Hi to all

In the line of my theses I have designed an antenna,
which I consider as prototype(?) and named it D-Dimond1.

The antenna was designed, simulated and examined
(and propably will be constructed) for educational reasons mainly
and not only to be practically exploitable.

The operating frequency will be somewhere between 900 and 1300 MHz.
However, the test frequency that I used for my measurements was 1111
MHz.

So, I would be very happy if you could spend some time
to take a look to some of its characteristics:

The following URL shows the geometry of the antenna in the 3D space.
As you can see, it lies at the yoz plane.
As you cannot see, the input source is considered to be
at the starting point of the axes, O.
http://antennas.ee.duth.gr/ooo/dt/05...ometry/geo.jpg

The following URL contains a text file with the coordinates of
the antenna's nodes and also the orientation of the current
running through the segments of the anntenna.
Its the input file to the program that I used
to compute the various characteristics.
http://antennas.ee.duth.gr/ooo/dt/05...etry/input.txt

The following URL will clear out the situation a little bit.
http://antennas.ee.duth.gr/ooo/dt/05...0analysis2.gif
It shows the current distribution (which is assumed to be sinusoid)
at the various segments of the antenna, as it results
from the application of the standing wave theory.
The antenna is composed of 7 dipoles lambda/2.
The angle between the 2 dipoles at both of the tops
of the antenna is 60 degrees.

The following URL shows the radiation pattern in 3D space.
http://antennas.ee.duth.gr/ooo/dt/05...ichwire/da.jpg

The following URL shows the comparison of the radiation pattern
at the 3 main planes (xoy, yoz, zox) at cartesian and polar coordinate
systems
between the analytical and the computational method.

http://antennas.ee.duth.gr/ooo/dt/05...analytical.doc

During the analytical method the antenna considered to be
polygonical and thinwire. The current distribution assumed to be
sinusoidal.
During the computational method I used a program called Richwire and is
based
at the Methods of Moments.


Finally, the following URL shows a series of measurements of various
characteristics
as the antenna is being divided at an increasingly number of segments.

http://antennas.ee.duth.gr/ooo/dt/05/hli/14/totals.txt

The columns of the txt file from the left are representing:
1.Segments, 2.Frequency [MHz], 3.Rinput resistance [O], 4.Xinput
reactance [O],
5.|Z| input impedance's magnitude [O], 6.Input impedance's phase
[degrees],
7.SWR(Zo=50O), 8.SWR(Z0=75O), 9.SWR(Zo=300O), 10.D directivity,
11.D[dB], 12.D [dBd],
13.Front to back ratio (Ef/Eb)

As you may notice the value of input impedance is too high.
therefore, SWR is very increased.
I've added lambda/2 and lambda/4 transmission lines at the source
which were situated perpendicular to antennas plane (at xoy plane)
in order to alter the input impedance's value.
However, the results from both attempts were not satisfying.

I look forward to hear proposals and advices in order to decrease SWR.
Are there any standard transmission lines at the market with Zo
aproximatelly
to my input resistance so I can recalculate SWR with better results?

I ask apologize for any mistakes and for my poor english
as it is not my native language.

Thank you in advance

Dimitris I.