It is an array of two tightly coupled loops with a bi-directional pattern. Both loops are linked to share a single feed point. This antenna can operate in the 14 to 28 MHz bands with the appropriate impedance matching. It is self-resonant when the perimeter of each loop is around one wavelength. In this example, each loop is 3 x 4.5 m and the resonant frequency is 19.8 MHz.
A balun can be modeled in AN-SOF using an equivalent generator, as the figure below shows. Since voltage sources admit an internal impedance, we can adjust its resistive part to match the antenna input resistance. Of course, we must previously cancel out the antenna reactance using an opposite lumped reactance.
This design is for 5 bands on a single pole. Each “J” corresponds to a band and therefore the feed point changes depending on the frequency. The resonance frequency is indicated in each case, which can be changed by moving the feed point. The height is about 5 m.
These are compact, lightweight antennas that can be used for DX applications. This 2-element array is the simplest we can build to get a directional antenna using delta loops. It is practically resonant with 50 Ohm of input impedance near the band center. This is an example where we need to enable the Exact Kernel option in AN-SOF since we have sharp angles between wires.