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\title{\small \bf EXPERIMENT 2.\\
     NETWORK ANALYSER and a 3D-ELECTROMAGNETIC SIMULATOR}
\date{}         
\begin{document}
\maketitle
\vspace{-2cm}
{\bf Network analyser }
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Network analyser(NWA) is an instrument used for measuring
scattering parameters (S-parameters) of passive and active microwave
devices. Two broad classes of network analysers exist, namely scalar
and vector network analysers. Scalar network analyser can only
measure the magnitude of S-parameters but vector network analyser can
measure both phase and magnitude of S-parameters. Fig. 1 shows how a network
analyser can be used for measuring scattering parameter $S_{ij}$ of an
arbitrary device under test (DUT).
\begin{figure}[htbp]
\epsfxsize 10cm
\centerline{\epsffile{NWA.eps}}
\label{fig }
\caption{S-parameter measurement using Network analyser.}
\end{figure}
Standing Wave Ratio (SWR) and Group Delay are examples of other
parameters (other than S-parameters), which can be measured
using a network analyser. In this lab we will find experimentally,
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1) S-parameters of a {\it circulator} and
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2) Standing wave ratios (SWR) on a {\it coaxial cable}. 
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using the Wiltron-360 network analyser.
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{\it Wiltron-360 network analyser} is a vector network analyser made
by WILTRON and it has 3 basic building blocks,
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1)source 2)test set and 3)network analyser
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The signal source provides the stimulus to the DUT. The frequency
range of the source and the test set establishes the frequency range
of  the vector network analyser. The test set is a 2-port instrument 
that samples the incident reflected and transmitted signals. The
transmitted signal is alternated between port 1 and port 2 . It internally
converts recieved signal to a lower IF signal that retains the phase and 
magnitude relation of the original signal. The network analyser
analyses the IF signals from the test set for phase and magnitude
data which are presented on the display. 
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Measurements are made by comparing the relative magnitude and phase
changes between the signal incident to the DUT and reflected or
transmitted signal from the DUT. 
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One of the important steps before starting the measurement is {\it
Calibration}. Purpose of  calibration is to remove systematic errors 
during measurements by means of standards. Standardized components used for
a typical calibration are open, short,thru and a broad band load.
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\\ 
{\it The Lab-instructor will show the calibration kit of the network
  analyser and show the different calibration standards used for
  calibration.}
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Since the exact calibration procedure is elaborate and beyond the
scope of this lab, you will not do the calibration. However for your
measurements, you have
the option of using the calibration data from a floppy diskette.
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{\bf Complete the following tasks.}
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{\bf Task A) Find the S matrix of the given circulator using network
analyser for three different frequencies in X-band (8-12GHz).}
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\begin{itemize}
\item{ Step-1)Recall Calibration data from floppy diskette}
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In calibration panel of NWA press the following keys in sequence,
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{\it Save/Recall :: Recall :: Calibration data from disk :: filename}
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Instructor will tell you the required file name where calibration data 
is stored.
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\item { Step-2)Adjust channel display properties.}
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Press following keys in sequence,
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{\it Channel-menu :: All 4 channels}
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Adjust,
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{\it Graph-type :: Log Magnitude-Phase}
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for all the four channels
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\item{Step-3) Measure the S-parameters of the circulator.}
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For doing this connect port 1 of network analyser to port {\bf i} of
Circulator and port 2 of network analyser to port {\bf j} of 
Circulator. Connect  matched load at the remaining port of Circulator. 
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Adjust,
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{\it  Marker-menu::Marker 1 ON::Read out marker}
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Adjust the marker to 3 different  frequencies  of interest and read
{\bf $S_{11},S_{12},S_{21},S_{22}$} from the 4 channels (both
magnitude and phase)
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Complete the procedure for {i=1,2,3, j=1,2,3} so that the full
S-matrix of Circulator can be calculated .
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(Covert dB into ordinary scale and write S-parameters in
Magnitude-Angle form.)
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1) Frequency =----------GHz.
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$S_{11}=--------S_{12}=--------S_{13}=-------$
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$S_{21}=--------S_{22}=--------S_{23}=-------$
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$S_{31}=--------S_{32}=--------S_{33}=-------$
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2) Frequency =----------GHz.
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$S_{11}=--------S_{12}=--------S_{13}=-------$
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$S_{21}=--------S_{22}=--------S_{23}=-------$
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$S_{31}=--------S_{32}=--------S_{33}=-------$
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3) Frequency =----------GHz.
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$S_{11}=--------S_{12}=--------S_{13}=-------$
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$S_{21}=--------S_{22}=--------S_{23}=-------$
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$S_{31}=--------S_{32}=--------S_{33}=-------$
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\item{Answer the following questions}
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A-1)Explain briefly how a circulator work and write two applications.
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A-2)Compare your results with the S(matrix) of an ideal circulator and
explain why practical S(matrix) is different from ideal case.
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\\
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\end{itemize}
{\bf Task-B)Using network analyser, for the given coaxial cable determine the standing wave
ratios for frequencies from 1-10GHz (matched load conditions).}
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In the network analyser front panel,
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\begin{itemize}

\item{Step-1)Adjust the frequency sweep to 1-10GHz}  
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\item{Step-2)Adjust channel properties to single channel}
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\item{Step-3)Adjust Graph type to {\it SWR}.}
\end{itemize}
\begin{figure}[htbp]
\epsfxsize 12cm
\centerline{\epsffile{table3.eps}}
%\label{fig }
%\caption{S-parameter measurement using Network analyser}
\end{figure}
Tabulate your readings.
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B-1)From your observations suggest an operating region for best  performance.
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{\bf A 3D-electromagnetic simulator}
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Currently a number of electromagnetic simulators are available in
market which have already become part and parcel of microwave
industry. Coupled with powerful computers, these simulators  can be
used for  designing  and optimizing electromagnetic structure of any complexity in least possible
time. Many of these simulators support visualization of
electromagnetic fields which helps an experienced designer in his designs.
\\
\\
Electromagnetic simulators commercially available  can be divided
broadly into two classes namely 2D and 3D simulators. 2D-simulators can only be used for
simulating planar structures for eg. microstrip and coplanar
structures in multilayers or single layers (An eg. of such a
simulator is MOMENTUM). 3D simulator can simulate 3D-structures like
cavities, wave guides, horn antennas etc. 
\\
Let us have a look at one  simulator available in our laboratory,
namely {\it High Frequency Field Simulator (HFSS)} from Hewlett
Packard which is a 3-D electromagnetic simulator. This simulator is
mathematically based on a technique called Finite Element Method (FEM).
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For using HFSS, there are three broad phases,
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1. Drawing phase, where we draw the complex electromagnetic structure,
specify the materials etc.
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2. Boundary definition phase, where we define various boundary
conditions of the structure.
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3. Simulation phase, where we set up FEM-mesh, frequency for which
simulation is needed etc. and then the final simulation.
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Typical memory requirement for a standard simulation is 250MB RAM
which grows with the complexity of the structure. In our laboratory
HFSS simulations are currently run under 550MB RAM. Time taken for the 
simulation depends on processing speed of computer and complexity of
the electromagnetic structure.
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Let us use the HFSS simulator to view electromagnetic
fields in a rectangular wave guide.
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{\bf Task-C) 3-D view  of $TE_{10}$ mode fields and standing waves 
in a rectangular wave guide.}
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This  project has already been set up and simulated for you and the
window you see is the drawing window (try to study the various keys of 
this window)
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\begin{itemize}
\item{{\it A) $TE_{10}$ mode fields,}}
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A-a)Study of E-fields,
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From drawing window, go to the post processor of the HFSS simulator.
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For doing this click the following keys of the simulator,
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A-a-1)\hspace{1cm}{\it POST :: POST-PROCESSOR(OK)}
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A-a-2)In the Post-processor window,\\ \\
\hspace{1cm}{\it PLOT::PLOT FIELD-DATA }
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\hspace{1cm}{\it Plot=E :: Plane=XZ :: Arrow-density=fine}
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A-b) Study of H-fields,
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Erase the E-fields for clarity,
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\hspace{1cm}{\it WINDOW :: ERASE}
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Repeat (A-a) with the following difference,
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A-a-2) {\it PLOT :: PLOT FIELD-DATA (Plot=H :: Plane=XY :: Arrow-density=fine)}
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\item{{\it B)  Standing waves}}
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Go to the project where a shorted wave guide is constructed,
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Note the difference in the drawing (here a short is drawn at one end)
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Repeat all the steps mentioned in (A) and study the difference
of fields of (B) from  (A) by carefully observing  the E and H plots.
\end{itemize}
\end{document}