AN91445 datasheet(21/33 Pages) RAMTRON

21 / 33 page

Antenna Design Guide

www.cypress.com

Document No. 001-91445 Rev. *B

Figure 26. Effect of Plastic Casing

Both Figure 25 and Figure 26 reveal some important observations:

 The resonant frequency shifts to a lower frequency when the antenna is placed near the plastic casing.

 The shift in resonant frequency is observed to be about 100 MHz to 200 MHz. The antenna must be tuned again

to bring it to the desired band. For antenna tuning, see Guidelines for Enclosure and Ground Plane.

In conclusion, increasing the ground plane size and plastic casing tends to decrease the resonant frequency of the

antenna by approximately 100 MHz to 200 MHz.

Guidelines for Enclosure and Ground Plane

 Ensure that there is no component, mounting screw, or ground plane near the tip of the antenna or length of the

antenna.

 The battery cable or mic cable should not cross the antenna trace on the PCB on the same side of the antenna.

 The antenna should not be covered by a metallic enclosure completely. If the product has a metallic casing or a

shield, the casing should not cover the antenna. No metal is allowed in the antenna near-field.

 The orientation of the antenna should be in line with the final product orientation so that the radiation is

maximized in the desired direction.

AN91445 Datasheet(PDF) 21 Page - Ramtron International Corporation