The 5G Antenna Technology Challenge

Forget your father’s garage experiments with ham radio rigs and huge dipoles, 5G antennas are a whole new world.

The recent Molex 5G “The State of 5G” survey has revealed that a successful 5G roll-out is complex and intricate and involves many moving parts. One key element that rarely makes the headlines is the mobile antenna.

To fully understand the formidable challenge of antenna design for 5G, we need to look at the whole picture, both for mast infrastructure and in terms of in-device antenna design. On a top-down basis, the industry is currently moving forward with a compromise on wavelength and frequency, the Non-Standalone (NSA) New Radio (NR), which continues to support 3G and 4G at sub-6GHz frequencies. However, the long-term goal for 5G communications is to use a combination of sub-6GHz and frequency spectra between, approximately 24GHz – 100GHz. The fundamental conundrum for radio designers is that as frequency rises, wavelengths shorten. This poses challenges, especially for antenna design. 

For 5G, there are still unknowns,  particularly in the area of millimeter wavelengths (mmWave) at relatively high frequencies. In times past, these were passed over for terrestrial communications because they travel only short distances before they ’attenuate’, say a few hundred meters or a kilometer at best.  Even the weather and a few wet trees might put a literal damper on performance. This is when the 5G hype makes many users want to scratch their heads.

It’s a Trade Off

Clearly, 5G deployments involve trade-offs. Higher mmWave frequencies support increased data throughput, but signal propagation becomes vulnerable. These are the phenomena encountered by engineers: multipath (communications break-up); path loss; and packet loss. As a result, there is an urgent need for a proliferating variety of new base-stations and small cells – including femto, macro, nano, and pico cells.

The essential core component of these base-stations and cells is an antenna array, meaning multiple antennas, for both reception and transmission. This technique is known by the curious initialism of MIMO (Multiple Input, Multiple Output). The technique is not new.

MIMO is a response to Multipath, the break-up of a signal, typically when it enters a building and tries to find its way through doors, windows, elevator shafts and so on, creating in the process, signal reflections. MIMO combines this chaos through the use of multiple antennas to maintain a coherent data transmission. On a large scale, this is so-called “Massive MIMO”. It’s a field of ongoing intensive research, not least by Molex, with all the acquired know-how and expertise of decades of involvement in antenna design. We can expect sub-6GHz communications to utilize 4 x 4 MIMO, and mmWave 5G to use 2 x 2 MIMO.

The directionality issue

Traditionally, radio waves propagate rather like a stone dropped into water. If the antenna is the stone, by analogy, normally the radio waves will spread out as ripples in a circular fashion.

In the case of mmWave 5G, though, the higher frequencies introduce a high degree of directionality to RF propagation and over a quarter of respondents of the “The State of 5G” survey, state that mmWave propagation issues are causing challenges (26%). With this in mind, antenna design becomes all-important to benefit from this near ‘line-of-sight’ propagation whenever this is possible. MIMO, in fact, when applied in really clever antenna designs, can not only mitigate multipath, it can possibly use “massive MIMO” techniques for ‘beam forming’ and ‘beam steering’, turning directionality to the advantage of the user.

Of course, if 5G base-stations are not to become an eyesore as they proliferate throughout a “dense urban” environment, where “dense” refers to communications as well as people and buildings, these 5G antennas should be relatively small.  Fortunately, that is likely to be the case.

5G in the hand

When it comes to 5G-capable consumer mobile devices, in addition to the current sub-6GHz, mmWave frequency bands are adding more complexity and crowding to the RF Front End. And so the additional active and passive components including the antennas must not only be small but miniaturized and able to co-exist with several other radios without interference and crosstalk. If 5G consumers are to continue to enjoy the sleek phone profiles they prefer, combined with highly reliable connectivity, the R&D challenge here is enormous and will be for years to come.

How to deliver?

Semiconductor designers, smartphone OEMS, manufacturers, carriers and R&D labs are already cooperating on aggressive innovative techniques for miniaturization of components in the RF Front End, such as Molex’s RF Flex to Board connectors and 3D Antennas.

“The State of 5G” survey reveals that the successful roll-out of 5G is complex and intricate and involves many moving parts. This isn’t a surprise to engineers when even a sliver of board solder can become a reverberating antenna at high frequencies. At higher 5G/mmWave frequencies, the important issue is not restricted to just the resonant performance of the device-plus-antenna, but also the antenna covering.

Be it metal, glass, plastic or even ceramic, the covering is not electrically thin, and this can have a significant impact on the radiating performance of the antenna. Also, the placement of the antenna with respect to the user’s hand has a significant effect on mmWave transmission and reception.

Nevertheless, R&D engineers do have options. Careful design and integration of the covering material with the antenna system can optimize the radiation patterns of mobile device antennas. Furthermore, antenna-tuning techniques such as aperture and impedance tuning can improve signal gain over wider bandwidths and improve battery life.

The antenna tuning system must also be able to support more tuner states as well as wider frequency bandwidth per tuner state, due to potentially higher order of carrier aggregation (CA) in 5G and additional cellular bands.  

As with many elements in 5G roll-out, antenna tech advancement must be pragmatic and incremental rather than revolutionary. This is where Molex, with its years of practical expertise across numerous geographies and industry sectors leverages its product and RF system manufacturing expertise, helping to make 5G an operational reality, and enabling manufacturers to deliver the sleek phones consumers have come to expect.

Director of Core Products, Micro Solutions