Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Phase array question
I've taken college classes in antennas and hence have a pretty good feel for
some of the mathematics behind it all, but I've found that at times I don't have good, intuitive explanations for various antenna behaviors -- and I'm not at all good at being able to look at some fancy antenna and start rattling off estimates of the directivity, front to back ratio, etc. -- so I wanted to ask a simple question on a two-element phased array: First, start with one antenna. Feed it 1W, and assume that in some "preferred" direction at some particular location the (electric) field strength is 1mV/m. Now, take two antennas, and space them and/or phase their feeds such that in the same preferred direction the individual antenna patterns add. I.e., we're expecting a 6dB gain over the single antenna (but only at that location). Since we start off by splitting the power to each antenna (1/2W to each), that initially seems impossible, since 1/2W+1/2W = 1W -- should imply the same 1mV/m field strength. But this is an incorrect analysis, in that powers don't add directly. Instead, the fields add... hence, each antenna alone will now produce 707uV/m (at the one particular location in question), so the two together produce 1.414mV/m which is the same as if the single antenna had been fed with 2W. Hence the 6dB gain we're after! (This analysis also implies there must be other locations that now receive 1mV/m in order to conserve energy.) Is that correct? "Powers don't add, field strengths do" is obvious enough, but definitely leads to some slightly non-intuitvely-obvious (to me) results. By extension of the above, though, it becomes obvious that (in theory) one can build an array with any desired amount of gain, the beamwidth just has to become narrower and narrower, of course. Thanks, ---Joel |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Central Electronics 20 A Phase shift question | Boatanchors | |||
1.2 GHZ collinear array | Antenna | |||
GAP & phased array | Antenna | |||
AX.25 parameter negotiation phase question | Digital |