Microwave PCB belongs to high-frequency PCB, also known as RF PCB. Mainly used in fields such as wireless communication, wireless networks, and satellite communication. With the development of technology, the demand for microwave PCB design continues to grow, and microwave PCBs are gradually entering other fields, becoming the main products in multiple fields such as national defense, aviation, and mobile networks. To produce microwave PCBs, the first step is to complete the microwave PCB design. During the design phase, it is necessary to select suitable high-frequency materials, such as starting with the specified frequency, Tg, DK, and DF values. This requires professional PCB layout design to complete this complex task.
The selection of high-frequency materials, Rogers series material, Taconic series material, etc., is the most well-known among the public. In addition, you can customize the corresponding materials according to the numerical requirements of your product.
Microwave PCB design
In most cases, PCB layouts containing RF and/or microwave circuits are difficult to design. Firstly, PCB designers need to understand that microwave signals are highly sensitive to noise. The possibility of causing ringing and reflection must be treated very carefully. Secondly, impedance matching is crucial for RF. Digital signals – even if they are very fast – have a certain tolerance. But for RF and microwave, the higher the frequency, the smaller the tolerance. Thirdly, the return loss must be minimized. This loss is caused by signal reflection or ringing. Return is the path used to return the current. At very high microwave frequencies, the return signal adopts an inductive path. The ground plane below the signal can provide this path well. At very high microwave frequencies, the return signal adopts an inductive path. The ground plane below the signal can provide this path well. The coupled signal flowing to the receiver constitutes forward crosstalk. Those moving toward the source constitute reverse crosstalk. Backward crosstalk is the sum of inductive coupling and capacitive coupling, while forward crosstalk is the difference between the two. Crosstalk is a major issue in high-frequency design. This is because it is proportional to the edge velocity of the active line.
Other factors are the proximity of the two lines and the distance they are parallel to each other. Therefore, the routing of high-speed signals should be as far as possible. Ideally, the distance from center to center should be at least four times the width of these signal traces. The distance between lines that are parallel to each other should also be kept to a limit. Other solutions include reducing the dielectric distance between the line and its reference plane or introducing a coplanar structure, where a grounding plane is inserted between the traces. Terminating the line at its characteristic impedance can also reduce crosstalk by up to 50%.
All wiring on the PCB does not require impedance control. Impedance control is only necessary when the total length of the wiring from the driver to the receiver is greater than 1/16 of the signal wavelength. 1/16 of the wavelength is called the critical length of the signal. When using RF circuits, designers need to consider the characteristics of the laminate, such as dissipation factor and dielectric constant (Dk) values and their variations. The dissipation factor of FR4 is higher than that of high-frequency laminates such as Rogers and Nelco. This means that the insertion loss is much higher when using FR4. These losses are also functions of frequency and will increase with increasing frequency. Secondly, the Dk value of FR4 can vary by up to 10%. This will change the impedance again. High-frequency laminates have more stable frequency characteristics.
When designing microwave PCBs, engineers need to consider various factors that have an impact on the design itself. Designing microwave PCBs is a very challenging task.
opcba.com has over 15-years practical experience in manufacturing microwave PCBs, and can produce your designs well. If you want to produce microwave PCBs, please feel free to contact us.