Stránky OK2PNQ
Tommypnq(kysela ryba)centrum.cz

Září 2016

Triple band feed from OK2ZTK

9. září 2016 v 15:47 Konstrukce
I have got antenna constructed by a friend OK2ZTK, to tune it to the precise resonances on three bands, 23,13,9cm.
The antenna is built according to design from DD7MH, with reduced reflector size down to 115mm.

The underlying paper is for another design with choke






I measured the return loss on all bands and the resonances were too high, so I had to change the loops for 23 and 13cm for longer ones. Then I iterated the lenght to get to the required frequencies. I started with the lowest frequency. When I got to 3.4 GHz, the change of 2.3G loop resulted in proper tuning and changing of the loop length was not necessary.

The original mistuned measurement for 23cm was lost during saving






Then I was curious about the radiation patterns, whether it is ok to feed the dish with f/D 0.5. Friend of mine made the measurement on the uni test range in the anechoic chamber.

The pattern looks good, with higher sidelobes on 23cm due to small reflector size

..E plane.H plane...average E, Hbeamwidth
.level [dB]angle leftangle rightangle leftangle rightbeamwidth Ebeamwidth Hbeamwidthaverage for all bands
..........
23cm-64350565693112102.594.3
.-1055647574119149134122.7
.........
13 cm-6434854549110899.5
.-1054617171115142128.5
.........
9 cm-634364349709281
.-104347586390121105.5
The table is constructed from graph values reading and averaging, it shows, that average opening for feed taper -10dB is 123degs, that means f/D a bit above 0.4. But when the freespace loss is added into equations, the feed seems good for 0.5 f/D which is shown below. The dark green lines present ideal position of feed taper for various f/D.
For angle opening and freespace loss computation I used spreasheet from
www.2ingandlin.se/Dish.xls