I'm assembling a switch box for a 2 element vertical phased array. My idea
is to create a system able to generate two alternate (and switchable)
cardioids using a delay line (90°, 1/4 wavelength) and a two ways, two
position relay in order to cover with an agle of 120° degrees one direction
(e.g. North) or the other. As you all know, if two elements are fed in
perfect phase the radiation pattern obtained is called broadside. This is
exactly what I want to obtain introducing a second relay in order to get a
third direction. At this point my question is: should I put a 10 w 100 ohm
resistance (non inductive) between the two antennas (it's called Wilkinson
power divider or power splitter) or the system works perfectly that way?
There are two different school of thought: the first consider the wilkinson
a must, since it lowers the swr and keeps it under control, the second
school thinks it burns useful power and does not transfer all power.
So what's your point of view?
Thanks a lot in advance for your contribute
Francesco ik8vwa

--
E il marconista sulla sua torre,
le lunghe dita celesti nell'aria,
riceveva messaggi d'auguri
per questa crociera straordinaria.
E trasmetteva saluti e speranze
in quasi tutte le lingue del mondo,
comunicava tra Vienna e Chicago
in poco meno di un secondo.

E la ragazza di prima classe, innamorata del proprio cappello,
quando la sera lo vide ballare lo trovò subito molto bello.
Forse per via di quegli occhi di ghiaccio così difficili da evitare,
pensò "Magari con un pò di coraggio, prima dell'arrivo mi farò
baciare".

Francesco DeGregori

On Feb 2, 3:28 pm, "Francesco L." wrote:
I'm assembling a switch box for a 2 element vertical phased array. My idea
is to create a system able to generate two alternate (and switchable)
cardioids using a delay line (90°, 1/4 wavelength) and a two ways, two
position relay in order to cover with an agle of 120° degrees one direction
(e.g. North) or the other. As you all know, if two elements are fed in
perfect phase the radiation pattern obtained is called broadside. This is
exactly what I want to obtain introducing a second relay in order to get a
third direction. At this point my question is: should I put a 10 w 100 ohm
resistance (non inductive) between the two antennas (it's called Wilkinson
power divider or power splitter) or the system works perfectly that way?
There are two different school of thought: the first consider the wilkinson
a must, since it lowers the swr and keeps it under control, the second
school thinks it burns useful power and does not transfer all power.
So what's your point of view?
Thanks a lot in advance for your contribute
Francesco ik8vwa

--
E il marconista sulla sua torre,
le lunghe dita celesti nell'aria,
riceveva messaggi d'auguri
per questa crociera straordinaria.
E trasmetteva saluti e speranze
in quasi tutte le lingue del mondo,
comunicava tra Vienna e Chicago
in poco meno di un secondo.

E la ragazza di prima classe, innamorata del proprio cappello,
quando la sera lo vide ballare lo trovò subito molto bello.
Forse per via di quegli occhi di ghiaccio così difficili da evitare,
pensò "Magari con un pò di coraggio, prima dell'arrivo mi farò
baciare".

Francesco DeGregori

If the loads are equal and they are fed through equal lengths of line,
then a resistor between them (I assume you mean at the transmitter end
of the feed lines) will never dissipate any power, since it has equal
voltage at each end.

A Wilkinson splitter (or combiner) is used to provide isolation
between the loads, so that if one load is disconnected, the other load
still receives the same power. As a combiner, it isolates the sources
so that power from one source doesn't get into the other source; this
is very useful for combining generator outputs for intermod
testing...but it does depend on proper loading of the output port, and
it's only good at or near the design frequency.

Cheers,
Tom

I highly recommend reading the "Phased Array Techniqes" part of Chapter
8 of any edition of the _ARRL Antenna Book_ for about the past 15 or 20
years. It was first written not long after Dana Atchley popularized the
use of the Wilkinson Divider for feeding phased arrays (and the error of
which he later saw), so it contained quite a bit of detail about why
that's a bad idea. When I re-wrote the section for the recent 21st
Edition, I reduced the amount of material regarding the Wilkinson
divider, since I thought it had finally faded away. I'm disappointed to
hear that there's still a "school of thought" which regards it as a
viable feed system after all these years.

If you have the 21st Edition, you'll find the complete text of the
earlier material on the included CD. It contains more detail about why
the Wilkinson divider isn't appropriate for this application.

Devoldere's _Low Band DXing_ also contains a lot of good information
about phased array feed systems.

Roy Lewallen, W7EL

Francesco L. wrote:
I'm assembling a switch box for a 2 element vertical phased array. My idea
is to create a system able to generate two alternate (and switchable)
cardioids using a delay line (90°, 1/4 wavelength) and a two ways, two
position relay in order to cover with an agle of 120° degrees one direction
(e.g. North) or the other. As you all know, if two elements are fed in
perfect phase the radiation pattern obtained is called broadside. This is
exactly what I want to obtain introducing a second relay in order to get a
third direction. At this point my question is: should I put a 10 w 100 ohm
resistance (non inductive) between the two antennas (it's called Wilkinson
power divider or power splitter) or the system works perfectly that way?
There are two different school of thought: the first consider the wilkinson
a must, since it lowers the swr and keeps it under control, the second
school thinks it burns useful power and does not transfer all power.
So what's your point of view?
Thanks a lot in advance for your contribute
Francesco ik8vwa

If you have the 21st Edition, you'll find the complete text of the earlier
material on the included CD. It contains more detail about why the
Wilkinson divider isn't appropriate for this application.

Devoldere's _Low Band DXing_ also contains a lot of good information about
phased array feed systems.

Thanks a lot to both of you. I have the two books mentioned above and I did
not suspect the cd rom contained all the former articles published. I did
not use it since the programs on the cd did not install on my pc ;-) About
the Low band dxing, it is very very complicate for a beginner like me and
even if I wrote to the author in order to get more info, he never replied.
So I'm gonna have a deep look at the ARRL cd and also trusting what you
summarized! I've also found a leaflet (published online in pdf ) by HyGain
where they suggest different combinations of phased arrays which use their
verticals and there are no schemes containing the resistor.
I asked since an Italian dxer (i4ewh) in its scheme considers this splitter
absolutely necessary. I spoke with him and he told me the swr was greatly
reduced by this solution. Anyway here is the link so you can have a look.
It's a four element phased array:
http://i4ewh.altervista.org/ShortWav.../Verticali.htm
Once again, I must repeat that low band dxing has no help for beginners and
better and simpler schemes can be found on the simple "vertical antennas" by
arrl and arrl antenna book. If you have any other site or web address where
I can find more material, please tell me.
A last question to both of you: I would like to use this system (centered
for the 20 meters band) also for 40 meters and 10 meters. Should an antenna
tuner suffice?
Francesco ik8vwa

Francesco L. wrote:
. . .
I asked since an Italian dxer (i4ewh) in its scheme considers this splitter
absolutely necessary. I spoke with him and he told me the swr was greatly
reduced by this solution.

The SWR has nothing to do with the antenna pattern. A good SWR can be
had with a feed system which produces a lousy pattern, and obtaining a
good pattern can result in a poor feedpoint SWR. But the feedpoint
impedance is easily fixed with a matching network. A poor pattern is
much harder to correct.

Anyway here is the link so you can have a look.
It's a four element phased array:
http://i4ewh.altervista.org/ShortWav.../Verticali.htm

It's entirely possible that this arrangement does produce some nulls and
peaks. But it almost certainly isn't producing the pattern that the
author thinks and, if the resistors are doing anything at all, they're
wasting power which could be radiated. The _Antenna Book_ explains why.

Once again, I must repeat that low band dxing has no help for beginners and
better and simpler schemes can be found on the simple "vertical antennas" by
arrl and arrl antenna book. If you have any other site or web address where
I can find more material, please tell me.

There's a great deal of information about phased arrays in books and on
the web. I haven't done a comprehensive survey, but would guess that a
solid majority is wrong. And if you're not pretty well aware of the
basic principles and problems of feeding phased arrays, you probably
won't be able to tell which is and which isn't. Look over the _Antenna
Book_ information, both in the 21st Edition and the material from the
20th which is on the CD. If you find it too hard to understand, drop me
an email.

A last question to both of you: I would like to use this system (centered
for the 20 meters band) also for 40 meters and 10 meters. Should an antenna
tuner suffice?
Francesco ik8vwa

No. All an antenna tuner does is transform the feedpoint impedance. It
does nothing to produce the element currents you need in order to get
the pattern you want. It is possible to make a reasonably good
multi-band receiving array as long as it's electrically small. (An HF
receiving antenna doesn't have to be efficient.) But to make a decent
transmitting phased array for multiple bands usually requires a separate
feed system for each band, and probably separate elements for each band
also. You can, of course, use any of a number of simple feed systems on
multiple bands which will give peaks in some directions and nulls in
others. But the patterns won't be anything like the textbook patterns
for properly fed arrays.

Roy Lewallen, W7EL

It's entirely possible that this arrangement does produce some nulls and
peaks. But it almost certainly isn't producing the pattern that the
author thinks and, if the resistors are doing anything at all, they're
wasting power which could be radiated. The _Antenna Book_ explains why.

Ok


Look over the _Antenna
Book_ information, both in the 21st Edition and the material from the
20th which is on the CD. If you find it too hard to understand, drop me
an email.

That's very very kind of you

A last question to both of you: I would like to use this system (centered
for the 20 meters band) also for 40 meters and 10 meters. Should an antenna
tuner suffice?
Francesco ik8vwa

No. All an antenna tuner does is transform the feedpoint impedance.

I was and still I'm conscious of this but my question was different
and maybe not so well expressed, so excuse me and read this please:
my intention is to use the two antennas also to radiate in the 7 mhz
band (spacing in this case would be 1/8 and the radiation lobe almost
omnidirectional) and 28 mhz (spacing would be 1/2 wavelength and the
radiation pattern should be end-fire). This is because the system
would be designed for the 20 meters band with 1/4 wave spacing between
the two elements, but as you know, that spacing corresponds to 1/8 and
1/2 respectively in the 40 and 10 meters band. I know the sensitivity
should not be the best but using an antenna tuner I think the
radiation patterns should be as predicted before, what do you think?

Francesco L. wrote:

I was and still I'm conscious of this but my question was different
and maybe not so well expressed, so excuse me and read this please:
my intention is to use the two antennas also to radiate in the 7 mhz
band (spacing in this case would be 1/8 and the radiation lobe almost
omnidirectional) and 28 mhz (spacing would be 1/2 wavelength and the
radiation pattern should be end-fire). This is because the system
would be designed for the 20 meters band with 1/4 wave spacing between
the two elements, but as you know, that spacing corresponds to 1/8 and
1/2 respectively in the 40 and 10 meters band. I know the sensitivity
should not be the best but using an antenna tuner I think the
radiation patterns should be as predicted before, what do you think?

It's easy to get the correct phasing with two identical elements which
are in phase or 180 degrees out of phase -- you simply feed them with
equal lengths of coax (in phase) or lengths which differ by 1/2
wavelength (out of phase). Alternatively, you can use a reversing
transformer for the out of phase case. You can also use other odd
multiples of 1/2 wavelength although the beam and SWR bandwidth gets
narrower as you use longer lengths. So as long as you create a feed
system which does this on every band, you'll be fine.

The problem is in making the 90 degree phased array on 20, which I
recall you wanted to do. (If not, disregard the rest.) The feed system
for that pattern will work only on the one band, so you'll have to
switch it out on the other bands. The L network feed systems described
in the _Antenna Book_ use equal length lines plus an L network for doing
90 degree feeds. So you could use the L network on 20, and switch it out
but use the same feedlines for the other bands to get two in-phase
elements on those other bands. You would need a tuner, though, since the
impedance at the common feed point will be different on each band.

Roy Lewallen, W7EL

The problem is in making the 90 degree phased array on 20, which I recall
you wanted to do. (If not, disregard the rest.) The feed system for that
pattern will work only on the one band, so you'll have to switch it out on
the other bands. The L network feed systems described in the _Antenna
Book_ use equal length lines plus an L network for doing 90 degree feeds.
So you could use the L network on 20, and switch it out but use the same
feedlines for the other bands to get two in-phase elements on those other
bands. You would need a tuner, though, since the impedance at the common
feed point will be different on each band.

Roy Lewallen, W7EL

Ok, thanks, as soon as I have the possibility to assemble the antenna, I'll
let you know. This newsgroup is great, as your kindness.
Francesco ik8vwa

Roy Lewallen wrote:
I highly recommend reading the "Phased Array Techniqes" part of Chapter
8 of any edition of the _ARRL Antenna Book_ for about the past 15 or 20
years. It was first written not long after Dana Atchley popularized the
use of the Wilkinson Divider for feeding phased arrays (and the error of
which he later saw), so it contained quite a bit of detail about why
that's a bad idea. When I re-wrote the section for the recent 21st
Edition, I reduced the amount of material regarding the Wilkinson
divider, since I thought it had finally faded away. I'm disappointed to
hear that there's still a "school of thought" which regards it as a
viable feed system after all these years.

If you have the 21st Edition, you'll find the complete text of the
earlier material on the included CD. It contains more detail about why
the Wilkinson divider isn't appropriate for this application.

Gee Roy, didja write the book on that one? ;-)

-=-

Smash

Roy Lewallen wrote:
I highly recommend reading the "Phased Array Techniqes" part of Chapter
8 of any edition of the _ARRL Antenna Book_ for about the past 15 or 20
years. It was first written not long after Dana Atchley popularized the
use of the Wilkinson Divider for feeding phased arrays (and the error of
which he later saw), so it contained quite a bit of detail about why
that's a bad idea. When I re-wrote the section for the recent 21st
Edition, I reduced the amount of material regarding the Wilkinson
divider, since I thought it had finally faded away. I'm disappointed to
hear that there's still a "school of thought" which regards it as a
viable feed system after all these years.

If you have the 21st Edition, you'll find the complete text of the
earlier material on the included CD. It contains more detail about why
the Wilkinson divider isn't appropriate for this application.

Devoldere's _Low Band DXing_ also contains a lot of good information
about phased array feed systems.

Roy Lewallen, W7EL


Probably because a lot of folks don't realize that the power isn't
divided equally among elements in most ham phased arrays. A lot of the
textbook examples are for microwave applications (e.g. radar) where they
do assume equal powers to each element, but that's where the array is
specifically designed to present 50 ohm resistive feedpoint impedances
at all ports, regardless of phasing, especially if it's an active array
with amplifiers at each T/R module.

There's also plenty of examples out there for microwave broadside arrays
of many identical elements at uniform spacing 1/2 wavelength, for which
a equal power divider actually works fairly well. (or, at least, it's
easy to analyze)