Air-filled square coaxial transmission line and its use in microwave filters

A suspended coaxial transmission line with an air propagation medium is presented. The transmission line is made only of metal, thereby avoiding dielectric and radiation losses. Shortcircuit stubs suspend the centre conductor of the coaxial structure which is used in the design of two dual-mode narrowband microwave filters. Stacked layers of copper sheets are used to form the square coaxial transmission line, which has low loss and low dispersion