How do I select a PCB laminate material for a circuit operating above 30 GHz?
Selecting High-Frequency PCB Laminates for mmWave Circuits
At frequencies above 30 GHz, the choice of PCB laminate becomes a defining factor in circuit performance. Conductor losses increase with the square root of frequency, and dielectric losses increase linearly, making low-loss substrates essential for any design with meaningful transmission line length.
Frequently Asked Questions
What is the best PCB laminate for 77 GHz automotive radar?
Rogers RO3003 and Isola Astra MT77 are popular choices, offering Df below 0.0017 at 77 GHz with good processability. These materials balance electrical performance with the volume manufacturing requirements of automotive applications.
Can I use FR-4 above 30 GHz?
Standard FR-4 is generally unsuitable above 10 GHz due to its high loss tangent (Df ~ 0.02) and variable dielectric constant. Some modified FR-4 variants exist for lower mmWave frequencies, but dedicated low-loss laminates are strongly recommended above 30 GHz.
How does substrate thickness affect mmWave circuit performance?
Thinner substrates (5-10 mil) reduce surface wave excitation and radiation losses at mmWave frequencies. However, thinner substrates also narrow the microstrip line width, increasing conductor loss. The optimal thickness balances these competing effects for your specific frequency and circuit topology.