antenna-theory.com

[SM.Physics]

As I was researching different antenna types and geometric shapes, I came across rhombic antennas. While I understand these in general, I came across the following: "It is directional towards the resistor end, so the termination end points towards the region of the world it is designed to serve. Even when unterminated (bi-directional) the rhombic is not perfectly bi-directional. This is because of losses in the system primarily caused by radiation, conductor resistance, and coupling to the lossy soil below the antenna."

Why would an antenna suffer losses due to the soil below the antenna and how is that loss unique to rhombic antennas? If they just used insulated poles to hold the wires, why should there be significant loss?

In addition, I was looking for guidance as to what antenna shapes have been found to be particularly successful. I am interested in biconical antennas and have been investigating the effect of different geometric arrangements of directional antennas.

I appreciate the help as always.

[Schubert]

There's nothing unique about rhombic antennas in my opinion. Whatever is going on there would apply to circular or square shapes, in general.

As for the soil losses, whenever you have a moderately conductive medium near an antenna, power is absorbed (i.e. not radiated). This effectively lowers the antenna's radiation efficiency. This is true for soil, and also in electronics when lossy plastics, glass or semiconducting material is present around the antenna.

As for optimal antenna shapes, it is entirely application dependent. If there are no constraints, then for a given volume you want to take up as much space as possible for the largest bandwidth. Bowtie antennas are popular because they are simple to construct and have large bandwidth as well.