Design Note DN033
Selection of Antenna Matching Components for Optimized Performance
The method of selecting the inductor value for the matching network is described in more detail in this section; refer to Figure 5 and Figure 9.
Figure 9: Relation Between CC1101-Q1 EM and Recommended Matching Circuit
The adjustment of the antenna can be conducted with the help of a network analyzer. Connect a coaxial cable to the feed point and measure VSWR with a network analyzer. Perform the adjustment to decrease VSWR at the desired frequency.
Method hereafter should be used to select values for the inductors of the matching network, based on measured VSWR data. As shown in Figure 10, inductors in the matching network play different roles clearly in the adjustment. In detail, L1, L2 affect resonance frequency as shown in Figure 10, while L3 affects impedance. Thus the following steps could be taken for adjustment:
Select values for L1 and L2 to tune the resonance frequency to the desired frequency.
Select value for L3 to decrease VSWR to a minimum value.
First, implement inductors with values for desired frequency as described in Section 4.1 and measure VSWR. If the resonance frequency is higher than desired, select a larger value for L1 or L2. On the contrary, if the resonance frequency is lower than desired, select a smaller value for L1 or L2. As a result, VSWR shows a minimum at the desired frequency. However, If VSWR at the desired frequency is not sufficiently small (around 1.5), alter the value of L3 to optimize impedance.
Figure 10: Functions of Inductors
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