77GHz radar primarily utilises Frequency-Modulated Continuous Wave (FMCW) technology: by transmitting a linearly frequency-modulated ‘chirp signal’ and analysing the frequency and phase differences between the reflected echo and the transmitted signal, it extracts information on the target’s range, velocity and bearing. This operating principle places key demands on PCBs, and Rogers PCBs, thanks to their precise material design and process control, perfectly meet these requirements.
Key Requirements for 77GHz Radar PCBs and the Rogers PCB Solution
1.Low-loss transmission: ensuring detection range and resolution
With a wavelength of only approximately 3.9 mm, 77GHz signals fall within the high-frequency millimetre-wave band, where transmission loss is highly sensitive to the material used. The core advantage of Rogers PCBs lies in their extremely low dielectric loss factor (Df). Taking RO4830™ Plus as an example, its Df is just 0.0015 at 10 GHz, with insertion loss as low as 1.5 dB/inch at 77 GHz, far superior to standard FR-4 (Df ≈ 0.02, with losses more than 10 times higher than those of Rogers materials).
These low-loss characteristics ensure minimal energy attenuation during long-distance transmission of millimetre-wave signals, enabling the radar to achieve an ultra-long detection range of 250 metres and supporting the high spatial resolution of 0.0375 metres provided by the 4 GHz bandwidth, thereby accurately distinguishing nearby targets.
2.Stable Dk characteristics: enabling precise impedance control
77 GHz radar requires extremely high precision in impedance control, typically needing to be maintained within a tolerance of ±3% to ±5%. Sudden changes in impedance can cause signal reflection, distorting the echo and affecting target identification. Rogers PCBs exhibit excellent temperature stability in their dielectric constant (Dk): for example, the temperature coefficient of Dk (TCDk) for RO3003™ is just -3 ppm/°C.
This ensures minimal Dk fluctuation within the automotive operating environment of -50°C to 150°C, guaranteeing impedance consistency. Furthermore, Rogers offers a selection of PTFE-based materials (such as RT/Duroid 5880, Dk=2.20) and ceramic-filled materials (such as RO4350B, Dk=3.48) to suit specific requirements, providing a stable impedance foundation for 50Ω RF transmission lines and preventing signal reflection and crosstalk.
3.Wide-Temperature Reliability: Adapting to Complex Automotive Environments
In-vehicle radar systems must be exposed to extreme temperature and humidity conditions ranging from -40°C to +125°C for extended periods, whilst withstanding mechanical stresses such as vibration and shock. Rogers PCBs utilise high-temperature-resistant resin systems (such as RO4830™ Plus, with a Tg of up to 285°C), ensuring no defects such as delamination or copper foil peeling occur during high-temperature reflow soldering or long-term operation.
Furthermore, their low moisture absorption rate (≤0.02%) effectively prevents a decline in insulation performance caused by moisture ingress. Combined with excellent resistance to CAF (Conductive Anodic Fibre), this ensures the radar operates stably over the long term in harsh environments, meeting the high reliability standards required for automotive applications.
Core Applications of Rogers PCBs in 77GHz Radar
1.Antenna Array Substrates: Determining Radar Detection Range
PTFE-based high-frequency materials (e.g. RO4350B, RT/Duroid 5880): Suitable for medium- to long-range radar, these materials maximise antenna gain and extend detection range thanks to their extremely low Df and stable Dk. They also support the precise layout of MIMO (Multiple-Input Multiple-Output) antenna arrays, thereby enhancing angular resolution.
Ceramic-filled thermosetting materials (e.g. RO4830™ Plus): Optimised specifically for 76–81 GHz corner radars, these materials feature a glass-fibre-free structure, thereby avoiding the ‘glass weave effect’ common in the millimetre-wave band. They are also compatible with standard FR-4 processes, striking an excellent balance between performance and cost, and have become the mainstream choice for mass-produced corner radars.
2.Radio Frequency (RF) Circuit Boards: Ensuring Signal Integrity
The RF circuitry of 77 GHz radars comprises core components such as transmitters, receivers and mixers, requiring low-noise, low-distortion signal processing. Rogers PCBs utilise low-profile copper foil (LoPro, Rz ≤ 0.5 μm) to reduce conductor loss and the skin effect, thereby minimising energy loss during signal transmission. At the same time, their superior shielding performance effectively suppresses electromagnetic interference (EMI), preventing interference between RF signals and in-vehicle entertainment systems, engine controllers and other equipment, thereby ensuring that the radar remains unaffected by noise when receiving weak echo signals.
3.Mixed-Signal PCBs: Integrating RF and Digital Circuits
77GHz radar systems integrate RF circuits with high-speed digital processing circuits. Rogers PCBs support high-frequency hybrid lamination processes, combining Rogers high-frequency materials with conventional FR-4 materials: the outer layers use Rogers materials to handle RF signals, whilst the inner layers use FR-4 to process digital signals. This approach not only reduces overall costs but also achieves efficient signal transmission through precise interlayer alignment. This hybrid structure meets the dual requirements of ‘high-frequency, low-loss’ and ‘high-density integration’, driving the development of radar modules towards miniaturisation and weight reduction.
Key Process Considerations and Selection Strategies for Rogers PCBs
1.Precise Material Selection: Matching Radar Applications
| Material type | Key features | Suitable scenarios |
| RO4350B | Dk = 3.48 ± 0.05, Df = 0.0037, low loss | Medium-to-long-range 77 GHz radar, balancing performance and cost |
| RT/duroid 5880 | Dk=2.20, Df=0.0009, ultra-low loss | High-end 77GHz radar, delivering the ultimate in signal integrity |
| RO4830™ Plus | Dk=3.03, Df=0.0015, no glass cloth | 77GHz corner radar: a cost-effective mass-production solution from Rogers Corp |
| RO3003G2 | Dk = 3.07, Df = 0.0011, excellent thermal stability | 77GHz automotive radar, reliable operation across a wide temperature range |
2.Precision Process Control: Overcoming High-Frequency Manufacturing Challenges
Impedance Control: A high-precision impedance tolerance of ±3% is employed, with precise control of dielectric thickness, copper foil thickness and trace width to prevent signal reflection. Grounded coplanar waveguide (GCPW) structures are prioritised for high-frequency transmission lines to enhance shielding effectiveness and reduce radiation loss.
Via Design: Back-drilling technology is employed to remove stubs, thereby preventing signal interference; via diameters are ≤ 0.2 mm, with spacing controlled within λ/10 (where λ is the wavelength of the 77 GHz signal), ensuring signal transmission consistency.
Surface treatment: Give priority to electroless silver or gold plating (ENIG) processes. Electroless silver offers excellent electrical conductivity and low Df, making it suitable for high-frequency signal transmission; electroless gold provides long-term oxidation resistance and superior soldering reliability, and can be selected based on the operating environment.
3.Design Optimisation Strategies: Maximising Performance Potential
Selection of low-profile copper foil: Use VLP (very low profile) copper foil throughout to avoid signal loss caused by surface roughness, whilst enhancing circuit resolution to accommodate fine-line designs.
Thermal Stress Optimisation: Rogers materials exhibit excellent thermal expansion coefficient (CTE) matching with copper foil, reducing warpage after multilayer lamination. Rational layout of heat dissipation vias, combined with high thermal conductivity substrates (e.g., RO4350B with a thermal conductivity of 0.6 W/m·K), reduces temperature rise during radar operation and ensures long-term stability.
Electromagnetic Compatibility Design: An isolation ground plane is established between the RF and digital circuits, and a ‘gourd-shaped’ ground via array is employed to suppress crosstalk, ensuring the 77 GHz radar operates reliably within complex in-vehicle electromagnetic environments.
Rogers PCBs Empowering the Future of 77GHz Radar
Upgraded Ultra-Low-Loss Materials: Rogers is developing a new PTFE-based material with a Df of ≤ 0.0005 to further reduce signal loss at 77GHz, enabling detection over ultra-long distances of more than 300 metres and supporting high-speed autonomous driving scenarios.
Breakthroughs in Integrated Manufacturing Processes: By combining Antenna-in-Package (AiP) technology, the antenna and RF circuits are integrated onto a single Rogers PCB. This reduces the size of the radar module and lowers costs, driving the widespread adoption of 77GHz radar towards low-cost, highly integrated solutions and accelerating safety upgrades for intelligent driving.
With its low loss, stable Dk and reliability across a wide temperature range, Rogers PCB fully meets the core requirements of 77GHz radar systems in terms of signal transmission, impedance control and in-vehicle reliability, providing crucial support for the performance realisation and mass production of millimetre-wave radar.
