# The HPBW of a helical antenna

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 ?

• One of them is wrong by an exponent in $\lambda$. Otherwise, with applying the basic calculus rules for division and roots, they are identical. – Marcus Müller Sep 18 at 20:13
• Hello Abdullah, and welcome to this site! :-) – Mike Waters Sep 18 at 21:28
• 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 $$HPBW = k \lambda ^{\dfrac{3}{2}}$$ – Tony Stewart Sunnyskyguy EE75 Sep 19 at 15:26
• Hello Abdullah, I replaced your equations in .png files with MathJax equations. Here's a quick introduction to MathJax. – rclocher3 Sep 29 at 16:21

• They're supposed to be the same, and one of them is wrong. Compare the exponents of $\lambda$... – Marcus Müller Sep 18 at 20:13