Page 288 - House of Maxell

268 ANTENNA BASICS

Here cos = and is the phase shift to be provided. Finally, we obtain

2
� +() 2
||
= (ℎ + ) − ||cos = (ℎ + ) − (5.112)

2
� +() 2
Step 3. The field intensity in the XZ-plane can be calculated as the fixed sum of fields emitted
by all radiators
(, ) = ∑ −(||cos− ) (5.113)
=−
Σ
Here cos = √ + .
2
2
⁄
Step 4. The results of numerical simulation for 2N + 1 = 201, = 0.1, = 10, ℎ =
31.42 are presented in Figure 5.6.9. Note that the intensity data are normalized to the peak (the
center of red sport). The RF focusing is not great as optical but quite satisfied and can be
improved by increasing the total number of array radiators.

Figure 5.6.9 Beam focusing illustration. Field intensity distribution in XZ-plane.

A significant advantage of such approach that the focal point position in space can be easily
changed electronically without the mechanical movement of any part of the array. The
described so-called near-field focusing, i.e. focusing the beam in the far field area of radiators,
is a well-known technique used for many applications. Note several of them:
Non-invasive medical therapy based on the limited non-thermal exposure of the human body
to low-level electromagnetic radiation. According to various types of research, it can help
healing cardiovascular disorders and wounds, treating diabetes, dermatitis, gastrointestinal
disorders, depression, relieving chronical pain, reducing the toxic side effects of chemotherapy,
etc. A quite the opposite effect is the “skin on fire.” Since the RF energy of higher level can
rapidly heat water molecules in the human skin, it causes intolerable pain and a burning
sensation. If so, the focusing microwave array can be used as a ‘gun’ to scatter large crowds of