Matthaei is with Superconductor Technologies, Santa Barbara, CA USA. Snyder is with the RS Microwave Company Inc., Butler, NJ USA. Thus, many or perhaps even most filter designs commence from a lumped-element low-pass prototype filter, and the concepts of susceptance slope parameters and coupling coefficients unify the theories (see Section III). An important academic aspect of lumped-element filters is that their study is an essential part of the understanding of distributed filters, which are based to a large extent on lumped-element theory. However, there is no escaping the use of larger distributed filters when insertion loss and perhaps power handling are of major concern, unless superconducting filter technology is employed. Of course, dimensions are much smaller than distributed filters, which is a major advantage. Such figures compare favorably with microstrip, and production costs are quite low. The unloaded, which is realizable depends on frequency, but averages about 200, and values over 800 may be achieved at lower frequencies, e.g., at 170 MHz. Lumped-element filters are now used at microwave frequencies up to about 18 GHz, and form a large percentage of microwave filters produced by the industry. One important aspect of microwave filters, which was not covered then, is the lumped-element filter, which was starting to make an impact at about that time, actually beginning in the late 1970s. ROLE OF LUMPED-ELEMENT FILTERS IN MICROWAVE IMPLEMENTATIONS AND DESIGN SIGNIFICANT developments have taken place since the publication of the previous survey published in the 1984 Special Centennial Issue of this TRANSACTIONS. Index Terms Bandpass, cavity, ceramic, coaxial, combline, diplexers, evanescent mode, filters, hairpin line, high-pass, high temperature, interdigital, low-pass, lumped element, microstrip, microwave, multiplexers, parallel coupled line, planar, stripline, superconducting, waveguide. Many types of microwave filters are discussed with the object of pointing out the most useful references, especially for a newcomer to the field. It is shown that the basis for much fundamental microwave filter theory lies in the realm of lumped-element filters, which indeed are actually used directly for many applications at microwave frequencies as high as 18 GHz. Snyder, Fellow, IEEE, and George Matthaei, Fellow, IEEE Invited Paper Abstract A survey of the major techniques used in the design of microwave filters is presented in this paper. 3, MARCH Design of Microwave Filters Ralph Levy, Life Fellow, IEEE, Richard V. dwidth.1 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. Now then lets not get confused with station or channel spacing on the AM bands another link i think will throw some light. Have a look at this link, see if it helps any. I don't think with all the racket around today from switch-mode power supplies and other interfering garbage it would be wise to go beyond 6Khz. Imagine listening to Coruso on a 500Hz CW i.f. and 6Khz would be ideal for say a MW radio for receiving speech and music. 3Khz would be ideal for SSB use (Single Sideband), for voice communication 4 Khz would be dandy. With regards to bandwidth it all depends on what fidelity you want, for example for music a bandwidth of say 3Khz is not going to sound very good, the wider the bandwidth the better the sound. there are one or two circuits using a 'transformerless' design, I've even used the ZN414 and it's clones as a IF amplifier and detector with a NE602 front end mixer. With ceramic filters you can do away with IF transformers by making the drain or collector load about 2K.