24.07.2018 Views

Practical_Antenna_Handbook_0071639586

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

474 P a r t V I : A n t e n n a s f o r O t h e r F r e q u e n c i e s<br />

Generator<br />

V<br />

Current<br />

Radiator<br />

V = c = 310 8 m/s<br />

Figure 20.20A Basic dipole antenna showing propagation.<br />

Figure 20.20B Basic dipole antenna.<br />

Directivity 0111057 FIG 18-20B<br />

The directivity of an antenna is a measure of its ability to concentrate RF energy in a<br />

subset of directions rather than in all (spherical) directions equally. Two methods for<br />

quantifying unidirectional antenna patterns are shown in Fig. 20.22. Figure 20.22A is a<br />

polar plot viewed from above, oriented such that the main lobe is centered on 0 degrees.<br />

The plot of Fig. 20.22B is a rectangular method for displaying the same information.<br />

Typical field patterns follow a (sin x)/x function or, for power, [(sin x)/x] 2 .

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!