Wireless communication board for smart-home hubs: routing RF on the host PCB, coaxial antenna connectors and isolating two 2.4 GHz radios on one board
The host circuit board that carries the radios of a smart-home hub or controller · 50 Ω lines and an unbroken ground plane from radio to connector, shield cans for 20 dBm paths, U.FL connectors rated for 30 matings, and the 45 dB that a +30 dBm Wi-Fi transmitter needs from a Zigbee receiver on the same board
The board pictured is the kind found inside a smart-home hub or gateway: it carries a processor, a Wi-Fi radio and a Zigbee, Thread or Bluetooth radio side by side, each under its own shield can, with short coaxial pigtails to antennas on the enclosure. Certified radio modules take care of what happens inside their cans; the board designer is responsible for everything after the module pin: the RF line to the connector, the ground under it, the connector itself, and how much of one radio's transmission reaches the other's receiver.
Host circuit boards that carry one or more radios in smart-home hubs, gateways and controllers: RF routing from radio or module to connector, ground planes and shield cans, board-mounted U.FL and SMA connectors with their pigtails, and isolation between co-located Wi-Fi and IEEE 802.15.4 or Bluetooth radios. Pre-certified radio modules themselves are covered on the Wireless module page and Wi-Fi modules on the Wi-Fi module page; end-of-line RF testing of module-based products on the Wireless Communication Module page; enclosed data-link transceivers on the Wireless transceiver page; complete cellular modems on the Cellular modem page; wired fieldbus modules on the Communication module for wired industrial networks page; RF connectors as a product on the High-frequency RF connector page and antennas on the Antenna system for wireless communication page.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
From radio pin to antenna connector: 50 Ω lines, an unbroken ground plane and shields on 20 dBm paths
Texas Instruments' hardware note for its CC13xx/CC26xx wireless MCUs sets out what the host board must preserve when a radio is placed on it: [1]
TI gives two shield options for the 20 dBm path: a fully enclosed shield, which forces the RF path to leave on another layer through transition vias that must follow the reference design, or a custom enclosed shield with a single opening for the RF trace, which keeps it on one layer; it recommends EM simulation of the shield cavity. Each decoupling capacitor should have its own via to ground, and a break in the layer-2 ground under a return path lowers RF performance and raises spurious emissions. [1]
For bring-up, TI recommends conducted measurements before any radio link: disconnect the antenna and measure at the SMA connector or at a semi-rigid coax soldered to the 50 Ω point, and place the receiver in a shielded box for accurate sensitivity. [1] Editorial note: that test point has to be designed into the board, which is one reason to bring each radio out to a coaxial connector rather than straight to a printed antenna.
Board feature
TI's guidance
Stack-up
Distance from top layer to ground layer must match the reference design; deviation changes parasitics and can force a redesign of the filter balun [1]
Ground under RF
Uninterrupted, solid ground plane under all RF components from the antenna back to the ground vias in the chip's exposed pad; no traces under the RF path [1]
RF line
Longer traces, such as from the LC filter toward the antenna, at 50 Ω [1]
Balun symmetry (sub-1 GHz)
Amplitude imbalance at most 1.5 dB and phase imbalance at most 10° [1]
20 dBm path
Remove header pins, use high-Q tight-tolerance inductors and capacitors, and a fully enclosed shield to reduce 2nd and 3rd harmonics [1]
Antenna matching
Pi-network placed as close to the antenna as possible [1]
Ask the board maker for the stack-up used, the impedance-controlled RF lines and their test coupons, the shield arrangement on each radio, and where the 50 Ω test point is.
02
The coaxial connector on the board: U.FL rated for 30 matings, VSWR 1.3 up to 3 GHz
Boards like the one pictured bring each radio to a board-mounted micro-coaxial connector with a pigtail to the enclosure antenna. Hirose's U.FL catalogue (August 2025) specifies: [2]
Hirose lists wireless LAN (Wi-Fi 6), Bluetooth and electronic measuring instruments among the applications, and its VSWR rises with thinner cable at higher frequency: φ1.32 mm assemblies reach 1.5 max. at 3–6 GHz and 1.7 max. at 6–8 GHz. [2] Editorial calculation: return loss = −20 log₁₀((VSWR − 1)/(VSWR + 1)); mismatch loss = −10 log₁₀(1 − |Γ|²).
U.FL property
Hirose specification
Editorial: what it means
Impedance and frequency
50 Ω; rated 0 to 8 GHz for soldered U.FL, some to 12 GHz; U.FL(A) to 18 GHz [2]
Specify connector type, pigtail cable diameter and length per radio, and how many mating cycles production test and service will use.
03
Two 2.4 GHz radios on one board: a +30 dBm Wi-Fi transmitter needs 45 dB isolation, small products achieve 15–20 dB
Silicon Labs' coexistence guidance for its WF200 Wi-Fi transceiver sets out the radios that share the 2.4 GHz band on a hub board: Wi-Fi with up to 14 overlapping 20/22 MHz channels at up to +30 dBm, Bluetooth with 40 channels at 2 MHz spacing at up to +20 dBm, and Zigbee or Thread with 16 channels of 2 MHz at 5 MHz spacing at up to +20 dBm. [3]
Editorial calculation: against 45 dB needed, 15–20 dB of antenna isolation leaves 25–30 dB to be found elsewhere. Silicon Labs' hardware measures are distance (in open-space far field, received power falls as 1/R², so doubling the antenna spacing gains about 6 dB), pointing the null along a monopole's axis toward the other antenna, and cross-polarising the two antennas. [3] The Embedded Computing Design article therefore turns to managed coexistence: packet traffic arbitration (PTA) signals between the radios so that Wi-Fi transmissions can be delayed while the Zigbee or Thread radio receives. [4]
Silicon Labs also recommends maximising channel separation when one host controls both radios, setting a Bluetooth channel map that avoids the Wi-Fi channel, and using retries, while warning that retries raise latency and can flood a mesh network under heavy interference; for the WF200 it recommends enabling PTA only in station mode. [3]
Quantity
Value
Isolation needed for a +30 dBm, 100 % duty Wi-Fi transmitter, 20 MHz, far-away channel, to receive a −80 dBm IEEE 802.15.4 message
1–11 in the USA, 1–13 in Europe, 1–14 in Japan [3]
State which radios share the board, their maximum transmit powers, the antenna positions on the enclosure, and whether PTA or another coexistence interface is wired between the radios.
04
What to send when ordering a wireless communication board
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Radios: [Wi-Fi / Bluetooth LE / Zigbee / Thread / sub-GHz; module or chip-down; max. transmit power]
Board: [layer count; stack-up; impedance control on RF lines; test coupons]
Shielding: [shield can per radio; RF exit through wall or vias]
Antennas: [U.FL / SMA; pigtail cable and length; antenna positions on enclosure]
Coexistence: [antenna isolation target; PTA lines; channel plan]
Test: [conducted test points; production RF test; certification evidence for modules used]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How much isolation do Wi-Fi and Zigbee radios on one board need?
One worked case: a +30 dBm Wi-Fi transmitter at full duty needs 45 dB to let a −80 dBm IEEE 802.15.4 message be received; small products achieve 15–20 dB, so radio coordination is used. [4][3]
How many times can a U.FL connector be mated?
Hirose specifies 30 matings, with contact resistance staying within initial + 5 mΩ. [2]
What must the host PCB keep under an RF path?
TI calls for an uninterrupted, solid ground plane under all RF components, no traces under the RF path and 50 Ω for longer RF traces. [1]
When does a radio on the board need a full shield can?
TI recommends a fully enclosed shield on its 20 dBm paths to reduce 2nd and 3rd harmonics. [1]
Sources and what still needs a direct check
Sources checked 2026-10-12. Board layout rules come from Texas Instruments' CC13xx/CC26xx hardware note; connector ratings from Hirose's U.FL catalogue; coexistence figures from Silicon Labs' WF200 coexistence guidance and an Embedded Computing Design article on managed coexistence.
