UPDATE: Radio Neutrino Project
Last update was Aug. 17, 1995. Much progress has been made since then. I will divide this discussion into three areas: receiver, antenna, and transmission.
We are looking into making our components take up as little space as possible. Then a smaller pressure vessel would be required to protect them. We have contacted Miteq Inc. and they are going to give us a quote on designing one component that will consist of the first amplifier, the bandpass filter, and the second amplification stage. Then we will be using the same detector diodes as the previous radio neutrino experiment, A.R.C.N.O., and some sort of "post-diode" amplification.
The receivers are still being planned to go inside the antenna body.
This is where most of my time has been devoted. I have continued to build and test antennas.
1/4 Wave Choke Bicone Antenna
I built the antenna with the 1/4 wavelength choke, but it was a rather unsuccessful attempt. I successfully constructed it out of sheet metal, but due to the difficulty of assembly, it is somewhat asymmetrical. The coax to antenna impedance match was fairly poor, and the field pattern was as disappointing as the other bicone antennas. I tried putting live cables down the middle of the antenna while testing it. It made little difference which is good news, but then again, I didn't ever check to see if it would make a difference with the other antennas. Field pattern was better than for the other two bicones.
It was basically decided that (since we were not going to deploy our antenna around the AMANDA cables) the choke idea was not going to be pursued.
Cylindrical Dipole Antenna
I purchased some aluminum pipe and constructed a fairly durable cylindrical antenna. Although this antenna had a good coax to antenna impedance match, it had a very poor antenna to free space impedance match. It's reflectance looked poor on both the scalar and the vector network analyzer.
Again, much was learned through its construction, but the idea needed work, which brought us to...
Slotted Cylindrical Antenna
A rather old concept, Giovanni stumbled across it in one of our antenna texts. The source papers that we dug up dated from the '40s. I was able to construct it rather cheaply and quickly and we found that it performed far better as an antenna than any of the previous models. It had a good overall impedance match, a well-defined bandpass (centered at about 765 MHz). Little internal reflection.
When I tested this antenna's field pattern the results were promising. One issue, however, was raised that had not been previously addressed. What polarization do we want for our antenna? Ideally, since the incoming Cherenkov radiation could have any polarization radial to its direction of travel, we would want a circularly polarized antenna. All of the previously designed antennas were vertically polarized. The slot antenna was unique in that it was horizontally polarized. Both of these results were verified experimentally, by measuring the field patterns. This antenna worked good though. This must be made clear.
We decided to explore the options as far as circular polarization goes. This led me to...
Helical Slotted Cylindrical Antenna
The concept for this antenna came from a conversation with Dr. Smoot about polarization. Although skeptical, I constructed it. When I tested its reflectance, it was not quite as good as the straight slot antenna, but the field pattern, interestingly enough, yielded some promising results. It wasn't completely circularly polarized, but it definitely helped, although there was significant power loss as a consequence of the polarization (a factor of 2 or greater). This antenna did not have the favoritism towards the direction of the slot in its horizontal field pattern, that the other slotted antenna had. Although slot size and antenna diameter can change that in both cases.
There is little possibility of applying the helical slot, but that is not to say there is none. Our search for circular polarization is leading us in one more direction...
Multi-feed Slotted Cylindrical Dipole Antenna
This antenna consists of a combination of two previous designs, noted by the title. It is proposed in Antennas by Krauss, but there is no resource on it. It consists of a horizontally polarized slotted antenna and a vertically polarized dipole. It has two difficulties: 1. If the two signals are combined together, it will be difficult to get them to overlap spacially. 2. If they are kept separate, then two receivers are needed and space is limited. I am considering building a test model of this antenna, but it is doubtful.
So I have been busy with antennas, but have learned that the slotted cylinder is probably our best bet at the moment. All the field patterns (graphed with Excel 4.0), are in the project's binder.
Also, there is still the possibility that Dave Nygren's work on the optical chip will be applicable, but we are not going to wait for that, but instead prepare as if that luxury will not be available.
In order to preserve my work and make what I have learned most accessible to others, in addition to my lab journal and these updates, I will be doing two things over the next couple of weeks. 1. Working on a web page which will make available our progress to the other groups working on this. and 2. Transferring my knowledge over to Martin Moorehead who will be working on what I have been once I return to Santa Barbara.
Another key realization is that without the coincidence of several antenna, we cannot be sure that any of our signals are really neutrinos or are just noise, random signals, or glitches in our electronics, although we want to reduce all of these as much as possible.
It would be nice to be able to confirm that signals are coming from neutrinos. No doubt about that.
Back to work...
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