Design skills of RF PCB and microwave PCB

Today's electronic products are no longer like TVs and refrigerators in the 1970s, consumers only update them every ten years. Now, almost every member of every family is a consumer of electronic products, and with the development of technology, smart phones, tablet computers, cars, and TVs are constantly bringing a variety of new features that people can afford, people buy new products every year.

One of the common features of these electronic products is the use of wireless technology, which is extremely dependent on radio frequency (RF) circuits. Unfortunately, even the most confident designers are often hesitant to RF circuits because it brings huge design challenges and requires professional design and analysis tools. Because of this, for many years, the RF part of the PCB has been designed by independent designers with RF design expertise.

Why is it so difficult to design RF and microwave PCB designs?

There are many problems in the design process, and may have a serious impact on quality and productivity. For example, when embedding a designer's radio frequency circuit into the PCB of another designer, because they often use different design formats, the efficiency is bound to be greatly reduced. In addition, designers are often forced to make changes in the design to coordinate the use of RF circuits. Since the simulation is often carried out in the radio frequency circuit, rather than in the context of the entire PCB, the significant impact of the circuit board on the radio frequency circuit may be missed, and vice versa.

With the continuous increase of RF content, PCB designers and engineers realized that in order to improve productivity and product quality, it is best for them to solve RF design challenges in their own design tools. Unfortunately, most desktop PCB design tools cannot help them simplify this task.

For example, after modeling the circuit with a radio frequency simulator, once the required electrical performance is achieved, the simulator will generate the copper foil shape of the circuit (usually in DXF format) for importing into the PCB design tool. This process often brings some troubles to the designer, for example, the DXF file cannot be converted into a copper foil shape because it cannot be converted correctly. In this case, the designer needs to manually import the DXF file, which may cause human errors in the shape and size, which will lead to the failure of the radio frequency circuit.

The challenges faced by PCB designers or engineers when trying to design RF and microwave circuits are far more than the above. Fortunately, there are some small solutions in your design tools that can play an important role in resolving these challenges. Chinese PCBA manufacturer-SysPCB will introduce you to six tips to help you simplify any RF PCB design tasks and reduce work pressure!

1. Keep intact and precise RF shape

Some serious errors similar to those described above may cause the circuit performance to be poor or even fail to work. In order to minimize errors, simplify RF design tasks and increase productivity, PCB design tools can provide import control for complex copper foil shapes. For example, you can create a usable copper foil shape by controlling the level in the DXF file and re-mapping it to the level of the CAD electrical system (Figure 1).

Figure 1: If the design tool allows the user to control the DXF import process, it will help reduce human errors, for example, when the imported file cannot be converted into a copper foil shape due to high complexity.

2. Keep the corner shape

When designing copper foil shapes for radio frequency and microwave applications, an important aspect is the ability to create Gerber files with sharp corners. Excellent PCB design tools can simplify this process. For example, compared with 50mm circular aperture, drawing a shape with 50mm lines often make the design has a smaller radius. When the design tool creates a Gerber file, it can obtain sharp corners by correctly automatically converting the line width (Figure 2).

Figure 2: An effective PCB design tool will automatically consider the line type used to draw the shape to calculate the accurate line width and help you easily create sharp corners.

3. Automatically generate chamfered corners

Chamfers are often used in RF and microwave circuits to reduce the segmented discontinuity impedance between the supply line and the capacitor, thereby improving the frequency performance of the MMIC. The distance between the 90º corner and the chamfer is critical. Therefore, the designer needs to adopt an automatic method to specify the required chamfer ratio based on the design. If PCB design tools can automatically enforce the required chamfer ratio based on design rules, designers and engineers will benefit from it, saving time while improving design quality (Figure 3).

Figure 3: The function of setting chamfering rules can simplify the design process and save time.

4. Use automation to help arrange coplanar waveguides and channel waveguides

Coplanar waveguides and channel waveguides are also common in RF and microwave designs. When set up manually, this task can be time-consuming and error-prone. The designer needs to control the specific distance between the trace and the via, as well as the distance between one via and another via, to ensure that the circuit has the performance that meets the design requirements. Design tools can also help in this regard by providing via usage control and automatic via usage to reduce complexity and improve quality (Figure 4).

Figure 4: If PCB design tools can control the establishment of coplanar and waveguide vias, it will help significantly reduce design errors and shorten design time.

5. Use automated stitching vias

Another important aspect of RF design is to ensure the correct use of vias to shield specific areas. Although this task can be performed manually by the designer, the process is extremely time-consuming. If the PCB design tool can automate this process, it will shorten the design cycle time and ensure compliance with all your design rules. Using such tools, designers can specify the via mode to generate specific rules, and all the remaining work is completed by the PCB design tool.

6. Use design rules to ensure "design is right"

PCB design tools that support RF design usually allow multiple design rules to be set: the type of via used in different copper foil areas; the type of net that the via itself needs to be connected to; the distance to be maintained from the edge of the copper foil area to the via; the distance of a via to the next via; the type of via mode; and whether a Faraday cage can be created only by adding vias to the outer edge of the copper foil area (Figure 5).

Figure 5: Using PCB design tools that support RF design, you can set design rules for generating via patterns and automatically enforce these rules in your design, saving you time and ensuring compliance with all your design rules.

In conclusion

Today's designers and engineers are facing ever-increasing design challenges, so it is necessary to have a PCB design tool that can efficiently support RF and microwave design. Manually creating complex copper foil shapes, chamfers, and via patterns is a time-consuming and error-prone process. By using effective design tools to improve the ability to manipulate RF and microwave elements, designers can concentrate on implementing more functions and reducing device size while maintaining high product quality.