Dr. Yagi & W1MDZ Dielectric Antenna Experiments
PUBLISHERS INTRODUCTION by Jack L. Stone
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73s, Jack L. Stone ~ firstname.lastname@example.org
|Introduction ~ Jack L. Stone||Part-1 ~ Stan's Story||Part-2 ~ K5CNF Interviews Stan|
Written Text Supplement
uring the course of my years in communications, I have run into a lot of interesting antennas. Some of them were novel and others were really strange but worked anywhere from moderately to excellent. But the first time I came into contact with the dielectric antenna was on a microwave horn antenna I found at a junkyard. This antenna had a piece of plastic mounted on the front and there were several smaller plastic pieces mounted on the front of the plastic that covered the front of the horn. After looking at the antenna I realized the plastic is configured in the form of a lens and the antenna was a combination antenna, with the gain of the lens and the size of the horn giving more gain than just the horn alone.
Later on I noticed a lot of the radar detectors people had in their cars had a lens on the front of the housing as well. One in particular had two plastic rods of different diameters sticking out from the front of the housing, allowing the detector to have gain antennas on two bands.
So when we received information from Stan Whiteman, W1MDZ, about his experiences with a dielectric antenna on two meters, it caught our attention. I found it most interesting to learn Stan had built a directional VHF aircraft antenna right after the war. Also, while stationed in Japan, he had met and talked with Dr. Hidetsugu Yagi (1886 1976) at the home of this famous Japanese Electrical Engineer and Physicist. Much to Stans surprise, he learned Dr. Yagi had worked on the dielectric technology two years earlier, except that his project applied to a use for radar on submarines during W.W.II. Dr. Yagi explained they needed a radar antenna that could be raised and lowered with the periscope and be impervious to salt water so as not to de-tune. They discussed and compared notes about the dielectric antenna Dr. Yagi had designed and the one Stan had constructed. I might add that Stan had previously spent some 10 years working in the laboratory of the USA CIA on various projects.
Stans dielectric antenna for the VHF aircraft band and had tested out to 100 miles with very good results. As one can imagine, Dr. Yagis periscope mounted radar antenna for submarines had to deal with the many environmental problems that any submarine has when diving and remaining at deep-sea levels. The Yagi design is shown in Figure 1. It was also for VHF on the two-meter band. The method of feeding the antenna is not known. All of the elements were encased in the dielectric.
The antenna Stan built is shown in Figure 2 and seems to be relatively simple. The driven element is encased in the dielectric and the rest of the antenna is out in the open and adjustable as to element spacing. It is also tunable by a capacitor located at the end of the driven element. Moving a wire clamp at the lower end of the element allows matching to the feedline. Figure 3 is a top view of Stans antenna design.
The objective of both designs was to come up with a very small efficient antenna. Both of these antennas are reduced in size as a result of the effect of the dielectric sealed encasement. The amount of size reduction depends on the dielectric constant of the material used to surround the antenna. The antenna Stan had designed was approximately 6.5 (16.51cm) inches tall and was also 6.5 inches long and had 5 dBd gain. He had it built in Japan and then tested it later in the Arctic. Various element configurations were tried, such as tapering the elements but the final result was that the elements were 5% shorter than the driven element. The radiator was top loaded with a capacitor which allowed tuning. The antenna preformed very well out to over 100 miles when tested with a MATS aircraft.
As for comparison between Dr. Yagi's design and the one Stan built, there can be none. The war ended and that ended the project for Dr Yagi. Stan never used his antenna again either. Since then, the majority of the work has moved up into the microwave regions and I am unaware of any more work being done in the HF range. It would be a very interesting project to see how much a HF antenna could be compacted and still have decent bandwidth.
One of the things that came out of the discussions that took place between Stan and Dr. Yagi was that the Germans were pretty far advanced in the area of ceramics R&D and its possible application to dielectric technology. Now if there was a story hiding in the forest waiting to be found, that is one. I wonder if there is anyone out there in the world that would be willing to expound on this subject of dielectric antenna experimentation that were done in Germany back thenor since? -30-
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