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What is the resonant frequency of an antenna?
The frequency corresponding to a zero determinant is called the resonant frequency. This is the frequency where the capacitive and inductive reactances cancel each other out. At this point, the antenna appears purely resistive, the resistance being a combination of the loss resistance and the radiation resistance.
Which is a non-resonant antenna?
Non-resonant Antennas are those for which resonant frequency does not occur. The wave moves in forward direction and hence do not form a standing wave. They are also called as Unidirectional travelling wave antennas, as the radiated wave moves in forward direction only, which means that only incident wave is present.
What is the impedance of a resonant antenna?
Irrespective of the feedline characteristics (assuming there is a feedline—could be fed directly by equipment), at its feed point, an antenna presents a certain impedance value as a function of frequency. The frequency for which this impedance is resistive (contains no reactive component) is the resonant frequency.
What happens at frequencies other than the resonant frequency?
At all frequencies other than its resonant frequency the antenna presents a reactive impedance component (inductive or capacitive) that adds to the resistive component. If the source impedance is still resistive, it is no longer matched to that of the antenna, so the power delivered to it is reduced.
What is the SWR of a resonant antenna?
A resonant antenna does not necessarily have a low SWR. Antennas with a feedpoint impedance of 5 + j0 or 500 + j0 are resonant, by this definition, but either will have an SWR of 10 : 1 when fed with 50 ohm cable. And either may still be a useful antenna.
Which is an example of a non-resonant antenna?
Use the antenna with the pattern you want, then match it to the feedline you want. The classic example is the 5/8 wave vertical antenna. A nice bit of low angle gain and not resonant. Use a high-quality coil to make it (electrically) a 3/4 wave antenna so it will match 50 Ω coax. Ask any engineer at any AM broadcast station.