Antenna Simulation Project

Question

Antenna Simulation Project

htgr2001 (Electrical)

(OP)

12 Apr 09 13:47

Hello guys,

I am not quite sure how to start this thread...

I am involved in this little project to simulate (using a software package called FEKO) the radiation pattern of a few antenna types under a variety of realistic conditions.

Most of all I will be creating 3d models on the package of a few types of antennas. To get your curiosity going I will post a few pictures:

Very simplistic model of a 5 element Yagi Antenna (no boom)

Radiation Patterns at 100MHz (left) and 95MHz (right)

I have used a few dimension formulas I found online to optimize the antenna for frequencies of 95.5 MHz. Still it seems to operate better at higher frequencies as you can see.

So at the moment where I would really appreciate your help is if you could provide or point me towards a reliable source of antenna dimensions.

VEBill (Military) · Answer 1 · 2009-04-12 16:54:29

A Yagi antenna has been described as a series of variables arranged along a boom. Forward gain, front/back ratio, bandwidth, and match are all separate measures of 'goodness', and that's not even a complete list. My point is that you need to define what you mean by the words 'optimize', and 'better'.

There are thousands of hits on Google on this subject.

Higgler (Electrical) · Answer 2 · 2009-04-13 20:33:34

Look at AHSystems and M2Inc websites, they give some dimensions which you can approximate the sizes of all radials. It gives gain versus frequency, etc.

Similar things for other antenna manufacturers. People who make and sell alot of antennas usually have photo's and dimensions (overall dimensions). They are good starting points because you know they work.

You might be able to talk them into giving you exact dimensions with an NDA clause and have you optimize their designs for free. Try M2Inc on these, they're the smaller of the two companies and might be up for that.

kch

htgr2001 (Electrical) · Answer 3 · 2009-04-16 12:47:39

Thank you for the repplies guys i have pretty much found the antena dimensions i needed.

But i am finding it hard to information reagardin the gap spacing in between the driven elements on the dipole:

Is the necessary gap size dependent on any factor or any distance is pretty much fine?

Also I am modelling the yagi antenna using aluminium tubing, I looked around but for what I could see almost every manufacturer use a different tube diameter. Is there any standard tube diameter or any guidelines when choosing one?

.

VEBill (Military) · Answer 4 · 2009-04-16 12:57:19

The gap of the dipole simply needs to match the spacing of the wires that make up the transmission line.

But, the transition from the cable to the driven element can also be used to effect an impedance match.

Higgler (Electrical) · Answer 5 · 2009-04-16 13:51:24

If that choc block isn't a some form of transformer/balun, you don't have an efficient antenna, and you'll never get it to tune up properly for good VSWR and patterns.

Isn't that chock block just some insulated piece of hardware to keep the lines separated?

It's likely you think there's a critical gap spacing that's needed for your VSWR to become wonderful, when you really need to add a balun? just a guess based on your sketch.

kch

htgr2001 (Electrical) · Answer 6 · 2009-04-16 15:27:58

Sorry if that picture was misleading, I got it from the web simply to show which distance I was referring to, my main concern is to space the driven elements correctly.

Actually in the software I am using there is no need to model how the "feed" to the antenna is carried out. Meaning there is no need to model the balun or even the cable, we simply define a port with an excitation in the correct area of the elements.

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