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: 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: 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 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 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 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 unitary feed structure for sliding installation in a passage in the insulative core of a dielectrically-loaded antenna comprises the unitary combination of a tubular outer shield conductor and elongate inner conductor which extends through the shield conductor and is insulated from the latter. The shield conductor and inner conductor have oppositely directed radially extending connection members at an end of the feed structure, these connection members being integrally formed as part of the respective conductors so that the feed structure can be inserted as a unit into the passage in the antenna core so that the connection members engage respective connection portions formed on an end face of the core adjacent on end of the passage. Soldering of the connection members to the connection portions can be performed as a single operation so as to connect the feed structure to conductive antenna elements plated on the outer surface of the core.

Abstract: In a dielectrically-loaded quadrifilar antenna for operation with circularly polarised signals, four coextensive composite helical elements are plated on the outer surface of a cylindrical dielectric core, each composite element comprising two mutually adjacent conductive tracks defining between them an elongate channel or slit. The track edges bounding each channel are longer than the opposite edges of the respective tracks in that they follow parallel meandered paths, with the result that each channel deviates from a mean helical path and is longer than the corresponding portion of the mean helical path. At a frequency within the operating band of the antenna, the channels have respective electrical lengths equivalent to a half wavelength. The bandwidth of the antenna is greater than the bandwidth of a correspondingly dimensioned antenna having single-track helical elements.

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.