# stripline power divider

One of the ways to improve the over all performance of any radio station is to put up bigger

antennas. Antenna improvements affect both the transmitted and received signal and thus increase your

operating range. Once you reach a certain point, the only practical way to get “bigger” antennas is to put

up multiple antennas phased in such a way so that the total gain of the array increases (hopefully).

For VHF and above this usually requires the ubiquitous power divider.

Over the years I have built power dividers using coaxial cable or round copper tubing to achieve

the necessary matching of the various antennas in an array. Recently, I have been using waveguide to

construct 2 and 4 way power dividers. The waveguide has the advantage of being rectangular which

greatly facilitates the attachment of the coaxial cable connectors. It is also made of copper, unlike

power dividers made of square or rectangular aluminum tubing, which means the whole assembly can be

soldered for long lasting, waterproof, electrical connections.

A few words on how power dividers work is in order. Once you understand the simple theory of

operation of a power divider (combiner also) then you may come up with another way of building 1/4l

transmission line transformers that better suits your needs or available materials list. The basic

objective is to build transmission lines with the proper characteristic impedance to match two different

RF impedances. The shape or size of the transmission line doesn’t matter as long as it is the right

impedance.

The two most common configurations are intended to combine either 2 or 4 antennas, each with a

nominal impedance of 50 ohms. If you were to merely connect 2 antennas with equal lengths of 50 ohm

cable together the resulting impedance at the joined ends would be 25 ohms. This really isn’t too bad,

but we can do better. If we could somehow “transform” the 50 ohms at the end of each cable to 100 ohms,

then when we joined the new ends together we would be back to 50 ohms (The impedances combine like

resistors in parallel). Such a impedance transforming device is an electrical (compensated for the

velocity factor of the transmission line) 1/4l (at the frequency of interest) piece of transmission line

having a characteristic impedance (Z0)

Free download http://www.scribd.com/doc/8616044/RF-Antenna-Power-Dividers

What is described here is just one way of building power dividers. There are other

configurations such as having two or four antennas connected to one end of a power divider and use a

single 1/4l transformer to step up to 50 ohms. The theory is the same for all cases, just different

numbers. I think you will find the construction of the actual device is easier in the configurations

described here.

Below is an end view of a stripline transmission line. In typical stripline applications the sides

are not present. When used as a power divider, the presence of the sides of the waveguide do not effect

the results because of the distance from the center conductor. Eagleware RF design software was used to

calculate the width of the center conductor (w) that is required to achieve the 70 and 50 ohm

characteristic impedances needed for the 2 and 4 way power dividers.