Solution
description
Solution
options
Near fields -
The Near fields option is used to define the locations for near
field calculations.
Radiation pattern -
The Radiation pattern option is used to define azimuth and zenith
angles for radiation pattern calculations.
Two-port coupling -
The Two-port coupling option is used to define the location
of the two ports for the calculation of coupling.
Medium wave array synthesis -
Following a process
used by the Federal Communications Commission (FCC), this option can be used
to design a broadcast array. The FCC process uses a per unit pattern based upon
the relative contribution (in the horizontal plane) to the radiation pattern
of each radiating tower in the broadcast array. The relative contribution is
described in terms of complex field ratios (e.g., magnitude and phase). The
voltages at the bases of the towers in a broadcast array can be related to the
field ratios and phases that result from the FCC AM directional antenna design
procedure. The field ratios are the array parameters that are inputs to the
FCC program RADIAT which is used to compute the electric field pattern and the
constraints that determine the behavior of AM medium wave standard broadcast
directional antennas in the United States.
The objective of
this option is to determine the base and node voltages and currents that will
produce the desired field ratios. For a self-check of consistency, these base
node voltages can be used as sources for the defined broadcast array. The current
moments can then be computed. If the computed current moments are equal to the
field ratios, the design has been validated.
Planar array phased array
New array definition -
The New array definition option is used to define a transmit
or receive planar antenna phased array from a given antenna element defined
in the Geometry definition and a source node defined in the Electrical definition.
Source/load modification - The
Source/load modification option is used to modify the amplitude and phase distributions
for a transmit or the loads for a previously defined planar antenna phased array.
Log Periodic Dipole Array -
The Log periodic dipole array (LPDA) dialog box is used to provide
an optimized array for maximum directive gain.
Specific antennas -
Specific antenna descriptions, such as a Vee dipole antenna,
loop antenna, dual quad antenna, and three element Yagi antenna, become available
under this heading.
Other run options
FCC ground wave -
FCC ground wave calculates the ground wave electric field intensity
at given frequencies and distance for given electric ground constants. This
computation predicts the ground wave propagation used by the FCC in the AM broadcast
band.
Stub matching -
The Stub matching option is used to define transmission lines
for a single stub matching of a load to a lossless transmission line. Short
lengths of transmission line, short-circuited or open-circuited at one end,
are often used as reactances in impedance matching circuits.
Tower footing impedance -
The Tower footing impedance option provides calculations to assist
the user in determining a tower footing impedance. The "footing" impedance method
is an approximation which uses a lumped load in series with the base of a tower
on a perfect conducting ground plane to model the effects of a "lossy ground"
with a given conductivity and dielectric constant.
Auxiliary options
Antenna matching -
Antenna Matching aids in the design of a matching network for
a broadband antenna. An optimization algorithm using the method of steepest
descent finds the values of the passive components (i.e., inductors and capacitors)
that minimize the input reflection coefficients.
Impedance interpolation -
Impedance Interpolation interpolates the antenna impedance over
a user specified frequency band using model based parameter estimation (MBPE).
MBPE is a form of "smart" curve fitting because it uses a fitting model that
is based on the problem physics as opposed to standard curve-fitting approaches.
Impedance Interpolation uses the commonly employed rational-function interpolation
or Cauchy's technique. An adaptive frequency sampling is also available to the
user. Sample frequency points will be suggested to the user to better match
the frequency interpolation. The user can then select that these selected frequencies
be added to the current project definition. Currents for these selected frequencies
will be computed and added to the previous current calculations.
Multi-port analysis - Multi-port analysis provides information that will support multi-port analysis. This includes self admittance and transfer admittance between user selected ports. In addition the patterns for each of the user selected ports are also computed and made available to the user. Each port is excited while the other ports are short-circuited.
Pattern synthesis - Pattern
Synthesis optimizes the voltage sources to provide a desired radiation pattern.
SWR analysis - VSWR analysis calculates the reflection coefficient, return loss in dB, the power loss in percentage and mismatch loss in dB for a user specified range of VSWR values.
Computation
time
The computational algorithms
in Expert MININEC are implemented in FORTRAN 90. This increases speed and helps
to make maximum use of available memory to set array sizes. The speed of computation
is dependent on the platform and the type of problem. As an example, a dipole
in free space with increasing number of segments was run on a Desktop Pentium
with 3.2 GHz CPU. The results are presented in the following
segments computation time
1500 4 seconds
2000 15 seconds
2500 21 seconds
3000 34 seconds
3500 54 seconds
4000 80 seconds
4500 114 seconds
5000 1560 seconds
The
computation time for an individual problem is dependent on the number of wires
defining the problem and the existence of a ground plane. However, in general,
as the number of unknowns increases, the computational speed changes from a
dependency on the square to the cube of the number of unknowns. For the simple
problem of a dipole the computational time will be close to the cube of the
number of unknowns in Expert MININEC. As the number of unknowns is increased
the computer will begin to use virtua`l memory and the coefficient will increase
above 3.
Sample calculations
The formulation in Expert MININEC Series has been changed from earlier
versions of MININEC to use triangular testing functions rather than pulses.
This results in greater accuracy.
The short segment limit is accurate to approximately machine
accuracy. The conductance can be computed as a function of the segment length
in wavelengths for a short dipole. Ten segments are used to model the antenna.
The segment length to radius ratio is 100. The Expert MININEC Series
shows the proper behavior for conductance down to the numerical limit of computation
for a personnel computer. Both conductance and susceptance for short dipoles are a
function of frequency. The conductance is a direct function of the frequency
to the fourth power. The susceptance is a linear function of frequency. For
small loops the conductance and the susceptance are well behaved down to .0005
wavelengths in circumference.
The Expert MININEC Series treatment of
bent wires has also been improved so that square loops can be accurately modeled.
In the Expert MININEC Series it is not necessary to employ a tapered
segmentation scheme to model wires of acute angles.
In addition, a Fresnel reflection coefficient
approximation improves the calculation of currents in the vicinity of real ground.
It is can also be applied as a correction to radiation patterns.