Publication number: 20150311882
Filed: Oct 23, 2013
Publication Date: Oct 29, 2015
Patent Grant number: 9887688
Inventor: Senad Bulja (Blanchardstown)
Application Number: 14/442,776.
Abstract: In this invention, a new type of RF filter, termed feed-forward filter, is introduced, Fig. 1.
This realisation is termed “feed-forward”, due to the fact that it draws its operational principle from the concept of the feed-forward amplifier .
The operational principle of the feed-forward filter is as follows. The input signal is initially filtered using Ceramic filter 1, which, even though it provides an adequate insertion loss performance, does not provide enough attenuation in the stop-band. The filtered signal, S1, is then passed through a loosely coupled directional coupler, which, provides a very low attenuation in the direct path, but it creates an attenuated replica of the signal filtered by Ceramic Filter 1, Φ(ω).
The coupled signal, Φ(ω) is then passed through a notch filter (in this realisation the notch is formed by a circulator and Ceramic filter 2), which greatly attenuates the pass band of the filter with a minimal effect on its stop-band. The signal obtained in this way is now amplified and phase compensated and, together with the inter-stage signal, Si, fed into the directional coupler at the output. Now, since the correction signal, Φf(ω) is very low in the pass band of signal Si, it will have very little or no effect on the insertion loss performance on the resulting signal at the output. However, in the stop-band region, the correction signal is equal in magnitude and in antiphase to the correction signal Si, which results in a very sharp stop band attenuation characteristic of the output signal.