In short: Antenna screens, rooftop enclosures and covers on telecom sites are often made of fiberglass (FRP) because it is non-metallic, strong and weatherproof. But non-metallic is not the same as RF-transparent. Every material slows and reflects radio waves to some degree, and the effect grows with frequency. An industry test of common FRP and molded fiberglass panels found losses above the usual 0.5 dB budget in the 3.7–3.98 GHz C-band used for 5G. Good results come from design, not luck: low dielectric constant and loss, the right wall thickness, care with fillers and coatings, and a test at the real frequency. FIBROVX builds RF-transparent screens and enclosures as custom / available on request, and radomes are a future item.
How this guide fits with our others
This guide is about radio performance of FRP near antennas. For the mechanical side of telecom work, such as cable supports, covers and marker posts, see FRP for telecom infrastructure. Our pair article, FRP rebar and bridge decks, looks at another frontier use of composites in infrastructure. Other sectors are on our industries page and emerging industries page.
Why telecom sites use FRP near antennas
Telecom sites need structures that hide or protect antennas without blocking them. Typical uses are:
- Screen walls and rooftop concealment that hide antennas from the street
- Enclosures and boxes for radios and small cells
- Frames and supports made from pultruded profiles
- Cable trays and supports for feeder and fiber cables
Metal would reflect the signal. FRP is non-metallic, light, does not rust and can be molded or pultruded into many shapes. A 2017 study from Malaysia noted that FRP is commonly used there for camouflaging wireless sites, and that many companies were not aware it can affect signal strength. Its simulations at 900 MHz and 1800 MHz showed that the FRP thickness and the distance between the cover and the antenna face both changed the signal.
Non-metallic is not the same as RF-transparent
An RF concealment manufacturer explains the history well. When many macro sites were built over the last 20–30 years, little thought was given to materials beyond using non-metallic ones. Signals below 1 GHz pass through most concealment materials, especially fiberglass. C-band 5G is different. The same manufacturer tested two common enclosure materials, FRP and molded fiberglass, from 3.7 GHz to 3.98 GHz, at 0 and 30 degree angles. The loss was typically well above the 0.5 dB limit that most operators allow for concealment.
The honest takeaway: an FRP panel that worked for 4G may not work for 5G. Each band needs its own check. The same manufacturer sells competing materials, so read its figures as one maker's test results, but the physics behind them is well established.
5G bands at a glance
The same manufacturer's guide groups 5G spectrum in three ranges, and each one treats a concealment panel differently:
- Low band (FR1), about 700 MHz to 2.7 GHz. Long range, measured in miles, with peak rates around 100 Mbps. Most fiberglass panels pass these signals well.
- Mid band, including C-band at about 3.3–4.2 GHz. Peak rates around 1 Gbps. This is where many legacy fiberglass panels start to cause problems.
- Millimeter wave (FR2), 24.25 GHz to 52.6 GHz. Peak rates up to 10 Gbps, but range of only hundreds of meters, and signals are open to substantial impact from concealment and other surroundings.
The higher the band, the more carefully the panel must be designed. A single site often carries several bands, so the panel has to suit all of them.
The three numbers that set signal loss
1. Dielectric constant (Dk or εr)
The dielectric constant shows how much a material slows a radio wave compared with air. Air is 1. Inside a material, the wavelength becomes shorter, roughly the free-space wavelength divided by the square root of εr. A higher Dk means a bigger mismatch with air and more reflection at the front and back faces of the panel.
Laird, a radome maker, gives typical values:
- Most resins: about 3
- E-glass composites: about 4.5
- S-glass composites: about 4.2
- Quartz fiber with cyanate ester resin: about 3.6, with a lower loss tangent
2. Loss tangent (tan δ)
The loss tangent shows how much energy a material turns into heat as the wave passes. Higher loss means more attenuation. A 2021 study measured glass fiber composite samples and found loss tangents from about 0.01 to 0.05. One 2.32 mm sample had εr of 4.72 and tan δ of 0.045 at 5.65 GHz. Permittivity rose with frequency and with the number of layers.
3. Wall thickness
Thickness interacts with Dk and frequency. Laird notes two rules:
- Use the thinnest wall that is mechanically feasible.
- For a single frequency, a wall half a wavelength thick (inside the material) lets reflections from the two faces cancel, giving very little loss at that frequency.
As a worked example (our calculation, not a design): at 3.7 GHz the wavelength in air is about 81 mm. In a laminate with εr of 4.5 it is about 38 mm, so a half-wave wall would be about 19 mm thick. At 28 GHz the same rule gives about 2.5 mm. A half-wave wall only works near its design frequency, which is a problem for sites carrying many bands.
Texas Instruments' radome guide adds that loss comes from reflections at the boundaries and multiple reflections inside the wall, and that Dk and loss tangent should be measured at the operating frequency. Values copied from another frequency can mislead. Its guide states the wall should be an integer multiple of half the wavelength in the material to be "nearly transparent" at the intended band.
TI also notes that, for a flat wall, the path through the material gets longer as the wave arrives at a steeper angle, so loss changes across the beam. It adds that the gap between the antenna and the inner face of the cover can be tuned so reflected waves stay in phase with the transmitted wave, and warns against metal fixings and metallic paint.
Design choices that help
- Choose low-Dk, low-loss materials. E-glass is common and economical; S-glass and quartz fibers lower Dk. Research at the University of Rennes found a quartz/urethane acrylate laminate to be a low-loss option for microwaves.
- Keep walls thin, or use a sandwich. Laird notes that the most popular "A sandwich" uses thin composite skins over a low-Dk foam or honeycomb core, combining strength and good radio performance.
- Avoid conductive content. No metal mesh, carbon fiber, metallic paint or conductive fillers in the signal path. Check fire retardant and pigment fillers too, since they change Dk and loss.
- Watch coatings and water. Paint layers and films are part of the wall the signal crosses. Specify only coatings tested for the band.
- Leave space. The Malaysian study showed that the gap between the antenna and the cover matters. Agree the gap with the radio engineer.
- Keep metal out of the beam. Use FRP fasteners, frames and trays where they sit in front of antennas, and keep metal hardware behind or beside the beam.
Retrofit checks for existing sites
The same manufacturer points out that carriers adding C-band radios to existing macro sites will need to evaluate the enclosures already in place, because many are fiberglass that can interfere with the new band. Reusing an existing site has advantages, since power, backhaul and the site itself are already there. A practical retrofit check looks like this:
- Identify the panel. Find the original material, thickness and coating, if records exist.
- Inspect the surface. Look for cracks, fiber blooming, repaint layers and trapped water, all of which add loss.
- Measure or model. Test a cut sample or an identical spare at the new bands, or model the wall with known properties.
- Replace only the panels in the beam. Often only the sections in front of the antennas need an RF-tuned replacement; frames and side panels can stay if they are sound.
Honest limits of FRP enclosures
- Not all FRP is RF-friendly. General-purpose panels may exceed the loss budget at C-band and above.
- Higher bands are harder. As frequency rises, the same wall is electrically thicker, so loss and reflection change. Millimeter-wave bands need specific design and testing.
- Weathering changes things. UV, fiber blooming and water uptake change the surface. See our guide on UV degradation of FRP.
- Structure still matters. Screens carry wind and ice loads. Thin walls for radio performance must still meet the structural design.
- No blanket claim. RF performance belongs to a specific panel, thickness, coating and band. We make no certification or RF performance claims without a test of the exact build.
How to specify an RF-transparent FRP screen or enclosure
- List the bands. Give every frequency band, now and planned, plus polarization and the angles of incidence.
- Set the loss budget. Agree the allowed insertion loss with the operator, for example the 0.5 dB range cited by an RF concealment manufacturer.
- Define the build. Fiber type, resin, thickness or sandwich layout, fillers, coating and color.
- Test a sample panel. Measure insertion loss across the bands at the stated angles before production.
- Lock the recipe. Once a panel passes, keep resin, glass, thickness and coating fixed; any change needs a retest.
Where FIBROVX fits
FIBROVX makes pultruded profiles, cable trays, cable supports and marker posts that are used on telecom sites today. RF-transparent screens, enclosures and frames near antennas are custom / available on request: we work to your band list and loss budget, choose thin laminates or sandwich layouts, and arrange sample panels for third-party RF testing. Radomes are a future item. We do not claim any RF certification for standard products.
Need a quote or a drawing check?
FIBROVX manufactures FRP products in our own factory in China and builds every item to order: sizes, resin system, color, molds and OEM branding. Send your application, dimensions or drawing, quantity and destination port.
Request a QuoteKey parameters at a glance
| Band / parameter | Range or value | Note |
|---|---|---|
| Low band (FR1) | ≈ 700 MHz – 2.7 GHz | Most fiberglass panels pass well |
| Mid band incl. C-band | ≈ 3.3 – 4.2 GHz | Where legacy panels start to cause problems |
| mmWave (FR2) | 24.25 – 52.6 GHz | Strongly affected by concealment |
| Glass composite loss tangent | ≈ 0.01 – 0.05 | 2021 study |
| Example sample | 2.32 mm, εr 4.72, tan δ 0.045 at 5.65 GHz | 2021 study |
| Half-wave wall, εr 4.5 | ≈ 19 mm at 3.7 GHz; ≈ 2.5 mm at 28 GHz | Our calculation, not a design |
| Loss budget example | ≈ 0.5 dB | Cited by the same manufacturer |
FAQ
Is fiberglass transparent to radio waves?
Partly. It is non-metallic, so it does not block signals like metal, but it slows, reflects and absorbs some energy, and the effect grows with frequency.
Will an old FRP screen work for 5G C-band?
Not necessarily. Tests of common FRP and molded fiberglass found losses above the usual 0.5 dB budget at 3.7–3.98 GHz.
What is a good dielectric constant for a screen?
Lower is better for reflection. E-glass composites are about 4.5; S-glass about 4.2; quartz with cyanate ester about 3.6.
How thick should the panel be?
As thin as mechanically feasible, or half a wavelength in the material for a single band. Sandwich designs can do both.
Does paint affect the signal?
It can. Paint and films are part of the wall the signal crosses, and TI warns against metallic paint in particular. Use only coatings tested for your bands.
Why does the gap between the antenna and the cover matter?
Reflections from the cover can add to or subtract from the transmitted wave. Studies and radome guides show the gap changes the result, so set it with the radio engineer.
Do millimeter-wave sites need special panels?
Usually yes. At 24 GHz and above, the right wall thickness is only a few millimeters, and small changes in thickness or coating have a bigger effect.
Can I use carbon fiber?
Not in the signal path. Carbon fiber is conductive.
Do you supply certified RF-transparent enclosures?
No certification claim. These are custom / available on request, with sample testing arranged for your bands.
Related: FRP Pultruded Profiles: A Guide to Shapes, Properties and Specification; FRP Cable Tray: A Complete Guide to Types, Standards and Selection; Custom FRP Manufacturing: Sizes, Resins, Colors, Molds and OEM Explained.
Sources
- An RF concealment manufacturer, C-Band Site Concealment Materials Guide
- Laird, Robust Low Dk Radomes: https://www.laird.com/sites/default/files/2025-02/Robust%20Low%20DK%20Radomes.pdf
- Texas Instruments, mmWave Radar Radome Design Guide (SWRA705): https://www.ti.com/lit/an/swra705/swra705.pdf
- Electrical characterization of glass fiber reinforced polymer (GFRP) composites for future metasurface antenna applications, Materials Research Express, 2021: https://doi.org/10.1088/2053-1591/ac02fe
- Performance of radio frequency signal strength on fiber reinforced plastic material, IEEE TENCON 2017: https://doi.org/10.1109/tencon.2017.8228348
- Sergolle et al., Structural composite laminate materials with low dielectric loss, Composites Part C, 2020: https://hal.science/hal-02971767v1/document