Choosing the right filter is an art balancing size, cost, performance, and fabrication time. There are many approaches available in the X-Microwave system for both off-the-shelf and custom filter solutions.
Off-the-shelf Filter Library
Hundreds of read-made filters are available using a wide range of technologies including Lumped element and LTCC filters from MiniCircuits, MLO Filters from AVX, thin film ceramic from DLI/Knowles, tunable filters from Analog Devices and Atlanta Microwave, and MMIC wire bondable filters from Marki Microwave (to name a few). They offer a relatively quick, convenient, and low cost way to design a filter into your system.
When a specific filter passband, rejection, or bandwidth are needed to achieve the spectral purity requirements a custom filter may be needed. In these cases the best option may be to cascade a lowpass and high pass filter together to create a custom bandpass filter, or to create an entirely new custom filter design.
Cascaded Highpass / Lowpass Filters
Often times you can achieve custom performance with a small impact to insertion loss by placing a high pass and low pass filter in series. The combination of off-the-shelf filters often provides the quickest path to “near custom” performance. The X-MWsystem makes it easy to cascade filters in this manner, and trade them out as needed to tune performance of the system. Simply place two filers in series on the grid or use one of our integrated HPF-LPF filter boards.
X-Microwave Filter Design Services
Given a set of filter specifications, we can work with our partner network to delivery a custom filter in the X-Microwave format using a variety of technologies. Please email email@example.com with passband, insertion loss, and rejection frequency and level information and we can pull together a quote and timeline for a custom filter design.
Custom Filter Blanks
You can also design your own thin-film ceramic filter and place it in an X-Microwave filter blank. Thin film processes offer a convenient method for designing compact high frequency, high performance custom filters. Common ceramics include Alumina (Al2O3), Beryllium Oxide (BeO), and Aluminum Nitride (AlN) among others enabling tightly controlled repeatable designs. When designed to a standard set of dimensions, these filters can easily be mounted on ‘blank’ X-Microwave RF board for use on the grid.
In the X-Microwave format, thin film filters utilize the same format as DIE parts in the X-Microwave format. The filter is installed directly on the copper moly (CuMo) boss in the center of the cutout of 8-mil RO4003. Wire bonding or solder ribbon is used to attach the filter to the RF trace.
The white thin film ceramic filter above was attached to the copper moly boss of board 582 with epoxy used to attach the filter to the coppery moly base. The RF traces are connected to the thin film traces using ribbon and silver epoxy. We have now transitioned to wire bonding in most cases.
With an NDA in place, DXF files are available for the top layer metal for each of these filter blanks.
- MTOP = Layer 1, top metal and RF traces
- Cutout = cutout in the 8-mil RF board exposing the boss from the underlying copper Moly base
- Moly = Dimension of the boss coming up from the underlying copper molly base.