In handheld wireless devices, inaccuracies in specifying the correct filter ultimately translate into frequency conflicts that result in crosstalk, dropped calls, loss of data, and interrupted network connections. The wireless product may then fail a qualification test, forcing it back to the drawing board. Anatech Microwave Co. provides eight important tips on correctly specifying filters for RF and microwave applications in the four-page white paper, "Getting It Right the First Time When Specifying FiltersWhat Electronic Design Engineers Need to Know."
This concise document begins by advising engineers to know the basic filter response curves, which include bandpass, lowpass, highpass, bandstop, diplexer, and duplexer. Each respective profile determines which frequencies are passed and which are rejected. Second, engineers should provide all necessary specifications, such as center frequency, cut-off frequency, and cut-on frequency. They also should specify characteristics like bandstop, isolation, insertion loss, and more.
Through the specification process, the engineer should be mindful not to seek unrealistic filter performance. Rejection is gradual rather than abrupt. In addition, the engineer should strive for a reasonable voltage standing wave ratio (VSWR), such as 1.50:1. Power handling is key too, as filter size is essentially a function of power-handling capability. The specification of any part invites trade offs that must be considered. If the cut-off points are closer to the center frequency, for instance, the filter will be more complex and insertion loss will be greater. With these tips in mind, it is possible to limit production expenses while increasing the end product's chance of success.
Anatech Microwave Co.,
70 Outwater Ln.,
Garfield, NJ 07026;
(973) 772-4242, FAX: (973)772-4646,