G3TXQ

Amateur Radio (G3TXQ) - A family of wire beams

2 element wire beam shapes

During the computer modelling and experimental work I carried out to develop the broadband hexbeam described elsewhere on this web site, it became evident that this antenna is just one of a large family of antennas which share a common structure and which can be "multibanded" using construction techniques similar to those commonly used with the Hexbeam.

The drawings on the right (click for the full-size version) show a subset of all these 2-element wire beam arrangements based on 3-sided thru 6-sided figures. The common characteristics of this subset are:

The diagrams were drawn using a simplistic scaling which assumes that the total wire length for each shape will be about the same. The (%) figure shown on each diagram is the relative turning radius referenced to a full-size 2-element Yagi.

Some of the options are well known to us: H2 - Broadband Hex; H3 - Classic Hex; S1 - VK2ABQ; S3 - X beam. Others are less familiar. The classic X-Beam appears to have little to commend it - it is marginally larger than the broadband Hexbeam and its Bent-Reflector can be expected to make its F/B performance relatively narrow-band.

The "Bent-Driver/Perimeter-Reflector" options - H2, P2, S2 and T2 - are attractive. They deliver a useful reduction in size without the narrowband performance inherent in the "Bent Reflector" options, and they provide a good match to 50 Ohms. They were selected for further detailed performance modelling.

broadband hexbeam pentbeam square beam tri beam

A systematic approach was taken to "optimise" the wire dimensions for 20m versions of the four antennas:

The final dimensions, using #16 gauge wire, which evolved from Free Space performance optimisation, were:

The Free Space performance of the four antennas is compared below, alongside the performance of a full-size 2 element Yagi for reference:

Front to back ratio SWR Forward gain

Observations

Conclusions: