AU2005100456A4 - HF Loop Antenna for Manpack or Portable Radio - Google Patents

Description

Specification High frequency Loop Antenna System for Manpack or Portable use This invention relates to an HF (high frequency) loop antenna system used on a manpack or portable radio for NVIS (Near Vertical Incidence Skywave) Communication.

High frequency loop antenna systems have been described in theliterature. They comprise a closed loop radiating structure, tuned by a variable capacitor means and a means of exciting a radiofrequency current into the loop.

High frequency loop antennas have conventionally been available as stand-alone discrete installations on buildings or with means to allow mounting on vehicle roofs.

These antenna systems have a number of impediments when configured for manpack or portable use. They are generally cumbersome to deploy and do not readily allow ambulatory use without the danger of snagging on obstacles.

By configuring the radiating loop as an inverted triangle comprising two highly electrically conductive vee pattern rods along with a highly electrically conductive wire connecting the tops of the rods, the practical implementation is simplified.

The incorporation of a highly conductive connector means in the conductive wire allows the wire to part without damage in the event of snagging during ambulatory use.

Figure 1 shows the equivalent circuit of the half-loop antenna and current injector. Electrically it comprises a high-Q tuned circuit where the inductance L is the antenna arm, the capacitance C is the lumped constant variable capacitor required to bring the circuit to resonance at the required frequency and the resistance R comprises a loss resistance due to the imperfect nature of the materials in addition to the radiation resistance which is the sought after loss due to effective electromagnetic radiation. Power is coupled to the system via a current injection transformer means T, in such a manner to maximise power transfer.

Figure 2 illustrates an implementation of the Manpack and Portable High frequency Loop Antenna System.

This comprises a metal housing means 1, with two insulated electrical connectors 2 and 3 allowing the connecting in vee configuration of two highly electrically conducting rods 4 and 5 with a highly t electrically conducting wire 6 connecting the tops of the rods to one another. This wire is fitted 0 o with a highly electrically conducting connector means 7 which allows parting of this connection without snagging, in the event of encountering obstacles. An electrically insulating spring means, 7 holding the rod means 4 and 5 apart, ensures that the wire means 6, forming the top of the inverted triangle remains stable and taught.

A current injector means 8, feeding out to rod 4, through insulator 2 allows radiofrequency Sexcitation of the loop antenna. The current injector means 8, comprises a current transformer of the correct ratio to obtain maximum power transfer from the radiofrequency excitation means 9 which 0 is connected to the loop system via coaxial connector means 10. Rod 5 is connected through insulating connector 3 to a variable capacitor means 11, allowing tuning of the antenna system to the frequency in use. The antenna current is monitored by a radiofrequency current detector means 12, the output of which which is fed to a servocotroller 13, which obtains maximum antenna current by controlling the position of the variable capacitor means 11 using an electric motor 14.

Claims (3)

1. Two vee configured high conductivity rods combined with a high conductivity wire joining the tops of the rods forming a closed radiating loop structure allowing simple erection and ambulatory use combined with effective ground isolation and radiation towards zenith.

2. A high conductivity connector means incorporated into the above high conductivity connecting wire allowing safe parting of the wire in the event of snagging upon an obstacle during ambulation.

3. A current injector means incorporated at the base of one vee rod and a variable capacitor tuning means incorporated at the base of the second rod allowing both tuning and power matching to be obtained.