First appearing in the 1990s, genetic antennas, also known as “evolved antennas,” resemble intricately bent paperclips attached to a radio frequency connector. They are designed entirely by an optimization algorithm, which can be a genetic algorithm or some other iterative method, having no input to their theory of operation by a human engineer.
Genetic antennas go through “Evolutions.”
Similar to manually designed custom antennas, it often takes multiple attempts and iterations to come up with the most optimal genetic antenna design for the specified application. However, genetic antennas are not existing designs modified by optimization. Rather, each iteration, designed entirely by a computer, is a new antenna altogether.
To design a genetic antenna, the computer program starts with rather simple shape. Using its own calculations and algorithms, the program modifies the shape, either by adding or reshaping elements. These new characteristics will have different effects on the antenna’s performance. After the said modifications, a new shape, thus, a new antenna, is formed. These new shapes are essentially different “evolutions” of the original antenna.
After a good number of second-generation antennas are developed, each one is evaluated to determine how well they fulfill the design requirements; they are assigned a numerical score accordingly. The antennas with the worst performance scores are then discarded. This process of eliminating the poorest performing candidates and keeping the best performing candidates, mirrors Charles Darwin’s concept of “natural selection.” The computer then repeats the procedure of modifying elements, this time, using the best performing candidates from the second generation.
Essentially, the computer program develops multiple generation of antennas until it finds the best performing antenna. The resulting shapes are often very complicated and difficult to conceptualize by human engineers.
Loop antennas come in many forms, but their overarching distinction is that they are relatively simply constructed, yet very versatile.
Loop antennas are generally classified under two categories: electrically small and electrically large. If the loop’s overall length (circumference) is less than about one-tenth of a wavelength (C < λ/10), it is usually considered an electrically small antenna. On the other hand, an electrically large loop’s circumference is about a free-space wavelength (C ~ λ).
Electrically small antennas have proportionately small radiation resistances that are usually smaller than their loss resistances, rendering them ineffective for radio communication. They are better suited as probes for field measurements and as directional antennas for radiowave navigation.
Conversely, electrically large loop antennas are primarily used in directional arrays, including helical antennas, Yagi-Uda arrays, and quad arrays. These applications require the maximum radiation of the loop to be directed towards the axis of the loop to form an end-fire antenna. The proper phasing between turns enhances the overall directional properties.
A loop antenna could take virtually any shape, flexible or rigid. Due to its convenient geometrical arrangement the most popular configuration is the circular loop, particularly the small circular loop.
The loop’s mounting orientation will determine its radiation characteristics relative to its ground plane. placing multiple loops side by side on the same plane is one way to form an array.
Most applications of loop antennas are within the high-frequency (HF), very high-frequency (VHF), and ultra-high-frequency (UHF) bands.