Variable-impedance matching between the antenna and the RF-frontend provides several potential advantages, including changing operational frequency, compensating for unintentional mismatch, improving ...scanning capability, and reducing noise and interference signal levels. In this article a concept of tuning the operational band of an antenna by variable-impedance matching is presented. In this investigation a 65 nm CMOS RF-frontend capable of changing its input-impedance is used to tune the operational band of a microstrip antenna. It is shown that by properly selecting the input-impedance of the RF-frontend, the operating frequency of the antenna can be shifted, which increases the total operational bandwidth from 10 MHz to more than 30 MHz.
Spectrum sensing for cognitive radio requires a high linearity to handle strong signals, and at the same time a low noise figure (NF) to enable detection of much weaker signals. Often there is a ...trade-off between linearity and noise: improving one of them degrades the other. Cross-correlation can break this trade-off by reducing noise at the cost of measurement time. An existing RF front-end in CMOS-technology with IIP3=+11dBm and NF<6.5dB is duplicated and attenuators are put in front to increase linearity (IIP3=+24dBm). The attenuation degrades NF, but by using cross-correlation of the outputs of the two frontends, the NF is reduced to below 4dB. In total this results in a spurious-free dynamic range (SFDR) of 89dB in 1MHz resolution bandwidth (RBW).
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