Can Theta Be Determined from Antenna Field Pattern Equations?

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SUMMARY

The discussion focuses on determining the angle \(\theta\) from the antenna field pattern equation \(\frac{1}{N} \left[\frac{\sin(N\theta)}{\sin\theta}\right] = 0.7071\), where \(N\) is an integer greater than 1. The identity \(\sin N\theta = \sum_{k=0}^N \binom{N}{k} \cos^k \theta\,\sin^{N-k} \theta\,\sin\left(\frac{1}{2}(N-k)\pi\right)\) is suggested to derive a polynomial in \(\sin \theta\). For values of \(N\) greater than 3, numerical methods are necessary to solve for \(\theta\).

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yungman
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This is part of the antenna field pattern calculation, I want to find out is there any way to find the \;\theta\; of this:

\frac 1 N \left[\frac {\sin(N\theta)}{sin\theta}\right]\;\hbox { = 0.7071 where N is an integer bigger than 1}
 
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you can use the identity
\sin N\theta = \sum_{k=0}^N \binom{N}{k} \cos^k \theta\,\sin^{N-k} \theta\,\sin\left(\frac{1}{2}(N-k)\pi\right)
to obtain a polynomial in \sin \theta which can then be solved for \theta. However, you will probably need to solve it numerically for N>3.
 

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