With the current concentration of RF and microwave activity it is becoming increasingly important to eliminate unwanted signals so that the signal can come through loud and clear. Given the importance of providing users with filters to enable them to offer high performance equipment, Reactel Inc.

has developed a line of ultra narrowband notch (band reject) and bandpass filters. These ultra narrowband units are offered for frequencies from a few megahertz to 10 GHz. Leading the charge in this endeavor is model number 4R9-2000-X1.45S11.

Technical Considerations

The model 4R9-2000-X1.45S11 is a notch filter which is centered at 2000 MHz, with a 1.45 MHz 3 dB bandwidth. This calculates to an eye popping 0.0725 percent bandwidth.

The new notch filter is able to achieve such a narrow percent bandwidth by utilizing a precise blend of traditional notch filter design and high Q cavities. This approach combines the best of all worlds: low loss, ultra high selectivity and extremely deep attenuation. Using a standard design, the narrowest bandwidth one could hope for would be along the lines of 10 MHz or so with a center frequency of 2000 MHz.

Figure 1 represents actual measurements of this unit. The unique design yields a 3 dB bandwidth of 1.45 MHz and rejection of greater than 85 dB at the center of the notch. Additional specifications include insertion loss of less than 0.15 dB and a size of 2.5" x 2.5" x x 18.0". Connector options are virtually limitless as all traditional coaxial RF connectors can be utilized (see Table 1).


This particular unit was intended for a test equipment manufacturer. However, units have been manufactured that are also suitable for military, commercial and industrial applications.

Typical uses for ultra narrowband units include GPS applications for any of the GPS frequencies, spot frequencies for a unique application, or in any instance where there is close-in interference that must be eliminated.


The Reactel model 4R9-2000-X1.45S11 notch filter offers a unique approach to solving co-location interference problems. The industry leading performance allows users to utilize as much of their spectrum as possible resulting in superior system performance. Additional information on this notch filter or any of the company’s co-location interference ultra narrowband units or any Reactel product may be obtained via e-mail at reactel@reactel.com.

Reactel Inc.
Gaithersburg, MD
(301) 519-3660

RS No. 303