Design of 900MHz antenna's

[Joe.G]

HI All,

I have Tx which transmitts at 915MHz.

I am look for web info book, application notes on how to
make 900MHz antenna.

I am looking to create a special radiation pattern and may be phase harnes 2
or more antennas to cover certian
radiation patterns.

Sny pointers would be apprecite.

Joseph

 

[Charles Schuler]

"Joe.G" <joe.g@optusnet.com.au> wrote in message
news:41fb0c0c$0$25526$afc38c87@news.optusnet.com.au...

HI All,

I have Tx which transmitts at 915MHz.

I am look for web info book, application notes on how to
make 900MHz antenna.

I am looking to create a special radiation pattern and may be phase harnes
2
or more antennas to cover certian
radiation patterns.

You might want to Google for "patch antenna."

 

[John Woodgate]

I read in sci.electronics.design that Mac <foo@bar.net> wrote (in
<pan.2005.01.30.00.49.48.953016@bar.net&gt about 'Design of 900MHz
antenna's', on Sun, 30 Jan 2005:

The simplest antenna to make is the folded dipole. You can make one from
300-Ohm twinaxial cable as follows:

I don't think you mean 'twinaxial cable', which is a shielded twisted
pair. I think you mean '300 ohm unshielded parallel feeder'.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Rich Grise]

On Sun, 30 Jan 2005 08:58:40 +0000, John Woodgate wrote:

I read in sci.electronics.design that Mac <foo@bar.net> wrote (in
pan.2005.01.30.00.49.48.953016@bar.net&gt about 'Design of 900MHz
antenna's', on Sun, 30 Jan 2005:

The simplest antenna to make is the folded dipole. You can make one from
300-Ohm twinaxial cable as follows:

I don't think you mean 'twinaxial cable', which is a shielded twisted
pair. I think you mean '300 ohm unshielded parallel feeder'.

Also known as "twin-lead". But at 915 MHz, the thing would almost be wider
than it is long! What's the wavelength?

lessee.. 300,000,000 m/s / 915,000,000 c/s = 33 cm. Half of that, 16.5 cm.
That's less than an inch long.

You'll need to do some tricks - UHF antennas are like black magic, like
switching power supplies. ;-)

Look at stuff like helical antennas, slot antennas, scimitar antennas,
stacked loop arrays, collinears, etc, etc, etc...

I've been entertaining notions of building a little Yagi for channel 56
here. I'm not sure of matching it to the input of my little $5.00 TV, but
hand-tuning my random wire seems to be working so far; I'd just like to
slap together something that has some gain.

Good Luck!
Rich

 

[Rich Grise]

On Sun, 30 Jan 2005 19:57:41 +0000, Mac wrote:

On Sun, 30 Jan 2005 18:54:16 +0000, Rich Grise wrote:

lessee.. 300,000,000 m/s / 915,000,000 c/s = 33 cm. Half of that, 16.5
cm. That's less than an inch long.

We may as well use accurate numbers. 299 / 915 = 0.3268 m = 32.68 cm.
Half of that is 16.34 cm. There are exactly 2.54 cm per inch, so that is
6.43"

D'oh!!!

Somehow I translated cm to mm in my headbone. ?:-|

Thanks,
Rich.

 

[John Perry]

Mac wrote:

On Sun, 30 Jan 2005 08:58:40 +0000, John Woodgate wrote:

...
I don't think you mean 'twinaxial cable', which is a shielded twisted
pair. I think you mean '300 ohm unshielded parallel feeder'.

Well, actually "shielded twisted pair" is misleading. Twinaxial
actually refers to controlled-impedance shielded pairs, which look very
much like coax with two wires inside rather than one.

Shielded twisted pair generally refers to normal insulated pairs simply
twisted together and run through a shield. Their impedance is not well
controlled, which is why they aren't used for wideband applications that
need good waveform fidelity and such.


John Perry

 

The following two links might be helpful

http://www.ScienceOxygen.com/electrical359.html
http://www.ScienceOxygen.com/electrical148.html

 

[Rich Grise]

On Mon, 31 Jan 2005 11:20:58 -0500, Mark Jones wrote:

Rich Grise wrote:

D'oh!!!

Somehow I translated cm to mm in my headbone. ?:-|

Last I heard, you were hitting the bong and rambling on about Mother and God...
so...

Only when I'm philosophizing. ;-) I refuse to blame drugs for my own
stupidity/carelessness.

Thanks,
Rich

 

[Mac]

On Sun, 30 Jan 2005 18:54:16 +0000, Rich Grise wrote:

On Sun, 30 Jan 2005 08:58:40 +0000, John Woodgate wrote:

I read in sci.electronics.design that Mac <foo@bar.net> wrote (in
pan.2005.01.30.00.49.48.953016@bar.net&gt about 'Design of 900MHz
antenna's', on Sun, 30 Jan 2005:

The simplest antenna to make is the folded dipole. You can make one from
300-Ohm twinaxial cable as follows:

I don't think you mean 'twinaxial cable', which is a shielded twisted
pair. I think you mean '300 ohm unshielded parallel feeder'.

Also known as "twin-lead". But at 915 MHz, the thing would almost be wider
than it is long! What's the wavelength?

lessee.. 300,000,000 m/s / 915,000,000 c/s = 33 cm. Half of that, 16.5 cm.
That's less than an inch long.

We may as well use accurate numbers. 299 / 915 = 0.3268 m = 32.68 cm. Half
of that is 16.34 cm. There are exactly 2.54 cm per inch, so that is 6.43"

I have built UHF antennas using the described method for UHF TV reception,
so I knew that the size was reasonable.

You'll need to do some tricks - UHF antennas are like black magic, like
switching power supplies. ;-)

Narrow-band, wide-beam, UHF antennas are not black magic at all. They are
easy to make. You can use 12 gauge single-strand wire or flexible copper
pipe to prototype them. This can give you an impedance much closer to 50
or 75 Ohms, depending on how you do it.

The son of a friend of mine built a functional ~400 MHz Yagi antenna using
some scrap wood and some 12-gauge single-strand wire.

Look at stuff like helical antennas, slot antennas, scimitar antennas,
stacked loop arrays, collinears, etc, etc, etc...

I've been entertaining notions of building a little Yagi for channel 56
here. I'm not sure of matching it to the input of my little $5.00 TV, but
hand-tuning my random wire seems to be working so far; I'd just like to
slap together something that has some gain.

In the US, terrestrial broadcast TV channel 56 is 723.25 MHz.
(Source: http://www.arrl.org/tis/info/catv-ch.html)

That means that the half wavelength is:

299 / 723.5 * 100 / 2 = 20.7 cm, or 8.135". I wonder if you could fit the
whole Yagi antenna on a circuit board the size of a sheet of paper? I
would try the cheap, easy, folded dipole first.

Anyway, have fun.

Good Luck!
Rich

--Mac