SCATTERING PARAMETERS OF CIRCULATOR
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project report helper
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#1
01-11-2010, 05:27 PM



.doc   EXP 8 SCATTERING PARAMETERS OF CIRCULATOR.doc (Size: 1.75 MB / Downloads: 136)
SCATTERING PARAMETERS OF CIRCULATOR

SCATTERING PARAMETERS OF CIRCULATOR


AIM: To study the operation of ferrite circulator and hence measure
i. Insertion loss ii. Isolation iii. And to determining S parameters

EQUIPMENT: Microwave Source (RKO/GO), Isolator, Variable Attenuator, Frequency meter, Slotted line , Tunable probe with detector, detector mount with detector, VSWR meter, Circulator and Matched Terminations-2.

THEORY: The circulator is a multi port junction that permits transmission in certain ways. The wave incident at nth port can be coupled to (n+1)th port only.
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seminar flower
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#2
21-08-2012, 02:21 PM

S (scattering) Parameters


.pdf   scattering.pdf (Size: 20 KB / Downloads: 116)

Scattering, or S, parameters are another extremely useful design aid that most manufacturers provide for
their higher frequency transistors. While Y-parameters utilize input and output voltages and currents to
characterize the operation of a two-port network, S parameters use normalized incident and reflected
traveling waves in each network port. There is no need to present a short circuit to the two-port device. This
termination often causes an active device, such as a transistor, to become unstable, thus making
measurements impossible.
Instead, the network is always terminated in the characteristic impedance of the measuring system and this
is, in most cases, purely resistive 50 Ohms. In addition, the 50-Ohm source and load seen by the two-port
network forces the device under test, if active, to be stable and not oscillate.
I. Transmission line theory.
To understand the concept of S-parameters, it is necessary to first have a working knowledge of
transmission line theory.
Voltage, current , or power emanating from a source impedance Zs and delivered to a load Zl can be
considered to be in the form of incident and reflected waves traveling in opposite directions along a
transmission line of characteristic impedance Zo.

SMALL SIGNAL AMPLIFIER DESIGN:

Transistors can be completely characterized by their S parameters that vary with frequency and bias level.
With these parameters, it is possible to calculate potential instabilities (tendency to oscillation), maximum
available gain, input and output impedances, and transducer gain. It is also possible to calculate optimum
source and load impedances either for simultaneous conjugate matching or simply to help choose specific
source and load impedances for a specified transducer gain.

Unilateral Input/Output Gain Circle

Unilateral Figure of Merit, U.
All two-port models are bilateral, so both the forward and reverse signal flow must be considered. If the
signal flow in the reverse direction is much smaller than the flow in the forward direction then it’s possible
to make the simplification that the reverese flow is zero. The Unilateral Figure of Merit, U is a quick
calculation that can be used to determine where this simplification can be made without significantly
affecting the accuracy of the model.
A transistor is said to be unilateral if the signal/power bounced back from the output to the source is equal
to 0. This occurs if the reverse transmission coefficient, S12 or the reverse transducer power gain, |S12|2 is
equal to 0.
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