Frequency-independent suppression of strong RF signals superimposed on weak signals

A common problem with radiofrequency (RF) receivers is that in addition to the desired signal, there is an interfering signal of much greater total power. These receivers can be for communications, radar, interception, etc. The interference can arise intentionally, such as from intentional jamming, or unintentionally, such as radiofrequency interference from a nearby transmitter. There is a need for some form of interference suppression. Furthermore, it is desirable to keep this augmentation at a low cost. Such interference suppression (also called rejection or excision) has become the subject of much research. For example, for suppression techniques applied to spreadspectrum communications, see [1,2] and the references therein. Suppression can be carried out using numerous techniques which tend to be in the form of band-stop filtering, notch filtering, or adaptive filtering. These techniques can be implemented with a number of different technologies, such as surface acoustic wave devices and fast Fourier transforms. All of these techniques tend to have one thing in common -there is an attempt to remove interfering frequency tones. This approach is thus limited to suppressing one or a few CW tones. Therefore, they are of benefit primarily to interference that is very narrow band and is relatively static; i.e., its frequency and amplitude do not change with time. In this paper, an alternative approach, the frequency-independent strong-signal suppressor (FISSS) [3-51, is introduced. This approach can provide tens