Filtering functions to reject unwanted signals are being made
smaller through a variety of circuit configurations, with
packages that include drop-in and tiny surface-mount styles.
Smaller filters are a requirement for a growing number of
commercial and military applications. With available spectrum
becoming ever more crowded, filtering requirements are
increasingly more severe, but filter suppliers are being asked
to shrink their packages to fit more portable and compact
applications, from cellular telephones with embedded Global
Positioning System (GPS) receivers to tactical radios for
miniature military unmanned aerial. A variety of different
technologies are used to achieve smaller microwave filters,
including lumped-element, stripline, and microstrip circuit
approaches and the use of select materials, such as ceramic
substrates to reduce circuit dimensions. Merrimac Industries,
for example, relies on its patented Multi-Mix multilayer
fabrication technology to create fusionbonded stripline filter
circuits