# Relationship of antenna size to gain and directivity

This question is derived from certain answers I received for a previous question I posted.

Case : Let's say I have two GSM antennas of the exact same shape, design and material. The only difference is that one is 10 times larger in size than the other.

Question : What sort of impact would this have in the second antenna's directivity & gain?

• I'd check the data sheets for the detail. – Andy aka Oct 8 '14 at 14:05

For the simple case of a dipole antenna, the best performance (in terms of power transfer) will be obtained with half the wavelength of the signal to be transmitted or received. You also get local minima in the impedance for values of $k \lambda + \frac{\lambda}{2}$, and increasing lambda will mean more directionality on the main lobe(s) but also more side lobes. Shortly put, it can be worse and typically $\frac{\lambda}{2}$ is the best.