Table of contents:
- Gain (to amplify the weak antenna signals to levels that can be more easily processed by a demodulator, AD converter etc.)
- Mixing (to convert the -often rather high- input frequency to a more convenient -usually lower- intermediate frequency that can be more easily filtered and further processed)
- Filtering (to suppress interferers and isolate the wanted signal
These steps are typcally followed by equalizer, demodulation, detection, clock recovery, frame detection, error correction etc. These steps can then be carried out at relatively low frequencies, conveniently high signal levels and in the relative absense of interferers, and are usually not considered RF circuits any more: they can be implemented as (low frequency) analog circuits or (nowadays quite often) digital circuits. There is a trend, especially for lower frequency receivers, to move more and more signal processing into the digital domain, ultimately ending with data conversion very close or at the antenna, blurring the distinction between RF and data converter design.
However, this is usually not the case for design at the highest frequencies: since the RF circuits for such receivers operate at or near the boundaries of the technology, traditional RF/microwave/mm-wave/THz techniques are usually applied. In other words: architectures are a means to map available technologies onto required functionality and performance. If the gap between required receiver performance and available technology performance is large (i.e. if the technology is "too good") then "low frequency" analog and digital signal processing and related architectures can be used. If the gap is small, circuits need to operate at the limits of feasibility and RF architectures are used.