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A Design Guide for Radio Frequency (RF) and Microwave PCB Assembly

 Jun 29, 2021

RF and microwave PCBs

Radio Frequency (RF) and Microwave PCBs are popular types of high-frequency PCBs. These PCBs are extensively used in embedded electronic systems and they have been an integral part of electronic circuitry for defense and aerospace industries. The RF and microwave PCBs can work efficiently in high-frequencies. However, their operational capabilities are heavily dependent on the design efficiency of these PCBs. Consideration of material, electronic circuitry, etc requires meticulous attention and application of advanced technologies during the design of RF and microwave PCB assemblies. That is why this post offers a few guidelines to enhance the quality of RF and microwave PCB designs.

RF and Microwave PCBs

Before getting into design guidelines, it is essential to understand the basics of RF and Microwave PCBs. Thus, here are a few basics of RF and microwave PCBs.

  • Radio Frequency (RF) and microwave PCBs consist of components that can sustain the transmission of high-frequency signals.
  • In industrial applications like aerospace electronic circuitry, electronic setups exposed to high noise and vibration, electronic equipment located in electromagnetic/radio frequencies/microwave frequencies, etc these PCBs are of great significance.
  • These PCBs can sustain wave frequencies between 3 kHz and 300 GHz. The frequency range is categorized into the following subcategories.
    • Low-Frequency Signals: Signals up to 50 MHz frequencies fall under this category.
    • RF Signals: Radio frequency signals between 50 MHz and 1 GHz frequencies fall under this category.
    • Microwave Signals: High-frequency microwave signals between 1 GHz to 30GHz frequencies fall under this category.

Note: These PCBs can be exposed to analog or digital signals.

To design and fabricate the high-capacity PCBs that can sustain the above-mentioned range of wave frequencies, consideration of several factors is essential. Let us discuss a few guidelines to design RF and microwave PCBs.

Guidelines to Enhance Design of RF and Microwave PCBs

The following practices can enhance the design efficiency of RF and microwave PCBs.

  • Multilayer Layout: The multilayer construction of PCBs is an ideal solution for the distribution of stress developed due to exposure to high frequencies. Having multiple layers with the topmost layer being a power layer can enhance the sustainability of the RF and microwave PCBs.
  • Reduction of Noise Exposure: High-capacity PCBs are sensitive to noise. Being utilized in harsh industrial applications, these PCBs may be exposed to different types of noises like white noise, band-limited noise, thermal noise, avalanche noise, etc. To reduce the noise exposure of such PCBs, band pass filters can be integrated into PCB design. These filters mitigate the noise by filtering the noise based on specified frequencies.
  • Components Distancing: Direct interaction between low-level analog parts, RF components, and digital components, etc should be avoided. They must be distanced on calculated scales. This can reduce the catastrophic problems in these PCBs.
  • Impedance Control: The impedance control and management of RF and microwave PCBs are essential to design considerations. These PCBs are tolerant to the impedance to some extent, however, as the frequency increases the tolerance to impedance drops. To maintain impedance balance, the following practice is helpful. Reduce skin effect loss by gold plating the PCB surface. This reduces impedance and electronic movement causing skin effect loss.
  • Reduction of Return Losses: Return losses are caused due to signal reflection on the PCB surfaces. To reduce the return losses, the surface uniformity from the driver to the receiver should be reduced. If it is not ensured, the ringing noises may be generated in the PCBs.
  • Reduce Crosstalk: Crosstalk occurs when unintended energy transfer between two conductors takes place. To prevent crosstalk, the following practices can be adopted. Separate signals, Minimize the number of parallel lines, Reduce dielectric spacing, Adopt co-planar/multilayer structure, Terminate the open electric lines
  • Laminate and Substrate Properties: Select the laminate material such as FR4, for high sustainability. The substrate material should contain high relative permeability.

Considering all the above-mentioned factors can help in enhancing the design efficiency of RF and microwave PCBs. However, while sourcing the PCB fabrication services, the contract PCB manufacturer should follow these guidelines. That is why you should source these services from trusted manufacturers like Accelerated Assemblies. The offer PCBs certified by Quality Assurance Systems (QAS) International.

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