Contents
Introduction ..................................................................................................... 2Why Choose Micro Harmonics Products? ........................................................ 2
WR-12 Isolators ................................................................................................ 3
WR-10 Isolators ................................................................................................ 4
WR-8 Isolators .................................................................................................. 5
WR-6.5 Isolators ............................................................................................... 6
WR-5.1 Isolators ............................................................................................... 6
WR-4.3 Isolators ............................................................................................... 7WR-3.4 Isolators ............................................................................................... 7WR-2.8 & WR-2.2 Isolators .............................................................................. 8
Cryogenic Isolators ........................................................................................... 8Warranty .......................................................................................................... 8WR-15 Circulators ............................................................................................ 9
WR-12 Circulators ............................................................................................ 9WR-10 Circulators .......................................................................................... 10WR-8 & WR-5.1 Circulators ............................................................................ 11
MMW Flange Identifier Tool .......................................................................... 12
Drop-in Isolators............................................................................................. 13
Diamond Heatsink Technology ...................................................................... 14
Isolators Designed for Low-Insertion Loss ..................................................... 16
The Micro Harmonics Advantage ................................................................... 191Introduction
Micro Harmonics is a small high-tech company located in Fincastle, Virginia.
We specialize in advanced ferrite components including Faraday rotation
isolators and circulators. We offer a complete line of Faraday rotation isolators
covering 60-325 GHz in every standard waveguide band from WR-12 throughWR-3.4. We plan to extend this line to the WR-2.8 band (260-400 GHz) andpossibly to the WR-2.2 band (330-500 GHz). We are currently developing a lineof isolators designed for optimal performance at cryogenic temperatures.
Initial prototypes in WR-10 will be fully evaluated during the fall of 2018.
Cryogenic models at bands from WR-12 through WR-3.4 will follow.
We design and manufacture all of our products in the United States. Ourcomponents were developed under an SBIR grant through NASA JPL. Becauseof language in the congressional SBIR authorization, our products can be solesourced for government acquisitions.

Why Choose Micro Harmonics Products?
Our products are the most advanced on the market today. They exhibit stateof-the-art performance in terms of low-insertion loss, broad-bandwidth andlow port reflections. Our isolators employ a unique diamond heatsink forimproved power handling and reliability. Every component is tested over thefull band on a vector network analyzer to ensure compliance. All constituent
parts are thoroughly examined for dimensional tolerance. Belcore testing(thermal stress testing) is periodically performed. We use nylon thread lockers
to ensure that our components stay assembled in the field. All of our products
are fully warranted. Yet with all of these technical advantages, ourcomponents remain competitively priced.
We encourage you to read some of the enclosed technical articles on ourdiamond heatsink technology, drop-in isolator technology and our methods
for minimizing insertion loss.

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WR-12 Isolators

3

WR-10 Isolators

4

WR-8 Isolators5

WR-6.5 Isolators

WR-5.1 Isolators

6

WR-4.3 Isolators

WR-3.4 Isolators

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WR-2.8 & WR-2.2 Isolators
We are currently developing an isolator to cover the WR-2.8 band (260400 GHz). Once that development is complete we will extend the work to theWR-2.2 band (330-500 GHz). The primary challenge is not EM design but
rather fabrication and alignment of the constituent parts. Please visit ourwebsite for updates on our progress.

Cryogenic Isolators
We are currently developing a line of cryogenic isolators through an SBIR grantwith NASA JPL. There are numerous material issues that must be addressed toensure that the isolators are able to withstand the rigors of thermal cycling.
Also, the ferrite saturation magnetization is temperature dependent. An
isolator designed for room temperature operation will perform poorly whencooled. The degradation results from a roughly 20% increase in themagnetization which gives rise to a 9° over-rotation of the EM field. The end
result is a slight rise in the insertion loss and a significant drop in isolation. Thiscan be compensated by changing the ferrite length and retuning thetransitions.
The initial development is being done in WR-10 (75-110 GHz). These units
should be fully characterized by the end of 2018. During the ensuing two-year
period 2019-2020 we will develop cryogenic isolators at every band from WR12 through WR-3.4.

Warranty
All Micro Harmonics products are fully warranted for one year from the timeof purchase. Please visit our website for more information.

8WR-15 Circulators

WR-12 Circulators

9WR-10 Circulators

10WR-8 & WR-5.1 Circulators
The graphs below show initial measured results from our WR-8 and WR-5.1
prototypes. The high insertion loss is primarily due to waveguide loss which isconstrained by the flange dimensions. The tuning is highly sensitive to changes
in the ferrite dimensions. Please visit our website for more information on ourcirculator development.

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MMW Flange Identifier Tool
This tool is designed as a low-cost way to identify
waveguide flanges from WR-15 to WR-0.65 (50 GHzto 1.7 THz). It comprises a microscope withadjustable zoom (20-40 X), adjustable focus, LED
illumination and a reticle. The reticle has features toidentify the waveguide flange. A pair of waveguideflange alignment pin holes are located at the bottomof the microscope. Slide the alignment pins of theflange you wish to identify into the holes at the baseof the microscope. The reticle is slightly recessed sothat it will come into close proximity but not touch
the flange.
When the microscope is held to a lighted background(no waveguide flange attached), all of the featureson the reticle are visible as shown in the left side of
the graphic below. Before attaching to a waveguideflange, adjust the focus and magnification. When themicroscope is attached to a waveguide flange, thearea on the interior of the waveguide will go dark
since there is no reflecting surface. For example, the graphic on the right shows theilluminated reticle with the microscope attached to a WR-8 waveguide flange.
Although the markings for the 15, 12, 10 and 6.5 are still visible, only the “8” marker
spans the exact length of the broad-wall of the waveguide thus identifying the flange
as WR-8.

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Drop-in Isolators
We developed a Faraday
rotation isolator that can be
integrated with othercomponents in a single
waveguide block. The dropin isolator comprises a
centerplate that houses thecore assembly (ferrite,cones, absorber, magnets, armatures) and an E-plane split waveguide blockthat houses the centerplate and provides stepped waveguide twists on boththe input and output ports.
The graphic below shows how the centerplate assembly fits into the E-plane
split waveguide block. The photograph shows a centerplate assembly sitting in
the base half of the E-plane split waveguide block.

Our drop-in isolators are shipped with the centerplate assembly housed in theouter waveguide block. This provides protection of the centerplate assembly
and allows the drop-in isolator to be used as a standalone component. If thecustomer wishes to integrate the isolator into their system, they can remove
the outer housing and return it to Micro Harmonics for a reimbursement.
Please visit our website for more information.
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Diamond Heatsink Technology
Our isolators employ a modern design yielding much lower insertion loss thanother commercial products. They also work over much broader bandwidths inexcess of standard waveguide bands. But there is another importantdifference that sets them apart from the competition. Our isolators employ adiamond support disc that channels heat from the resistive layer in the cone tothe metal waveguide block and thus they can handle greater reverse power
levels. To our knowledge no other commercial isolators offer this advantage.
At the heart of a Faraday rotation isolator is a pair of alumina cones and acylindrical ferrite core. The cones are used to couple EM fields from thewaveguides to the ferrite. The cones are bisected by a resistive layer along
their central axis. In most commercial Faraday rotation isolators, the ferriteand cones are suspended by a pair of washer-shaped supports as shown in thesketch below.

The cone & ferrite assembly is inserted through the inner support holes andthen attached with a non-conductive epoxy. The support material is typically
BOPET, Styrene, a resin or some other material with a low dielectric constantand low loss at millimeter-wave frequencies. Materials with thesecharacteristics are generally in the class of thermal insulators and thus thecones and ferrite are thermally isolated from the metal block.
Power entering the output port of the isolator is absorbed in the resistive layer
bisecting the input alumina cone. The absorbed power is converted to heat
energy. Very little of this heat energy can be channeled away by thermal
14conduction through the washer-shaped supports, rather it must be dissipatedthrough a radiative process or by means of convection through thesurrounding air. The resistive layers are thus subject to high heat levels andeven damage if too much reverse power is incident on the device. Historicallythis was not an issue as there was very little power available at thesefrequencies. But as higher power sources are becoming available there is arenewed interest in the power ratings of these devices.
At Micro Harmonics we have replaced the input support washer with auniform high-grade optical CVD diamond disc. The diamond disc does not havea hole at the center. Diamond is the ultimate thermal conductor approaching
2200 W/mK, more than five times higher than copper. The graphic below
shows a split-view of the isolator to give a better view of the constituent parts.

The diamond disc is sandwiched between the base of the input cone and theferrite. The diamond disc is in intimate contact over the entire area of thecone base. This is the optimal location for the diamond disc since it is theregion subject to the highest heat levels. The diamond disc is attached to themetal waveguide block over its entire periphery and thus provides an excellent
conduit to channel heat away from the resistive layer. The red arrows indicate
the path of heat flow. This topology is clearly superior for thermal conduction
and thus our isolators will operate at lower temperatures.
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Isolators Designed for Low-Insertion Loss
Commercial Faraday rotation isolators have been around since the 1970’s.
Traditional builds have good isolation throughout the microwave andmillimeter-wave bands. The insertion loss is low in the microwave bands, but
steadily increases with frequency. At mm-wave frequencies the insertion loss
becomes problematic. For instance, in the WR-10 band (75-110 GHz) theinsertion loss can exceed 3 dB. In the WR-3.4 band (220-325 GHz) the insertion
loss can be more than 7 dB. There are few manufacturers in the bands above
50 GHz. Isolators in the WR-4.3 and WR-3.4 bands were manufactured many
years ago but are now difficult to find. At these high frequencies theconstituent parts are very small, and difficult to fabricate and align. And with >7 dB insertion loss, there isn’t much demand.
At Micro Harmonics we design isolators that are optimized for low-insertion
loss. The typical insertion loss is about 1 dB for our WR-10 isolators and about
2 dB for our WR-3.4 isolators. These numbers are game changers and mmwave system developers are now reconsidering their use. So how do we do it?
There are many factors to consider, but here we focus primarily on;1) Minimizing Ferrite Loss
2) Minimizing Waveguide Loss
3) Precision Fabrication and Alignment1) Minimizing Ferrite Loss - A good starting point is to consider the equation
for EM field rotation in a Faraday rotation isolator.
=4ϒ√
2Where,4πMz is the axial magnetization
ϒ is the gyromagnetic ratio (8.795x106xg rad/s/Oe)
is the ferrite lengthc is the speed of lightis the ferrite dielectric constant16

This equation shows that the field rotation is directly proportional to theferrite length and the axial magnetization. Minimum insertion loss andmaximum isolation occur when the EM field is rotated by 45° as it passes
through the ferrite. Ferrites are lossy at millimeter-wave frequencies, so it isessential that the length be reduced as much as possible. The traditional
method used to tune Faraday rotation isolators is to use ferrites that aresubstantially longer than the minimum required length and then tune themagnetic bias field to achieve optimal performance. At Micro Harmonics we
use a saturating magnetic bias field and the minimum possible ferrite length.
We measure our magnetic
bias fields to insure theferrites are saturated. We
use magnetic armatures toachieve a focused, uniform
bias field in the ferrite. The
graph shows the measured
magnetic bias field near
the surface of the ferrite
core. The peak measured
value of 2000 Oe is substantially more than what is required for saturation.
The measurements extend well outside of the area of the ferrite.
2) Minimizing Waveguide Loss – Since the EM
field is rotated by 45° as it passes through theferrite, it is necessary to realign the flanges. In
traditional builds this is accomplished bytwisting extruded waveguide (see photo). The twist must be implemented
over a sufficiently long distance to avoid damaging the extruded guide. In theWR-10 through WR-3.4 bands the total length of extruded waveguide is about
2.3 inches in traditional builds, with some variations from band-to-band andbetween manufacturers.

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At Micro Harmonics we use machined twist steps
which are substantially shorter than the extruded
waveguide twists. They yield good broadband
performance and reduced waveguide loss. The
total flange-to-flange length of a Micro Harmonics
WR-3.4 isolator is 0.45 inch (see photo to theright). At WR-10 the reduction in the waveguideloss is only 0.2 dB, but at WR-3.4 the reduction is
0.9 dB and at WR-2.8 it is 1.3 dB.
3) Precision Fabrication and Alignment – There are substantial challenges infabricating and assembling the isolators at the higher bands. The parts become
increasingly smaller and some of the materials are very difficult to machine.
Aside from the myriad fabrication complications there are considerablealignment difficulties that must be overcome.
Small misalignment of the cones and ferrite by a few degrees can result insignificant degradation of the isolator performance. The area near the ferrite
can support more than thirty modes. Misalignment can cause significant
coupling to the higher order modes resulting in unwanted structure in theresponse, increased insertion loss and port reflections as well as decreased
isolation. Misalignment can alter the orientation of the resistive layers so thata component of the E-field of the forward travelling wave is in the plane of theresistive layer, resulting in higher insertion loss and lower isolation.
The assembly process is an art form. No two isolators have exactly the same
signature. At Micro Harmonics we continually strive to improve our techniques
and the uniformity of assemblies. We also comprehensively test every isolator
on a calibrated vector network analyzer to insure it meets our specifications.
Some competitors spot-check their components at a few frequencies using
less sophisticated systems. This can lead to erroneous test data and missed
signatures in the response. We also periodically perform thermal stress testingto verify the mechanical reliability of our devices.
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The Micro Harmonics Advantage
At Micro Harmonics we are advancing the state-of-the-art in mm-wave
isolators and circulators. The significantly reduced insertion loss of ourisolators makes them suitable for use in mm-wave systems where signal
power is at a premium. For example, a traditional WR-3.4 isolator covering theband 220-325 GHz can have an insertion loss of more than 7 dB while a MicroHarmonics isolator in the same band has a typical insertion loss of less than
2 dB. Our advanced ferrite products offer:

Compact size

High isolation

Low insertion loss

Extended bandwidth

50 GHz to >325 GHz

Diamond heatsinks

Cryogenic options

Competitive prices

Micro Harmonics Corporation
20 S Roanoke St, Ste 202
Fincastle, VA 24090

Ph: 540.473.9983
Fax: 844.449.1561
MicroHarmonics.com

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