To Peter - DJ7GP,
tnx Peter, I have seen it after your message. Wili performed very nice job. However, some parameters of antennas were not published (axial ratio, impedance match).
To Remco -PA3FYM,
a. I modelled and calculated feed, as it was published in DUBUS magazine. I do not have any upgrade version of your design. I wrote about it in upper section.
b. Properties of Nylon 6 from Internet:
Nylon is hygroscopic, meaning that it attracts and absorbs water from the surrounding environment. The composition of the plastic is changed as water molecules are suspended between the molecules of the material. Over time Nylon 6 will swell considerably and begin to degrade.Nylon is hygroscopic, meaning that it attracts and absorbs water from the surrounding environment. The composition of the plastic is changed as water molecules are suspended between the molecules of the material. Over time Nylon 6 will swell considerably and begin to degrade.
Nylon 6 is not UV resistant. When placed in sunlight over time the physical and mechanical properties of nylon will degrade. It will often turn yellow and become brittle.
Nylon 6 is generally not chemically resistant. It performs poorly in acids and halogens such as fluorine and chlorine.
c. Offset parabolic reflector has more variables to be set. See attachment. I did not write, that it is not possible, but it is more complicated.
It seems, that analysis of hamradio design must be written without cons. So the next part will consist only from physical properties without any + and - comments
It will be published in part 2 (like a soap opera ). I am working on it.
In the latest DUBUS magazine (2/2019), I found a description of the dual-band feed for an offset reflector antenna, published by Mike Willis – G0MJW, Remco den Besten – PA3FYM and Paul Marsh-M0EYT. Since I am generally interested in reflector antenna and authors have not published more information about the performance of their antenna design, I performed a computer analysis of this feed. Maybe some members of this forum are also interested in a performance of this feed, so I am sharing my calculated results here.
Thanks to RF spin s.r.o. company, I was able to use CST MW Studio software for modeling and calculation. For feed performance calculation, I used time domain solver approach. For the whole antenna performance calculation, I- solver was applied. The feed radiation patterns were calculated and generated in 5 deg. increments of angles Phi and Theta and inserted into a focus of the parabolic reflector as a far field, shifted with amount of the phase center position (23.6 mm). Subsequently, next calculation was done in I-solver For directivity calculation of whole antenna assembly, I used a model of prime focus parabolic reflector, since geometry of offset reflectors are not unified. The expected error with this simplification should be smaller than few percent.
Conclusion for X band
- Simple design
- Symmetrical radiation patterns for both E and H planes - good efficiency for dishes with f/D ratio of about 0.5 – 0.65
- Good impedance match
- Worsening of LNB noise figure (0.2 – 0.3 dB), due to use of lossy dielectric material (Nylon 6, dissipation factor 0.2)
- None UV resistance
- Difficult adjustment in offset parabolic reflectors for the best performance
Hi Ed, we have 40 deg. C these days in Doha. In summers, temperature rises up to 50 deg. C. A cover can not be transparent, due to greenhouse effect. Requirements on cover are - good thermal stability, excellent UV resistance, RF transparency, white color (to avoid thermal absorption) and low weight. Possible materials are PTFE (Teflon), PVDF (Kynar) and Kapton. The best shoud be a Teflon bag, but it was not available at my size, Kapton is too dark. So Kynar bag with teflon foil beneath is doing this job.