H.F Dish Antenna update
 

In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.
The band width is wider than a typical yagi in that the major portion
of the radiation is to the front this.This band with is expected to
narrow and to increase gain when individual elements are shaped to a
parabolic form and
it is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )

"art" wrote in message
oups.com...
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.
The band width is wider than a typical yagi in that the major portion
of the radiation is to the front this.This band with is expected to
narrow and to increase gain when individual elements are shaped to a
parabolic form and
it is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )


F/B looks too high, you should have some big splinters off the backside.
(with a dish it can be hard to get 30)
Gain looks to be high for a 1 driven and 5 reflectors.
Does model take into account mutual effects of the reflectors?

"art" wrote in message
oups.com...
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.

CORRECTION
The BEAM width is wider than a typical yagi in that the major
portion
of the radiation is to the front .This BEAM width is expected to

narrow and to increase gain when individual elements are shaped to a
parabolic form
It is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )

"hnkie" wrote in message
...

"art" wrote in message
oups.com...
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.
The band width is wider than a typical yagi in that the major portion
of the radiation is to the front this.This band with is expected to
narrow and to increase gain when individual elements are shaped to a
parabolic form and
it is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )


F/B looks too high, you should have some big splinters off the backside.

Why? Do you have splinters in a parabolic dish?
(with a dish it can be hard to get 30)
Gain looks to be high for a 1 driven and 5 reflectors.
If you picture a balloon squashed at one end more than
normal would not the gain increase?

Does model take into account mutual effects of the reflectors?
Yes
Art

A plain dipole 76 feet above perfect ground has a gain of about 8.6 dBi
- surely you've modeled one with AO. So the gain of your antenna over a
dipole is about 5.3 - 5.5 dB. (This would be a more meaningful way to
state gain.) This is just slightly more than the gain from a three
element Yagi, and less than a typical four element beam. The F/B ratio
and bandwidth might be better than that of a typical three or four
element Yagi (or they might not be -- a Yagi can be adjusted for a wide
range of characteristics), but the gain is certainly not exceptional.

Roy Lewallen, W7EL

art wrote:
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.
The band width is wider than a typical yagi in that the major portion
of the radiation is to the front this.This band with is expected to
narrow and to increase gain when individual elements are shaped to a
parabolic form and
it is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )

" wrote in message
news:1k%vd.198273$V41.135426@attbi_s52...

"hnkie" wrote in message
...

"art" wrote in message
oups.com...
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.
The band width is wider than a typical yagi in that the major portion
of the radiation is to the front this.This band with is expected to
narrow and to increase gain when individual elements are shaped to a
parabolic form and
it is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )


F/B looks too high, you should have some big splinters off the backside.

Why? Do you have splinters in a parabolic dish?

You have individual elements, a parabolic has continous surface. Antennas
always have splinters, with just 5 elements and no blocking you probably
have major lobes on the back side, between elements.
There will be places on the back side of your antenna that add in phase with
two or more elements, which is a lobe or splinter.
Parabolics have a rolloff on the edge to decay the field to minimize the
back lobe.

(with a dish it can be hard to get 30)
Gain looks to be high for a 1 driven and 5 reflectors.
If you picture a balloon squashed at one end more than
normal would not the gain increase?

What is the capture area? Each element captures RF energy and reflects it
back to the driven element in phase with the others.

Your idea has been tried very sucessfully at 450 to microwave, and they now
use flat antennas with each element phase adjusted for delay (same as
curverature of a parabolic dish) One antenna has over a thousand elements.


Does model take into account mutual effects of the reflectors?
Yes
Art

Roy Lewallen wrote:
A plain dipole 76 feet above perfect ground has a gain of about 8.6 dBi

Is that true? I've always heard it was slightly over two dB. I re-read
your post and I don't think I'm taking what you said out of context. Did I?

73,
kz1o

http://www.radio-electronics.com/inf...ivity_gain.php
http://www.tmeg.com/tutorials/antennas/antennas.htm
http://www.starantenna.com/omni_dire...le_antenna.htm
http://www.softwright.com/faq/engine...Y%20UNITS.html
http://www.ventenna.com/faq.html
http://tinyurl.com/5zste

On Wed, 15 Dec 2004 16:27:40 -0500, Dave Bushong wrote:

A plain dipole 76 feet above perfect ground has a gain of about 8.6 dBi

Is that true? I've always heard it was slightly over two dB. I re-read
your post and I don't think I'm taking what you said out of context. Did I?

Hi Dave,

Wrong context. Not many can hoist a dipole that high, and finding
perfect ground is even more difficult to find - but once they do, that
2+ dB is undoubtedly measured in dBd (which is to say, compared to a
dipole in free space) which at least one of your links uses also.

73's
Richard Clark, KB7QHC

"Roy Lewallen" wrote in message
...
A plain dipole 76 feet above perfect ground has a gain of about 8.6 dBi -
surely you've modeled one with AO. So the gain of your antenna over a
dipole is about 5.3 - 5.5 dB. (This would be a more meaningful way to state
gain.)

W4RLN ???? said he prefered dbi if I remember correctly. Can't remember the
reason why

This is just slightly more than the gain from a three element Yagi, and
less than a typical four element beam.

Difficult to compare Roy as the top reflector position moved beyond the
feed point albiet also much higher.

The F/B ratio and bandwidth might be better than that of a typical three
or four element Yagi (or they might not be -- a Yagi can be adjusted for a
wide range of characteristics),


Well I thought the F/B was exceptional, especially because it stayed
relatively constant
over the band width as did the gain. I especially liked the fact that the
impedance
was in the 50 ohms vicinity where optimum characteristics of an yagi antenna
usually drives
the impedance to a low level. Force 12 emphasises that to get optimum gain
one must accept
unrealistic impedance values among other things
Can you point to a 4 element yagi where its characteristics are better in
every way?
( there must be something where this excels. grin)



but the gain is certainly not exceptional

I agree, but because it is relatively constant across the band I would
consider it very good.
On the other hand the elements are all straight from end to end on that
model. I may
be optimistic but I am anticipating up to 2 db increase in gain when I
reduce the beam
width to 60 degrees from 70 degrees by shaping the elements into a quasi
parabolic shape.
All in all it seems it will perform quite well and does put into focus the
question of not only
having more than one reflecter but having a reflecters that also provides a
consistent 50 ohm plus impedance.!
This is just an experiment that I am sharing with the antenna group in an
area where I have not seen
any examples in print and not something that one can say... 'Dah Da the
yagi replacement !'
But it does show a method where antenna attributes can be made consistent
across the band
which can be wider than the norm. Comparisons with the Yagi is also
difficult to make because
where a yagi is at a constant height in this case certain elements have an
increased height.

Thanks for the comments, tho I must say I do view the model with more
enthusiasm than you do,
but I do defer to your broader experience and knoweledge.

Best Regards
Art

..

Roy Lewallen, W7EL

art wrote:
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which
emulate a dish in it's crudish form not only in position of reflectors
but also the elements were not shaped at this time.
The following table follows what one would get for a reflective dish
used on frequencies in the giga hertz range where the bandwidth is
broader than
that obtained with the yagi format PLUS relevant atributes stay more
constant over a frequency range than that obtained with a super gain
type array.
The band width is wider than a typical yagi in that the major portion
of the radiation is to the front this.This band with is expected to
narrow and to increase gain when individual elements are shaped to a
parabolic form and
it is hoped that forward side lobes will not occur as is normal for a
long boom multi element yagi form as used on 440 Mhz.
The driven element is at a height of 76 feet over perfect ground.

Normally one would say that if results seem out of the ordinary one
should question it, so comments are requested regarding my explanations
which
lead me to think that they really are what one should expect.



Freq 14.0 14.1 14.2 14.3 14.35

Gain dbi 13.86 14.05 13.99 13.9 13.87

F/B 30 25.6 27.47 33.17 32.5

Zr 45.9 44.5 43.8 43.2 42.8

Zi -12.87 -6.52 0.6 7.84 11.54

SWR 1.32 1.2 1.14 1.25 1.34


I do not advocate the replacement of the normal yagi with the above
because of building difficulties tho it is my intention to build it.

Regards
Art

(Modelled using AO PRO with 80 segment/half wave and set up by a
consumate error generator Grin )

No, you read it correctly.

The gain of a dipole *in free space* is about 2.15 dBi. The gain of a
dipole over ground (compared to the standard reference of an isotropic
antenna in free space, which is what dBi means) is considerably greater.
You get an automatic 3 dB in field intensity when you put a dipole over
ground just because the radiated power is concentrated in a hemisphere
rather than a whole sphere. Then there can be additional gain due to
pattern shaping by interference between the direct and reflected signals
-- the effect is exactly the same as you get from a two element array
with the elements fed out of phase. This additional directive gain from
pattern shaping can be as high as about 5 dB. (See the two element array
patterns in Chapter 8 of the ARRL Antenna Book.) So the gain of a
horizontal dipole over ground is typically between about 5 and 10 dBi.
This is, of course, at the angle at which the pattern is maximum, which
is never at the horizon for a horizontally polarized antenna, and in
some cases is at a fairly high and perhaps useless angle.

Except for very high radiation angles, ordinary ground is nearly as
reflective as perfect ground for horizontally polarized fields. So the
above conclusions apply also to real ground as well as perfect ground.

I've argued many times against the use of "dBd" as a measure of antenna
gain, unless the meaning of dBd is carefully spelled out. A good deal of
misunderstanding results if one person assumes it means the gain
relative to a dipole in free space (2.15 dBi) and another believes it
means relative to a dipole at the same height as the antenna being
discussed (in which case it means about 5 - 10 dBi). I've seen at least
one antenna manufacturer cleverly make use of this misunderstanding to
make their antennas sound like they have a lot higher gain than they do.
A casual reader might have gotten this same impression from reading
Art's data, although I know he's not intentionally trying to mislead anyone.

If any of the sources you referenced contradict what I've said, I
recommend dropping them a line and suggesting that they correct what
they've published.

Roy Lewallen, W7EL

Dave Bushong wrote:
Roy Lewallen wrote:

A plain dipole 76 feet above perfect ground has a gain of about 8.6 dBi


Is that true? I've always heard it was slightly over two dB. I re-read
your post and I don't think I'm taking what you said out of context.
Did I?

73,
kz1o

http://www.radio-electronics.com/inf...ivity_gain.php
http://www.tmeg.com/tutorials/antennas/antennas.htm
http://www.starantenna.com/omni_dire...le_antenna.htm
http://www.softwright.com/faq/engine...Y%20UNITS.html
http://www.ventenna.com/faq.html
http://tinyurl.com/5zste