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<p>The landing of aeroplanes can be facilitated by emitting from the landing field a vertical beam of radio-frequency electromagnetic radiation. A type of transmitting coil antenna has been devised for this purpose by J.A. Willoughby, of the Bureau of Standards. The behaviour of this transmitting coil antenna is calculated in the paper. Formulæ are worked out for the current received in a coil aerial and in an antenna oriented in a known manner at a sufficient distance from the transmitter. It is found that if a vertical coil aerial is used for reception and if the aeroplane flies horizontally a maximum signal is obtained when the distance l makes an angle of 30° with the vertical. The influence of the earth is also
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