Method and apparatus for minimizing intermodulation with an asymmetric resonator

Abstract

A method and apparatus to control intermodulation in a circuit for filtering over the air signals by creating an asymmetric resonator is disclosed. By creating the asymmetric resonator, the intermodulation from out of band signals is reduced while keeping the filter size relatively unchanged. In general, the intermodulation is reduced by lowering the current density in the resonator (e.g. so as to maintain the linearity of the electrical characteristics of the resonator), and more specifically by utilizing the principle that the inductive elements in a resonator experience the largest currentchanges. Therefore, the size of the inductor is changed in order to accommodate the larger power. An additional feature of the present invention is that not every inductive element of the filter needs to be enlarged. Generally only the first (or alternatively the first and second) resonators need to be increased in size. Another feature of the present invention is the physical order in which the filters are laid out. Laying out the components with the bandpass filter first can prevent (or significantly reduce) intermodulation generated by those components due to out-of-band interference signals.

Description

[0001] This application is filed as a PCT International Patent Application and the applicant is Conductus, Inc., a US national corporation, which is the designated applicant on February 19, 2003 for all countries except the United States. technical field [0002] The present invention relates generally to filters for electrical signals, more particularly to minimizing intermodulation in narrowband filters, and more particularly to methods and apparatus for controlling intermodulation from airborne signals using asymmetric resonators. Background technique [0003] Narrowband filters are particularly useful in the communications industry and are especially useful in wireless communication systems utilizing microwave signals. Currently, wireless communications have two or more service providers operating on respective frequency bands in the same geographic area. In this case it is important that the signal from one provider does not interfere with the other provider's signals. ...

AI Technical Summary

Problems solved by technology

However, in this type of environment where small filter sizes are required and when the out-of-band interfering signals are strong, then the non-linear nature of the HTS can produce high levels of intermodulation signals in-band so that the channel is unusable

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