Allison wrote:
On Fri, 2 Jun 2006 07:35:24 +0100, Ian White GM3SEK
wrote:

Sal M. Onella wrote:

"Ian White GM3SEK" wrote in message
...


Those were the phased arrays for the earlier VHF radar, and consisted of
two or four two-element yagis clustered around the nose (of a
two-engined aircraft, obviously). This gave a fairly good
forward-looking capability. Both sides did much the same, and given the
relatively long wavelength, it's hard to think how better to do it.

The huge benefit of the magnetron was that it operated at much shorter
wavelengths, which frees up the antenna design and provides much better
spatial resolution - witness the downward-looking "H2S" radar which was
the magnetron's first major deployment.

The VHF radars were still around into the late 1970's, maybe beyond. The US
Navy had them on carriers for air search. I think the nomenclature was
AN/SPS-29 and/or AN/SPS-37. The one I recall was in the 218 - 220 MHz and
it was hell on TV channel 13! The antenna was referred to as a bedspring
array; the rectangular framework for the dipole radiating elements resembled
a giant bedspring.


Sure, but none of those would fly very well. The discussion was really
about airborne radar, where there are tough limits on antenna size.

P38s, Spitfires and other aircraft setup for night attack or bombing
did have a smaller high VHF radars using smaller 8 element bedspring
arrays. They proved very effective.


As far as I know, these VHF arrays were only installed on the nose of
twin-engined or four-engined aircraft. On a single-engined aircraft like
the Spitfire, the antenna would have been behind the propeller. Did you
mean the Mosquito?

There were also some rearward-looking VHF/UHF radars using a simple
2-element antenna, to warn of aircraft approaching from anywhere within
a large rearward beamwidth.

A common feature of all these early airborne VHF/UHF systems was that
the antennas were fixed, so the view was always relative to the
direction of the aircraft.


VHF and UHF radar has a better ability to peek over the horizon and at
the time when reciever for uhf were still new tech offered the best
range/power ratios.

Hence VHF/UHF was favored for shipborne use, where the horizon range is
limited by the relatively low antenna height.

The magnetron moved effort to the milimeter bands
at high power outputs where small high gain antennas were practical
thus negating the need for high gain recievers.

Yup... and the small size eventually opened the way to steerable
antennas too.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek