Kevin Walker, senior director, technical business development, Benchmark
Benchmark Lark Technology has transformed traditional radio frequency (RF) filters into small, surface mountable components with a significant reduction in size and weight when compared with legacy designs. Achieving new levels of performance in much smaller packages was made possible by the expertise of Benchmark Lark Technology engineers.
The challenge: designing high performance lightweight filters for microwave and millimetre wave (mmW) applications
Wireless technologies, such as commercial 5G wireless and cutting-edge military communication systems, require ever-smaller electronic devices operating at higher frequencies with increasingly sophisticated electronics.
Passive and active RF components are the building blocks in the design of these applications; generating, blocking and receiving signals at specific frequencies to transmit data from point A to point B without interference. These components must be miniaturised to enable the next generation of innovation.
Conventional waveguide technology provides high-quality (Q) and low-loss characteristics but is also bulky and difficult to integrate with planar technology, such as surface mount technology (SMT), or stack with other components. RF filters, which select or block bands of frequencies received by RF or microwave devices, are often required in large quantities in communication systems. Optimising the size, weight, power and cost (SWaP-C) while maintaining or improving filter RF performance has the potential to greatly improve the performance of the overall system in a number of ways.
For these reasons, the greatest potential for improvement lies in creating miniaturised components that can be easily integrated in an RF system.
The solution: unique circuit design and fabrication technology
Benchmark Lark Technology has been providing high-quality microwave and RF filters for telecommunications, medical, computer, aerospace and defence applications since 1986. Today, the company offers high-performance RF components to solve tough SWaP-C challenges. This combination of skills and experience was essential to the design of smaller, lighter filters.
To arrive at smaller, high-performance filters that address many of the disadvantages of conventional waveguide technology, engineers at Benchmark Lark Technology have created a new line of surface-mountable filters. Using substrate-integrated waveguide (SIW) technology, engineers developed a family of filters that offer high quality, small size and easy integration with existing planar technology, all while reducing the manufacturing cost to a point where they are viable for use in high-volume commercial microwave applications.
To solve the many challenges of successfully miniaturising RF filters, the Benchmark Lark Technology team, working in conjunction with high-performance circuit fabrication engineers, has developed a technology that takes advantage of some of the newest capabilities for fine line processing and tight dimensional control in the industry to provide extremely repeatable millimetre wave filters in very small packages. Utilising this technology gives the Benchmark teams multiple tools for miniaturising device footprints, while maximising RF performance.
Choosing the best material for the substrate was a major consideration for optimal performance at microwave and mmWave frequencies. The engineering team experimented with many filter topologies and substrate options at lower frequencies in order to quickly identify and overcome initial design problems, as well as identify the best materials for further trials.
The team then designed higher frequency filters and produced prototypes, such as the one shown in figure 1, in fused silica, a low loss, ultra-stable over temperature material for narrowband filters. But fused silica is limited to one-layer designs.
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Fused silica surface mount technology (SMT) band pass (BP) filter: (a) size comparison versus a conventional WG filter, (b) measured results.
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Fused silica surface mount technology (SMT) band pass (BP) filter: (a) size comparison versus a conventional WG filter, (b) measured results.
There are a wide variety of material systems that have excellent characteristics for multilayered broadband filter designs, and these yielded several viable material options. The team ultimately chose materials with excellent electrical and mechanical characteristics, such as very stable dielectric constant, low dielectric loss tangent and stable performance measured against moisture absorption and temperature varying environments.
However, there were still obstacles to overcome; RF filters must be manufactured with precise dimensions to perform to specification, which initially presented challenges for the circuit design and manufacturing teams. Through several iterations, the team found solutions to precisely control circuit thickness and in the end created the multilayered miniaturised high-performance filter shown in figure 2, which performed to expectations.
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Liquid crystalline polymer (LCP) SMT BP filter: a) actual size, (b) measured results.
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Liquid crystalline polymer (LCP) SMT BP filter: a) actual size, (b) measured results.
The result: new RF module architectures that provide better performance in a smaller package
Benchmark Lark Technology has transformed microstrip (MS) bandpass filters into small, surface mountable stripline filters, which enable a significant improvement in SWaP-C. The filter shown in figure 3 measures 0.25 x 0.25 x 0.032 in. and weighs only 0.0032 oz. (0.09 g). This is five times lighter in weight than an interdigital microstrip bandpass filter fabricated on a Rogers RO40031 substrate.
Comparison of microstrip BP filter and stripline filter.
The company is currently developing new microwave and mmWave filters that afford frequencies of up to 40 GHz. High-performance substrates are used to deliver excellent high-frequency performance as well as optimise SWaP-C. In RF systems with dozens of filters, this new technology can have a major impact on system capabilities and economics.
Switch filter modules and other multi-component modules can also be designed and fabricated using a stacked filter topology, as shown in figure 4, which represents future development work on Benchmark Lark Technology’s product roadmap. Moreover, passive and active components can be integrated to not only reduce the size of the module but also improve performance.
Switched filter bank showing stacking LCP BP filters.
Benchmark Lark Technology
Reference1Rogers RO4003C laminates are proprietary woven glass reinforced hydrocarbon/ceramics with the electrical performance of polytetrafluoroethylene (PTFE)/woven glass and the manufacturability of epoxy/glass.