Phase
shifters
Updated January
2, 2010
Below is an outline of all of
our material on phase shifters. This collection of material is easily
the best free phase shifter resource on the planet. And it keeps
getting better! Check out what Wikipedia
offers on phase shifters, it's slim pickings... you'd think
that Wikipedia's crappy phase shifter page would link to this good
one!
Types of phase shifters
Switched
line (delay line) phase shifters
Switched
filter phase shifters (new for December 2009!)
High-pass/low-pass
phase shifters
Spreadsheet
for high pass/low pass phase shifter calculations
Loaded-line
phase shifters
Ferroelectric
phase shifters
Reflection
phase shifters
180
degree hybrid phase shifters (such as rat-races)
Quadrature
hybrid phase shifters
Varactor
phase shifters
180
reflection bits using PIN diodes
Reflection phase shifters
using circulators (coming soon)
True
time delay
Vector
modulators (new for July 2009!)
Schiffman
phase shifters
MEMS
phase shifters (new for January 2010!)
Multi-state
phase shifter simulations in Agilient's ADS (new for January
2010!)
Phase
shifter data example 1
MMIC phase shifter examples
Example
1: AMTL six bit S-band phase shifter
Example
2: Marconi six bit C-band phase shifter
Applications of phase shifters
Frequency
translators
Phased
arrays
Residual phase noise measurement
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.
Active versus passive phase
shifters
More to come
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
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