Transmission Line Filters Approximating a Constant Delay in a Maximally Flat Sense

An exact method is presented to find transmission factors of transmission line filters which approximate a constant delay in a maximally flat sense. The class of filters considered is a doubly loaded arbitrary cascade of transmission lines and open- or short-circuited stubs in series or in shunt, all elements being of equal length and nondispersive. This includes a variety of transmission line filters:
\lambda/4
transformers, distributed lowpass filters, stub filters of various configurations, interdigital filters, etc. Explicit expressions, valid for any order
n
of the filter, are derived for the normalized transmission factor, and for its squared magnitude, and its phase on the imaginary axis. In addition, a table and design curves are provided for the cases
n = 2, 3, 4
, and 5 and an example is given to demonstrate their use.