A bow-tie antenna may be thought of as a construction of a monopole wedge above
ground where the perfect ground plane is removed and the image under the ground plane
is replaced by a physical structure as illustrated in Figure 4.17.
A three-parameter model for the bow tie can be developed using a detailed study
undertaken of results ?¬?rst published by Woodward for a monopole wedge above ground.
The empirical model for an equivalent circuit for a bow-tie antenna is shown in Figure 4.18.
The model, which is derived from our experimental results that con?¬?rm Woodward??™s
results, has an associated reactance X(v) which is that of a capacitor CB, whose value is
that of the self-capacitance of the bow tie, and an inductor LB, placed in the series circuit
shown. The radiation resistance of the bow tie is represented by RBr.
Calculating the self-capacitance as depicted by the ?¬?eld lines of Figure 4.19 of the bow-tie
antenna by seeking analytical solutions to Laplace??™s equation presents a dif?¬?cult problem.
Nevertheless a numerical solution is tractable and has been performed using the method of
moments to provide a suitable numerical approximation to the self-capacitance of a bowtie
antenna.
The radiation resistance outlined in the model parameters has signi?¬?cance in two ways.
It allows the amount of radiated power to be calculated for a transmitting antenna, and
also provides for a label antenna a means of calculating, using the reciprocity theorem, the
effective electric ?¬‚ux collecting area of the antenna as depicted in Figure 4.
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