Then a new method-combination frequency difference is proposed,which improves the performance of ranging under the same number of frequencies and the same condition.

Based on the nonlinear electromagnetic theory,general coupled-mode equations for difference-frequency coupling in nonlinear left-handed metamaterials(LHM) are studied.

Based on observation data in the basin,the stage design flood at the dam site is calculated by area interpolation method,compared with the maximal value of design flood,and the quantitative relations between them are also worked out by introducing the conception of combined frequency.

This paper investigates various combined frequency interference in integrated and double-converted transceivers, and points out that the reason is the non-linearity of frequency mixer and amplifier.

In order to do a good work on flood control works and to seek for a better calculation method, this paper describes the theory and its application of frequency combination method and compares it with the traditionally used method via the practical examples.