Hello to all of you. Sorry for use of English, my Russian is already forgotten and my Czech, Slovak, or Polish are not better languages for this forum. I hope someone may translate it here for friends who are not English speakers. But I wrote it that way, because I have something to this issue. We are using MMDS dishes for 23cm about ten years with full success. See more pics on our web page: http://www.ok2kkw.com/equ_cz.htm (Remind ER1LW report here, when he took a part in our Field day Contest in July).
Our MMDS dishes (we use 175x125cm eliptic dishes) are good for 23cm, however not very good for 13cm, because the grid of dish is not "dense enough" and radiation through the dish is huge. But back to 23cm: we are using modified DL4MEA radiator. The circular radiator (not the reflector) is a bit flatten down to eliptic shape in horizontal direction to improve radiation of the eliptic dish and decrease overradiation in place, where the dish is thinner. Radiator is tuned up for reflections below 20dB in free space and installed into a focus place. The phase plane of this radiator is about 5mm deeper from eliptic radiator of the feed. Then the antenna has about 18 dBd gain. We tried to measure it, but who did such antenna gain measurment in amateur radio conditions, knows very well, that the 1dB deviation is normal. Then we started with consulation with OM6AA (www.om6aa.eu) to improve it. Problem is, that the radiator by DL4MEA has about 7dB reverse radiation attenuation only due to the very small reflector. And such reverse radiation decrease the overall gain. Larger radiator close to 1 lambda size however screened centre of relatively small dish and decrease gain again. Finally we move the radiator a little bit back to get reflected phase and parazitic reverse radiation phase of the feed into same phase shift. It increased a little bit sidelobes, but improve the gain up to 19dBd (aproximately). A bit worse sidelobe radiation is even positive, because there are not so deep holes of minimum radiation and it increase probability of response to our CQ during the contest. (In 2010 we even won UHF Contest on 23cm in all of Europe, hi.) For final: why use this eliptic MMDS dish and not standard rounded solid dish. MMDS dish is better for contest, because our QTH is above 1000m asl and there are sometimes really strong winds. So solid dish is not the best idea for this contest QTH. And why eliptic? The beam from the antenna is sharper in vertical plane and larger in horizontal plane. It mean, we are able radiated with good signal larger territory and it increase probability of response. And - at last but not least, 125cm width of dish is the maximum size, which we are able to move the dish through the window into our old camper to transport it to the contest site :-) Thats all, fox. But if you will have any question to it do not hesitate ask me. I'm still able (somehow) read Russian, but not write. Sorry. Best 73 to all from Prague. Vladimir OK1VPZ
PS: another simple 23cm antenna: http://www.ok2kkw.com/antena23cm.htm
