Hardware Guide

4 Circuit Design

Indicator

Description

Recommended Value

Input power

- -

Peak power >33 dBm

(2 W) in GSM system

Average power >23 dBm

in WCDMA&LTE systems

VSWR

- -

≤ 2:1

4.5.2 Impedance Design

For modules that do not have a RF connector, you need to route a RF cable to connect to

the antenna feeding point or connector. It is recommended to use a microstrip line. The

shorter the better. The insertion loss should be controlled less than 0.2 dB, and

impedance should be controlled within 50Ω.

In general, the impedance of the RF signal route is determined by the dielectric constant

of the material, the route width (W), the ground clearance (S) and the height of the

reference ground plane (H). The control of the characteristic impedance of the PCB

usually is implemented in two ways: microstrip route and coplanar waveguide. To

illustrate the design principles, the following figures show the structural designs of

microstrip route and coplanar waveguide when the impedance line is at 50Ω.

 Microstrip cable complete structure

Figure 28. Two-layer PCB microstrip line structure

 Coplanar waveguide complete structure