Antenna and an antenna feed structure
View Patent ↗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.
1. A unitary antenna feed structure for sliding installation in a passage in an insulative core of a dielectrically loaded antenna, wherein the feed structure comprises a unitary combination of:
a tubular outer shield conductor;
an elongate inner conductor extending through the shield conductor and insulated from the shield conductor, and
a laminate board extending laterally outwardly from a distal end of the shield conductor,
the laminate board comprising:
a proximal surface having first and second proximally-directed conductive surface portions for connection to respective first and second conductors on the antenna core adjacent an end of the passage, the first proximally-directed conductive surface portion and the outer shield conductor being electrically connected;
a non-proximal surface or layer having a first non-proximal conductive portion adjacent the inner conductor and being electrically connected thereto; and
a linking conductor which electrically connects the first non-proximal conductive portion and the second proximally-directed conductive surface portion.
2. A unitary antenna feed structure for sliding installation in a passage in an insulative core of a dielectrically loaded antenna, wherein the feed structure comprises the unitary combination of:
a transmission line section including a length of transmission line for insertion into the passage of the core, the transmission line section defining a feed axis; and
a matching section including a laminate board extending laterally outwardly from a distal end of the transmission line,
the laminate board comprising:
a proximal surface oriented perpendicularly to the feed axis and having first and second proximally-directed conductive surface portions for connection to distal conductors on the antenna core, the proximally-directed conductive surface portions being in electrical communication with conductors of the transmission line.
3. A unitary antenna feed structure according to claim 2 , wherein the matching section includes a shunt capacitance coupled across first and second conductors of the transmission line.