Measurement of Aircraft-Antenna Patterns Using Models

Methods of measuring the patterns of airborne antennas using models have been investigated. The conditions which have to be satisfied in a model for accurate simulation are well known. However, in a practical model it is generally impossible to satisfy these conditions exactly, so it is necessary to consider the approximations which are permissible. Methods for measuring directly the patterns of transmitting and receivng antennas are described. For low frequencies it has been found advantageous to operate in a vertical direction instead of horizontal when making such measurements, in order to control ground reflections. The equipment which has been used for measuring patterns over a wide frequency range is discussed. A new method for measuring the patterns of antennas which makes use of the energy reradiated from a receiving antenna when excited by a plane wave has been developed. The reradiated field is distinguished from the exciting field by its modulation, which results from varying the impedance of the receiver periodically. The method has been found to be useful in determining the right- or left-handedness of elliptically polarized fields. The accuracy of model-antenina-pattern measurements is discussed. Short radial antennas mounted on cylinders have been found to be very useful in evaluating the accuracy of measurements, since their patterns can be calculated. Models have been used for measuring the patterns of a wide variety of antennas, including simple arrays. Propeller modulation of patterns can be studied with models.