As automotive electronics continue to evolve toward higher levels of driver assistance and automated driving, radar has become an important sensing technology for modern vehicle safety systems. Advanced Driver Assistance Systems (ADAS) increasingly rely on radar, cameras, LiDAR, and other sensors to monitor the vehicle’s surroundings and provide information for functions such as blind-spot detection, adaptive cruise control, forward collision warning, and automatic emergency braking.

As radar operating frequencies increase, the performance requirements placed on the underlying PCB also become more demanding. The selection of PCB Materials can directly affect antenna efficiency, insertion loss, impedance stability, signal integrity, and long-term reliability.

For automotive radar applications operating in the 24 GHz, 77 GHz, and 79 GHz ranges, engineers need to carefully evaluate dielectric properties, copper characteristics, thermal stability, mechanical reliability, and manufacturing consistency.

The Role of Radar in Automotive ADAS

Radar uses electromagnetic waves to detect objects surrounding a vehicle. A radar transmitter generates a radio-frequency signal, which is radiated toward the environment through an antenna. When the signal encounters an object, part of the energy is reflected back toward the receiving antenna.

The radar system analyzes the received signal to determine information such as:

• Target distance
• Relative velocity
• Direction or angle
• Target characteristics
• Radar cross section (RCS)

The basic relationship between propagation time and target distance can be expressed as:

R = c × t / 2

where:

• R is the target distance
• c is the propagation velocity of the electromagnetic wave
• t is the round-trip propagation time

The factor of two is required because the signal travels from the radar to the target and then returns to the radar receiver.

In practical automotive radar systems, signal processing is considerably more sophisticated than this basic relationship. Modern radar systems combine timing, frequency, phase, Doppler information, antenna arrays, and advanced algorithms to estimate the position and movement of multiple targets.

FMCW Radar for Automotive Applications

Frequency-Modulated Continuous Wave (FMCW) radar is widely used in automotive sensing applications because it can provide information about multiple targets, including range and relative velocity, while supporting angle estimation when combined with multiple antenna channels.

Unlike a simple continuous-wave radar that primarily measures velocity through Doppler shift, FMCW radar transmits a frequency-varying waveform. The frequency difference between the transmitted and received signals can be processed to determine target range, while changes across successive measurements can provide velocity information.

The performance of an FMCW radar system depends on many parameters, including:

• Operating frequency
• Signal bandwidth
• Chirp configuration
• Antenna characteristics
• Receiver sensitivity
• Transmitter output power
• Phase noise
• Signal-processing algorithms
• PCB transmission-line performance

As radar frequencies increase, the RF interconnect between the transceiver and antenna becomes increasingly sensitive to PCB material and layout characteristics.

From 24 GHz to 77 GHz and 79 GHz Radar

24 GHz radar has been used extensively in automotive applications, particularly for short-range sensing and functions such as blind-spot monitoring.

However, higher-frequency radar bands have become increasingly important for modern automotive radar because they can support smaller antenna structures and, depending on the allocated bandwidth and system architecture, higher spatial resolution.

The 77 GHz and 79 GHz ranges are now particularly important for automotive radar development.

Different radar modules may be optimized for different sensing ranges and applications, including:

• Short-range radar (SRR)
• Medium-range radar
• Long-range radar (LRR)
• Blind-spot detection
• Lane-change assistance
• Adaptive cruise control
• Forward collision warning
• Automatic emergency braking
• Cross-traffic detection

The exact operating frequency, bandwidth, antenna architecture, and radar performance depend on regional regulations and the requirements of the specific vehicle platform.

                                                                       

Why PCB Material Matters at 77 GHz and 79 GHz

At millimeter-wave frequencies, the PCB is not simply a mechanical carrier for electronic components. The PCB itself becomes an important part of the RF system.

Transmission lines, antennas, vias, connectors, and dielectric structures all influence RF performance.

For this reason, selecting appropriate PCB Materials is critical.

Two important material parameters are dielectric constant (Dk) and dissipation factor (Df).

Dk influences the electromagnetic propagation characteristics and transmission-line impedance, while Df is closely associated with dielectric loss.

At 77 GHz and 79 GHz, even relatively small variations in material properties or physical dimensions can affect the performance of the RF channel.

Dielectric Constant and RF Performance

The dielectric constant, or Dk, describes the electrical polarization behavior of the dielectric material.

For PCB transmission lines, the effective dielectric constant influences propagation velocity and impedance.

A simplified relationship can be expressed as:

v ≈ c / √Dk_eff

where Dk_eff represents the effective dielectric constant experienced by the transmission line.

However, the effective Dk of an actual PCB structure depends on factors such as:

• Trace geometry
• Dielectric thickness
• Copper thickness
• Material construction
• Resin distribution
• Frequency
• Transmission-line configuration

Therefore, the Dk value published on a material datasheet should not automatically be treated as the exact value experienced by every RF structure on the PCB.

For automotive radar, stable and predictable dielectric behavior is particularly important because small changes can influence impedance, phase, and antenna characteristics.

Dissipation Factor and RF Signal Loss

The Dissipation Factor (Df) is another critical property for millimeter-wave PCB applications.

Df is associated with dielectric loss. As a high-frequency electromagnetic signal travels through the PCB, some of its energy is dissipated within the dielectric material.

Higher dielectric loss can increase signal attenuation and reduce the available RF power reaching the antenna or receiver.

For this reason, Low-Loss PCB Materials are commonly considered for demanding automotive radar designs.

However, selecting the lowest possible Df is not always the only objective. Automotive applications also require excellent thermal stability, mechanical reliability, moisture resistance, dimensional stability, and compatibility with high-volume manufacturing.

The material should therefore be selected based on the complete RF and automotive reliability requirements.

Conductor Loss and Copper Roughness

Dielectric loss is only one part of total RF transmission loss.

At millimeter-wave frequencies, conductor loss also becomes increasingly important because of the skin effect.

As frequency increases, RF current becomes concentrated closer to the conductor surface. Consequently, the physical condition of the copper surface can have a greater influence on conductor loss.

Copper roughness can increase the effective current path and contribute to additional attenuation.

For a 77 GHz Radar or 79 GHz Radar PCB, copper selection should therefore consider:

• Copper roughness
• Copper thickness
• Surface treatment
• Adhesion
• Etching characteristics
• Manufacturing tolerances
• RF loss performance

Smoother copper may provide electrical advantages in high-frequency applications, but copper adhesion and manufacturing reliability must also be maintained.

PCB Antenna Performance

The antenna is one of the most important elements of an automotive radar module.

A typical PCB Antenna may be integrated directly into the RF PCB or formed as part of a dedicated antenna structure.

Important antenna parameters include:

• Gain
• Radiation efficiency
• Radiation pattern
• Beam width
• Polarization
• Return loss
• Impedance matching
• Phase consistency

The PCB material influences these characteristics because the dielectric environment directly affects electromagnetic propagation around the antenna.

At 77 GHz and 79 GHz, manufacturing tolerances can become particularly important. Small variations in dielectric thickness, trace dimensions, copper geometry, or layer registration may affect antenna performance.

Therefore, antenna design and PCB manufacturing should be treated as a closely integrated process.

Designing RF Transmission Lines for Automotive Radar

The transmission line connecting the radar transceiver to the antenna must maintain controlled impedance and low insertion loss.

Depending on the design, RF transmission lines may use microstrip, stripline, grounded coplanar waveguide, or other controlled structures.

Designers should consider:

• Characteristic impedance
• Trace width
• Trace thickness
• Dielectric thickness
• Ground spacing
• Via placement
• Copper roughness
• RF connector transitions
• Bends and discontinuities

At millimeter-wave frequencies, small geometric changes can produce measurable electrical effects.

Therefore, RF routing should avoid unnecessary discontinuities and abrupt changes in transmission-line geometry.

Via Design at Millimeter-Wave Frequencies

Vias can introduce parasitic capacitance, inductance, and discontinuities into RF signal paths.

At lower frequencies, a small via-related discontinuity may have limited influence. At 77 GHz or 79 GHz, however, the same physical structure can have a more significant effect.

Designers should carefully evaluate:

• Via diameter
• Pad size
• Anti-pad dimensions
• Via spacing
• Via stubs
• Ground-via fences
• Layer transitions

Where possible, unnecessary RF layer transitions should be minimized.

Simulation is often the best way to evaluate whether a particular via structure meets the required RF performance.

Automotive Radar Reliability Requirements

Automotive radar modules operate under demanding environmental conditions.

Unlike laboratory RF equipment, vehicle electronics may experience:

• Wide temperature changes
• Thermal cycling
• Mechanical vibration
• Shock
• Humidity
• Moisture
• Contamination
• Long operating periods

The selected High-Frequency PCB material must therefore provide stable electrical performance while maintaining mechanical and thermal reliability.

Important material characteristics may include:

• Low and stable Dk
• Low Df
• Low moisture absorption
• Stable CTE
• High thermal reliability
• Dimensional stability
• Strong interlayer adhesion
• Compatibility with lead-free assembly

Electrical performance and reliability should be evaluated together rather than independently.

Material Selection for Different Radar Applications

Different automotive radar applications may have different PCB material requirements.

For example, a short-range radar module may have different loss, antenna, and range requirements from a long-range radar system.

Longer RF transmission paths generally make insertion loss more important. Highly integrated radar modules may also place the antenna, RF front end, processor, and power circuitry within a compact area.

Therefore, the material selection process should consider:

Frequency

Determine whether the design operates around 24 GHz, 77 GHz, 79 GHz, or another frequency range.

Bandwidth

Higher bandwidth can improve range resolution, but it also places greater demands on the RF channel.

Transmission Distance

Longer PCB RF paths can increase accumulated insertion loss.

Antenna Structure

The antenna geometry and dielectric environment must be considered together with the laminate.

Thermal Environment

The material must maintain stable performance throughout the vehicle’s operating temperature range.

Manufacturing Capability

The material must be compatible with the required PCB fabrication process and volume-production tolerances.

Integrating Radar PCB Design and Manufacturing

A successful automotive radar PCB cannot be designed solely from a schematic.

The RF layout, material selection, stackup, antenna, manufacturing process, and testing strategy should be developed together.

For example, if the PCB material is changed after the antenna has already been optimized, the antenna characteristics may also change.

Similarly, changes in dielectric thickness or copper geometry can affect impedance and RF loss.

Therefore, engineering teams should establish the material and stackup early in the development process.

Simulation and Validation

Because automotive radar operates at millimeter-wave frequencies, electromagnetic simulation can be an important part of the design process.

Engineers may use simulation to evaluate:

• Antenna radiation
• Return loss
• Insertion loss
• Impedance
• Coupling
• Via transitions
• Crosstalk
• Electromagnetic fields
• Thermal behavior

Simulation should be followed by physical validation.

Test coupons and prototype boards can be used to verify actual material properties, impedance, insertion loss, antenna performance, and manufacturing consistency.

Kingda’s Support for Automotive Radar PCB Applications

At Kingda, automotive RF and radar PCB projects can be evaluated from both electrical and manufacturing perspectives.

For demanding Automotive Radar PCB applications, material selection, stackup construction, controlled impedance, copper characteristics, antenna geometry, and manufacturing tolerances need to work together.

Kingda can support engineering discussions around PCB Materials, high-frequency stackups, RF routing, antenna structures, and manufacturing requirements to help customers develop reliable PCB solutions for advanced automotive electronics.

Conclusion

The rapid development of ADAS and automated driving technologies is increasing the demand for reliable automotive radar systems.

As radar moves toward higher-frequency millimeter-wave applications, the PCB becomes an increasingly important part of the RF system.

For 77 GHz Radar and 79 GHz Radar, material characteristics such as Dk, Df, copper roughness, dielectric thickness, and dimensional stability can significantly influence RF performance.

At the same time, PCB Antenna efficiency, controlled impedance, via design, manufacturing tolerances, and automotive reliability must be considered as part of the complete system.

Choosing appropriate Low-Loss PCB Materials is therefore only one part of the solution. The best results come from combining suitable materials with optimized stackup design, RF simulation, precise manufacturing, and comprehensive validation.

With the continued development of ADAS and vehicle automation, high-performance High-Frequency PCB technology will remain an important foundation for the next generation of automotive radar and sensing systems.