With the development of communication technology, hand-held radio frequency circuit technology is used more and more widely, such as wireless pager, mobile phone, wireless PDA, etc. The performance index of the radio frequency circuit directly affects the quality of the entire product. One of the biggest characteristics of these handheld products is miniaturization, which means that the density of components is very high, which makes the mutual interference between components (including SMD, SMC, bare chips, etc.) very prominent. If the EMI signal is not handled properly, the whole circuit system may not work properly. Therefore, how to prevent and suppress EMI and improve EMC has become a very important topic when designing RF circuit PCB. The performance indicators of the same circuit with different PCB design structures will vary greatly.

1. Selection of sheets

Substrates of printed circuit boards include organic and inorganic materials. The most important property in the substrate is the dielectric constant ε R. Dissipation factor (or dielectric loss) tan δ、 Thermal expansion coefficient CET and moisture absorption rate. among ε R affects circuit impedance and signal transmission rate. For high-frequency circuits, the dielectric constant tolerance is the most important factor to be considered, and the substrate with small dielectric constant tolerance should be selected.

2. PCB design process

Since the use of Protel99SE software is different from Protel98 and other software, the process of PCB design using Protel99SE software is briefly discussed.

① Because Protel99SE adopts the project database mode management, which is implicit under Windows99, a database file should be created first to manage the designed circuit schematic diagram and PCB layout.

② Schematic design. In order to realize network connection, all components used in the principle design must exist in the component library, otherwise, the required components should be made in SCHLIB and stored in the warehousing file. Then, just call the required components from the component library and connect them according to the designed circuit diagram.

③ After the schematic design is completed, a network table can be formed for PCB design.

④ PCB design. a. Determination of PCB shape and size. The shape and size of the PCB are determined according to the position of the designed PCB in the product, the size and shape of the space, and the fit with other components. At MECHANICAL