Coaxial Line Filters

Author: J.B. Hoag

It is possible to build filter circuits out of resonant coaxial lines, of such a nature as to provide comparatively sharp cutoff; to pass certain frequencies and suppress others.

Fig. 36 S. A coaxial filter equivalent to a shunt impedance, Z

Figure 36 S shows the construction of a coaxial element which is the equivalent of a shunting impedance, and Fig. 36 T shows a possible structure for a series impedance.

Fig. 36 T. A coaxial filter equivalent to a series impedance, Z

The dimensions are such that the branches operate essentially as quarter-wave resonant lines. Combinations of these elements have been used as high-pass filters in the frequency range from 40 to 100 MHz. Obviously, the physical dimensions will be less as the frequency is raised.