Below we present an overview of the current state of isolator technology at Micro Harmonics. Our near term goal is to develop a full line of components operating from 60 GHz to 325 GHz with significantly improved performance over the current state-of-the-art. Our long term vision is to extend coverage to 400 GHz and beyond. These components will find immediate use in a broad range of commercial and scientific systems. Please contact us to discuss how we can apply our capabilities to your requirements.
Isolators are useful for controlling standing waves in a wide variety of millimeter-wave and terahertz systems. For example, in submillimeter-wave multiplied local oscillator systems standing waves arise due to impedance mismatches between the highly tuned frequency multipliers. This in turn gives rise to dips or even nulls in the output of the multiplier chain. Because of the lack of availability of suitable isolators, the standing waves are typically mitigated through complicated impedance matching techniques that are performed on a case-by-case basis at a great cost in time and money.
At frequencies above 75 GHz, there are relatively few vendors and the available components are unsuitable for many systems due to high insertion loss. Most of the commercial components were developed more than forty years ago and there has been little effort at modernization. Using modern electromagnetic simulation tools, we have demonstrated isolators that exhibit significantly reduced loss and improved bandwidth. Our simulations and supporting test data indicate that our isolators work well over significantly broad bands in excess of the standard waveguide bands.
Compact Isolators Micro Harmonics has been pursuing a two pronged approach to millimeter-wave isolator development. The first approach utilizes three stacked plates as described by Erickson [1, 2]. The graphic to the right shows an exploded view of the three-plate isolator on the left and a photograph on the right. These isolators are available with a diamond substrate between the input cone and ferrite. Power incident on the isolator output port is absorbed in the lossy film bisecting the input cone. The subsequent heat energy is efficiently channeled to the block through the diamond substrate. Most, if not all commercial isolators do not use diamond supports but rather use supports that are in the class of thermal insulators.
 N. R. Erickson, “Very Low Loss Wideband Isolators for mm-Wavelengths,” 2001 IEEE MTT-S Dig., pp. 1175-1178.
 N. R. Erickson and Ronald M. Grosslein, “A Low-Loss 74–110-GHz Faraday Polarization Rotator,” IEEE Trans. Microwave Theory Tech., vol. 55, no. 12, Dec. 2007.
Drop-In Isolators We refer to our second approach as a “drop-in” isolator. The drop-in isolator comprises a center plate that houses the core assembly and an E-plane split waveguide block that houses the center plate and contains a stepped waveguide twist on both the input and output ports.
An exploded view diagram of the center plate is shown in the top part of the graphic. The gold rectangular piece is the machined center plate. The two silver discs are neodymium bias magnets. The magnetic armatures are at the far left and far right. The alumina cones, diamond support disc, and ferrite core are shown together to the left of the center plate.
The sketch in the lower left corner shows how the centerplate fits into the E-plane split waveguide block. The photograph in the lower right shows the centerplate mounted in the bottom half of the split-plane block.
The drop-in isolator topology offers some unique advantages. First, the waveguides on the flanges are perfectly aligned in the drop-in isolator whereas in stacked plate isolators the waveguides are typically aligned at 11.25 degrees rotation from the normal. Although this difference is mostly cosmetic, it is important to some users. Second, the drop-in topology makes it possible to include interior access to two of the four waveguide flange screws on each flange which is an important feature for many users. And third, the drop-in topology makes it possible to integrate the isolator with other waveguide components in an E-plane split waveguide block.
If you are interested in integrating the drop-in isolator into your system, please contact Micro Harmonics for more information.
Isolators are now available for sale at WR-12, WR-10, WR-8 and WR-6.5. For more information please go to the isolators product page by following the link below.
Isolators at Higher Frequencies - We are currently testing prototype isolators at WR-5.1, WR-4.3 and WR-3.4. The possibility of extending this work to WR-2.8 (265-400 GHz) is also being evaluated.
The data shown to the right are from simulations of our WR-5.1 isolator. The simulations predict a best-case scenario since all of the constituent parts in the model are perfectly dimensioned and aligned. In the real world there are subtle variations that can degrade performance.
In the simulations the isolation is greater than 20 dB over the extended band from 130-230 GHz (the standard WR-5.1 band is 140-220 GHz). The port reflections S11 and S22 are less than -20 dB from 136-230 GHz or a VSWR of 1.2:1. The insertion loss is less than 0.5 dB over the standard WR-5.1 band.
The preliminary measured test data for our WR-5.1 prototype are shown in the graph to the right. The insertion loss is less than 2.3 dB over the band 160-220 GHz. The measured isolation is greater than 20 dB and the port reflections less than -17 dB (VSWR < 1.4:1) over the same band. These units are available for sale. Please call for more information.
The standard WR-4.3 band is 170-260 GHz.
The WR-4.3 simulation data are shown in the graph to the right.
Measured data for one of our WR-4.3 isolator prototypes are shown in the graph at the right. The data cover the extended band 160-265 GHz. The measured insertion loss ranges from 2 dB at the low end of the band to 4 dB at the high end with a 5 dB peak near 233 GHz. This is a preliminary result and we are working to get the insertion loss closer to 2 dB across the band. Isolation is greater than 20 dB from 175-265 GHz but rolls off at the low end of the band. Please call for more information.
The simulation data indicate input and output reflections less than -20 dB over the standard WR-3.4 band 220-325 GHz. The isolation is more than 30 dB and the insertion loss less than 2 dB over the extended band from 210-340 GHz.
The initial measured data from a WR-3.4 prototype are shown in the lower graph to the right. The data were measured over the extended band from 210 GHz to 340 GHz. Insertion loss ranges from 2 dB at the low end of the band to 4.5 dB at the high end. It should be possible to get the insertion loss near 2 dB across the entire WR-3.4 band.
The measured isolation is greater than 20 dB across the extended band 210-340 GHz. The isolation data was fairly uniform for all of the tested prototypes. To our knowledge we are currently the only manufacturer of WR-3.4 isolators worldwide. Please call for more information.
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