TRAP antennas

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TRAP antennas, TRAP, antennas, filters, oscillatory circuits, range, frequency, wavelength, resonance, parallel circuit, open circuit, dipole, chokes, frequency response, half-wave, collinear antennas, tunable circuit, inductance, magnetic flux, tuning, KPI , variable capacitor, amateur radio,
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TRAP antennas are antennas that contain parallel oscillatory circuits in their canvas. In other words, they are sequentially connected sections of the web connected through circuits, at best, or simply through chokes.
TRAP antennas allow you to work in several ranges with good efficiency. This is their main purpose. The word TRAP itself means a trap, QC does not transmit waves in the canvas at its resonant frequency.
What is the principle of operation of TRAP antennas?
We all know that parallel QC is an open circuit at the resonant frequency. This QC property can be easily used in order to tear the antenna sheet at certain frequencies.
How is this implemented?
Imagine an ordinary dipole, let's say at a frequency of 300 MHz. The wavelength is one meter, hence the magnitude of the half-wave dipole is half a meter.
And now we hang on the ends of the dipole oscillatory circuits at a frequency of 300 MHz. Will the antenna efficiency drop due to them? Not at all. But now we have the opportunity to connect more sections of the canvas from the outside, adding another range to the antenna. Suppose we lengthen the canvas to a meter, having the opportunity to work also at a frequency of 150 MHz.
Vibrational loops at a frequency of 300 MHz break the web, so the 300 MHz dipole works as if the web ends on an oscillating circuit.
And for a frequency of 150 MHz, the contours do not constitute a barrier, so the entire meter dipole operates at 150 MHz.
Thus, using oscillatory circuits, we forced one canvas to work in two ranges. In principle, in this way a lot more ranges could be added if the contours were perfect.
But the contours are not perfect. They create both losses and wave leakages between the web sections.
Moreover, in practice, you can often find TRAP antennas in which the oscillatory circuits are replaced simply by chokes, because the reactance of the inductor is directly proportional to the frequency. For a higher frequency, the inductor represents more resistance than for a low frequency. However, the use of chokes instead of QC kills the antenna efficiency in the trash, so I would not recommend using chokes.
There is one more feature. Because Since Q factor is limited, they usually try to make TRAP antennas into bands that differ well in frequency, usually twice. With this ratio of frequencies, the frequency response of the circuit does not go to a lower frequency of a larger dipole, and therefore the efficiency of the system is quite acceptable.
But to make TRAP antennas in close ranges, i.e. when the size of the larger dipole is only slightly larger than the size of the internal dipole, it is completely meaningless, because QC will completely block the waves inside the large dipole.
In TRAP antennas, not only small and large dipoles can resonate, but also web sections connected to the edges of the antenna as independent half-wave vibrators.
This property is used to create collinear antennas. In this case, the lengths of the extreme segments and the internal dipole coincide. For example - all the same half-meter segments, and their contours will be divided exactly at 300 MHz.
If there were no contours, then every half-wave the current in the sheet would change direction in the opposite direction. But thanks to the CC, the current in all half-wave segments is codirectional, such a system at a frequency of 300 MHz will work as a collinear antenna.
In addition to the fact that the system will operate at 300 MHz, it will still have an additional range at 100 MHz, like a dipole measuring one and a half meters.
It is very rare to find TRAP antennas with a large number of segments and tunable KK. Such systems allow flexible control of frequency properties.
However, it is worth remembering that the weak point of all TRAP antennas is precisely the oscillatory circuits. The most commonly used circuits with open inductance. They are easy to tune to a given frequency by changing the number of turns, but it is such inductances that have the largest losses due to the fact that they have an open magnetic flux.