FEATURE ARTICLE
Figure 9 shows the simulated and measured gain of the proposed hybrid Adcock/loop topology versus the
gain of a pure Adcock of equivalent size. The plots reveal the hybrid topology achieves up to 30 dB more
gain at low frequencies, in line with the sort of performance obtained by a loop antenna. Patterns of the
elements are as shown in Figure 10.
Figure 8. Gain [dBi] of loops and Adcock dipole array
Figure 9. Simulated and measured gain for hybrid Adcock
loop compared with a pure Adcock element
Conclusion
In closing, a new topology of using loops in Watson-Watt DF
applications has been presented. The loop antenna technology
is able to suppress cross-polarized gain typical of traditional
loops and when used in an Adcock array provides enhanced
sensitivity when the array size is electrically small.
Practical Applications
The new technology has been implemented into several products by Alaris antennas:
DF-A0016
The DF-A0016 is a crossed-loop/monopole direction finding
antenna for use with Watson Watt method, with a large diameter to achieve a high sensitivity. The loops make use of Figure 10. Measured normalised antenna patterns
patented cross-polarisation cancelling technology that elimi- for hybrid Adcock/loop element
nates disturbances due to cross-polarisation from on-horizon
sources. This offers enhanced, reliable accuracy in real-world applications and field trials over traditional
crossed-loop designs.
The antenna is collapsible for transport and storage. It is made of aluminium and brass elements and coaxial cable, with aluminium and composite mechanical parts. A lightweight composite quad pod supports
the antenna above the ground. The quad pod collapses to a similar size to the antenna.
DF-A0069
The DF-A0069 is a wideband vehicle-mounted Adcock DF antenna intended for direction-finding from 20
to 3,000 MHz. The antenna uses a combination of crossed-loop and Adcock array principles for the various
bands providing maximum possible sensitivity for its compact form factor. The loop designs incorporate patented technology to mitigate cross-pol disturbance. Each band offers an omni-channel output that can also
be used for monitoring. The antenna presents patterns suitable for the Watson-Watt estimation method.
For more information visit www.alarisantennas.com.
18
Antenna Systems & Technology Fall 2016
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Table of Contents for the Digital Edition of Antenna Systems & Technology - Fall 2016