Patent number: 9887688
Filed: Oct 23, 2013
Date of Patent: Feb 6, 2018
Patent Publication Number: 20150311882
Assignee: Provenance Asset Group LLC (Essex, CT)
Inventor: Senad Bulja (Blanchardstown)
Primary Examiner: Dean Takaoka
Assistant Examiner: Alan Wong
Application Number: 14/442,776
In this invention a new type of RF filter is presented, 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 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 a 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.