Phase shifters

Updated June 15, 2009

Click here to go to our page on vector modulators (new for July 2009!)

Click here to go to our page on frequency translators

Click here to go to our page on RMS error calculations

Click here to go to our page on switched line phase shifters

Click here to go to our page on loaded-line phase shifters

Click here to go to our page on ferroelectric phase shifters

Click here to go to our page on reflection phase shifters

Click here to go to our page on high-pass/low-pass phase shifters

Click here to go to our page on Schiffman phase shifters

This collection of material is rapidly approaching the best phase shifter resource on the planet!

Some phase shifter background

Phase shifters are used to change the transmission phase angle (phase of S21) of a network. Ideal phase shifters provide low insertion loss, and equal amplitude (or loss) in all phase states. While the loss of a phase shifter is often overcome using an amplifier stage, the less loss, the less power that is needed to overcome it. Most phase shifters are reciprocal networks, meaning that they work effectively on signals passing in either direction. Phase shifters can be controlled electrically, magnetically or mechanically. Most of the phase shifters described on this web site are passive reciprocal networks; we will concentrate mainly on those that are electrically-controlled.

While the applications of microwave phase shifters are numerous, perhaps the most important application is within a phased array antenna system (a.k.a. electrically steerable array, or ESA), in which the phase of a large number of radiating elements are controlled to force the electro-magnetic wave to add up at a particular angle to the array. The total phase variation of a phase shifter need only be 360 degrees to control an ESA of moderate bandwidth. Networks that stretch phase more than 360 degrees are often called line stretchers, and are constructed similar to the switched line phase shifters to be described below.

Analog versus digital phase shifters

Phase shifters can be analog or digital. Analog phase shifters provide a continuously variable phase, perhaps controlled by a voltage. Electrically controlled analog phase shifters can be realized with varactor diodes that change capacitance with voltage, or non-linear dielectrics such as barium strontium titanate, or ferro-electric materials such as yttrium iron garnet. A mechanically-controlled analog phase shifter is really just a mechanically lengthened transmission line, often called a trombone line. Analog phase shifters are a mere side-show and will not be covered here in depth at this time. If you are interested in more information on any of these analog phase shifter topics, let us know and we will try to accommodate you.

Most phase shifters are of the digital variety, as they are more immune to noise on their voltage control lines. Digital phase shifters provide a discrete set of phase states that are controlled by two-state "phase bits." The highest order bit is 180 degrees, the next highest is 90 degrees, then 45 degrees, etc, as 360 degrees is divided into smaller and smaller binary steps. A three bit phase shifter would have a 45 degree least significant bit (LSB), while a six bit phase shifter would have a 5.6 degree least significant bit. Technically the latter case would have a 5.625 degree LSB, but in the microwave world it is best to ignore precision that you cannot obtain. If you can't comprehend this point, you might want to consider a different career such as accounting.

The convention followed for phase shifters is that the shortest phase length is the reference or "off" state, and the longest path or phase length is the "on" state. Thus a 90 degree phase shifter actually provides minus ninety degrees of phase shift in its "on" state.

If you know of any phase shifter topologies not covered on one of our phase shifter pages that should be described here, drop us a line and we will add your knowledge to this chapter! Want to donate a photo of a phase shifter you designed? Send it our way and we might get your 15 minutes of fame if we decide to put it on this page…

Applications of phase shifters

Phased arrays

Frequency translators