Size, weight and power (SWaP) are key considerations in the component selection process for RF systems. MMIC processes have a proven track record as the technology platform for high performance components throughout the various sub-blocks in the RF signal chain. However, MMIC technology has become a viable option for high volume filter development only recently. This is largely due to the growing importance of size reduction.
Figure 1 MFBT-00003PSM insertion loss.
In an ideal world, filters would be selected early in the system design phase. These filters can be commercial off-the-shelf solutions and in some cases, frequency plans can be changed to accommodate filters available in the market. Unfortunately, due to the presence of unexpected spurious products that may only present themselves during testing, a real-world receiver will also have several “oh no” filters. The job of these filters is to suppress these unexpected tones. For projects where time to market is key, this presents a problem as these filters will be custom designs that require engineering and manufacturing lead-times. For this reason, modern custom filter designs must be fast-turn designs that are right the first time.
In recent years, Marki Microwave has developed a novel design flow for MMIC filter design including standard response types (bandpass, highpass and lowpass) as well as some more advanced concepts like notch, reflectionless and configurable filters. Marki Microwave’s proprietary design flow has demonstrated a high level of agreement between initial simulations and measured results, leading to first-pass design success for custom filter solutions. This enables rapid filter development and reduced cycle times. Due to the inherent advantages of the MMIC platform, these solutions are repeatable from unit to unit and wafer to wafer and are scalable to high volume.
RECENT MMIC FILTER DEVELOPMENTS
MMIC is well suited not only for common filter response types but also for more advanced concepts. Marki Microwave recently released a family of varactor diode tunable filters that allow users to create bandpass filters with variable center frequencies and percent bandwidths through independent analog tuning of the highpass and lowpass sides. This makes them well-suited for adaptive filtering applications such as LO tracking. These impedance-insensitive filters utilize a balanced design to feature low return loss in both the passband and stopband. Table 1 shows the performance results.
Figure 1 demonstrates the tuning capability of Marki Microwave’s MFBT-00003PSM, which features a wide center frequency tuning range of 8 to 30 GHz. The top chart in Figure 1 shows the MFBT-00003PSM sweeping lowpass and the bottom chart shows the MFBT-00003PSM sweeping highpass.
FILTER DESIGN TOOLS & PRODIGY™ FILTER DESIGNER
Figure 2 shows several filter design tools that Marki Microwave hosts on its website to enable the development of accurate fast-turn solutions:
Figure 2 Marki Microwave’s web-based filter design tools.
LC Filter Design Tool: Uses a lumped element model to calculate LC filter circuit values for lowpass, highpass and bandpass responses, using either Chebyshev, Elliptic, Butterworth, Bessel or Legendre filter topologies. It is a great tool to see whether a filter is theoretically possible. If a filter cannot be realized using this tool, it is unlikely that it is a realizable filter.
Microstrip Filter Tool: Provides an ideal design of a distributed-element microstrip filter. This tool allows you to design on various dielectric substrates, using Chebyshev or Butterworth filter types, to get a first approximation of a filter design. This demonstrates what is possible, but results should be verified and optimized in 3D EM simulations.
Prodigy Filter Designer: Custom filter solutions often need to be developed quickly to prevent delays. The standard filter development flow is an iterative process between a customer and manufacturer on filter specification negotiations and system validation that can take weeks. Marki Microwave developed Prodigy Filter Designer to streamline the development flow for system designers and reduce time to market.
WHAT IS PRODIGY?
Figure 3 Matrix of known good filter designs generated by HOTMESS.
The LC Filter Design Tool and Microstrip Filter Design Tools can be thought of as calculators to see what is theoretically possible, whereas Prodigy Filter Designer is a MMIC filter design tool that produces a real FEM-designed filter with known design variables and size. It uses machine learning to calculate real S-parameters nearly instantaneously, including all the 3D effects like metal loss, parasitics, cross-coupling, etc. Prodigy is powered by HFSS optimization through microwave element surrogate simulation (HOTMESS), which is Marki Microwave’s proprietary automated 3D FEM solver. HOTMESS generates a set of 3D FEM-validated S-parameters, including the physical layout of the filter. Marki Microwave uses HOTMESS to create databases of known good filters by filter type and filter topology. This is the foundation of the Prodigy Filter Designer. Prodigy takes the known good filter designs and uses machine learning algorithms to interpolate between these points to design a filter based on customer inputs. This idea is shown, conceptually, in Figure 3.
Users can select the filter best suited to their specific requirements and input desired center frequency and percent bandwidth from the growing list of topologies. The S-parameter file and die dimensions of their filter are instantly provided from these inputs. Designers can then take that S-parameter file and validate the design in their system. Prodigy essentially pushes the iterative process of specification negotiation to the customer without having to involve a Marki engineer, saving weeks in the process. Once they are happy with a design, Marki’s engineers take it from there. If a customer desires a filter to be packaged into a surface-mount package, Marki’s engineers can take their filter design, apply packaging effects and send back a validated set of S-parameters.
Currently, Prodigy can be used to design bandpass filters and it will continue to grow as more topologies and filter response types are added. Prodigy Filter Designer is currently available on www.markimicrowave.com.
Marki Microwave
Morgan Hill, Calif.
www.markimicrowave.com