Forum: Technology

Hello! I have a question. Can mechanically scanned slotted waveguide radar been defined "phased array" radar?
Thank You
bye!

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Not clear on your question...please edit or rephrase. But if you mean Can mechanically scanned slotted waveguide radar be defined as a "phased array" radar? the answer is no. They operate on completely different principles. I could elaborate, but will wait to see what your question really was...

Hello! Sorry for my bad english, I wrote "been" but I meant "be" Razz

so your interpretation is correct : "Can mechanically scanned slotted waveguide radar be defined as a "phased array" radar?"

I asked this, becouse I have read on Encyclopaedia Britannica this phrase: "The individual radiating elements of a phased-array antenna need not be dipoles; various other types of antenna elements also can be used. F

or example, slots cut in the side of a waveguide are common, especially at the higher microwave frequencies. In a radar that requires a one-degree, pencil-beam antenna, there might be about 5,000 individual radiating elements (the actual number depends on the particular design).

The phased-array radar is more complex than radar systems that employ reflector antennas, but it provides capabilities not otherwise available." and this other one (under a photo) :"The AN/APG-66 radar in an F-16 fighter aircraft. The mechanically scanned planar phased-array antenna with radiating horizontal slots is 29 inches wide by 19 inches high."
Thank you!

But slotted wave guide radars use one transmitter (usually a big honkin' magnetron-like substance) and pump the energy through wave guides and out the slots. No phasing of the signal is possible. Note that the APG-66 and it's big brother the APG-69 are in fact slotted, mechanical antenna and are not phased array radars.

Phased array antenna have multiple transmitters. Each can transmit at slightly different times to delay the sinusoidal cycle of it's relative to other transmitters. A wave front is a collection of signals, all at the same phase. By "phasing" the peak of the outputs, you can steer the wavefront without physically moving the antenna.

I'll correct myself...some newer solid state radars use many small high power amplifiers instead of the magnetron.Klystron/etc family of transmitters. However, they still all transmit in phase and drive the signal through wave guides and slots just like the older ones. AN/TPS-77 is an example of a solid state, mechanically scanned array.

Hello!

I have some doubts about what you wrote. You said phased array antenna have multiple trasmitters...but only active phased array radars have multiple trasmitters, indeed passive phased array have a central trasmitter wich "pumps" signal in all radiant elements (wich are coupled with phase shifters if I am correct). Maybe Encyclopaedia Britannica meant that slotted waveguide radars are phased array just becouse they have multiple radiant elements wich are in phase each other.

Goodbye!

Yea, I think you're right about the passive vs active, but if britannica claimed that slotted wave giude antennas were a type of Phased array that are flat mistaken.

Salute!

you finally cracked the code Mimmo.

There are hybrid phased-array radars that use "active" elements to shape and direct the radar beam, but the elements are not radiating energy, only directing it. So you can use a large source of the microwaves behind the "antenna", and the antenna acts like an optical lens.

You can also have an antenna with completely passive "slots" that shape and direct the beam.

later..............

Forum Veteran Joined: Nov 07, 2003 - 09:12 PM Posts: 901

hi MimmoMerelli,

"phased array" is usually the term we associate with "electronic steering/scanning" (Here is a pretty nice article.)

And "slotted waveguide", on the other hand provides an attractive solution for radar antenna design.

I feel it is misleading for Encyclopaedia Britannica to mention the AN/APG-66 has mechanically scanned planar phased-array antenna. The Westinghouse antenna is commonly refer as "planar-array".

There are however application that employs slotted waveguide antenna for phased-array radar. MESSENGER spacecraft will be one.

For the question, as mentioned in other replies, AN/APG-66 is not a "phased-array radar" and I feel mechanically scanned slotted waveguide radar should not be defined as a "phased-array" radar.

cheers,

Thank You for your kind answers Smile

Now I have clearer ideas about slotted waveguide radar and phased array.
I would have another little question...what does it precisely mean "highly directional in the plane of the antenna"?

Oh, another thing...could you suggest me some interesting and complete book inherent radar principles and technics?

Goodbye!
P.S.: I live in Italy
Cheers

Forum Veteran Joined: Nov 07, 2003 - 09:12 PM Posts: 901

MimmoMerelli wrote:

I would have another little question...what does it precisely mean "highly directional in the plane of the antenna"?

Oh, another thing...could you suggest me some interesting and complete book inherent radar principles and technics?

hi MimmoMerelli,

Directivity (the ability of an antenna to focus energy in a particular direction) and Gain are two key characteristic of antenna design. I stand to be correct, my understanding to the line is, the importance to the spacing of the slots, impacts "the desired directivity along the boresight line of the antenna".

For reading material, I would like to suggest <a href="http://www.amazon.com/exec/obidos/ASIN/1891121014/threefournineA/" target="_blank" rel="nofollow">Introduction to Airborne Radar</a> by George W. Stimson. I hope it is available in your location.

Happy reading.

cheers,

PS: Definition of directivity extracted from this <A href="http://www.wirelessisland.net/basic%20antenna%20concepts.htm" target="_blank" rel="nofollow">article</a>.

Forum: Technology

Slotted Waveguide Radar