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Design Note DN033

Figure 5: Recommended Matching Circuit

Figure 5 shows a matching network to obtain an optimum performance of the antenna at the desired frequency. Usually, inductors are used for the matching and the method will be described in section 3.2.

When implemented on customer module, the position of the matching network and the antenna can be changed according to the shape of the module. However, the performance of the antenna will change due to the effect of size and geometry of PCB and ground plane. When used in combination with other modules etc., the performance of the antenna will be affected by the objects in vicinity of the antenna. Effects of plastic encapsulation in which the module is placed should also be considered.

Figure 6 and Figure 7 show some points to improve the performance of the antenna. As shown in Figure 6, the PCB trace between the matching network and the antenna should be as long as possible, and the gap between the antenna and the ground plane should be as wide as possible. Moreover, as shown in Figure 7, RF circuit with a longer ground plane tends to show a better performance; even an extended trace of ground plane with 1 mm width is effective. Figure 8 shows the design of the antenna board implemented on the CC- Antenna-DK [2].

Type of inductors will affect the performance of the antenna. Although low-Q type has a cost merit, high-Q type is advantageous for power gain, thus is recommended. The CC1101-Q1 EM is using high-Q type chip inductors for matching.

Figure 6: Recommended PCB Design

SWRA307A

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