other. No groundplane 2 is provided underneath the radiating sections 4.
• This prior art antenna device has a narrow bandwidth in operation, and is acknowledged in the prior art to be unsuitable for mobile communications for this reason.
• Figure 2 shows another prior art antenna device, also comprising a dielectric substrate 1 with a conductive groundplane 2 on its underside and a printed microstrip line 10 on its upper side.
• the line 10 terminates in a 'fat' section 11, which is significantly wider then the main section of the line 10, so as to define a radiating section 11.
• No groundplane 2 is provided under the radiating section 11.
• An edge 12 of the groundplane 2 acts as a groundplane for the radiating section 11.
• This antenna device has good bandwidth, but does not provide antenna diversity.
• Figure 3 shows a first preferred embodiment of the present invention, comprising a dielectric substrate 1 in the form of an FR4 or Duroid® PCB.
• An underside of the substrate 1 is provided with a conductive groundplane 2 by metallization or any other suitable process.
• the conductive groundplane 2 extends to the edges of the substrate 1, but does not extend into the comers 9. In this embodiment, the groundplane 2 can be seen to have a generally hexagonal shape.
• Four feedlines 13 extend across the upper surface of the substrate 1 from feed points 14 to comer regions 9.
• the feedlines 13 are disposed in a mutually parallel configuration in a central part of the upper surface of the substrate 1 (although it is sometimes preferred that the feedlines 13 are arranged at 90 degrees to each other in the central part of the substrate 1), and are then diverted into the comer regions 9 so that end sections 15 of the feedlines 13 are disposed mutually at right angles to each other.
• Not visible in Figure 3 are connectors on the underside of the substrate 1 that provide connections to the feed points 14 from the underside of the substrate 1 in a similar manner the prior art device of Figure 1.
• a wedge shaped ceramic dielectric element 16 is soldered onto the end section 15 of each feedline 13, with a pointed edge 17 of each element 16 pointing outwardly from its respective comer region 9.
• the dielectric elements 16 together with the end sections 15 of the feedlines 13 act as wideband antennas when an appropriate signal is input to the feed points 14.
• Each end section 15 and its associated dielectric element 16 defines a radiating point in the context of the present application.
• the groundplane 2 extends, on the underside of the substrate 1, to edge parts of the substrate 1 between the radiating points, thus helping to provide isolation between the radiating points.
• Figure 4 shows the Sn return loss for one of the four end sections 15 before application of a dielectric ceramic element 16.
• the gain of the antenna defined by this single end section 15 is about 1 dBi.
• the second Sn profile (line marked “small pellet”) is produced which shows increased bandwidth and up to 3 dBi gain.
• a larger piece of ceramic element produces the third Sn profile (line marked "large pellet”) and positive gain across a very large bandwidth.
• the bandwidth, as measured at the -6dB level stretches from 1700 MHz to beyond 3 GHz, although the return loss is marginal at a frequency near 2200 MHz. It is this antenna, with the larger ceramic elements 16, that is shown in Figure 3.
• an antenna device of an alternative embodiment of the present invention may be obtained by providing three further equivalent dielectric elements 16 in the comers 9 of the partial structure shown in Figure 5.
• Figure 6 shows the embodiment of Figure 3 with a Cartesian co-ordinate system shown superimposed on the Figure.
• the z axis is vertically up from the substrate 1, with the x and y axes in the plane of the substrate 1.
• Figures 7 to 12 show the radiation pattern of one of the antennas (i.e. radiating section 15 and dielectric element 16) of the device of Figure 6 at frequencies of 1900 MHz, 1967 MHz, 2034 MHz, 2101 MHz and 2168 MHz with reference to the coordinate system of Figure 6.
• Figure 7 shows the xz plane co-polar radiation pattern
• Figure 8 shows the yz plane co-polar radiation pattern
• Figure 9 shows the xy plane co-polar radiation pattern
• Figure 10 shows the xz plane cross-polar radiation pattern
• Figure 11 shows the yz plane cross-polar radiation pattern
• Figure 12 shows the xy plane cross- polar radiation pattern.
• Figure 13 shows the antenna device of Figure 3 with an indication of the 3-D cross- correlations between the antenna radiation patterns of Figures 7 to 12, these having been calculated using an Ansoft HFSS® electromagnetic simulation package.
• the diagonal cross-correlation coefficient is 0.17
• the cross-correlation coefficient across the width of the substrate 1 is 0.001
• the cross-correlation coefficient across the length of the substrate 1 is 0.023.
• Figure 14 shows an example of a beam pattern that is expected to give rise to good directional diversity.
• the area of groundplane 2 removed beneath each dielectric element 16 and radiating section 15 is smaller than that removed from the antenna used to measure the plots in Figures 7-12.
• the antenna device has good diversity and a low front-to-back ratio, where the 'back' direction is defined as the direction of maximum radiation of a similar antenna disposed back-to- back. (Usually, the backlobe direction is taken to be 180 degrees from the front lobe, in the same plane, i.e. down through the PCB substrate in this case.
• the results presented show that placing antennas at comers of a handset can create an antenna system having a very wide impedance bandwidth and effective radiation patterns with positive dBi gain from 1.7 - 3 GHz. Up to four antennas can be fitted onto a handset PCB. The antennas have very low cross correlations indicating that excellent diversity should be obtained from this antenna system.
• FIGS 15 and 16 show an alternative, compact embodiment of the present invention, with like parts being numbered as before.
• the feedlines 13 are arranged so as to be at 90 degrees to each other in the plane of the substrate 1.
• two of the radiating sections 15 and associated dielectric elements 16 are located in adjacent comer regions 9 of the dielectric substrate.
• the remaining two radiating sections 15' and dielectric elements 16' are located at edge regions of the substrate 1 rather than in comer regions, with the groundplane 2 removed from the underside of the substrate 1 underneath the radiating sections 15' and dielectric elements 16' located on the upper side of the substrate 1. In this way, the radiating sections 15, 15' and dielectric elements 16.
• Figure 17 shows a similar arrangement to that of Figures 15 and 16, but with low- profile oblong dielectric elements 16, 16' soldered onto the radiating sections 15, 15'.
• the particular shape of the groundplane 2 of the embodiments of Figures 15 to 17 may be defined as being "comef'-shaped. Starting with a rectangular groundplane with two longer sides and two shorter sides, a trapezoidal section is removed from each of the two longer edges, and a comer section is removed from each side of one of the shorter edges. In this way, the radiating points are isolated from each other by portions of the groundplane while still leaving sufficient groundplane for mounting various other items of control electronics (not shown) on the PCB substrate.
• Figure 18 to 21 show the reflection and transmission plots and S 21 radiation patterns measured, respectively, for each of antenna elements a, b, c and d of the embodiment of Figure 17, thereby giving an indication of Sn impedance bandwidth and S transmission loss for various antenna elements a, b, c and d.
• FIG 22 shows an embodiment of the second aspect of the present invention, with like parts being numbered as before.
• This embodiment uses the same "comef'- shaped groundplane 2 as in Figures 15 to 17, but does not include dielectric elements at the radiating points, nor does it employ 'fat' monopoles at the radiating sections 15, 15'.
• This may be considered to be a microstrip antenna (MSA).
• MSA microstrip antenna
• Figure 23 shows the reflection and transmission plots and radiation patterns for the antenna element defined by the radiating section 15 at position a, and may be compared with the plots shown in Figure 18 for the equivalent antenna with a dielectric element of Figure 17. It can be seen that the antenna element a of Figure 22 radiates with good bandwidth, but starting at a higher frequency and with lower gain.
• Figures 24 to 26 show three different antenna geometries, with like parts being numbered as before.
• Two or four elements thus present the best opportunity to get diversity on a handset, with four being preferable because of the increased diversity options and the possibility of implementing multiple-input multiple-output communications techniques such as the Lucent® BLAST® method.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Details Of Aerials (AREA)
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• Variable-Direction Aerials And Aerial Arrays (AREA)

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• 2003
  • 2003-02-07 GB GBGB0302818.0A patent/GB0302818D0/en not_active Ceased
• 2004
  • 2004-02-09 EP EP04709284A patent/EP1590855A1/en not_active Withdrawn
  • 2004-02-09 US US10/544,478 patent/US7245259B2/en not_active Expired - Fee Related
  • 2004-02-09 GB GB0402710A patent/GB2399683B/en not_active Expired - Fee Related
  • 2004-02-09 EP EP07103310A patent/EP1798811A1/en not_active Withdrawn
  • 2004-02-09 JP JP2006502256A patent/JP2006517074A/ja active Pending
  • 2004-02-09 WO PCT/GB2004/000511 patent/WO2004070874A1/en not_active Ceased
  • 2004-02-09 KR KR1020057014488A patent/KR20050098896A/ko not_active Ceased
  • 2004-02-09 CN CN200480003756.6A patent/CN1748339A/zh active Pending

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