A less instinctive approach to the best antenna selection requires considerations and evaluations that often escape our attention.
Here are some reasons why it is worth preferring a Delta Loop antenna.
GAIN / NUMBER OF ELEMENTS / BOOM LENGTH
Among the main features of a Delta Loop antenna system is for sure the higher forward gain developed in relation with the boom length.
Antennas consisting of array elements on rigid booms are mainly represented by logarithmic systems (called log-periodic antennas or LPDA) and Yagi antennas.
A log periodic antenna always has a lower gain compared to a Delta Loop with the same boom length.
On the other hand, there is a rich literature about the comparison between Loop systems and Yagi antennas, fostered since the Loop antennas came out.
The comparison between the two systems shows that the Loop antennas’ forward gain turns to be always higher, up to 5-6 elements, than an homologous Yagi-Uda system.
Usually a Loop antenna exhibits a higher gain than a Yagi with the same number of elements (W. Orr W6SAI and S. Cowan W2LX). Taken from the ARRL Antenna Book (ed. 21), what follows is an interesting diagram which compares two 5-element on 21 MHz having the same boom length (abt. 8.5 m).
As can be seen, the Loop antenna’s forward gain stays higher than Yagi-Uda one along the whole band.
However, there are no records of a Yagi sysyem’s forward gain exceeding an homologous Loop antenna, even in conditions of a smaller gap between the two antennas.
INFLUENCE OF THE GROUND
Delta Loop antennas are characterized by the fact that they completely develop above the joint with the mast.
Such characteristic also allows installations which have a minimum distance from the ground to reach very low take off values (elevation angle above the horizon of the main lobe).
This is extremely important for long distance DX via the ionosphere because smaller is the take off angle, larger is the distance of the bounced RF signal transmitted by the antenna.
The diagram shows a comparison between typical elevation angle trends vs. height from the ground of Yagi and Delta Loop antennas.
The electrical barycenter of a Delta Loop antenna is placed at about 2/3 of the Loop’s height.
As a consequence, the antennas turn to have a particular performance even if they are installed at low heights from the ground or buildings’ roofs.
It is commonly known that closed loop antennas are not affected by the electrostatic noise. Thus a Delta Loop antenna keeps working even when the electrostatic noise makes the use of other antenna systems impossible.