RF and Microwave: miniaturisation and high efficiency are the keys

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As 2017 gets under way we are seeing 5G continuing to be one of the major topics of interest for new development activity, and it’s an area where Plextek RFI is already very active. There is a huge amount of development effort under way to realize practical mm-wave systems that are capable of allowing the very high speed access to mobile devices that 5G will offer. At the moment many different strategies and frequency bands are under investigation. While there will inevitably be rationalisation of both the overall approach and frequency bands by the time real-world 5G systems are deployed, the technological advancements developed can provide benefits across a range of applications.

Most mm-wave 5G systems are based on phased-array antenna architectures, and we are currently involved in designing custom MMICs for these prototype systems. We also see new opportunities emerging for microwave test instrumentation suppliers, as the prototype systems under development will need to be evaluated and optimized. In addition to proving system implementations, we expect progress to be made during 2017 in allocating international frequency bands and in starting to finalise some of the 5G standards, and this will lead to additional opportunities for the supply of component parts in high production volumes. Figure 1 shows a 28GHz Single Pole 4 Throw (SP4T) switch chip that we recently realised on a newly released PIN diode IC process from WIN Semiconductors; it was designed with 5G systems in mind.

The IoT is another application that is generating enormous interest because of the potentially huge volumes in which products will be deployed. However, there will not be a single standard for IoT applications. Indeed there are many IoT applications already active with a range of connectivity solutions including Bluetooth, LTE Cat-0 and Cat-1, and WiFi, as well as proprietary ISM band solutions. We already have wireless street lights, fleet management and vehicle tracking, and a host of other M2M applications—these are all IoT solutions. Newer LTE cellular standards—Cat-M1 and NB-IoT—will begin to make their mark during 2017 and the deployment and application of IoT connected devices will continue to grow rapidly. In terms of the benefits of IoT to the RF and microwave industry, these are potentially huge. At Plextek RFI, we have clients interested in the development of multi-chip modules and custom packages to support product miniaturisation.

Although most of our work towards 5G and the IoT is centred on GaAs MMIC technology, for many other applications we are seeing GaN technology continuing to grow in importance. GaN permits the realisation of RF and microwave power amplifiers with very high output power levels and efficiencies. New devices (both discrete and MMIC) with impressive performance will continue to be released during 2017, and new GaN components and processes offering performance to 40GHz and beyond will become increasingly available. GaN transistors have high breakdown voltages and are capable of reliable operation at high channel temperatures, making them an ideal choice for the realization of high power solid state amplifiers. The high power densities and operating voltages of GaN lead to challenges for the design engineer. Selection of an appropriate substrate material and the use of adequate heatsinking are both essential, and output tracks need to be carefully designed to ensure adequate RF power handling. Matching capacitors need high Q (low ESR) to minimize losses and maximize efficiency; they also need high breakdown voltages to cope with DC bias plus RF voltage swings. GaN transistors have considerable available gain, which increases as frequency decreases. Care must also be taken to ensure unconditional stability both in-band and well out of band, particularly at low frequencies.

The defence market, while not growing at such a high rate as commercial telecoms applications, remains a significant market for RF and microwave devices and subsystems. It is likely to retain its focus on funding the development of technologies with the potential to reduce the overall cost of operations. Cyber security is a key area of interest, which is growing as increased connectivity brings an increased risk of hacking and of breaching existing defences.

The control and communications of Unmanned Aerial Vehicles (UAV), or drones, is another important application. As UAV technology continues to develop, so will drone detection and jamming technology. The cost and performance of commercially available drones is such that they represent a potential security threat to airports, power stations and other critical infrastructure. For the RF and microwave industry, the miniaturisation of components and subsystems, along with high efficiency power amplification, are likely to be two key areas of demand. High resolution radar systems are a crucial to enable the detection of small highly manoeuvrable drones, and GaN technology offers the solution to providing adequate power to jam their control links. High-performance, low-cost GaN transistors capable of generating adequate power across the relevant bands are now readily available. Plextek RFI has ongoing programmes for the development of custom GaAs MMICs and GaN PAs (discrete and MMIC). Figure 2 shows a 125W PA module with 20dB gain and 70% efficiency, realised using a single commercially-available GaN transistor.

by Liam Devlin, CEO, Plextek RFI

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