Abstract: In a dielectrically-loaded multifilar helical antenna, a conductive phasing ring is arranged between and couples together feed nodes and the helical radiating elements. The phasing ring includes an annular conductive path having an electrical length equivalent to a full wavelength at the operating frequency so as to be resonant at that frequency. The helical elements are coupled to the outer periphery of the phasing ring at respective spaced apart coupling locations. The helical elements may include open-circuit or closed-circuit elongate conductive tracks, or a combination of both. In the case of the helical elements being closed-circuit tracks, these tracks are interconnected by a second resonant ring, which is resonant at the same frequency as or a different frequency from the first resonant ring. The invention is applicable to both end-fire and back-fire helical antennas.

Abstract: A dual-band dielectrically loaded multifilar antenna has a first group of helical conductive antenna elements extending from feed connection nodes to an annular linking conductor 20U, and a second group of conductive helical antenna elements extending from the feed coupling nodes in the direction of the linking conductor to substantially open-circuit ends spaced from the linking conductor. The helical elements of the first group are half-turn elements having an electrical length of approximately one half wavelength at a first operating frequency of the antenna. The helical elements of the second group are approximately quarter-turn helical elements having an electrical length in the region of one quarter wavelength and a second operating frequency of the antenna. Each group of elements is associated with a respective mode of resonance for circularly polarised radiation.

Abstract: A dual-band dielectrically loaded helical antenna for circularly polarised signals has two groups of helical antenna elements. In each group there are at least four such elements and they are connected at their distal ends to a respective feed coupling node and at their proximal ends to a common linking conductor. Each group includes pairs of neighbouring such antenna elements, each pair having one electrically short element and one electrically long element, and the arrangement of the elements is such that in each group the number of pairs in which, in a given direction around the core, the short element precedes the long element is equal to the number of pairs in which, in the same direction, the long element precedes the short element.

Abstract: A dielectrically-loaded helical antenna has a cylindrical ceramic core bearing metallised helical antenna elements which are coupled to a coaxial feeder structure passing axially through the core. Secured to the end face of the core is an impedance matching section in the form of a laminate board. The matching section embodies a shunt capacitance and a series inductance.

Abstract: A dielectrically loaded quadrifilar helical antenna has four quarter turn helical elements centred on a common axis. Each helical element is metallised on the outer cylindrical surface of a solid dielectric core and each has a feed end and a linked end, the linked ends being connected together by a linking conductor encircling the core. At an operating frequency of the antenna the helical elements and the linking conductor together form two conductive loops each having an electrical length in the region of (2n?1)/2 times the wavelength, where n is an integer. Such an antenna tends to present a source impedance of at least 500 ohms to receiver circuitry to which it is connected. The invention includes an antenna assembly including a dielectrically antenna and a receiver having a radio frequency front-end stage with a differential input coupled to the feed ends of the helical elements.

Abstract: A dielectrically-loaded helical antenna has a cylindrical ceramic core bearing metallised helical antenna elements which are coupled to a coaxial feeder structure passing axially through the core. Secured to an end face of the core is a circular laminate board having feed-through holes for receiving the end portions of feeder structure conductors. Coupling conductors on the face of the board that faces the core extend radially outwardly from connections with the feeder structure conductors to plated edge portions of the board. The board is of a diameter substantially equal to that of the core and bridging conductors overlying the plated edge portions connect the coupling conductors to the helical elements. The board incorporates a matching network.

Abstract: A dielectrically-loaded antenna has a cylindrical ceramic core, a three dimensional antenna element structure comprising co-extensive helical conductors plated on a cylindrical side surface of the core and a dielectrically-loaded antenna has a solid cylindrical core made of a ceramic material, helical antenna elements made of a ceramic material, co-extensive helical antenna elements plated on the core, connecting conductors on a distal end surface, a matching section in the form of a printed circuit board overlying the core distal end surface and a coaxial feeder housed in an axial bore passing through the core. For ease of manufacture, the laminate board of the matching section contains a ball grid array having a plurality of solder elements which serve to connect the matching network to both the surface connection elements on the distal core end surface and to the feeder.

Abstract: A dielectrically loaded backfire helical antenna has a cylindrical ceramic core and a feed structure which passes axially through the core to a distal end face of the core where it is connected to helical conductors located on the outside of the core. Opening out on the proximal end face of the core is a cavity which is coaxial with the feed structure. A conductive balun layer encircling a portion of the core extends over the proximal end face of the core and the wall of the cavity to connect the helical elements to the feeder structure when it emerges into the cavity. The presence of the cavity and accommodating some of the length of the balun in the cavity allows a reduction in the size and weight of a dielectrically loaded backfire antenna.

Abstract: A dielectrically loaded multifilar antenna has an electrically insulative solid core bearing an antenna element structure having four pairs of substantially helical radiating elements spaced apart around a central axis of the antenna. Each pair of oppositely located antenna elements forms part of a conductive loop having an effective electrical length in the region of N guide wavelengths at the operating frequency, where N is an integer and is at least 2. Typically, each helical element executes substantially a full turn around the axis on the outer surface of the core. The antenna offers an improved gain-bandwidth product compared with typical prior dielectrically loaded multifilar helical antennas, and a 3dB beamwidth of at least 90° for circularly polarized radiation.

Abstract: A dielectrically-loaded helical antenna has a ceramic cylindrical core and, formed on the cylindrical surface of the core, a plurality of conductive helical antenna elements. The antenna elements are coupled to a pair of feed connection conductors generally centrally located on an end surface of the core, the coupling between the antenna elements and the feed connection conductors being by way of a matching section comprising a laminate board having at least three conductive layers and insulative layers between the conductive layers arranged in an alternating manner. Each conductive layer has a first portion forming part of a respective shunt capacitance, the conductive layers and the insulative layers together acting to form a plurality of capacitors shunt-connected across the antenna elements. One of the conductive layers includes a second portion forming a series inductance between one of the feed connection conductors and at least one of the antenna elements.

Abstract: A dielectrically-loaded multifilar helical antenna has a ceramic cylindrical core and, on the core outer surface, coextensive generally helical conductors arranged in an opposing configuration. Located on an end surface of the core is a feed connection nodes and a connection structure connecting the helical conductors to the feed connection nodes. The connection structure comprises, as a conductive coating of the core end surface, conductive paths linking a respective helical conductor and a respective feed connection node, the connection structure further comprising a series reactive link in one conductive path and a shunt reactive link interconnecting the feed connection nodes, one of the reactive links being inductive and the other being capacitive to form a matching network.

Abstract: A dielectrically loaded multifilar helical antenna having an operating frequency in excess of 200 MHz has an electrically insulative core with a relative dielectric constant greater than 5 occupying the major part of the interior volume defined by a three dimensional antenna element structure having, in one embodiment, eight coextensive helical tracks and, in another embodiment, six such tracks. The antennas are backfire or endfire antennas, all helical elements being phased so as to contribute to a circular polarisation resonance at the operating frequency.

Abstract: An antenna arrangement which includes two antennas which are resonant at a common operating frequency. The arrangement includes a circuit which combines output signals from each of the antennas to provide a combined signal output. Each antenna has an electrically insulative core of solid material having a relative dielectric constant greater than 5 and a three-dimensional antenna element structure. The structure includes at least a pair of elongate conductive antenna elements disposed on or adjacent a surface of the core.

Abstract: An antenna system for operation at frequencies in excess of 200 MHz, comprises an antenna, a transmission line and a receiver stage, the transmission line electrically connecting the antenna to an input of the receiver stage, and the antenna having: an antenna core of a solid insulative material having a relative dielectric constant greater than 5, the material of the core occupying the major part of the volume defined by the core outer surface, and a three-dimensional antenna element structure disposed on or adjacent the outer surface of the core; wherein the antenna is fed by the transmission line at a proximal end of the dielectric core; the receiver stage comprises an amplifier and an electromagnetic radiation screen, the amplifier being positioned within the screen; and the transmission line includes a current choke arranged to provide a substantially balanced condition at a feed connection of the antenna.

Abstract: In a method of producing a quadrifilar antenna for circularly polarised radiation at frequencies above 200 MHz, the antenna is tuned by coupling it to a test source, measuring the relative phases and amplitudes of currents at predetermined positions in the individual elements of the antenna by means of probes capacitively coupled to the elements, and laser etching apertures in the elements to increase their inductance, the sizes of the apertures being computed according to the deviation of the measured relative phases from predetermined values.

Abstract: A radio communication receiver which includes an antenna array having at least two antennas to provide antenna diversity. The receiver is for receiving signals containing orthogonally coded data sub-streams derived from a source data stream. The receiver also has receiver circuitry, coupled to the antenna array, having a detection stage to detect the data sub-streams and a combiner stage for combining the detected data sub-streams to recover the source data stream. Each antenna has an electrically insulative core of solid material having a dielectric constant greater than 5. Each antenna also has a three-dimensional antenna element structure disposed on or adjacent the outer surface of the core.

Abstract: A dielectrically-loaded helical antenna has a cylindrical ceramic core bearing metallised helical antenna elements which are coupled to a coaxial feeder structure passing axially through the core. Secured to the end face of the core is an impedance matching section in the form of a laminate board. The matching section embodies a shunt capacitance and a series inductance.

Abstract: A dielectrically-loaded multifilar helical antenna has a ceramic cylindrical core and, on the core outer surface, coextensive generally helical conductors arranged in an opposing configuration. Located on an end surface of the core is a feed connection nodes and a connection structure connecting the helical conductors to the feed connection nodes. The connection structure comprises, as a conductive coating of the core end surface, conductive paths linking a respective helical conductor and a respective feed connection node, the connection structure further comprising a series reactive link in one conductive path and a shunt reactive link interconnecting the feed connection nodes, one of the reactive links being inductive and the other being capacitive to form a matching network.

Abstract: A mobile communication device has an antenna assembly comprising the combination of an inverted-F antenna and a dielectrically-loaded quadrifilar helical antenna, the latter mounted on the distal end of an elongate radiator element of the inverted-F antenna.

Abstract: A dielectrically-loaded helical antenna has a cylindrical ceramic core bearing metallised helical antenna elements which are coupled to a coaxial feeder structure passing axially through the core. Secured to an end face of the core is a circular laminate board having feedthrough holes for receiving the end portions of feeder structure conductors. Coupling conductors on the face of the board that faces the core extend radially outwardly from connections with the feeder structure conductors to plated edge portions of the board. The board is of a diameter substantially equal to that of the core and bridging conductors overlying the plated edge portions connect the coupling conductors to the helical elements. The board incorporates a matching network.