Some years ago Jim Breakall, WA3FET, devised the Optimized Wideband Antenna. It is a Yagi with close-spaced first director that provides low SWR over a wide bandwidth with direct 50Ω feed. Although the OWA has less forward gain than a conventional design with matching network, its wide SWR bandwidth and feed simplicity make it popular.
Bending the OWA driven element can improve forward gain while retaining wide SWR bandwidth and direct feed.
I used AO 9.66 to maximize forward gain for a 4-element OWA on a 570″ boom with F/R no less than 22 dB and SWR no greater than 1.4 over 7.0 to 7.3 MHz. The blue curves show the response. Then I let the driven element bend in the center and reoptimized with the same constraints. The red curves are for a 7.2° bend. Bending additional elements can provide up to 0.3 dB more gain.
To explore the gain/pattern trade-off, I reoptimized with maximum SWR of 1.4 and varied minimum F/R.
To explore the gain/SWR trade-off, I reoptimized with minimum F/R of 22 dB and varied maximum SWR.
Some OWAs are designed for a good pattern at the low end of the band but allow it to degrade higher up where it may not be needed. Relaxing F/R bandwidth yields much higher forward gain. A bent driven element offers less advantage for these designs. The dashed curves below are for OWAs with narrowband F/R. The solid curves, from above, are for wideband F/R.
Enhanced OWA Free Space Symmetric 7 7.075 7.15 7.225 7.3 MHz 4 6061-T6 wires, inches ang = -7.20994 x1 = 0 x2 = 138.63 x3 = 245.5951 x4 = 570 y1 = 413.1038 y2 = 404.9571 y3 = 386.8065 y4 = 365.7719 1 x1 0 0 x1 y1 0 1.4 rotate end1 z ang 1 x2 0 0 x2 y2 0 1.4 rotate end 1 x3 0 0 x3 y3 0 1.4 1 x4 0 0 x4 y4 0 1.4 1 source Wire 2, end1 Enhanced OWA - Narrowband F/R Free Space Symmetric 7 7.1 7.3 MHz 4 6061-T6 wires, inches ang = -8.210171 x1 = 0 x2 = 156.1316 x3 = 275.1442 x4 = 570 y1 = 412.7051 y2 = 403.4081 y3 = 386.9267 y4 = 371.5446 1 x1 0 0 x1 y1 0 1.4 rotate end1 z ang 1 x2 0 0 x2 y2 0 1.4 rotate end 1 x3 0 0 x3 y3 0 1.4 1 x4 0 0 x4 y4 0 1.4 1 source Wire 2, end1
I used AO 9.67 to maximize forward gain for a 6-element OWA on a 570″ boom with F/R no less than 22 dB and SWR no greater than 1.3 over 21.0 to 21.45 MHz. I repeated for 28 dB F/R. Then I let the driven element bend in the center and reoptimized with the same constraints.
The bent driven element improved forward gain just 0.2 dB at 22 dB F/R but 0.55–0.85 dB at 28 dB F/R. The enhanced OWA with 28 dB F/R has slightly more gain than the conventional OWA with 22 dB F/R.
Enhanced OWA - 22 dB F/R minimum Free Space Symmetric 21 21.2 21.37 21.45 MHz 6 6061-T6 wires, inches ang = -6.403389 x1 = 0 x2 = 41.09755 x3 = 94.9448 x4 = 228.5655 x5 = 418.725 x6 = 570 y1 = 138.3705 y2 = 134.5689 y3 = 129.3241 y4 = 126.3879 y5 = 124.7475 y6 = 123.3673 1 x1 -y1 0 x1 y1 0 .84 rotate end1 z ang 1 x2 0 0 x2 y2 0 .84 rotate end 1 x3 -y3 0 x3 y3 0 .84 1 x4 -y4 0 x4 y4 0 .84 1 x5 -y5 0 x5 y5 0 .84 1 x6 -y6 0 x6 y6 0 .84 1 source Wire 2, end1 Enhanced OWA - 28 dB F/R minimum Free Space Symmetric 21 21.2 21.37 21.45 MHz 6 6061-T6 wires, inches ang = -7.300423 x1 = 0 x2 = 45.73473 x3 = 98.67726 x4 = 232.771 x5 = 416.7147 x6 = 570 y1 = 138.2157 y2 = 134.8994 y3 = 129.3929 y4 = 125.8002 y5 = 125.1475 y6 = 120.4598 1 x1 -y1 0 x1 y1 0 .84 rotate end1 z ang 1 x2 0 0 x2 y2 0 .84 rotate end 1 x3 -y3 0 x3 y3 0 .84 1 x4 -y4 0 x4 y4 0 .84 1 x5 -y5 0 x5 y5 0 .84 1 x6 -y6 0 x6 y6 0 .84 1 source Wire 2, end1
88–108 MHz