Tuesday, June 25, 2024

Making Millimeter-Wave Technology More Accessible

Parent Category: 2022 HFE

By Yonghui Shu and Andrew Laundrie


The Millimeter-wave spectrum generally refers to the frequency range of 30 to 300 GHz. In recent decades it has found wide application in space, aviation, military, science, industrial, commercial and consumer systems due to its unique wavelength characteristics. It is not a new technology, although it is still considered by many to be an expensive technology because of historically high entry barriers. Advancements in semiconductor devices, packaging, and manufacturing techniques have been slow to change this attitude. To a large degree the mm-wave electronics industry continues to favor custom solutions rather than adopting more of the prototyping and manufacturing approaches that have successfully reduced hardware costs at lower frequencies. To overcome these historical barriers to new applications, the mm-wave industry is increasingly turning to standard component packages and new RF interfaces that provide alternatives to traditional coaxial and waveguide connections. Improvements in test and measurement techniques have also lowered some of the hurdles that impeded mm-wave hardware development. This article reviews significant improvements in the areas of commercial off-the-shelf (COTS) mm-wave components, novel waveguide connectors for lower-cost packaging, and contactless waveguide flanges that can streamline the measurement of waveguide components. These achievements have accelerated the development of new mm-wave systems while reducing the cost of transitioning to higher rates of production. As a result, mm-wave technology is much more accessible and more affordable for new applications.

The mm-wave spectrum has significant advantages over its lower-frequency RF and microwave counterparts. Widely accepted to comprise 30 to 300 GHz, this frequency range offers smaller wavelengths and wider bandwidths. These features have specific advantages. Smaller wavelengths are attractive because they allow users to take advantage of additional electromagnetic spectrum. Also, for a given antenna aperture size, smaller wavelengths enable narrower beams to improve the angular resolution of radar systems used in weapons, guidance systems, aircraft, and remote-sensing satellites. Wider bandwidths support higher data rates in communications systems and improve distance resolution for target identification in radar systems. Increased bandwidth can also improve the sensitivity and resolution of passive imaging systems, as well as provide systems with greater immunity from jamming and other interference [1], [2], [3], [4]. Despite these advantages mm-wave technology is often seen as too expensive or impractical for many new applications.

Until recently the mm-wave frequency spectrum was mainly used for military, aerospace, and scientific research applications. It has been generally limited to weapon guidance, seekers, radars, military communication equipment, remote control, remote sensing, radiometry, radio telescopes, material science, and other areas of research and development. In recent years, technological advances — especially those related to simulation and design tools, semiconductor device performance, and manufacturing methods — have allowed mm-wave technologies up to 170 GHz to reach their current stages of maturity [5], [6], [7].

As mm-wave technology continues to find increasing opportunities in traditional markets, potentially explosive opportunities are seen in a wide range of new applications. There is increasing interest in topics such as improved internet connectivity, enhanced safety and security, as well as “smart” cities, homes, and appliances. As a result, mm-wave technology may experience vastly more growth in new commercial and consumer-oriented applications. Research and development is growing in many areas including the Internet of Things (IoT), high data-rate communication, passive imaging, transportation safety and management, driverless cars, security systems, commercial satellites, and test/measurement equipment. This activity confirms that the mm-wave electronics industry is healthy and growing [8], [9], [10], [11].

As the opportunities for mm-wave technologies have grown, the technical and business landscapes have often been difficult to navigate due to a lack of manufacturing standards and few stable building blocks for system integration. Reasons for not having standard building blocks in the industry include the limited bandwidths that are typically achieved using traditional design approaches. This has resulted in the continued need for customization to cover specific frequency ranges. Further, complex interconnections between building blocks can limit system performance due to high insertion loss or poor impedance matching. At higher mm-wave frequencies approaching 300 GHz, waveguide sections with low insertion loss are costly to produce. These and other factors have made the industry reluctant to develop standard building blocks. Instead, many developers of mm-wave hardware continue to favor customized design approaches. Revolutionary packaging and testing technologies are needed to speed up the development process and reduce prototyping costs so that new applications can be demonstrated and implemented as quickly as possible.

Historical Considerations

Traditionally, mm-wave hardware development required a large amount of design activity at the component level. An advanced Engineering degree with considerable training in electromagnetic theory and network analysis were commonly regarded as prerequisites for entering the field of microwave and mm-wave component design. Furthermore, the machinery required to make precision mechanical parts for mm-components was lacking while machinists with the necessary skills were limited. Experienced, hands-on technicians required many years practice to develop the “know-how” needed to compensate for imperfect designs and machining tolerances. In recent years the emergence of advanced design software has greatly reduced the need to apply electromagnetic theory and network analysis methods to the development of mm-wave components and systems. Meanwhile advanced mechanical design software such as Solidworks, as well as improved CNC machinery, have helped to reduce the need for highly experienced manufacturing personnel, improved mechanical parts accuracy, and eliminated “skill” dependency tremendously.

Now, the need to design systems at the component level is being reduced by the increased availability of COTS hardware. System developers can thus focus more of their efforts on building proof-of-concept prototypes and pre-production systems. As a result, it is increasingly possible to evaluate new applications faster and study their economic feasibility with lower up-front investment.

Another common barrier to entry for mm-wave product development is the need for advanced test equipment. Basic instrumentation includes signal generators, amplifiers, signal analyzers, and network analyzers. Traditionally such equipment was expensive to purchase and maintain, and much of it required special training and skills for proper operation. In recent years the cost of test equipment has declined significantly, but it still represents a major investment for anyone seeking to harness mm-wave technology.

For advanced instruments such as Vector Network Analyzers (VNAs), especially those operating at mm-wave frequencies, high levels of operator training have been essential to achieve reliable measurement results. Further, slow test procedures have limited the number of devices that could be tested over a given time period. Recent advancements in VNA test equipment are making it easier to perform component tests, allowing test equipment to pay for itself sooner due to increased productivity and lower operating costs.

Choosing Suppliers

For those involved in the development of mm-wave systems for new applications, some of the more difficult challenges include surveying and selecting component suppliers. This is especially true in systems where one component can impact the performance of several others. Moreover, the depth and breadth of a supplier’s understanding of these dependencies must be discovered as soon as possible to ensure that integrated systems can achieve the best possible performance. For many years Eravant, formerly SAGE Millimeter (Torrance, CA), has been investing heavily to build up its standard modular products, encompassing a wide range of broadband coaxial and waveguide components with focus on mm-wave bands from 30 to 325 GHz. These standard modules are generally designed to cover full waveguide bandwidths, or bandwidths that are as wide as possible using available technologies.

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Figure 1 • Typical communication front-end block diagram


Some standard models span multiple octave bandwidths. For example, amplifier model SBB-0117033015-VFVF-E3 covers 10 MHz to 70 GHz with 30-dB nominal gain and +15 dBm output power at 1-dB compression. The broadband nature of Eravant’s standard modules offers opportunities for system integrators to find suitable building blocks that meet their system requirements without paying for non-recurring-engineering (NRE) and waiting for someone to address their particular frequency range. Eravant’s standard COTS product categories cover almost everything needed to develop mm-wave wireless systems.

Eravant has also introduced a series of novel waveguide connectors under the trademarked name, “Uni-Guide”. This product line offers an RF interface concept that is similar to coaxial connectors. The Uni-GuideTM connector series is offered to the mm-wave component and subsystem industry to reduce the need for customized device packages, and to shorten development and manufacturing cycle times [12].

In mm-wave frequency bands, rectangular waveguide is the most common transmission-line medium due to its low loss and high power capacity. Unlike coaxial cables, waveguide connections are rigid as well as polarized. As a result, custom waveguide port locations and orientations are frequently desired for system integration purposes. In addition, hermetically sealed waveguide windows are often needed. Such windows are difficult to implement and expensive to produce [13]. Alternatively, a Uni-Guide waveguide connector can preserve the hermetic seal of a component package if standard glass beads are used for RF port sealing.

The Uni-Guide waveguide connector series can also help to minimize packaging inventories, as well as simplify inventory management. Component manufacturing costs are lowered by using standard housings that were already developed for coaxial connectors. As a result, the waveguide connector is expected to be a revolutionary package technology that eliminates many custom-designed packages while reducing product development cycle times and lowering design and production costs.

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Figure 2 • E-Band subsystem constructed using COTS modules


Test Challenges

Testing waveguide components and systems has always been challenging. Any misalignment, small gap, or excessive mechanical tolerance in waveguide connections can lead to inaccurate system calibration, time-consuming adjustments, and redundant efforts. There are many research papers and application notes that address these topics [15], [16], [17]. To increase testing and calibration speeds, as well as improve overall repeatability, Eravant developed the Proxi-FlangeTM contactless waveguide flange and the WaveGlideTM rail positioning system. These innovations greatly improve the productivity and reliability of mm-wave test systems [18]. Additionally, lower-cost mm-wave VNA frequency extenders and calibration kits are available to further lower the cost barriers for new and budget-limited system developers.

Millimeter-wave System Configuration

Communication and radar systems tend to include a variety of component types in their functional block diagrams. Antennas, antenna feed networks, amplifiers, up-converters, down-converters, control devices, oscillators, filters, diplexers, power distribution networks, and interconnection products are commonly used. Figure 1 shows the block diagram for a typical microwave or mm-wave communication system front end. Various common components, i.e., building blocks or modules, are included. These functional modules are largely available from the Eravant website as standard COTS products covering frequencies up to 220 GHz, with an increasing number of component selections available for frequencies approaching 325 GHz.

Eravant’s large pool of standard products, as well as its extensive design library and established manufacturing processes, support the rapid development of customized modules by altering or updating standard models at a fraction of the usual costs and lead times. This design approach speeds up system development, reduces the realization cycle time, and lowers overall program costs. Further, these products are readily configured with standard waveguide interfaces for direct connections to other components. Additional interconnection devices, such as adapters and transitions, as well as waveguide components including straights, bends and twists, may be eliminated when individual modules are offered with more configuration options.

With approximately 5,000 COTS models, Eravant stands ready to support rapid system concept demonstration, scientific apparatus development, test-lab tooling, as well as a variety of instrumentation needs. All of Eravant’s products are designed and manufactured using rigorous processes. Many are readily qualified for space and military applications after the required environmental testing is performed.

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