24 GHz vs. 77 GHz Radar PCB Material Selection: What Changes at Millimeter Wave?

77 GHz radar is a high-frequency millimeter-wave sensing technology widely used in automotive ADAS and industrial detection systems. Compared with legacy 24 GHz radar, it offers higher resolution, a smaller antenna, and stronger performance in modern sensing applications.

For PCB designers, this shift is not just about frequency. It directly changes how the board must be designed, especially regarding material loss, stackup structure, routing behavior, and manufacturing tolerances.

That is why a PCB material strategy that works at 24 GHz is often not enough at 77 GHz. As radar moves deeper into the millimeter-wave range, material selection becomes a much more critical part of overall system performance.

This article explains how 24 GHz and 77 GHz radar designs differ, and what those differences mean for PCB material selection.

Quick Answer

If you only need the short version, here it is:

• 24 GHz radar usually offers greater design flexibility and more cost-performance trade-offs.
• 77 GHz radar demands tighter control over loss, dielectric stability, copper roughness, routing geometry, and stackup structure.
• At 77 GHz, the PCB is no longer just a support structure. It becomes part of the RF system itself.
• Good radar PCB material selection is not just about Dk and Df. It also involves copper profile, thickness control, phase consistency, environmental stability, and manufacturability.

24 GHz vs. 77 GHz Radar at a Glance

Typical use	Legacy radar, simpler short-range systems	Modern ADAS, corner radar, long-range radar, imaging radar
Bandwidth potential	Lower	Much higher
Range resolution	Lower	Higher
Antenna size	Larger	Smaller
PCB loss sensitivity	Moderate	High
Tolerance sensitivity	Lower	Much higher
Material demands	More flexible	Much stricter
Stackup complexity	Often simpler	Often more advanced or hybrid

What 77 GHz Radar Means for PCB Designers

Modern 77 GHz radar is not just a single RF path on a board. It is usually part of a dense, multi-channel, phase-sensitive system.

That matters because radar modules now support functions such as:

• adaptive cruise control
• automatic emergency braking
• blind-spot monitoring
• cross-traffic alert
• parking assistance
• high-resolution imaging radar

As radar systems become more advanced, the PCB must do more than just route signals. It must support:

• low-loss RF transmission
• stable phase behavior
• repeatable antenna performance
• tight dimensional control
• consistent multi-channel behavior

At 24 GHz, a design can often tolerate more electrical and manufacturing variation. At 77 GHz, that margin shrinks fast.

Why the Industry Moved from 24 GHz to 77 GHz

The move from 24 GHz to 77 GHz happened for good reasons.

Higher resolution

Wider available bandwidth allows radar to distinguish objects more precisely. That improves distance resolution and target separation.

Smaller antennas

A shorter wavelength means the antenna can be made much smaller for the same field of view and gain target.

Better suitability for modern ADAS

As automotive systems moved toward more advanced sensing, 77 GHz became the better fit for:

• long-range forward radar
• corner radar
• imaging radar
• higher angular resolution systems

Why 24 GHz and 77 GHz Do Not Use the Same Material Logic

This is where many articles tend to be too general.

A designer may assume that radar PCB material selection is just a matter of picking a “better” high-frequency laminate. But in reality, 24 GHz and 77 GHz often require different selection logic.

At 24 GHz

Material choice is often a balance of:

• acceptable RF loss
• manufacturing convenience
• cost control
• stable enough electrical behavior

For some shorter-path or lower-complexity designs, a more practical low-loss approach may be enough.

At 77 GHz

The focus shifts toward:

• lower insertion loss
• tighter phase consistency
• more stable dielectric behavior
• smoother copper surfaces
• thinner and better-controlled RF structures
• Higher manufacturing repeatability

In other words, 77 GHz is usually not just “more high frequency.”
It is a different design environment.

The Material Properties That Actually Matter

Many engineers start by looking at Dk and Df, which is correct, but incomplete.

Here are the properties that matter most.

1. Dielectric Constant (Dk)

Dk affects:

• transmission-line dimensions
• impedance
• antenna size
• electrical length
• phase behavior

At 77 GHz, Dk stability can matter as much as the nominal value itself. A material with a good published Dk number is not enough if that value shifts too much with temperature or frequency.

2. Loss Tangent (Df)

Df helps determine dielectric loss.

As frequency rises, dielectric loss becomes more important. At 77 GHz, even small differences in loss can affect:

• feed line efficiency
• receiver sensitivity
• signal integrity
• antenna system performance

That said, Df should not be evaluated alone. A material with low Df but poor manufacturing repeatability may still be the wrong choice.

3. Copper Roughness

This is one of the most overlooked variables in radar PCB design.

At 77 GHz, the condition of the conductor surface matters much more than many designers expect. Rougher copper increases conductor loss, especially in thin RF structures.

Copper roughness can influence:

• insertion loss
• phase consistency
• effective signal behavior at mmWave frequencies

This is one reason why two boards built on similar dielectric materials can still perform differently.

4. Thickness Control

Board thickness and dielectric thickness directly affect RF routing behavior.

At 77 GHz, small changes in dielectric thickness can shift impedance and phase more significantly than they would at lower frequencies.

Thickness control matters for:

• microstrip dimensions
• coplanar waveguide performance
• antenna feed networks
• Overall RF repeatability

5. Environmental Stability

Radar boards often operate in demanding environments.

For automotive and industrial radar, the PCB material may need to tolerate:

• wide temperature swings
• humidity exposure
• long service life
• Repeated thermal cycling

A material that performs well in the lab may not be the best choice in a harsh real-world environment.

6. Manufacturability

This is where many material comparisons fall short.

A radar PCB material is not just chosen for electrical performance. It also has to fit the real production process:

• lamination
• drilling
• plating
• registration control
• yield stability
• cost at scale

The best material on paper is not always the best material for actual production.

Why Stackup and Routing Matter as Much as the Material

Material selection cannot be separated from the routing structure.

At 77 GHz, the routing method becomes part of the selection decision.

Common routing structures include:

• Microstrip
• Stripline
• Grounded coplanar waveguide (GCPW)

For many 77 GHz radar boards, grounded coplanar waveguide is especially attractive because it provides better control in compact RF routing environments.

What stackup planning must consider

A good radar stackup should account for:

• signal layer location
• reference plane continuity
• dielectric thickness
• routing geometry
• antenna integration
• RF isolation
• digital and power section separation

Why hybrid stackups are common

Not every layer on a radar board needs the same material.

In many designs:

• The RF or antenna layers use a low-loss high-frequency laminate.
• The digital, control, or power layers use FR-4 or another more economical material.

This hybrid approach helps balance:

• RF performance
• manufacturability
• total board cost

That is often a better solution than trying to build the entire board on a premium RF laminate.

Material Selection by Use Case

Instead of asking for the single “best” radar PCB material, it is better to ask what the application actually needs.

Cost-sensitive 24 GHz radar modules

These designs may prioritize:

• manageable cost
• process compatibility
• acceptable RF performance
• lower manufacturing complexity

In these cases, the best solution may be a practical low-loss material strategy rather than the lowest-loss laminate available.

77 GHz corner radar

Corner radar typically pushes the design toward:

• smaller structures
• tighter tolerances
• better phase consistency
• improved routing control

Material choice becomes more demanding, especially when the design includes board-mounted antennas or multiple RF channels.

77 GHz long-range radar

Long-range radar generally requires stronger performance in:

• link budget
• signal consistency
• low-loss transmission
• high repeatability

This often justifies a more advanced material and stack-up approach.

77 / 79 GHz imaging radar

This is one of the most demanding use cases.

These designs may involve:

• MIMO architectures
• high channel counts
• tighter angular resolution goals
• stronger dependence on phase alignment and channel consistency

In this case, material behavior and stackup execution are both critical.

Industrial and traffic radar

77 GHz radar is not limited to automotive use.

It is also used in:

• traffic monitoring
• intersection sensing
• industrial motion detection
• mobile equipment detection

These applications can introduce additional requirements for environmental durability and long-term stability.

A Practical Material Selection Workflow

A more useful way to choose radar PCB materials is to follow a decision sequence.

Step 1: Define the application

Start with the real system target:

• automotive or industrial
• short-, mid-, or long-range
• standard radar or imaging radar
• board-mounted antenna or external antenna

Step 2: Define the operating band and bandwidth

Clarify whether the design is:

• 24 GHz
• 76–77 GHz
• 77–81 GHz

This affects both performance goals and PCB difficulty.

Step 3: Define the board architecture

Decide early whether the system will use:

• a single-board approach
• a separate antenna board
• a hybrid stackup
• a split RF and digital structure

Step 4: Choose routing geometry

Select the routing structure based on the stackup and frequency:

• microstrip
• stripline
• grounded coplanar waveguide

Step 5: Match material behavior to system needs

Now evaluate the material based on:

• Dk
• Df
• copper roughness
• thickness control
• stability over the environment
• manufacturing compatibility

Step 6: Check manufacturability before finalizing

Before committing to the material, confirm that the PCB fabricator can support:

• the required tolerances
• the required copper structure
• the required stackup
• the required yield expectations

This step prevents many costly redesigns.

Common Mistakes in 77 GHz Radar PCB Material Selection

These mistakes often appear in real projects.

1. Looking only at Dk and Df

Those values matter, but they are not enough.

2. Treating 24 GHz and 77 GHz the same way

A strategy that works at 24 GHz may fail at 77 GHz.

3. Ignoring copper roughness

At mmWave frequencies, the copper profile can significantly affect loss.

4. Choosing a material without considering the routing structure

Material and transmission-line geometry must work together.

5. Ignoring thickness and tolerance sensitivity

Small physical changes matter more at 77 GHz.

6. Focusing on lab performance only

Real-world automotive and industrial conditions can expose weaknesses that are not obvious in early prototypes.

7. Choosing by brand name alone

A well-known material family does not automatically mean the best fit for your radar design.

24 GHz vs. 77 GHz Material Selection Priorities

Cost flexibility	Higher priority	Still important, but less dominant
Low loss	Important	Critical
Dk stability	Important	Very important
Copper roughness control	Useful	Highly important
Stackup complexity	Moderate	Often high
Tolerance sensitivity	Moderate	High
Hybrid stackup value	Sometimes useful	Often very useful
Manufacturing repeatability	Important	Essential

FAQ

Final Takeaway

The move from 24 GHz to 77 GHz changes more than the radar frequency. It raises the demands on PCB materials, stackup design, routing control, and manufacturing consistency.

At 24 GHz, designers often have more room for compromise. At 77 GHz, small differences in loss, copper profile, dielectric stability, and board structure can have a much greater impact on performance.

That is why radar PCB material selection should never be based solely on laminate data. The right choice depends on how well the material, stackup, and routing strategy fit the actual radar architecture.

FastTurnPCB works with advanced RF and high-frequency PCB designs that require consideration of both electrical performance and manufacturability.