can someone tell me what are the formulas of HPBW for a helical antenna?

I've searched a lot and I saw that there are two different formulas of HPBW for the helical antenna,

this one,

$$ \mathbf{(HPBW)} = [\frac{52}{C} \sqrt{\frac{\lambda^2}{NS}}] $$

and this one,

$$ \mathrm{HPBW} \simeq \frac{52}{\frac C\lambda \sqrt\frac{NS}{\lambda}} \mathrm{degrees} $$

so what is the difference between both ?

  • $\begingroup$ One of them is wrong by an exponent in $\lambda$. Otherwise, with applying the basic calculus rules for division and roots, they are identical. $\endgroup$ – Marcus Müller Sep 18 at 20:13
  • $\begingroup$ Hello Abdullah, and welcome to this site! :-) $\endgroup$ – Mike Waters Sep 18 at 21:28
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    $\begingroup$ The Gain is extremely sensitive to the error in winding geometry from an ideal helical shape thus the latter equation from Kraus leads to higher gain than best effort by a few dB using $$HPBW = k \lambda ^{\dfrac{3}{2}}$$ $\endgroup$ – Tony Stewart Sunnyskyguy EE75 Sep 19 at 15:26
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    $\begingroup$ Hello Abdullah, I replaced your equations in .png files with MathJax equations. Here's a quick introduction to MathJax. $\endgroup$ – rclocher3 Sep 29 at 16:21

They're the same, but the second one is better :)

It's more intuitive to separate the diameter and the spacing, and it's clearer that the whole thing is unitless.

Be aware that this only holds for a narrow range of diameters and spacings.

| improve this answer | |
  • $\begingroup$ They're supposed to be the same, and one of them is wrong. Compare the exponents of $\lambda$... $\endgroup$ – Marcus Müller Sep 18 at 20:13
  • $\begingroup$ Oh, yes. Let me scratch in my Klaus, he invented all of these approximations. $\endgroup$ – tomnexus Sep 18 at 21:40

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