10 GHz antenna gain measurements part 2

The continuation of the 29 th April was on the 12 th of August 2000. There were 4 antennas to measure.

• PA0WSO, a 70 cm dish with a so called chaparral style feed
• PE1RQY, a 12 slot omni directional
• PA3GSX, a 59 cm dish with a Procom corner reflector feed
• A so called Chaparral feed (Download chapter 6-3 from the W1GHZ online antenna book for more information)

The same measuring method was used as on the 29 th April 2000.

The feed mounting of the PA0WSO dish was replaced by a mechinical stable one.

The Chaparral feed had movable choke rings. These rings were moved to find out the influence on the diagram.

The omni antenna was adjusted for minimum VSWR at 10.368 GHz.
 

Owner	Diameter	f/D	Theoretical gain @ 50% eff	Measured gain	Efficiency
PA0WSO	0.75	0.45	34.9	34.7	47.7
PE1RQY	12 slots	-	-	15.2	n.a.
PA3GSX	0.59	0.42	33.1	32.3	41.5
PE1AEO	Feed	-	-	????	n.a.

Diameter in meters.
Gain in dBi.
Efficiency in %.

Results in graphical format:

Pictures:

10 GHz Omni antenna	Chaparral feed

Conclusions:

The stable feed mount showed a good behavior. There was no difference in gain by mounting the antenna upside down.

The PA3GSX antenna was mounted with a PROCOM feed. Efficiency is not bad at all. But its still far below the 50 %. This feed might be a simple alternative for 24 GHz and higher specially for people who are not the best in machinering/mechanics.

The 10 GHz omni directional antenna is designed by db6nt and based on a design in UKW berichte (1 and 2 1991). A big mistake was made by the designer of the 10 GHz antenna. Probely due to a lack of understanding the theory of such an antenna. In the original design a waveguide with a smaller b-size as normal L-band waveguide was used.

After some talk with Frans PA3DDN he suggest to model the measured antenna and simulate the pattern. The result of this simulation showed an good match with the measured pattern. Note that the simulated gain is not absolute gain and the diagram is just half the antenna. The other half is symmetrical.

Simulation also showed that making the height (b-size) of the waveguide smaller the pattern was moving to a circle. This gave us the confidence that an antenna build with the newly calculated dimensions may work as an omni directional antenna. (b-size=1, 0.5, 0.1, times the original)

After some discussion on the mechanical construction of the new design and understanding why the pattern had this shape the suggestion was made to broaden the broadside of the waveguide. Results from the simulation are promising. This solution might be an easier one when compared to the previous one. (a-size=1, 10, 20, times the original)

A future measurement must be done to verify the simulation. We have a lot of confidence that the measured results come very close to the simulated ones.

Look for information on dish feeds at the (W1GHZ online antenna book) W1GHZ (ex N1BWT) has done some nice simulations on this subject.
 

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(c) PE1CQQ Last update 31-12-2001