Boy you academics sure have a hard life. =) I wish I knew how it feels to be the smartest guy in the room ...
They do not radiate, neither do reflectors in a Yagi-Uda. They reflect exactly like a corner reflector reflects. You might go as far as to say they re-radiate because power does get consumed in the process. You don't get as much out as you put in.
I am not an academic. I do some scholarly things, but through corporate affiliation. Yes, it was tough (for me) -- some of the time. I can't speak for others. I have no idea what you mean by your last comment. Never mind. I retired from academia 17 years ago. I often get asked to go back and always say no. Schools are just too liberal for my tastes--your opinion may differ, and that's OK. That chapter is completed--for me. I've got lots to do otherwise in the final pages 73, Chip W1YW
I am a former academic and only a slightly knowledgable about antennas. Howerver, reflectors and directors in a Yagi do radiate. The E-Field from the driven element induces a current in the paratisitic elements that is effectively re-radiated. Practiacally, this is a lambertian reflection I guess. They are near 100% efficient, but you are correct there is some power loss to heat
I should have said the energy is re-radiated without the word effectively. You are saying it is reflected and I am saying is is actually re-radiation. I guess you could model it as a reflection, but then how would you treat the directors (forward parasitic elements)?
You are right, not sure what I was trying to say when I made that assertion. I did say reflect and that isn't as good a choice as "re-radiate". The word "effectively" could be eliminated or replaced with "actually" because it actually re-radiates. In the end it is all about phasing the various fields, isn't it? You can't model the directors in a Yagi-Uda as reflectors. They have to be modeled as radiators (re-radiators).
Its out of phase interference (back) , in phase (front) caused by a re-radiated, baseline time delay plus a reactive phase delay. The re-radiation causes a 180 degree effect, just as with happens in a transmission line. Then you have baseline and reactive components of phase delay. People forget that reactance differences to the driven also produce phase delays. Present company excluded, of course.
re: "Generally when the term end-fire array is used they are referred to arrays with multiple driven elements. In general, this terminology is not used with beams (yagis). " Endfire, here, from a short, fat radiator fed differentially in the center (this is a class of antennas not addressed by physics heretofore): Listen for (nulls/nulling off the sides and maxima off the ends)
Yawn ... Repeating what was already written for the explicit purpose of impressing people ... not particularly seemly.
That is totally obnoxious and out of line. It is totally, totally wrong. That was NOT my motivation. Disseminating knowledge was my motivation. I don't care if you don't like me. That's OK. But be civil and appreciate the relevant contributions of others. I was reminding OTHERS that reactance produces a(n additional) phase delay. That is NOT common knowledge within the amateur radio community. Thank you.
Obnoxious was implying that you do not forget things ... Now, I don't dislike you. I dislike your attitude. That said, we are done here. You have a nice day.
You should be ashamed for publicly berating me--falsely. I have done nothing on this thread to harm or berate anyone. You seem to object to who I am and thus want to publicly pose me in a way that makes me look like a person that others should not either listen to or associate with. Why do you do this? Are you an unhappy person? I do hope you treat other people that HAVE to associate with you with SOME respect and empathy. I am not your whipping boy. I am a 63 year old man who has worked very hard to improve himself and the lives of others. I know who I am and am comfortable in my own skin. Shame! Sir, you are disrespectful :-( Why don't you help others understand exactly how a Yagi works? Explain to them HOW a driven, and reflector element parisitic, for example, produce phase cancellation on the back side, given that the spacing of the reflector is typically 1/8 wave. Show us where and how the out of phase (modulus) happens: phase cancellation requires waves , if produced by two sources, that are 180 degrees out of phase and of equal amplitude, in the far field. 1/8 wave corresponds to any offset of about 45 degrees. 180....45..... explain please how to get these two to make sense. The reflector is not a brick wall/ mirror. If I put a probe antenna just in back of the reflector parisitic I measure a heck of a field. I will be happy to assist, sincerely, if you get stuck on the explanation. Do you know the explanation? Can you articulate it in words, please?
Normally I would not bother to respond further. I will make this ONE exception. 1) I do not know you and so can not "know who you are". However, in my experience, people who assume I know whom they are have an inflated opinion of their contribution in life. That might be your problem but as I said, I don't have a clue who you are. 2) I am not unhappy. I treat all men (and women) as equals. I don't look down upon people and I am quick to admit my mistakes (as can be seen here in this thread). 3) You most certainly are not my whipping boy. I don't actually own a whipping boy. 4) I have not done anything for which to be ashamed. 5) We were explaining how Yagi's work, and doing it quite well I suppose. 6) You just can not resist questioning the ability of those with whom you interact, can you? Then you take offense when they point it out to you. Pretty good psychological gambit you have going there although patently obvious, do you think it will continue to work? This thread went off the rails about ten pages back. I suppose at this point I am as guilty as anyone else for having caused that to happen. I apologize for that and that alone. Now we really are done here. There is no point in dragging this out publicly. If your panties are still in a bunch, feel free to IM me and we can insult each other privately until one of us gives up. Be advised I can be somewhat raw privately. We really are done here, though.
I pray for you. It is sad that you feel you have to be 'raw' with anyone, ever. I am sorry that you cannot explain to us how a Yagi-Uda antenna works (see my post #148), but being curious creatures, I hold out hope for all of us, including myself. Wisdom of the old, I guess. If anyone (else) wishes, I will dig out a nice cartoon from the web that hints at how that works. 73 to all, Chip W1YW
