Microstrip array "help for design "

HI:

I don not know which point should i start,my project assigment about design Microstrip rectangular patch antenna array WORKING ON 2.8ghz
but I do not have that knowledge to design for one patch ok,but 4 element ,don't know,the lectuer told me to study about power divider

,the desgin using CST, Any Idea regarding to that.

If you know how to build a single patch element (assuming I read that correctly), then you need to create an array of patch elements. Open your textbook and look for the chapter on arrays.

The simplest approach for patch antennas is to space them 1/2 wavelength apart and feed them in-phase. Regions along the horizon (assuming your PCB is lying flat on the ground) will receive very little power, since the radiated fields from the two elements cancel each other. However, if you look at the field patterns from "above" the array, the radiated fields from the two patches appear in-phase and you get an improvement in directivity/gain.

For power dividers, look at Wilkinson power dividers.
Wilkinson power splitters- Microwave Encyclopedia - Microwaves101.com

One example (using "lossless" splitters): Image

thanks " enjunear " , plz help me i have less than 3 weeks to design it , and I actually my major in networking more than antenna,so my knowledge a little bit about antenna.The problem no reference books, and lecture notes not useful at all ,
if i understand your answer correctly ,so first I'll design single patch working on 2.8 and I'll make 4 element same design. and next apply "Wilkinson power splitters " to connect four of them .to the waveguide port, if that how many wilknson stage should I apply,and what is the equation of dimestion,I stuck

Steps:
1) Design a patch antenna
2) Put down 2 patch antennas, use a simple lossless divider to drive the array (make a T using three 50 ohm microstrip lines... input and two outputs to the patch elements).
3) Put down 4 patch antennas (copy what you already have), then add another T to split one input into two, then the second set of tee's (already done from step 2) will split those two into four outputs to drive the four patches.

Here are some reference pages to get you started (most of this design information can be found if you hunt around in Google for things like "microstrip patch antenna design equations").

Patch antenna:
Microstrip Patch Antennas - Microwave Encyclopedia - Microwaves101.com
Microstrip Patch Antenna: From Simulation to Realization
http://www.highfrequencyelectronics....9_Tutorial.pdf

If you notice on many of the drawings, the microstrip line that feeds the patch is inset from the edge. This is to make the best match to 50 ohms possible, since the 50 ohm point doesn't always lie directly on the edge of the patch. The easiest way to determine the best inset feed point is using a reference like Balanis' Antenna Theory textbook. Failing that option, you can watch your return loss (S11), and keep increasing the depth of the inset until you reach a minima (better than -10 dB would be good; the more negative, the better). If you start approaching 1/3 to 1/2 way into the patch, then you missed it... or the best point may be right at the edge.

Using 50 ohm lines as T junctions will not give you the very best performance, but it's a good place to start. If you want to do better, your 50 ohm lines from each patch should hit a Tee, then the input line will be a 25 ohm line (two 50 ohm outputs in parallel = 25 ohms). Then, the two 25 ohm lines from your patch-pairs will come together in another T (in the center) and join with a 12.5 ohm line (two 25 ohm loads in parallel = 12.5 ohms). Then your excitation port should be 12.5 ohms to best match the transmission line you are putting signal into.

Starting with your 2-element array, start with a spacing of 1/2 wavelength at your freq of interest. Move them closer/farther apart, watching your radiation pattern to get the best gain/pattern. Repeat this process with four elements to get the spacing "tuned".

Thanks it's really helpful ,I'll start the design and post result but just simple enquire :

I draw what i thought i understand it from you on this link

http://shareimage.org/images/mbc9pf3c1qid82ouocu.jpg

I do not want to ask many questions until review the theory to start single patch .

Thanks again

You're pretty close, however, the transmission lines are a little off. If each patch is designed to a 50 ohm input impedance, that means that the four lines running to each patch will also be 50 ohm microstrip (instead of 25 as you have it shown). After the first T's the middle lines will be 25 ohms (instead of 12.5) and the single-point input will be 12.5 ohms. The image you have shows (I believe) a coaxial feed point. If you looked at it from the side, it might look similar to this (ignore the placement of the patch):

If you wanted to feed the 4-element array with a microstrip line, you would add another Tee where you indicated the waveguide port, and route it to the edge of the board. If CST will let you do a single-point input (never used it before), then you could set it up with Z=12.5 ohms, since you are feeding two 25 ohm lines in parallel.

(Hint: in the case where you end up with a 12.5 ohm input, I"d add a quaterwave transformer to change the characteristic impedance of the microstrip input line back to 50 ohms).