RF and Antenna

In your circuit design, please add a π-matching network between the RF port (LNA_IN) and the antenna, for antenna matching purpose. A CLC network is preferred, as shown in Figure 5.9. The parameters of C8, L2, and C9 in the matching network are subject to the actual antenna and PCB layout.

Figure 5.9. CLC circuit for ESP32-C3 RF matching

The antenna can be selected based on product design and the overall cost. You can choose PCB onboard antenna, or an external antenna such as rod antenna, FPC antenna, ceramic antenna, 3D metal antenna, etc. Commonly-used antenna types are shown in Figure 5.10. Their installation methods and characteristics are provided in Table 5.3.

Figure 5.10. Commonly-used antenna types

Table 5.3. Installation methods and characteristics of commonly-used antenna types

Antenna TypeInstallation MethodsCharacteristics
PCB onboard antennaPCB onboardLow cost, medium gain, usually integrated on modules
Rod antennaExternal connection through I-PEX connectorHigh cost, high gain, less susceptible to interference, good omni-directional performance
FPC antennaAdhesive installationMedium cost, medium gain, can be adhered to the package, suitable for products with restricted structure
Ceramic antennaPCB mountingMedium cost, low gain, small size, suitable for small-sized modules
3D metal antennaPCB mountingHigh cost, high gain, less susceptible to interference, good omni-directional performance

The RF performance can be optimised through antenna matching. After matching, you can use CMW500, WT-200, IQ View, IQ Xel or other comprehensive RF testers to test RF performance of the ESP32-C3 core board. RF test includes conducted test and radiatied test.

Conducted test

In conducted tests, use a 50 Ω RF cable to connect the RF output port of the ESP32-C3 core board to the tester's RF port, and run the RF test software on the PC. Through the software, you can communicate with the ESP32-C3 core board and the tester, thus controlling the test. The conducted test set-up is shown in Figure 5.11.

Figure 5.11. Conducted test set-up for ESP32-C3 core board

Radiated test

When performing a radiated test, place the tester's antenna and ESP32-C3 board's antenna close to each other in the shield box. It is recommended that the distance between the two antennas be about 10 cm. Control the test through PC software. The radiated test set-up is shown in Figure 5.12.

Figure 5.12. Radiated test set-up for ESP32-C3 core board

For Wi-Fi RF performance test, the primary test parameters are target transmit power, EVM, receiver sensitivity, and frequency error, as shown in Table 5.4.

Table 5.4. Key parameters for Wi-Fi RF test

Working Mode and RateTarget TX Power (dBm)EVM (dB)Receiver Sensitivity (dBm)Frequency Error (ppm)
IEEE 802.11b, 1 Mbit/s21.0±2.0<-24.5<-98±25
IEEE 802.11g, 54 Mbit/s19.0±2.0<-27.5<-76.2±20
IEEE 802.11n, MCS7 HT2018.5±2.0<-29<-74.4±20
IEEE 802.11n, MCS7 HT4018.5±2.0<-28<-71.2±20

Figure 5.13 shows the spectral mask requirements in different working modes.

Figure 5.13. Spectral mask requirements in different working modes