Re: NEC-LIST: How to design a dual band and high gain directional antenna

Hi,

At 21:46 11.11.2004, chen xing wrote:
>Hi All,
>I'm trying to design a dual band (610MHz-900MHz,
>1400MHz-1850MHz) directional antenna with very high
>gain( >=14dBi in the lower band and >=16dBi in the
>higher band ).

Yeah... That sounds pretty much like you need something for NATO bands II
(610-960 MHz) and III (1350-1850 MHz), isn't it?

The gain figure you supply are the typical specifications of products for
the tactical communications market (antennas for transportable equipment).
You can do a little bit better than the figures you quote, depending on how
much weight and wind load you can afford.

>I'm don't know what kinds of antennas can meet the
>requirements. Perhaps a corner reflector is a possible
>choice.

This is one alternative, which saw much use for the US military band
equivalent to NATO band II. Such reflectors are described in Kraus. The
usual military designs have an adjustable opening angle.

Some alternatives :
http://www.ericsson.com/microwave/images/antenn_stor.jpg
http://www.mars-antennas.com/tactiacl_radio.htm
http://www.mtiwe.com/militaryok.asp?id=65&cat_id=57&prod=1
http://members.fortunecity.com/emerald/ms12.html

For band III, I saw grid parabolic reflectors, but this is not the only
solution :
http://www.mtiwe.com/militaryok.asp?id=72&cat_id=57&prod=1
http://www2.rfsworld.com/RFS_Edition3/pdfs/Microwave_Grid_Antennas_413-426.pdf

http://www.racalantennas.com/pdfs/Military/Remote_Antennas/UHF/Directional/V%20UHF%20Radio%20Relay%20Bands%201,2,3.pdf
http://www.rolfheine.de/band-ii-antenna-en.htm

Antennas for both bands are manufacteurs in China :
http://www.dynamiceng.com.cn/chinese/product/Antenna/menu2.htm

I've personally never seen both bands combined together in a single
antenna. What would be the point ? The radios are not that broadband, and
the band II reflector would be too heavy and have too narrow a beamwidth at
band III.

If you really insist on combining two antennas, I think the easiest way
would be to spatially combine two independent arrays on a common plane. You
could have separate feeds, or a common feed with a duplexer.

IMHO, the real difficulty is the feed which should provide about one half
octave bandwidth. Reflectors are mostly textbook stuff - wbat you need to
consider is wind load, ruggedness and weight (I still suppose you want to
mount this on a telescopic tower; I can tell you from personal experience
that you'll get strong biceps from cranking your prototype up and down -
unless you have a well equiped antenna range).

Here's one reference dealing with feed design. I haven't seen the paper,
which should be one and one half pages long at the most as is customary in
Electronic letters :
http://ieeexplore.ieee.org/xpl/abs_free.jsp?arNumber=743000

You might want a look at "Jane's defense electronics" (I think this is how
it's called), or some cannon peddler magazine.

Alexandre

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