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V2X — vehicle-to-everything — is an umbrella term spanning V2V (vehicle-to-vehicle), V2I (vehicle-to-infrastructure), V2P (vehicle-to-pedestrian), and V2N (vehicle-to-network) communication. From a PCB design standpoint, that breadth collapses into a more specific set of problems: RF antenna engineering at 5.9 GHz, integration into a tightly packed multi-radio module, and automotive-grade hardware qualification, all on the same board or module assembly. This guide focuses on the RF and antenna-board side of that problem, where the genuinely V2X-specific design decisions live, alongside the regulatory and architectural context needed to make sense of them.
For most of the last two decades, DSRC — built on IEEE 802.11p — was the only sanctioned technology in the US 5.9 GHz ITS band. That changed with the FCC’s November 2020 First Report and Order, which reallocated the lower 45 MHz of the band to unlicensed Wi-Fi and reserved only the upper 30 MHz for ITS use, explicitly citing DSRC’s limited deployment after two decades of reserved spectrum. The FCC’s November 2024 Second Report and Order finalized the technical rules for C-V2X in that remaining 30 MHz, took effect February 11, 2025, and set a firm transition deadline: existing DSRC licenses can be renewed, but not beyond December 14, 2026. Automakers are already targeting C-V2X integration for 2026 and 2027 model-year vehicles. Practically, that means any new V2X hardware design in the US market today should be built around C-V2X, not DSRC — a shift mirrored globally, with South Korea selecting C-V2X in late 2023 (DSRC switch-off targeted for June 2027) and China having built its national Internet of Vehicles strategy around C-V2X from the outset, with roadside units already deployed across more than 90 cities.
| Channel | Frequency Range | Use |
|---|---|---|
| Channel 177 (adjacent, not ITS) | 5.850–5.895 GHz | Unlicensed U-NII Wi-Fi |
| Channel 180 | 5.895–5.905 GHz | Legacy DSRC during transition |
| Upper block | 5.905–5.925 GHz | C-V2X (20 MHz) |
The detail that matters most for RF front-end design is that Channel 180 sits directly adjacent to unlicensed Wi-Fi spectrum, creating real out-of-band interference exposure for anything operating near that channel edge. That adjacency is exactly why filter selectivity in the RF front end — not just antenna gain or bandwidth — deserves dedicated attention in a V2X design, particularly for hardware still bridging the DSRC-to-C-V2X transition.
C-V2X operates over two distinct interfaces. PC5 is direct sidelink communication between devices — vehicle to vehicle, vehicle to roadside unit, vehicle to pedestrian device — without needing cellular network infrastructure, and it’s what carries the low-latency safety messaging V2X is built around. Uu is the conventional cellular uplink/downlink path through network infrastructure, used for V2N applications like cloud-delivered traffic information. Both interfaces are handled by a dedicated V2X baseband chipset, which connects to the antenna board through a controlled-impedance RF transmission line or coax run. Whether a design implements PC5-only or dual-mode PC5/Uu changes the rest of the board significantly, but it has limited bearing on the antenna and RF layout fundamentals that are this guide’s focus.
Most production V2X antennas share a rooftop housing with GNSS, cellular, Wi-Fi, and sometimes satellite radio or FM elements — the familiar “shark-fin” module. Published designs squeeze this multi-radio set into genuinely tight volumes, with some documented implementations as compact as roughly 90×15×30 mm. To fit that many radiating elements into so little space, some designs split the antenna assembly across two PCBs — a horizontal base substrate and a vertical radiating substrate — rather than trying to print every element onto one flat board.
This is the design challenge most specific to V2X antenna boards. GNSS reception in the L1 band (roughly 1559–1606 MHz) works with extremely low received signal power, while the V2X transmitter shares the same compact enclosure at comparatively high power — any leakage, harmonic energy, or out-of-band emission landing near the GNSS band can desense the receiver and degrade positioning accuracy that downstream ADAS functions may depend on. Published shark-fin antenna designs address this primarily at the antenna level: placing the GNSS element physically apart from the V2X and cellular elements, and shaping radiating structures (frequency-selective stubs are a common technique) so they deliberately avoid resonating in GNSS bands. Even well-isolated designs in the literature report isolation figures that vary by band pair — commonly better than 10–15 dB, but sometimes only 5–10 dB where two services directly overlap — with additional filtering added at the circuit level wherever antenna-level isolation alone can’t close the gap.
It’s worth being precise about material requirements here, because they’re easy to overstate. At 5.9 GHz, V2X sits at a far less demanding frequency than the 76–81 GHz automotive radar covered in our ADAS PCB design guide, and published multiband shark-fin antenna designs are commonly built on standard FR-4 — typically cited with a relative permittivity around 4.4 and loss tangent around 0.02 — which is entirely workable for most V2X link budgets. Designs pushing for maximum range, or packing multiple closely spaced radio elements where every dB of isolation margin matters, can step up to an enhanced low-loss FR-4 system, the same class of material compared in our FR408HR vs Megtron 6 guide, without taking on the cost or fabrication overhead of the PTFE or ceramic-filled laminates that 77 GHz radar genuinely requires.
Until C-V2X evolution pushes into mmWave bands — a future-facing consideration as 5G NR-V2X matures, not today’s reality — routing the antenna feed network on the surface layer is fine, provided a solid ground reference sits on the next layer down to set impedance and isolate board sections from each other, which matters directly for the multi-radio coexistence discussed above. A copper pour on the top layer is commonly used to form a coplanar waveguide feedline for the main antenna trace, giving controlled impedance (Z0) without needing a stripline construction. Keep coax connector placement close to each radiating element to minimize cable run length and the insertion loss that accrues before the signal even reaches free space; for non-line-of-sight coverage planning between vehicles and roadside units, free-space path loss still follows the standard relationship:
LFS (dB) = 20 × log10(d) + 20 × log10(f) + 32.44
where d is distance in kilometers and f is frequency in MHz — a useful sanity check when budgeting how much antenna gain and isolation margin a given deployment scenario actually needs.
V2X boards mounted inside a rooftop shark-fin module still need to meet the same qualification framework covered in our automotive PCB design guide — IPC-6012FA bare-board requirements, AEC-Q200-qualified passives, and an IATF 16949-aligned supply chain — with the added environmental load of a fully exposed rooftop location: UV exposure, wider ambient temperature extremes, and water-ingress protection that’s typically handled at the housing level but still benefits from conformal coating on the board itself.
NextPCB fabricates V2X and C-V2X RF antenna boards within our broader high-frequency PCB and automotive PCB capabilities, supporting both standard and enhanced low-loss FR-4 builds depending on your isolation and range requirements. Before fabrication, our HQDFM software can verify impedance and clearance specifications on your antenna board. Ready to move forward? Get started with our advanced PCB quote tool, or reach our engineering team through contact us for help with stackup or material selection.
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