Yu.B. Nechaev, D.N. Borisov, I.W. Peshkov
At present the necessity of implementation of smart antenna with digital beamforming arises because of increasing requirements to wireless communications. Use of smart antennas allows to reduce measurements and mass, to improve sensitivity of a receive section and to realize control of amplitude-phase distribution for spatial division in real time. In real task it is required to process low-level signals so it is necessary to amplify them. Additionally it is necessary to cancel interchannel interferences using multiple channel processing technology.
In the paper a choice of elements for a pre-processing analog signal module with a operating bandwidth from 1.5 GHz to 1.75 GHz is done. This module can process an input signal power of 90 20 dBm and amplify them up to 2 dBm. The module allows eliminating adjacent channel interferences more by 43 dB and beyond operating bandwidth interferences more by 43 dB.
The pre-processing analog signal module depends on nominal values of its elements. Deviations of these values can appear in case changing a temperature, fault of individual elements or deviations of the nominal values from correct values declared by manufacturer. Studies showed that the small deviations of the nominal values of the elements more than 1.7% result in considerable degradation of smart antenna performances – decreasing the signal-to-interference-ratio more than 60 dB.
Influence of the small deviations of the nominal values of the elements on key features of smart antenna can be eliminated by using calibration. An algorithm compensating phase and amplitude error shifts is used as calibration algorithm. These error shifts can be evaluated using an external reference signal source.
Thus the choice of the nominal values of the elements for existing receiver circuits has allowed to improve operation of the pre-processing analog signal module with smart antenna. Use of calibration allows to eliminate the amplitude and phase errors appearing because of tolerances of the elements of the pre-processing analog signal module.