3.2 Shielded microstrip tranmission linesMatlab program
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Fig. 3.2C.1 | Shielded microstrip transmission line |
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The presented program serves to the computation of electric-field intensity of modes,
which propagate along the shielded microstrip transmission line. The shielding waveguide
is of the dimensions 12.700 mm x 12.705 mm and is fabricated from the perfect-electric conductor. At the bottom of the waveguide, a
dielectric substrate is placed (lossless dielectrics of the relative permittivity εr = 4.2 and
height h = 1.27 mm). At the center of the upper side, a microstrip of the width w = 1.27 mm and of the negligible
thickness t ≈ 0 mm is etched; a perfect electric conductivity of the microstrip is assumed again. Above the
substrate, vacuum is expected. Thanks to the symmetry of the structure, a half of the
transmission line is analyzed only. Plane of symmetry is replaced by perfect electric
conductor is odd modes are computed, and by perfect magnetic conductor if even modes
are investigated. The term even (odd) mode is related to such modes, which electric-field
intensity distribution is even (odd) function with respect to the plane of the symmetry.
The program microstrip can be found (including all the necessary m-files) here.
Hence, we have to run Matlab and have to set the path to the folder Microstrip.
Typing microstrip to the command window of Matlab, the program is started. The next steps follow:
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Fig. 3.2C.2 | Finite-element mesh for the analysis of shielded microstrip transmission line |
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We type εr1 (see fig. 1) to the input line relative permittivity of substrate,
we type tan δ to the input line dissipation factor of substrate and we type the frequency, on which
the analysis is performed, to the input line frequency [GHz]. Then, we select modes
(buttons Even modes, Odd modes) we want to compute. Then, the program performs analysis
of the transmission line using the finite-element mesh, which is depicted in fig. 2.
- When the selected type of the analysis is finished, a dialog containing the line Mode number is opened. The lowest mode is of number
1, higher modes are numbered sequentially according to the magnitude of the phase
constant. Requested mode can be chosen by the scrollbar. Only modes, which can propagate along the transmission line
on a given frequency, are available. Pressing the button
Draw, two results are displayed: the first one shows the distribution of the transversal components of
electric-field intensity, the second one shows the distribution of the longitudinal component.
- Pressing the button End, the program is terminated.
The program microstrip is described from the programmer's point of view in the layer D.
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