PCB Challenges for 5–6 GHz Radar Design

Summary

In this video, Zach Peterson from Altium Academy explores the design of FMCW radar systems in the 5-6 GHz range. He discusses the feasibility of using discrete components for radar signal chains, covering synthesizers, amplifiers, and antennas. Zach explains the importance of material choices like FR-4 and the challenges of using dense BGA packages, highlighting the necessity of HDI techniques for compact, high-frequency designs. The video offers practical insights on designing radar systems, selecting components, and optimizing PCB layouts, providing both technical details and advice for enthusiasts and professionals interested in RF design.

Takeaways

• 😀 Designing FMCW radar systems at five to six gigahertz is possible with discrete components, but it requires careful selection and configuration of components for amplification, signal processing, and antennas.
• 😀 Amplifying radar signals at high frequencies can introduce unwanted intermodulation products, which can affect signal clarity and tracking performance.
• 😀 FR-4 PCB material can be used for radar designs in the six gigahertz range, but low-loss variants are preferred for better performance at higher frequencies.
• 😀 The plating choice on PCBs (e.g., ENIG, immersion silver) impacts signal loss, but at six gigahertz, the differences are minor compared to cost variations.
• 😀 For high-frequency designs, the use of BGA (Ball Grid Array) packages is common, requiring precise via design and potentially using HDI (High-Density Interconnect) techniques.
• 😀 Fine-pitch components in BGA packages (such as 0.65mm pitch) necessitate the use of advanced routing techniques to ensure signal integrity without overcrowding the PCB.
• 😀 To manage space and prevent internal layer congestion, designers use blind vias on outer layers for routing coplanar waveguides that connect to antennas.
• 😀 As component density increases, blind and buried vias may be required, which in turn demands the use of thinner laminates to accommodate fine-pitch vias and complex routing.
• 😀 Understanding HDI stack-ups is critical when designing high-frequency PCBs, particularly when working with fine-pitch components and achieving optimal signal routing.
• 😀 Consulting with PCB fabricators is essential to ensure that designs meet the manufacturing capabilities and tolerances, especially when using advanced design techniques like HDI.

Q & A

What is the primary focus of the video discussed in the transcript?

The video focuses on how to design a frequency-modulated continuous wave (FMCW) radar system, specifically in the 5-6 GHz frequency range. It covers challenges, feasibility, and design considerations for such a system using discrete components and PCB design.

What was the origin of the question that prompted the video?

The question was asked by a viewer named Kah Kai, who reached out via LinkedIn. Kah Kai was interested in designing an FMCW radar system as a learning project and wanted to know if operating in the 5-6 GHz range was feasible with discrete components.

Is it feasible to design a radar system at 5-6 GHz using discrete components?

Yes, it is technically feasible to design a radar system operating at 5-6 GHz using discrete components, including signal synthesis, amplification, and antennas. However, the design will come with several challenges, particularly in terms of component selection and PCB design.

Why is FR-4 not the ideal material for high-frequency radar systems, and how does it perform at 5-6 GHz?

FR-4 is generally not recommended for high-frequency applications due to its higher losses. However, at the 5-6 GHz range, the losses in most FR-4 materials are tolerable, making it suitable for lower-cost designs. For critical high-frequency designs, low-loss FR-4 variants or advanced materials like Rogers might be preferred.

What are the common components in a radar system signal chain?

The signal chain of a radar system typically includes a synthesizer for signal generation, a power amplifier for signal amplification, antennas for broadcasting and receiving, low-noise amplifiers (LNA) for received signal amplification, a mixer for signal mixing, a band-pass filter, and an ADC for digitizing the received signal.

What role does the FPGA play in the radar system?

The FPGA (Field Programmable Gate Array) is typically used as the system host to process the received radar signals. It runs algorithms to calculate range and heading information for detected objects, essentially performing signal processing tasks that allow for object tracking.

How does the use of ENIG plating impact the performance of high-frequency radar circuits?

ENIG (Electroless Nickel Immersion Gold) plating introduces higher losses compared to other plating materials like immersion silver or HASL (Hot Air Solder Leveling). This can affect signal integrity at high frequencies like 5-6 GHz, but the impact is relatively small, typically around 0.3 dB per inch.

What antenna design considerations should be made when designing a radar system at 5-6 GHz?

At 5-6 GHz, antenna size becomes a challenge. For example, microstrip patch antennas at this frequency will be very large, making them impractical for an antenna array. Designers may need to explore alternative antenna designs or solutions like phased arrays with series-fed patch antennas to optimize performance and size.

What is the importance of using HDI (High-Density Interconnect) techniques in radar PCB design?

HDI techniques become important when dealing with fine-pitch components like BGAs (Ball Grid Arrays) and routing dense signal paths like coplanar waveguides for antennas. HDI techniques, such as using blind and buried vias, help manage the complexity of routing high-frequency signals in a limited space and prevent signal degradation.

How do power amplifiers and their intermodulation products affect radar performance?

Power amplifiers in radar systems are often run near their linear saturation limits to achieve higher amplification. This can lead to the generation of intermodulation products (sidebands), which can interfere with the desired signal. Proper filtering is required to minimize the effect of these unwanted signals and ensure accurate signal reception.