Multiband RF Front-Ends for Radar and Communications Applications
The development of software-defined radios (SDRs) should pave the way for achieving compact equipments capable of acquiring multistandard/multiband services . An analogue-to-digital converter (ADC) just after the antenna would directly implement the concept . Unfortunately, available ADC sampling rates and resolutions do not currently permit large radio frequency (RF) bandwidths to be handled. As a result, novel and revisited RF front-end configurations for SDR applications are now under research to overcome this bottleneck. Note that these schemes may be used not only for telecommunications purposes but also for other modern systems such as multifrequency radars. This introduction presents a brief summing-up of previously devised solutions for the realization of RF front-ends with emphasis on the SDR framework.
10.1.1 Standard Approaches for RF Front-Ends
From the receiver perspective, some alternatives to RF front-ends are interesting. One example is the superheterodyne architecture incorporating several mixing stages . Figure 10.1(a) shows its RF receiver chain. Here, the incoming signal is down-converted to a low frequency after filtering, where the acquisition is done. The first local oscillator (LO) usually varies its frequency ...