Re: NEC-LIST:Band width of Yagi

For truly wide bandwidth Yagis (say, 15% and more) you might check the
old Jasik handbook (~1961) which had a chapter on single channel and
WB Yagis for VHF-UHF TV.

Basically these are very highly compromised designs giving up ~5 dB
gain for the bandwidth, and should be considered primitive.

Finney (sp?) company years ago made a good 4 element FM Yagi
(20% BW) that used two close-spaced driven folded dipole elements, but
again, likely with a forward gain penalty.

I have used various optimization programs which can yield good designs,
but have not stressed truly wideband. Hopefully someone who has worked
in this direction would comment.

Note, the OWA approach may, or may not be, suited to truly WB Yagis
(20%); perhaps the authors would comment.

Beyond this, one naturally goes towards the log periodic structures
having modest gain ~7 dBi (10 log 3 + 2.15) where 3 is the typical number
of 'lighted' elements.

Keep in mind, the Yagi is a lowpass filter. On the downside it may be horribly
mismatched, the reflector may not be reflecting, etc. but it will radiate to some
degree. On the upside however, immediately as any director resonates, typically
only a few percent above the operating band, the director then flips phase and
acts like a reflector with disastrous results.

dab

  At 09:08 AM 6/16/2002 +0200, zvi frank wrote:
>HI All,
> This is probably an old question but what is the bandwidth of a
>YAGI. As far I know it is very small . Is there away of broadening the
>bandwidth ? How much can one get ? For low Gain YaGI's (3 or 4 elements) Is
>the bandwidth wider ?
>By Band width I mean both the VSWR and Gain perameters
> Thanks in advance for all comments regards,
>
>Zvi
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