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I need to add a clarifier to this post.
If the phases and and magnitudes of the paired elements are exactly the same, then radiation to the rear is zero. In the real world this is difficult if not impossible to do. It certainly cannot be done with a yagi unless possibly, when elements are contorted to ensure pure resistance feed at the appropiate frequency However, what is possible with a alternate design is to have maximum front to back at max gain when the max gain is constant over a range of frequencies such that the max front to back which is usually a peak, can appear at a point where the gain is still at a maximum. Regards Art .........KB9MZ " wrote in message news:dySVd.30807$r55.174@attbi_s52... I have just come to realise that if one drew a polygon of element phases in a array and all elements were 180 degrees to its companion element and excluding the driven element, the max gain and max front to back will occur at the SAME frequency! Until now I was of the understanding that these two max figures could not occur at the same frequency. Is there anything written about this possibility? Regards Art |
Gene Fuller wrote: Buck, I agree with you. I too cannot figure out what Art is trying to say. Don't feel like the lone ranger...I've been following this thread for a week, and I still don't have a clue what he is trying to describe. 73, Gene W4SZ Buck wrote: Art, Your description is too vague for someone who doesn't have some form of reference (maybe this is a continuation of a discussion from elsewhere?) What he said.... |
Buck
If your background is not in science then it is natural that you would have difficulty with what I stated. If your background was in science then this stuff would be studied in 101 i.e from first principles. With a firm understanding of scalar quantities you are then fully armed to deal with antenna "curl" and other interesting facets of antennas. It would appear to me that many of this group do not have a science background but have got by in life because of a good memory and where knoweledge of first principles is not a requirement. Ofcourse age can take that advantage away which appears to have happened with past engineers of this group.........amazing! Regards Art "Buck" wrote in message ... On Tue, 08 Mar 2005 05:29:03 GMT, " wrote: "Buck" wrote in message . .. On Fri, 04 Mar 2005 05:41:29 GMT, " wrote: I have just come to realise that if one drew a polygon of element phases in a array and all elements were 180 degrees to its companion element and excluding the driven element, the max gain and max front to back will occur at the SAME frequency! Until now I was of the understanding that these two max figures could not occur at the same frequency. Is there anything written about this possibility? Regards Art Art, Your description is too vague for someone who doesn't have some form of reference (maybe this is a continuation of a discussion from elsewhere?) Anyway, since a polygon is any shape with more than two sides in which all sides and angles are equal, It does! then I have used the incorrect term. In a yagi type diagram you can calculate the current and phase of each elemrnt but what one is interested in is the summation of the whole array and you can do this in the same way as you would do a vector diagram of forces. With the yagi array you would first start with the reflector and draw to scale a line reflecting both phase angle and magnitude. You then add lines in cosecutive order for all other elements in the array. The end of this 'toe to tail' some what erratic line will finish up some distance from the starting point, but this distance, if drawn, represents the phase and magnitude of the array as a whole. As a former mechanical engineer I am not ... You may be using a term familiar to your trade and I am unfamiliar with. I would be a layman in respect ... that could be the misunderstanding. I was trying to envision the antenna you were describing... can you imagine what I was seeing in my mind? :) but now nothing ,I was taught the term "polygon of forces" which is a cumulative vector array but the shape did not necessarily consist of "equal "sides as you stated.. But then I am English born and it is known that Americans completely messed up the Elizabethan era language which a true cockney still adheres to , where as others in the same country have learned to talk in such a way it sounds as if they are trying to retain a marble in their mouth.without swallowing it. Actually, I like the UK accents. As I believe my misunderstanding has nothing to do with the queen's English, but rather techno-speak for your trade, I will pack up my octagon shaped array of dipole antennas and gracefully move on to another topic. Good luck and I'll catch you in another thread. Buck Regards Art -- 73 for now Buck N4PGW |
Good point ! But I have already checked this out even
wit "Dave Platt" wrote in message ... In article k1FXd.109090$tl3.58979@attbi_s02, wrote: I need to add a clarifier to this post. If the phases and and magnitudes of the paired elements are exactly the same, then radiation to the rear is zero. In the real world this is difficult if not impossible to do. It certainly cannot be done with a yagi unless possibly, when elements are contorted to ensure pure resistance feed at the appropiate frequency You might want to take a look at systems which use two or more directly-driven radiators (rather than a driven radiator and a parasitic element), with a chosen physical offset and phase offset between them.e phase Good point! I tried this with a radiator that was of opposite phase but the origanal feed method still came out best. That method has not been tested for other bands This is a classic way to get a 180-degree-only pattern. It's often used with vertical antennas. I took a quick glance at Arnold Bailey's "TV and other receiving antennas" text (written in 1950) and he shows a similar sort of antenna using two horizontal half-wave dipoles, connected together via a transmission line and fed at the center of the rear dipole. Very clean 180-degree pattern. This sort of arrangement might be a good starting point for your "move all of the energy from the rear lobes into the forward half" quest. You might be able to combine this sort of dual-driven-radiator unidirectional beamer with additional parasisic elements, to create more forward gain. A bunch of directors out in in the front would be the obvious choice for a first experiment But that defeats the issue where boom length can be erradicatred as an issue. There's a gotcha to this, though... the 180-degree pattern from a pair of phased radiators depends on the radiators being driven with equal currents, which (in this simple arrangement) requires that they have equal feedpoint impedances. Stick a bunch of parasitic directors out in front, and the feedpoint impedance of the forward radiator is going to change (drop, most likely) and affect the current relationship between the two radiators, and thus mess up the pattern. I can think of a couple of possible ways to compensate for this: - Matching network at the forward radiator (maybe shorten it a bit and use a hairpin inductor match)? I always require a near 50 ohm feed that does not require matching. - Tapered transmission-line section between the two radiators? - Try installing some parasitic elements behind the rear driven element... possibly in a corner-reflector arrangement? This might tweak the rear element's feedpoint Z enough to make it easier to match the two, might also help suppress any rear lobes which develop as a result of the mismatch. A corner reflector does not have true reflectors as all elements are of the same length and equaly spaced, they also carry low but similar current flow. I have my doubts as to whether all of this work will pay off with enough of an increase in forward gain, F/B ratio, cleanliness of pattern, reduction in lobes, broadening of bandwidth, etc. to be worth the effort over a classic Yagi, but I'm certainly willing to be proven wrong. This cannot beat the simplicity of a yagi. Good for you Dave, you have an open mind despite the massive studies over the years. But there is no way of convincing the masses who demand expensive trials and measurements which if conclusive ,changes the mode of attack to the method of testing, This is usually the method taken by even educated engineers who with huge experience in the field refuse to believe they could have passed over something. As for this antenna it is purely to satisfy me. Regards Art .. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
wrote:
If the phases and and magnitudes of the paired elements are exactly the same, then radiation to the rear is zero. If you rotate the elements by 90 degrees, can you make the radiation toward the ground zero? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Interesting question Cecil, and I suspect the answer is yes
if you are refering to the array pointing upwards. If you are referring to turning the array sideways i.e vertical polarisation then I doubt rear radiation could be zero because the earth has more influence over vertical polarisation compared to horizontal at one wave length high. For instance pairs of elements could not have equality. You can ofcourse accomplish such if the array was reflective as with a dish but not with normal coupling and resonances where the focussing aproach is absent. Best regards Art "Cecil Moore" wrote in message ... wrote: If the phases and and magnitudes of the paired elements are exactly the same, then radiation to the rear is zero. If you rotate the elements by 90 degrees, can you make the radiation toward the ground zero? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Dave Platt wrote:
"This is a classic way (2-element quarter-cycle phased array) to get 180 degree-only pattern. It`s often used with vertical antennas. I took a look at Arnold Bailey`s :TV and other receiving antennas" text (written in 1950) and he shows a similar sort of antenna using two horizontal half-wave dipoles, connected together via a transmission line (open-wire) and fed at the center of the rear dipole. Very clean 180 degree-only pattern." Yes. The directional patterns on pages 477 and 478 are excellent. This antenna also appears in Bailey`s catalog of antennas on page 521 as "Half-Wave Antenna and Connected Reflector". Its resistance at center frequency is 50 ohms where its gain is 4 dBd. Bandwidth is 60% for 3 dB down. I wonder why everybody isn`t using this antenna? Best regards, Richard Harrison, KB5WZI |
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This sounds like a switchable three element array that I once used
for CB ( As an alien I wasn't allowed a amateur license) I copied the design from a commercial antenna and with a switch box was able to point it in any one of three directions. The coax between them was a 1/4 wavelength I believe but the physical distance was much less than that. I believe I lost it when it iced up and broke the topsides of the vertical dipoles.. Regards Art "Richard Harrison" wrote in message ... Dave Platt wrote: "This is a classic way (2-element quarter-cycle phased array) to get 180 degree-only pattern. It`s often used with vertical antennas. I took a look at Arnold Bailey`s :TV and other receiving antennas" text (written in 1950) and he shows a similar sort of antenna using two horizontal half-wave dipoles, connected together via a transmission line (open-wire) and fed at the center of the rear dipole. Very clean 180 degree-only pattern." Yes. The directional patterns on pages 477 and 478 are excellent. This antenna also appears in Bailey`s catalog of antennas on page 521 as "Half-Wave Antenna and Connected Reflector". Its resistance at center frequency is 50 ohms where its gain is 4 dBd. Bandwidth is 60% for 3 dB down. I wonder why everybody isn`t using this antenna? Best regards, Richard Harrison, KB5WZI |
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