Download 10EC54_MicrowaveAndRadar-Unit4

Subject Name: Microwave and Radar- Unit 4
22/8/14
Subject Code:
10EC54
Prepared By:
Lakshmi C R, Dharani K G
Department:
ECE
Date:
10.11.14
UNIT 4
Microwave Network
Theory
Topic Details
•Microwave Network Theory
•Symmetrical Z and Y parameters for
reciprocal networks
•S matrix Representation of multi port
networks
Microwave Network Analysis
Solving Maxwell’s equations for microwave networks/transmission
line networks is bit hard, with many terms repeating some times.
While we removing the repeated terms (by cancellation or taking
arbitrary constant), a qualitative term will get – which can be defined
by “Voltage and Current” intern.
By further reducing the terms with RLC component, the problems
looks simple.
For such problems, we can apply old network analysis. That’s called
“Microwave network analysis”.
Keep in mind: where ever the components (especially the z
components) are same thought-out circuit, then we can apply MNA.
For example – A ferrite device shall change the phase (may not
allow in opposite direction), so a suitable parameter should be
introduced for such networks
Concept of Impedance
•The term “Impedance” has been coined by “Oliver Heaviside”.
•Impedance can be defined as “complex ratio of Voltage to Current”,
this has been used hugely in AC circuits.
•For example, pointing vector of one port network
•“Port” is a key word to define two-terminal-pair. In Microwave circuits,
instead of positive-negative line (pair), the ports have “Incident – Reflected
components” or “voltage – current”
•In case of “multi-port” problems, the use of matrices is very important.
Matrix form shall reduce plenty of complexity
So called “Port Parameters” or “Parameter matrix”
Impedance and Admittance Matrices
Must keep in mind, all port components are taken with respect to a reference
line (so during measurement, all components are in-phase), called position z
= 0.
Network properties
1. Reciprocal property
The impedance/admittance matrix is symmetry
Z ij  Z ji
Yij  Y ji
2. Lossless property
In word, real part of impedance is responsible for loss, so
for lossless:
Re Z ij   0
3.Matching property
Zii  Z0
Yii  Y0  1
Z0
Show that it’s impossible to construct a three port network with Matched,
Reciprocal and Lossless.
To begin: