The scope of this part of IEC 61337 is limited to filters using waveguide type dielectric resonators that are used for microwave applications such as portable phones, cellular base stations and radio links. It is not the aim of this standard either to explain the theory or to attempt to cover all the eventualities that may arise in practical circumstances. This standard draws attention to some of the more fundamental questions which should be considered by the user before he places an order for dielectric filters for a new application. Such a procedure will be the user's insurance against unsatisfactory performance. Standard specifications, such as those given in IEC 61337, and national specifications or detail specifications issued by manufacturers, will define the available combinations of mid-band frequency, pass band, insertion attenuation, pass-band ripple, return attenuation, spurious response, operating power, and so on. These specifications are compiled to include a wide range of dielectric filters with standardized performances. It cannot be over-emphasized that the user should, wherever possible, select his dielectric filters from these specifications, when available, even if it involves making small modifications to his circuit to enable standard filters to be used.