The HUSIR W-Band Transmitter (2014) [pdf] | Hacker News Reader

The HUSIR W-Band Transmitter (2014) [pdf]

ll.mit.edu

29 pointslokimedes6 comments

What is novel about an eight year old research paper on a radar system? The paper/article doesn't begin to describe what purpose the system serves.

I had no idea it was that hard to get a kilowatt at 100GHz. Automotive radars are running at 76-81 GHz, and are compact, low-cost solid state devices.

I don't get it, either. 95 GHz megawatt-scale CW sources have been around for some time: https://en.wikipedia.org/wiki/Active_Denial_System

The truck-mounted ADS is gyrotron-based like HUSIR, but apparently they are working on more-portable GaN-based sources (https://jnlwp.defense.gov/About/Frequently-Asked-Questions/A...).

The novel requirement must be the need for wider modulation bandwidth, or something like that.

Presumably those types of devices aren’t required to be particularly accurate in terms of frequency distribution, so could just focus on a single frequency or event just act as a noise source, rather than an instrument for transmitting information.

CW is not ultrawideband.

It is once you apply enough Carson's Rule to it. (At this level, the term CW is usually used in contrast to pulse modulation, rather than all forms of modulation in general as would be the understood usage at HF.)

That's the question, whether the ADS system has much modulation BW at all. HUSIR has 8 GHz, which is a fair bit. My guess is that the ADS uses its gyrotron(s) as single-stage oscillators, like the giant microwave oven it is, rather than as amplifiers for a carrier that's generated and modulated at a much lower level. Modulating a CW gyrotron oscillator directly would involve manipulating high magnetic or electric fields at unrealistic rates, and any useful degree of signal purity or short-term stability would likely be off the table entirely.

OTOH the .PDF talks about PRF and pulse width, and specifies a 40% duty cycle, so who knows. If it is indeed a pulsed system, I don't see how it differs from whatever ADS uses. The specs aren't particularly challenging.

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