Enhanced OWA

Some years ago Jim Breakall, WA3FET, devised the Optimized Wideband Array. 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.

Modeling Results

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.

Gain/Pattern Trade-Off

To explore the gain/pattern trade-off, I reoptimized with maximum SWR of 1.4 and varied minimum F/R.

Gain/SWR Trade-Off

To explore the gain/SWR trade-off, I reoptimized with minimum F/R of 22 dB and varied maximum SWR.

Narrowband Pattern

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 little advantage for these designs. The dashed blue curves below are for an OWA with narrowband F/R. The solid blue and red curves, from above, are for wideband F/R.

The brown curves are for four straight elements with hairpin match. The solid curves are for wideband F/R and dashed are for narrowband. The difference between the brown and blue gain curves is the cost of forgoing a matching network.

The green curves are for a 3-element Yagi with bent driven element and hairpin match. I think most amplifiers should handle the SWR to at least 7.25 MHz. This design has intermediate gain and a decent pattern over half of the band at lower material cost and wind load.

Antenna Files

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

3-Element Yagi with Hairpin
Free Space Symmetric
7 7.05 7.3 MHz
3 6061-T6 wires, inches
ang = -12.6433
x1 = 0
x2 = 275.3429
x3 = 570
y1 = 411.1258
y2 = 400.6867
y3 = 365.677
1  x1 0 0  x1 y1 0  1.4
rotate z end1 ang
1  x2 0 0  x2 y2 0  1.4
rotate end
1  x3 0 0  x3 y3 0  1.4
1 source
l1 = 209.726
Wire 2, end1 l1 pF

June 18, 201888108 MHz