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TechWaTch March, 2024
Solving the Issue of Reflected Waves at D Band
By Greg Rankin
second (Gbps), the D band will un- lock a number of technologies across a wide range of industries. Wireless communication is often the focal point, but commercial ap- plications include high-precision sensing, radio astronomy, and air- port security detectors. For the military, the D band will open the door to the next generation of in- ter-satellite links, imaging radars, and stand-off detection. However, as research and de-
T
velopment teams attempt to deliv- er on the much-anticipated move into the frequency range between 110-170 GHz, they are running in- to a common problem of signal re- flections, also known as mismatch- es. These undesirable waves, or ripples, can attenuate power out- put, distort the digital information on the carrier and, in extreme cas- es, damage internal components. “When you get above 110 GHz
it’s sort of uncharted territory,” ex- plains Ed Loewenstein, chief archi- tect at NI. “Your connectivity gets a little strange and cables don’t work very well anymore. So, most things are done in waveguides.”
he call for “more D band” has gone out. With the ability to transmit 100 Gigabits per
Suppressing Signal Reflections
Until recently, there has been
limited test and measurement equipment available at D band fre- quencies, with few standards and little-to-no traceability to NIST (National Institute of Standards and Technology). “What we often hear is that
once someone sets up their equip- ment to make a test or measure- ment at these frequencies and something doesn’t go quite right, they spend most of their time try- ing to figure out whether it’s their test equipment or the device that they’re testing,” adds Loewenstein. Therefore, the development
of the D band is dependent on companies like NI, formerly known as National Instruments, which create the equipment that engineers rely upon to efficiently and accurately perform compre- hensive research, testing, and val- idation. However, recently, as the company was looking to create new 6G sub-THz reference archi- tecture they ran into the issue of reflected waves themselves in the waveguides. In millimeter wave (mmW)
systems, the distance between components is often much larger than a wavelength. As you sweep frequencies, the phase changes
As research and develop- ment teams attempt to de- liver on the much-antici- pated move into the fre- quency range between 110- 170 GHz, they are running into a common problem of signal reflections, also known as mismatches.
and there are nulls, dips, and de- graded performance. To resolve that in microwave frequencies, en- gineers simply insert an isolator between components and the re- flected signal gets absorbed. However, as you move up the electromagnetic spectrum shorter wavelengths require smaller con- stituent parts. At mmW frequen- cies, the parts are tiny and even the smallest misalignment can sig- nificantly degrade performance. As demand for D band sys-
tems increases, so does the num- ber of isolator options available. Unfortunately, their performance
still lags behind what engineers have become accustomed to at low- er frequencies.
Advances in mmW Isolator Design
“We evaluated the isolators
on the market from what data was available and it was pretty easy arithmetic to see that Micro Har- monics was the most appropriate thing for us,” adds Lowenstein. Micro Harmonics Corporation
is a Virginia-based manufacturer specializing in the design of mmW components. Under a NASA con- tract, Micro Harmonics essentially reinvented the isolator so that it can operate well into THz frequen- cies.
The traditional method to
manufacture an isolator has been to use ferrites that are substan- tially longer than required, and then tune the magnetic bias field to achieve optimal performance. What Micro Harmonics did to
minimize loss was reduce the fer- rite length by as much as possible. The design developed for NASA saturates the ferrite with a strong magnetic bias field, which allows for the shortest possible length of ferrite to achieve the ideal 45° of rotation. This lowers the insertion loss to less than 1 dB at 75-110 GHz and only 2 dB at 220-330 GHz.
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Meeting Deadlines for D Band
NI needed to deliver its new
mmW test and measurement equipment as well as its advanced software-defined radios which can greatly accelerate prototyping and next-gen wireless innovation. Loewenstein says it was im-
portant that the isolator could cov- er the entire D band which the iso- lators designed for NASA could do. NI measured their systems
before and then after inserting the isolator and saw a noticeable im- provement in the ripple which they said was due to cleaning up the mismatched reflections. This al- lowed them to announce the 6G Sub-THz reference architecture that provides calibrated measure- ments with up to four gigahertz of
modulation bandwidth. Contact: Micro Harmonics, 20
S Roanoke Street, Suite 202, Fin- castle, VA 24090 % 540-473-9983 E-mail:
sales@mhc1.com Web:
www.microharmonics.com r
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