	W8JK

Originally designed by John Kraus, W8JK in about 1940, this antenna has some interesting properties. It's characterized by two closely spaced elements driven out of phase. Although the fields from the elements don't fully reinforce in any direction, gain is nonetheless achieved because of lowering of the radiation resistance due to mutual coupling. And lower it is -- note the feedpoint impedance of only 3.73 - j24.48 ohms. Compare this to a single element. The lower resistance results in heavier current, hence greater field strength, for a given power input. The difficulty is that system losses can quickly eat up the gain. Making this antenna from #12 copper wire (try it -- and include wire loss) drops the gain about 0.65 dB, not too bad. But great attention must be paid to losses in matching networks. And losses rapidly increase in significance as the spacing is made closer than the 0.1 wavelength of the example. When mounted low (0.25 wavelength for the example), W8JK-type antennas have a lower radiation angle than many other horizontal antennas due to the inherent lack of high-angle radiation. As an interesting exercise, save the pattern for later comparison. Then delete the second source, making the antenna into a Yagi. Note the increased gain. Even though the "takeoff angle" is higher, the Yagi gain is as good or better even at lower angles. In addition, the feedpoint impedance has increased to a much more manageable value. On the other hand, the W8JK will retain its performance over a much greater frequency range than the Yagi.
