Ultra-Miniature Filters

When the ultimate small size or small volume is required for applications with very limited space, MEMtronics utilizes its substrate integrated waveguide (SIW) technology to build ultra-miniature evanescent filters.

In these applications, the waveguide is sized such that the operating frequency is below the waveguide cutoff frequency. Although energy at the filter frequency cannot propagate in a traditional manner, there is still energy transference between filter cavities by near-field-coupling of energy in evanescent (diminishing) fields. Thus, evanescent cavities are a useful means for shrinking the filter dimensions smaller than could be achieved when utilizing a traditional propagating waveguide filter. There is a price to pay for shrinking the cavities, and that is a decreased quality factor. Evanescent filters will have lower Qu than those of propagating filters. However, in many cases the decreased performance is still sufficient for meeting customer requirements and is often better than can be achieved with traditional microstrip or stripline filters.

The layout of a typical evanescent SIW filter is shown below. This is a 4-pole X-band filter with a center frequency of 11.8 GHz and a bandwidth of 500 MHz (4.2%). This filter has a mid-band insertion loss of 1.1 dB, < 2.1 dB loss at the band edges, and a spurious rejection > 60 db. It comes with a size of 7.42 x 28.85 x 0.762 mm, for a total volume of 163 mm³ and a total weight of 0.36 grams. The unloaded quality factor of the filter resonators is > 400, more than double that achievable with a microstrip or stripline filter implementation.

MEMtronics has utilized this evanescent SIW technology to build a variety of even smaller filters spanning the 10-40 GHz frequency range, with bandwidths from 0.5% to > 50%. Examples of these filters are shown below.

If you have requirements for ultra-miniature filters, and are looking for a solution, send MEMtronics your requirements for a free evaluation and proposal.