Introduction
Micro Harmonics specializes in the design and manufacture of advanced ferrite components including
Faraday rotation isolators, hybrid circulators, voltage variable attenuators, cryogenic isolators, and Yjunction circulators. Our products cover every standard waveguide band from WR-28 (26-40 GHz)
through WR-2.8 (260-400 GHz).

Why Choose Micro Harmonics Products?
Our products exhibit state-of-the-art performance in terms of low-insertion loss, broad-bandwidth, andthe highest frequency coverage in the industry. We employ unique diamond heatsinks for improved
power handling and reliability. Our patented hybrid circulators offer unprecedented bandwidths at mmwave frequencies. Our compact variable attenuators have a 35 dB dynamic range.
Every component is fully tested on a vector network analyzer to ensure compliance. All parts arethoroughly examined for dimensional tolerance. We do reliability testing (Belcore) and cryogenic cycling
tests. We use nylon thread lockers to ensure that our components stay assembled in the field.
Our products are designed and manufactured in the United States. Many of our components weredeveloped under NASA SBIR grants. Because of language in the congressional SBIR authorization, theseproducts can be sole sourced for government acquisitions.
Many companies are engineering our components into their systems and seeing improvements insystem performance. Their systems are getting smaller and better. Join the growing number of engineers
and scientists across the globe who are using our isolators to unlock the full potential of their MMW and terahertz
systems.

 Lowest insertion loss Extended bandwidth Comprehensive test data Resist stray magnetic fields

 Highest power rating

 Lightweight gold-plated aluminum 25 GHz to 400 GHz

 Compact size Cryogenic options

 Anti-cocking waveguide flanges

Guarantee
No two MMW components have the same exact frequency response. Unique signatures arise from small
misalignments and variations in the internal parts. The differences can be substantial. Max, Min, andtypical specs are helpful, but what you need to see are the actual test data for the components you arebuying. Micro Harmonics tests every component across the full waveguide band on a vector network
analyzer. We supply the test data to the customer at no additional cost. Don’t settle for anything less.
1

Table of Contents
Page 3 - Faraday Rotation Isolators
26-400 GHz
WR-28 through WR-2.8
Full waveguide band

Page 9 - Hybrid Circulators
50-330 GHz
WR-15 through WR-3.4
24% fractional bandwidths

Page 11 - Voltage Variable Attenuators
75-170 GHz
WR-10, WR-6.5
Full waveguide band

Page 13 - Cryogenic Isolators
26-220 GHz
WR-28 through WR-5.1
Full waveguide band

Page 15 - Y-junction Circulators
50-140 GHz
WR-15 through WR-8
6 GHz bandwidths

Pages 17-19…… Appendices.

2

Faraday Rotation Isolators
Micro Harmonics offers a complete line of Faraday
rotation isolators covering 25-400 GHz in every
standard waveguide band from WR-28 throughWR-2.8. These isolators exhibit state-of-the-art
performance in terms of low-insertion loss, broadbandwidth, low port reflections, and the highest
frequency coverage in the industry. They are themost advanced isolators on the market today.
“They had an isolator with the single mostimportant parameter I needed, low insertion
loss. They were ultimately able to select one
with just 1.2 dB loss at 240 GHz, which ispretty phenomenal.”
Curt Dunnam, Director of Operations
ACERT National Biomedical Center at Cornell“The compact size, extremely low insertion loss,
and the wide bandwidth have allowed us to use
isolators in a wider variety of our systems than
was previously possible and have led tosignificant improvements in key system
performance metrics such as source power andsensitivity.”
Jeffrey Hesler, Ph.D.
CTO, Virginia Diodes

The graph below shows the insertion loss of our isolators ascompared to other vendors. The insertion loss of our WR3.4 isolator is only 2 dB! Don’t waste valuable mm-wave
signal power by using an isolator with high insertion loss.
Join the many companies who are using our isolators intheir systems and seeing tangible improvements in system
performance.

3

Faraday Rotation Isolators
Model
FR280*
FR188*
FR148M2*
FR122M2*
FR100M2*
FR90
FR80M2*
FR65M2*
FR51M2*
FR43
FR34M2*
FR28*† See pages 6-8.

Isolator webpage

Flange
(EIA)
WR-28
WR-19
WR-15
WR-12
WR-10
WR-9
WR-8
WR-6.5WR-5.1WR-4.3WR-3.4WR-2.8Band(GHz)
26 - 40
40 - 60
50 - 75
60 - 90
75 - 11082 - 122
90 - 140
110 - 170
140 - 220
170 - 260
220 - 330
260 - 400

Insertion Loss(dB, typ)
0.5
0.7
0.7
0.8
0.8
1.0
1.0
1.3
1.5
1.7
2.3
3.8

Isolation(dB, typ)
25
25
25
25
25
24
25
24
23
22
22
22

Max Power†
(W)
4.0
3.4
3.0
2.7
2.3
2.1
1.8
1.5
1.0
0.7
0.4
0.3

* These models have interior access to waveguide flange screws.

A typical specification sheet is shown below. Every component is thoroughly RF tested
and the data for each individual component is shared with the customer. Our isolators
employ a unique diamond heatsink for improved power handling and reliability. Our
isolators are resistant to stray magnetic fields. We use anti-cocking waveguideflanges. All our products are fully warrantied. We design and manufacture all our
products in the United States.

4

Faraday Rotation Isolators – Sample Test Data
FR122: 60-90 GHz

FR100M2: 75-110 GHz

FR80: 90-140 GHz

FR65: 110-170 GHz

FR51: 140-220 GHz

FR43: 170-260 GHz

FR34: 220-330 GHz

FR28: 260-400 GHz

5Isolator Power Ratings - In a Faraday rotation isolator, reverse power is absorbed in a resistive layer
and converted to heat energy. In the legacy isolators sold by other vendors, the resistive layer can get
hot because it is thermally isolated. But Micro Harmonics isolators employ a diamond disc that provides
an excellent path to conduct heat from the resistive layer to the metal block. Data from our thermal
simulations of WR-10 isolators are shown in the graph below. The simulations indicate a max
temperature of 50C in the legacy isolators at the rated power level of 1 W. A Micro Harmonics isolator
reaches 50C when absorbing 7 W. See “Diamond Heatsink Technology” on pages 7-8 for more info.
WR-10

The graph below shows the maximum reverse power ratings of our isolators (MHC) and the average ofother vendors. The MHC power ratings are conservative to ensure low temperatures and long life.

6

Diamond Heatsink Technology - Our isolators employ a unique diamond support disc that allows
them to handle greater reverse power levels and operate at lower temperatures. At the heart of a
Faraday rotation isolator are a pair of alumina cones and a ferrite rod. The cones are used to couple
signals from the waveguides to the ferrite. The cones are bisected by a resistive layer along their central
axis. In most commercial Faraday rotation isolators, the ferrite and cones are suspended by a pair of
washer-shaped supports as shown in the left-side sketch below. The support material is typically BOPET,
Styrene, a resin or some other material with a low dielectric constant and low loss at mm-wave
frequencies. These materials are generally in the class of thermal insulators and thus the cones andferrite are thermally isolated from the metal block.

Signals entering the output port of the isolator pass through the ferrite rod and are absorbed in theresistive layer bisecting the input side alumina cone. The absorbed power is converted to heat energy.
Very little of this heat energy can be channeled away by thermal conduction through the washer-shaped
supports, rather it must be dissipated through a radiative process or by means of convection throughthe surrounding air. The resistive layers are thus subject to high heat levels and even damage if too
much reverse power is incident on the device. Historically this was not an issue as there was very little
power available at these frequencies. 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 a uniform high-grade optical CVD
diamond disc. The diamond disc does not have a hole at the center. Diamond is the ultimate thermal
conductor approaching 2200 W/m·K, more than five times higher than copper. The diamond disc is
sandwiched between the base of the input cone and the ferrite rod and is in intimate contact over theentire area of the cone base. This is the optimal location for the diamond disc since it is the region
subject to the highest heat levels. The diamond disc is attached to the metal waveguide block over its
periphery and provides an excellent conduit to channel heat away from the resistive layer. The thermal
conduction path is clearly superior and thus our isolators operate at much lower temperatures.
The top graphic on the facing page shows the result of a thermal simulation of our WR-10 isolator. The
resistive layer in the left side cone is treated as a heat source equivalent to the power absorbed from a
1 W RF signal. The maximum temperature is 24°C in the left side cone. No thermal gradient appears
across the diamond disc. The high thermal conductivity of the diamond disc effectively ties the conebase to the aluminum block temperature. A 7 W RF source gives a max temperature of 50°C.
7

Our thermal simulations indicate a maximum reverse power rating of 7 W for our WR10 isolators. But we have taken a conservative approach and set the maximum
reverse power rating at 2.3 W. When a Micro Harmonics WR-10 isolator absorbs a
2.3 W signal travelling in the reverse direction, the maximum temperature should notexceed 8°C above the ambient waveguide block temperature. In contrast, thesimulations indicate a max temperature near 90°C for a legacy isolator (at 2.3 W).
Micro Harmonics
isolator power
ratings webpage.

The QR code to the left will take you to our power rating webpage where we provide
a more in-depth look at our thermal models and how we use them to establish power
ratings for our isolators.

Micro Harmonics Isolators are Insensitive to Stray Magnetic Fields
Have you seen the label on the legacy isolator that warns you to keep it awayfrom magnetic fields? You will not find that label on a Micro Harmonics
isolator because our isolators are highly resistant to external magnetic fields.
The legacy isolators use a highly tuned magnetic field that is easily perturbed
by even a small external magnetic field. This causes under- or over-rotation of
Microwave Journal
the signal and severe performance degradation. Micro Harmonics isolators
article on strayuse a highly saturated magnetic bias field which makes them insensitive to straymagnetic fields.
magnetic fields. The phenomenon is explained in more detail in an article published in
the April 2021 edition of the Microwave Journal.

8Hybrid Circulators
Micro Harmonics has developed a new mm-wave hybrid circulator technology that has a 20 dB fractional
bandwidth* of 24% in every waveguide band from WR-15 through WR-3.4. In contrast, the bandwidth ofa Y-junction circulator degrades rapidly at the higher mm-wave bands. Test data from our WR-5.1 hybrid
circulator are shown in the lower graph along with test data from a Y-junction circulator for comparison.
The insertion loss (not shown) of our WR-5.1 hybrid circulator is less than 2.2 dB.
*20 dB bandwidth - The band over which the isolation between circulator ports is more than 20 dB.

9The theory of operation for the hybrid circulator is very different than the Y-junction. In the hybrid, thecirculator function is achieved in a unique way that circumvents the bandwidth limitations found in the
Y-junction. Hybrid circulator development is currently limited to frequencies below 400 GHz due topractical limitations imposed by the fabrication process. A photograph and dimensional sketch of a WR5.1 hybrid circulator prototype are shown below. A more comprehensive technical description is given in
the following paper: D. W. Porterfield, "Broadband Millimeter-Wave Hybrid Circulators," in IEEE Trans.
Microw. Theory Tech., doi: 10.1109/TMTT.2023.3239886.

A WR-5.1 circulator with a 24% fractional bandwidth is a remarkable result. In fact, this would have to beconsidered an enabling technology. But the good news gets even better. In theory, the hybrid circulator
can be designed to cover full rectangular waveguide bands with fractional bandwidths exceeding 40%.
This requires a change in the geometry that is both more complicated and more costly to machine.
Therefore, the immediate development efforts will continue to be in 24% fractional bands.
Micro Harmonics has worked with NASA to develop a line of hybrid circulators in additional 24% bands
as indicated in the table below. Please visit our website for more information.
Model NameEIA Flange

Frequency (GHz)

HC148

WR-15

54 - 68

HC122

WR-12

70 - 86

HC100

WR-10

85 - 104

HC80

WR-8

107 - 133

HC65

WR-6.5118 - 150

HC51

WR-5.1150 - 190

HC43

WR-4.3196 - 250

HC34

WR-3.4258 - 330

The hybrid circulator technology is patent pending.
10Voltage Variable Attenuators
Voltage variable attenuators (VVA) find wide application in many microwave and millimeter-wave
systems. At frequencies above 50 GHz, most VVA’s are either based on PIN diodes or resistive vanes withmotor driven mechanical actuators. Both technologies cover full rectangular waveguide bands (40%
fractional bandwidths). PIN attenuators are available up to the WR-10 band (75-110 GHz) with 20 dB
dynamic range, 3 dB insertion loss, and 100 mW power ratings. Perhaps the primary appeal of the PIN
attenuators is fast switching speeds near 100 ns. On the downside, they are sensitive to ESD damage andin some cases may generate low level noise and harmonic content.
Electronically tunable resistive vane attenuators are large, heavy, and slow compared to PIN devices. But
they have a much flatter frequency response and significantly higher dynamic range. The resistive vaneattenuators are useful in lab environments but are unsuitable for many fielded systems. They employ
calibrated control circuits and motor driven actuators to precisely position a resistive vane within awaveguide. They are available up to the WR-2.2 band 330-500 GHz. In the WR-10 band they have 3 dB
insertion loss, 60 dB dynamic range, two second switching speed, and 2 W maximum power rating.
Micro Harmonics is developing a third technology that uses a Faraday rotator to rotate the RF signal
polarity into a fixed resistive layer embedded in a ceramic cone. This is similar to the resistive vane
technology but eliminates the mechanical motion of the vane. The new Faraday Rotation Attenuators(FRA) have some unique characteristics that make them attractive options for mm-wave applications.
The FRA technology is passive which makes it insensitive to ESD damage. FRAs have characteristics suchas flat response and high dynamic range that are much better than the PIN attenuators but not quite as
good as the resistive vane devices. There are no moving parts in the FRA. The dynamic range of the MHC
WR-10 FRA is 35 dB. However, a dynamic range up to 50 dB may be possible through refinements to thedesign. The FRA is lightweight and compact like the PIN attenuator. The FRA can be scaled to at least
330 GHz, well above the 110 GHz limit for commercially available PIN attenuators.
CVD diamond discs are used in the FRAs to channel heat away from the ferrite rods. The CW power
rating for the WR-10 FRA is more than 2 W which is comparable to some resistive vane attenuators andsignificantly higher than the 100 mW rating for the PIN attenuators. Measured port reflections for the
FRA are typically less than -17 dB. This compares favorably to the -10 dB level reflections in the PIN
diode attenuators. The FRA switching speed is 10 ms. This is about two orders of magnitude faster than
the resistive vane and five orders of magnitude slower than the PIN devices. And finally, the insertion
loss of the WR-10 FRA is 1 dB which is less than the 3 dB insertion loss of the PIN diode and resistive
vane attenuators.
The new attenuator is now available from Micro Harmonics in the WR-10 band (75-110 GHz). A WR-6.5
model covering 110-170 GHz will become available in August 2023. Models in other bands will follow.
Please check our website periodically for updates.
11Voltage Variable Attenuators
Our attenuator is configured so that maximum attenuation is achieved at 0 V bias. Measured data fromour WR-10 attenuator is shown below. The dynamic range is more than 35 dB. The attenuator uses
diamond heatsink technology and has a power rating in WR-10 of 2.3 W CW. Switching speed is 10 ms.
PIN diode attenuators are faster, but our attenuator has a flatter response, higher power handling, andhigher dynamic range. And it does not produce any intermodulation distortion products (none that wehave been able to detect).

Our WR-10 attenuator is shown to the left. The
attenuator is lightweight and compact with themain body measuring 0.75 x 0.75 x 1.2 inch
(19 x 19 x 30 mm). The small size makes theattenuator very easy to fit into millimeterwave systems. A DC control voltage is applied
through an SMP (M) connector.

WR-10 attenuator

12

Attenuator page

Cryogenic Faraday
Rotation Isolators
It is a common misconception that isolators designed to workat room temperature will work reasonably well at cryogenic
temperatures. The problem is that the ferrite materials have astrong temperature dependence that impacts the signal
rotation. This can cause significant over-rotation of the signal
and severely degrade performance at cryogenic temperatures.
“We can get down to less than 100
Kelvins with commerciallyavailable cryo-coolers…Our biggest
challenge was finding an isolator
that could perform at those temps.
Fortunately for us, a company
called Micro Harmonics had justdesigned some specifically forNASA.”
Dana Wheeler, CEO
Plymouth Rock Technologies“We tried using regular isolatorsfrom one vendor. We cooled themdown and assumed they would work,
but they weren’t behaving right.”
Alexander Anferov, GRA
Shuster Lab, University of Chicago

At Micro Harmonics we have developed a line of isolators designed
for optimal performance at cryogenic temperatures. The ferrite isbiased in magnetic saturation for minimal insertion loss and thelength of the ferrite rod is optimized to achieve the desired rotation
at cryogenic temperatures.
Sophisticated models are constructed to simulate the thermal stresslevels throughout the isolator as it is cooled. Materials are chosenthat reduce thermal stress. Reliability is verified through repeatedthermal cycling in a liquid nitrogen bath. Our isolators are built towithstand the rigors of repeated cryogenic cycling.

Our cryogenic isolators are routinely tested at 25 K in our cryostat. We use a
resistive thin film for isolation that is not in the class of super conductors. The
performance of our cryogenic isolators has been verified down to 1 K.
Cryogenic models are now available in bands from WR-15 through WR-5.1. A
model at WR-28 (FR280C) has also been released. Models at WR-4.3 and WR-3.4
will be added pending customer demand.

Cryogenic Isolators

Model

FlangeBand(GHz)

Insertion Loss(dB, typ @ 25 K)

Isolation(dB, typ @ 25 K)

FR280CFR148C
FR122C
FR100C
FR90C
FR80C
FR65C
FR51C

WR-28
WR-15
WR-12
WR-10
WR-9
WR-8
WR-6.5WR-5.126 - 40
50 - 75
60 - 90
75 - 11082 - 122
90 - 140
110 - 170
140 - 220

0.5
0.5
0.7
0.5
0.5
0.7
0.9
1.2

25
28
25
30
30
27
23
23

13

Cryogenic Faraday Rotation Isolators

14

Y-junction Circulators
Y-junction Circulators

Micro Harmonics offers a line of millimeter-wave Y-junction circulators in the WR-15, WR-12, WR-10,
and WR-8 bands covering the spectrum from 50-140 GHz. These circulators exhibit state-of-the-art
performance in terms of low-insertion loss, broad-bandwidth, and low port reflections.
Our Y-junction circulators do not employ complicated dielectric matchingelements. Rather, the impedance matching circuitry is implemented throughprecision CNC machined features in the waveguide block which are highly
repeatable and tightly controlled. The machined structures also make it easy toalign the ferrite cores with some precision and obtain a high degree of
uniformity between the three circulator ports.

Y-junction circulators

Model

Flange(EIA)

20 dB Band*(GHz)

Insertion Loss(dB, max)

Isolation(dB, min)

YC148-61
YC148-68
YC122-73
YC122-78
YC122-83
YC100-86
YC100-93
YC100-95
YC100-97
YC100-105
YC80-110
YC80-118
YC80-127

WR-15
WR-15
WR-12
WR-12
WR-12
WR-10
WR-10
WR-10
WR-10
WR-10
WR-8
WR-8
WR-8

58 – 64
65 – 71
71 – 76
75 – 81
81 – 86
83 – 89
90 – 95
92 – 98
94 – 100
102 – 108
107 – 113
115 – 120
125 – 129

0.4
0.5
0.5
0.5
0.6
0.6
0.7
0.7
0.7
0.7
1.1
1.1
1.1

20
20
20
20
20
20
20
20
20
20
20
20
20

*The band over which the isolation is greater than 20 dB.
Our initial offerings are targeted to bands where there
is widespread interest in the millimeter wave
community. Over time we will continue to add
products tuned to other sub-bands within the 50140 GHz window in response to customer requests.
Designs above 140 GHz will be considered on a caseby-case basis.

“We couldn’t find anybody that was capableof producing circulators in the frequency
band we required, much less with the highisolation and wide bandwidth we wanted…
Micro Harmonics fine-tuned the design tomeet the performance characteristics weneeded within a very precise band.”

Please do not hesitate to contact us to discuss how we
can apply our capabilities to your requirements. We
typically do not charge a design fee (NRE) to develop acirculator tuned to a specific sub-band. Our primaryconcern is to identify bands of interest and provide
components to serve the broader community.

Dr. Fred Daneshgaran, Professor, Chairman
California State University, Los Angeles15

We define the bandwidth as the band over which a circulator has more than 20 dB isolation. The graphbelow gives an estimate for the 20 dB bandwidth that can be achieved at a given center frequency. For
example, a circulator designed with a center frequency of 110 GHz has a fractional bandwidth near 5%.
The isolation would be greater than 20 dB across the band 107.3-112.7 GHz.

A typical Y-junction circulator specification sheet is shown below. The circulators can also be tuned forhigher isolation over more narrow bandwidths. The three flanges are equidistant from the Y-junction.

16

Insertion Loss -vs- Transmission Conversion Table
IL
(dB)

T
(%)

IL
(dB)

T
(%)

IL
(dB)

T
(%)

IL
(dB)

T
(%)

IL
(dB)

T
(%)

IL
(dB)

T
(%)

0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9

100.00
97.72
95.50
93.33
91.20
89.13
87.10
85.11
83.18
81.28
79.43
77.62
75.86
74.13
72.44
70.79
69.18
67.61
66.07
64.57

2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.01
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9

63.10
61.66
60.26
58.88
57.54
56.23
54.95
53.70
52.48
51.29
50.00
48.98
47.86
46.77
45.71
44.67
43.65
42.66
41.69
40.74

4.0
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9

39.81
38.90
38.02
37.15
36.31
35.48
34.67
33.88
33.11
32.36
31.62
30.90
30.20
29.51
28.84
28.18
27.54
26.92
26.30
25.70

6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7.0
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9

25.12
24.55
23.99
23.44
22.91
22.39
21.88
21.38
20.89
20.42
19.95
19.50
19.05
18.62
18.20
17.78
17.38
16.98
16.60
16.22

8.0
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
9.0
9.1
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9

15.85
15.49
15.14
14.79
14.45
14.13
13.80
13.49
13.18
12.88
12.59
12.30
12.02
11.75
11.48
11.22
10.96
10.72
10.47
10.23

10.0
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9

10.00
9.77
9.55
9.33
9.12
8.91
8.71
8.51
8.32
8.13

0
10
20
30
40
50
60
70
80

100
10
1
0.1
0.01
0.001
0.00010.00001
0.00000117

18

19