AS TIME TO MARKET for RF and microwave products has shortened, wireless service providers and consumers have unearthed many shortcomings in frequency management. Such shortcomings, which include noise, crosstalk, and signal dropouts, often have a solution in the simple filter. To provide tips on avoiding filter-related interference, Anatech Microwave has created a white paper titled, "Say What? My Cross-talk Problem is at the Component Level? A Filter, You Say?"
This four-page document notes that the difficulty in transmitting and receiving a clear signal stems largely from competition for band space. For example, the CDMA cellular-communications passband ends at 888.9 MHz while the GSM 900 passband begins at 890.1 MHz. Filters are the only components guarding against interference across such relatively narrow gaps. Yet in an increasingly outsourced design environment, filters tend to be overlooked as long as communications systems designs look good on paper.
To improve the performance of wireless products, the filter should not be treated as an afterthought. The engineer should prepare for interference and try to predict its sources at the start of the design. It also is important to not test the product in too "friendly" an environment. In addition, one should insist on a filter with sharp cutoff and high isolation. In case an unforeseen frequency conflict arises, the engineer should make sure that the filter manufacturer can change component characteristics on short notice. Because circuit real estate is shrinking as performance demands increase, filter size should be considered as well. With these tips, microwave engineers should be able to guarantee better performance in their wireless products.
Anatech microwave Co., 70 outwater Ln., Garfield, NJ 07026; (973) 772-6767, FAX: (973) 772-4646, internet: www.anatechmicrowave.com.