Antennas for millimeter wave solutions

“Anything is possible!

Around the world, people are gaining the power to create new communities, engage across boundaries, make the world more inclusive, and change the way we do business. Transformation is happening everywhere and in every culture, country, and industry”, extract from February 2nd, 2017.

End-user behavior and technology development interacts, iterates and increase the speed of innovation on a daily basis. This can be seen in every corner of society ranging from the dense metropolitan areas with “smart city” ambitions to the outskirt of rural areas, where a connected home or a connected village can be the difference between starvation and prosperity. This rapid development continuously puts new requirements on products and solutions and fuels innovation on a daily basis.

Bandwidth and speed are parameters of great interest when end-users consume “gigabits by the hour”. Traditionally, fiber based connections and optical technology has been seen as the only real future proof solution to support the never-ending appetite for capacity. Recently though, we have seen proof points that the fiber based approach does not solve this challenge since considerations around cost and speed of rollout needs to be taken into account to get a viable business case for the operator and the end-user.

It is not long ago we could read about Google Fiber, stating that they will use wireless technology as a strategic component when building a broadband network and providing broadband services to their customers. Recently in Sweden, we also saw a letter to the editor in the biggest financial newspaper [1], where it was highlighted that if the Government shall be successful in their aggressive plans to provide “broadband to the Swedish people”, they need to subsidize not only the fiber rollout, but also the wireless alternatives, i.e. it should be seen as a network wide approach and not only focused on the wireline parts of a network. To some extent, this is old news, but still very interesting when being active in the wireless arena.

This blog is focusing on millimeter wave RF technology and its position on the market and this time I want to highlight one important part of a millimeter wave solution; the antenna.

The antenna is a considerable part of the solution, both from a performance and a cost perspective. The antenna is the key component to address interference and distance. Depending on the antenna design, you can have a wider or more narrow antenna beam that can help you prevent interference and disturbance from other radio sources. You can also design an antenna to provide more or less antenna gain, where a higher gain will help you to reach further. Since the antenna concentrate the emitted energy into the antenna beam, the narrower the beam, the higher gain the antenna can offer.

Since this is “polluting” the open space with radio waves, normally the regulatory bodies have standardized how antennas can be use in various frequency bands. In the US, the Federal Communications Commission (FCC) put certain requirements on e.g. antenna gain or Effective Isotropic Radiated Power (EIRP). The EIRP is defined as the output power from a radio plus the antenna gain for a specific antenna. Traditionally, the minimum antenna gain has guaranteed a narrower antenna beam, which reduces interference outside the wanted antenna direction. Since the V-band (60 GHz) is subject to higher free atmospheric loss, the risk of interference is less and therefore the regulations have been changed in the US to allow for lower gain antennas and higher output power. The FCC V-band regulations now allow to have an EIRP of +40 dBm and it is up to the supplier to design with a high gain and low output power or a lower antenna gain and high output power. This type of less stringent regulations allow for other type of antennas, for example with lower gain and transceivers with higher output power, which for example could be WiGig based solutions, that fits the new paradigm much better.

Parabolic antennas
Traditionally the most common antenna technology has been the parabolic antennas for point to point connections. The parabolic antenna is widely used in various use cases ranging from huge satellite communication antennas with a dish diameter of several meters to the point to point radio link communication use case, where the dish diameter is typically 0.2 to 0.6m depending on frequency. The typical antenna gain is between 30 and 46 dBi. Since the traditional point-to-point communication is sending on one frequency and receiving on another simultaneously (FDD mode), there is a need to separate the received signal from the transmitted signal to avoid interference. This is done by using a diplexer between the antenna and the radio transceiver. These diplexers add both cost and complexity, since they often require tuning during production.

Lens antennas
Lens antennas use the mechanical shape of a plastic lens that is fed by a waveguide or planar (PCB) antenna element. It combines low cost, mechanical robustness, flexibility and good electrical performance also for millimeter wave frequencies. This technology can be combined with e.g. a patch antenna technology to improve the performance in terms of directivity and antenna gain. The typical lens antenna for point-to-point links offer a gain between 30 and 45 dBi. Lens antennas can also offer some steer ability if used with electrical beam steering.

Slot antennas
This antenna type often consists of a flat metal surface or even lower cost plastics with one or many holes or slots cut out. These slots are fed with the millimeter wave signal and radiate the electromagnetic wave. The antenna radiation pattern is determined by the shape, size and number of slots. The main advantage of this type of antenna is its size, the relatively simple design, flatness and lower cost in production compared to parabolic antennas.

GAP™ antennas
GAP™ antennas is a type of slot antenna but based on the gap waveguide technology [2], to offer an antenna that combines low cost with good performance and the possibility to integrate both diplexer functionality and beamforming support in its mechanical structure. According to Gapwaves, the first generation of antennas will be available with gain ranging from 26 to 43 dBi at E-band. This type of antenna is a cost competitive alternative to the more common parabolic antennas. Future versions of GAP™ antennas will also enable integration of active electronics into the antenna structure. This will open up the possibility for electrical beam steering and beam forming by using multiple send and receive channels. During Mobile World Congress, Sivers IMA used GAP™ antennas from Gapwaves in our live demo setup.

Patch antennas
An even less costly antenna type is the patch antenna. This is often made of PCB or ceramic low cost substrate, which allow for very low cost and very small form factor. The disadvantage is that it is not typically the type of antenna you use to get a very high gain, e.g. the typical antenna gain ranges from 10-27 dBi depending on antenna size. For example, a 24 dBi antenna for V-band is quite small, only 5×7 cm with less than 5 mm thickness, using 16Tx and 16Rx patches with 5 elements for each path. Recent FCC requirements, gives the possibility to use low gain antennas. This makes it easy to combine low cost, low gain patch antennas with the advantage of electronic beam forming. Typically, these antennas are used when transmitter and receiver are using the same frequency to send and receive during different time slots (TDD), which is the case for solutions like WiGig. Sivers IMA is developing beam forming patch antennas together with Uppsala University, within a project co-funded by Vinnova. It is also worth noticing that patch antennas with beam steering and beam forming will be a very important part in future 5G millimeter wave access solutions.

The antenna is a critical component in all point-to-point or point-to-multi point links, which significantly impacts link budgets and the robustness of the communication system. It is therefore a crucial component to address to achieve better performance, greater functionality and lower cost for a complete link solution.

The regulatory framework allows for the combination of a transceiver with relatively high output power together with a low cost, high performing antenna with relatively low gain and beam forming functionality. This is valid for key markets on the 60 GHz V-band, whereas regulatory discussions are ongoing to make relevant adjustments also for the E-band.

Since the antenna in various use cases will be a vital part in our customer’s implementation, it is necessary to focus and drive innovation also in the antenna space. Our ongoing antenna development together with Uppsala University is an absolute proof point to this, whereas it is also important to monitor the development of emerging technologies with a particular focus on antenna gain in combination with beam forming capabilities. Antenna technology will be critical success factors in both V- and E-band applications as well as for WiGig and 5G use cases.

Anders Storm
Sivers IMA