Some Advantages of the Crossed Field Antenna :
The Crossed Field Antenna presents a purely resistive load, and has no significant reactive component - inductive or capacitive. Due to this, the resultant voltages found on each component are much lower than encountered on a resonant antenna, where the high reactance (X) results in quite fierce voltages, up to several hundred thousand volts being measured.
Because the radiation field components (E and H) are in time phase with each other, there is a negligible 'near field' or induction field. This is due to the wave being formed by a different method (Poynting vector synthesis) than in a traditional resonant antenna.
The conical section at the top of the drum serves to depress the radiation which would normally travel directly upwards (vertically) down towards the ground where it reinforces the wave traveling outwards from the antenna along the ground (called the ground wave). This means the ground wave can be up to 5 dB stronger than found with a traditional resonant quarter wave mast antenna.
Waves from a quarter wave vertical antenna also exhibit another unfortunate quality - Wave Pockets. This is a sharp 'hole' in coverage found at varying distances from the antenna in the daytime. Wave pockets are not found when using the CFA, see Wave Pockets which discovered by Dr. Kabbary in Antennex Magazine.
The new DRM standard needs a wider bandwidth than is generally found on resonant antennas. Many low frequency antennas have very narrow bandwidth due to the high Q, due in turn to the high reactive components. The CFA does not have such problems.
Accordingly, the more even response across the bandwidth means a more linear response to the modulating frequencies and thus improved audio fidelity. When an antenna presents a transmitter with a narrow bandwidth or asymmetrical load, the transmitter often produces unwanted artifacts, which can also affect the quality of program transmitted; with the CFA this does not occur.
The CFA however is usually just 2 or 3 % of wavelength high, as opposed to 25%,. 50% or 62.5% of wavelength as is necessary for a resonant antenna. Therefore, the construction, maintenance and insurance costs are all much lower.
The smaller size leads to other advantages
Masts several hundred feet high also need guying arrangements spreading out over a quite wide area, which effectively means the ground they cover cannot be used for anything else.
This is a tremendous advantage to many city-based commercial radio stations currently enduring punitive after dark power restrictions.
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