As the global rollout of 5G infrastructure continues at pace, mobile operators must manage upgrades to existing 4G cell towers as well as dedicated 5G small cell towers for higher frequency mmWave technology. The need to simultaneously operate across a spectrum of frequencies will require the development of new antenna radomes, that combine structural strength with signal transparency. Here Juha Pesonen, segment leader for telecommunications at composites specialist Exel Composites, explains how a new generation of antenna radomes will make this growth possible.

According to Gartner, “Communications service providers (CSPs) in mature markets accelerated 5G development in 2020 and 2021 with 5G representing 39 per cent of total wireless infrastructure revenue.” China led this growth, generating $9.1bn in 2021; North America reached $4.3bn thanks to a major drive to install new mmWave base stations, and Western Europe generated $1.6bn with a focus on licensing spectrum and modernising mobile core infrastructure.

A hybrid approach

Despite 5G becoming the fastest growing segment in the wireless network infrastructure market, the reality is that growth will be seen across the spectrum. This includes 4G and low-band 5G up to 3.4 Ghz, mid-band MIMO 5G in the sub-6 Ghz frequency range, as well as high frequency mmWave 5G in the 24 Ghz frequency range and above.

However, this creates an infrastructure challenge, specifically for the radome, the structural weatherproof enclosure that protects the antenna.

The radome, typically made from fiberglass, has two main functions — it must deliver structural strength and provide signal transparency. It must be durable enough to withstand strong winds and rain as well as snow and ice but also be thin enough to let signals pass through without attenuation.

A composite dilemma

Signal transparency is becoming an increasing problem with the rise of 5G. Lower 4G frequencies between 1-2 Ghz can pass through the walls of a radome. However, with the much higher frequencies of 5G, and to make possible its related technologies such as beamforming, Massive MIMO, and low-latency response times, it’s necessary to make radome walls transparent to these signals. There are many ways of achieving this, but the most obvious way to do this is by making the radome walls thinner, which also has the added benefit of limiting the increase of size and weight.

This creates a problem, in that a single radome must be strong enough at its base to allow it to be mounted onto a tower pole, yet feature thin-walled RF transmission windows on the front to allow signals to pass through. Even the best composite radomes have struggled to achieve this.

A unique breakthrough

It’s a challenge that Exel Composites has been working on for four years, which has culminated in the company being granted a European wide patent in 2021 for a new innovation in making radomes. Using the specialised manufacturing technique of pultrusion, we can produce a continuous radome profile with varying thicknesses and containing reinforcing fibers made from different materials in the same product.

We’ve achieved this by integrating a closed cell thermoplastic foam sandwiched between surface layers. This middle layer has a much lower dielectric constant than the surface layers, making it much more radio transparent. Having this structural strength in the casing walls means we can make the transmission windows much thinner, containing just 20 per cent of the reinforcing fibers contained elsewhere in the walls, again allowing high frequency signals to pass through with ease.

This breakthrough means that we can provide radomes for the full spectrum of frequencies from low and mid-band all the way to high speed 5G — laying the groundwork for everything from mobile healthcare and smart traffic management to fully fledged smart cities of the future.

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