The antenna described in this document is a PCB meander monopole that users can configure by changing the BOM to operate as a single-band antenna or dual-band antenna. The resonance is set by the antenna PCB trace element and the antenna matching components. This allows the antenna to cover a wideband range with one antenna pattern design. The impedance of this antenna depends on the mode used. Referring to Figure 1-1, if the length of L4 is kept as shown, this is beneficial for operation around 433–510 MHz. If L4 is shortened to half the length (19.0 mm), this is beneficial when operating at 868–930 MHz.

The antenna layout is positioned on the top and bottom layer of the board as can be seen in Figure 1-1; this enables a lower resistive loss and gives a slightly wider bandwidth compared to a single-sided layout solution. With a single-sided layout; the area underneath the antenna can not be used for any other routing so it is more useful to utilize this area to optimize the antenna’s performance.

To obtain optimum performance, it is important to make an exact copy of the antenna dimensions. The antenna was implemented on a 1.6-mm thick FR4 substrate. Since there is no ground plane beneath the antenna, the PCB thickness is not critical. If a different thickness is used then it could be necessary to change the matching network to obtain optimum performance.

One approach to implement the antenna in a PCB CAD tool is to import the antenna layout from a Gerber file. Refer to files included in the LAUNCHXL-CC1352P-4 Reference Design.

If the antenna is implemented on a PCB that is wider than the antenna it is important to avoid placing components or having a ground plane close to each side of the antenna. If the CAD tool being used does not support import of Gerber files, Figure 1-1 and Table 1-1 can be used.

Figure 1-1 LAUNCHXL-CC1352P-4

The last antenna segment's optimum length will always be dependent on the geometry of the ground plane. For ground plane sizes smaller than the LAUNCHXL-CC1352P-4 (less than a quarterwave), the optimum length of the last segment could be increased or the antenna match re-calculated for the new ground plane size.

TI advises users to include an antenna matching network in order to tune and reduce the mismatch losses of the antenna. The geometry of the ground plane affects the impedance of the antenna. The antenna matching network can be used to compensate for detuning caused by encapsulation and other objects in close vicinity of the antenna. The type of antenna matching network depends on the mode of the antenna.

Recommend to use a pi-matching network for single-band mode at the feed point of the antenna. For further information on impedance matching and impedance measurements, see AN058. However, the antenna which is the subject of this app note is a dual-band antenna, designed to simultaneously support 433, 470–510, or 868/915/920-MHz (low-band) and 2.4-GHz (high-band) bands. Therefore, the pi-match is not a recommended solution and instead a LC, CL match network as shown in Figure 1-2 is recommended. This is also the matching network implemented on the LAUNCHXL-CC1352P-4 which is used for testing in this application note.

The LC (Z60 and Z61) part matches the high-band and CL (Z62 and Z63) matches the low-band.

For single-band operations, no 2.4-GHz resonance, Z60 can be replaced with 0 ohm and Z61 left as DNM. Z62 and Z63 can be both an inductor or capacitor in order to match the impedance to 50 ohm.

Figure 1-2 LC, CL Match Network for Dual-Band Operations.