Free Trials

Download a free trial to find out which Altium software best suits your needs

How to Buy

Contact your local sales office to get started on improving your design environment


Download the latest in PCB design and EDA software

  • Altium Designer

    Complete Environment for Schematic + Layout

  • CircuitStudio

    Entry Level, Professional PCB Design Tool

  • CircuitMaker

    Community Based PCB Design Tool


    Agile PCB Design For Teams

  • Altium 365

    Connecting PCB Design to the Manufacturing Floor

  • Altium Concord Pro

    Complete Solution for Library Management

  • Octopart

    Extensive, Easy-to-Use Component Database

  • PDN Analyzer

    Natural and Effortless Power Distribution Network Analysis

  • See All Extensions

    World-Renowned Technology for Embedded Systems Development

  • Live Courses

    Learn best practices with instructional training available worldwide

  • On-Demand Courses

    Gain comprehensive knowledge without leaving your home or office

  • Altium 365 Viewer

    View & Share electronic designs in your browser

  • Altium Designer 20

    The most powerful, modern and easy-to-use PCB design tool for professional use


    Annual PCB Design Summit

    • Forum

      Where Altium users and enthusiasts can interact with each other

    • Blog

      Our blog about things that interest us and hopefully you too

    • Ideas

      Submit ideas and vote for new features you want in Altium tools

    • Bug Crunch

      Help make the software better by submitting bugs and voting on what's important

    • Wall

      A stream of events on AltiumLive you follow by participating in or subscribing to

    • Beta Program

      Information about participating in our Beta program and getting early access to Altium tools

    All Resources

    Explore the latest content from blog posts to social media and technical white papers gathered together for your convenience


    Take a look at what download options are available to best suit your needs

    How to Buy

    Contact your local sales office to get started improving your design environment

    • Documentation

      The documentation area is where you can find extensive, versioned information about our software online, for free.

    • Training & Events

      View the schedule and register for training events all around the world and online

    • Design Content

      Browse our vast library of free design content including components, templates and reference designs

    • Webinars

      Attend a live webinar online or get instant access to our on demand series of webinars

    • Support

      Get your questions answered with our variety of direct support and self-service options

    • Technical Papers

      Stay up to date with the latest technology and industry trends with our complete collection of technical white papers.

    • Video Library

      Quick and to-the-point video tutorials to get you started with Altium Designer

    77 GHz Radar for Automotive PCBs: Routing and Signal Integrity

    Zachariah Peterson
    |  September 5, 2019

    77 GHz radar system for an autonomous vehicle

    Technology moves quickly these days, and automotive radar has transferred from primarily operating near 24 GHz to 77 GHz shortly after its introduction into new vehicles for object detection. Recent regulation changes have allowed the transition to 77 GHz, which provides a number of benefits. Shorter wavelengths facilitate wider bandwidths, and provide better resolution, smaller device form factors, and longer range. This band just happens to fall between two absorption bands for diatomic oxygen, while the 24 GHz band overlaps with an absorption band in water.

    The use of higher frequencies creates a range of design, simulation, and testing challenges for 77 GHz radar modules. In addition to the design of radar modules themselves, device layout, integration into smaller form factors, and integration into the larger ecosystem within a vehicle are all design challenges on the long road to fully-autonomous vehicles.

    Long-Range vs. Short-Range 77 GHz Radar

    As we described in a previous post, chirped GHz pulses are used to discriminate between multiple targets within a radar system’s field of view. The use of chirped pulses provides velocity and distance detection of multiple targets by measuring the Doppler shift and beat frequency with respect a signal from a reference oscillator. The use of a phased array antenna (3 Tx and 4 Rx SFPAs) provides directional emission, allowing angle-of-approach to be determined alongside the two aforementioned quantities.

    Antenna array geometry used in 77 GHz radar

    Antenna array geometry used in 77 GHz radar for automotive applications

    The chirp length (measured as a frequency range) is the primary determinant of the applicability of a given radar system. Long-range radar (LRR) uses 1 GHz linear chirped pulses (76 to 77 GHz), which short-range radar (SRR) uses 4 GHz linear chirped pulses (77 to 81 GHz). The frequency spread in these FMCW pulses has the potential to create some signal integrity and power transfer problems that can be solved with the right routing and layout scheme.

    The rate at which the pulse is chirped (i.e., the amount of time required to sweep over the entire chirp range) defines the length of the radar pulse. In forming a radar pulse, a technique very similar to mode locking in lasers is used to actively define the pulse length. Different frequency components are actively delayed by different amounts in the transmitter side.

    The pulse length is one important factor that affects the sensitivity and useful range of a system. Using shorter pulses provides higher resolution as smaller beat frequencies and Doppler shifts can be reliably detected, but these shorter pulses are more difficult to amplify as the amplifier must have broader bandwidth. This is particularly important on the receiver side of a 77 GHz radar module as the limited capability of an amplifier to properly amplify a shorter pulse skews measurement results. If the measurement determined for a driverless is incorrect, this could result in a serious accident. This particular issue needs to be addressed by RF circuit designers; working with some basic analog simulation techniques can help significantly in this area.

    Routing in 77 GHz Radar Systems

    If you’re in the business of designing SRR or LRR modules, there are a number of important points to consider. These points include a routing and grounding strategy, as well as a basic layout strategy to ensure signal integrity as the module operates. The corresponding grounding strategy is also important in these systems, and the grounding strategy may need to be adjusted to accommodate integration of a 77 GHz radar module into a larger system.

    The trace geometry you will have a major effect on signal integrity as you route the analog output from the transceiver module to your antenna module. If you look at data on insertion loss in different trace configurations, you’ll find that traditional microstrip traces start to have much higher losses than grounded coplanar waveguides at frequencies between ~30 and ~45 GHz. 

    Electronic road and autonomous car

    Comparison between insertion loss in microstrips and grounded coplanar waveguide from Rogers Corp.

    In order to keep form factors small, the Tx and Rx antennas are normally placed on the same board. This is where some isolation is required to ensure the Tx side does not self-jam the Rx side while emitting a radar pulse. Grounded coplanar waveguides provide excellent isolation without requiring extra shielding methods. Because current tends to be confined at the edge of the central conductor in a grounded coplanar waveguide, this helps suppress intermodulation products and harmonic that can arise in other structures with rough conductors.

    These aspects make grounded coplanar waveguide ideal for routing traces in 77 GHz radar systems for vehicles, in addition to plenty of other applications. Note that you’ll need to optimize these waveguides to work at 77 GHz, which will be a function of your board thickness (see below).

    Single or Multiple Boards?

    In general, boards for 77 GHz radar are very small, and the use of grounded coplanar waveguides can prevent inclusion of a transceiver module on the board, depending on its size. If the transceiver appears on the same board as the antenna array, the RF ground plane should span below the transceiver and run just past the edge of your antennas. If the transceiver and other circuitry take up too much space, then they can be placed on their own board.

    This is actually done in some commercially available 77 GHz radar systems. The board with the antennas is placed on a ceramic or high frequency laminate (e.g., Isola or Rogers substrates), while the transceiver and other signal conditioning and processing circuitry are placed on FR4 or similar substrate. As the operating wavelength for the 77 GHz radar signal will only be about 4 mm in free space (~1 mm in FR4), your layer thickness should be as thin as possible (ideally, between one-eighth and one-quarter wavelength) in order to suppress resonance between conductive elements in different layers.

    At this point, you will need to figure out the best way to connect such a high frequency line to the antenna module. Your interconnect length needs to be as short as possible, although at these frequencies your interconnects will behave as transmission lines. This requires proper termination at each end of the interconnect, and at least one return path should be routed through the conductor to provide a return path for high frequency signals.

    Any 77 GHz radar design team needs the best advanced RF PCB design software with a full set of layout and simulation features for any application. Altium Designer gives you all these important design tools and more in a single program. Now you can download a free trial of Altium Designer and learn more about the industry’s best layout, simulation, and production planning tools. Talk to an Altium expert today to learn more.

    About Author

    About Author

    Zachariah Peterson has an extensive technical background in academia and industry. Prior to working in the PCB industry, he taught at Portland State University. He conducted his Physics M.S. research on chemisorptive gas sensors and his Applied Physics Ph.D. research on random laser theory and stability.His background in scientific research spans topics in nanoparticle lasers, electronic and optoelectronic semiconductor devices, environmental systems, and financial analytics. His work has been published in several peer-reviewed journals and conference proceedings, and he has written hundreds of technical blogs on PCB design for a number of companies. Zachariah works with other companies in the PCB industry providing design and research services. He is a member of IEEE Photonics Society and the American Physical Society.

    most recent articles

    Back to Home