Feature: Wireless Technology


polarisation multiplexing became critical, and where Micro Harmonics’s OMT proved essential to the success of the demonstration.


The reason OMT matters An OMT is a three-port waveguide component. Two of its ports support single-mode propagation, typically rectangular waveguides, while the third, known as the common port, supports two orthogonal modes simultaneously. One is horizontally polarised, the other vertically. It is this ability to cleanly separate or combine polarisation states that makes the OMT so powerful in advanced RF systems. Polarisation multiplexing itself is not


new. It is a well-established method for doubling capacity in communication and sensing systems at lower frequencies. However, implementing it at sub-THz frequencies, especially with ultra-wideband signals, is far more diffi cult. “T ere are very few off -the-shelf


OMTs at these frequencies, and even fewer that can maintain the isolation and bandwidth we needed,” said Cliff Rowland, RF engineer and head of business development at VDI. “You can’t have signal leakage between the vertical and horizontal polarisations, or you’ll get distortion, and you can’t aff ord much insertion loss either, especially at these frequencies where every dB matters.” Micro Harmonics, which has been


developing a complete series of millimetre- wave OMTs across all standard waveguide bands from WR-15 (50-75GHz) to WR-3.4 (220-325GHz) supplied the component that made this demonstration possible; see Figures 2-4. T eir OMT combined high polarisation isolation with low insertion loss, two critical requirements for sending dual-polarised signals through the same physical channel without degradation. In this case, it enabled the system to carry 40GHz of combined bandwidth – 20GHz on each polarisation – over a single link. T at setup delivered aggregate data rates


exceeding 126Gbps and, importantly, the performance held up under full system integration. “We’ve made OMTs before in the lab, but


never as a standalone component at this level,” said Rowland. “Micro Harmonics


Figure 4: OMT in a lab setup www.electronicsworld.co.uk July/August 2025 13


Figure 3: Micro Harmonics’s D-band OMT


THz communication using polarisation multiplexing. T e result was not just a lab experiment, but a working end- to-end system capable of transmitting and recovering complex signals at over 100Gbps. T e 142GHz demonstration marks an


brought a high-performing part, and just as important, their team worked closely with us on the mechanical integration. Form factor, fl ange compatibility, port layout – all of it had to come together cleanly for this to work.”


Hardware integration T e signal chain did not end at the OMT. Keysight’s role was equally critical, bringing the digital signal generation, calibration and demodulation tools needed to drive and evaluate the link. Its instruments enabled the creation of high- speed, wideband modulated signals, along with the post-transmission measurement and analysis tools required to validate performance across both polarisations. Between Keysight’s digital capabilities


and VDI’s hardware, the demonstration formed a complete testbed for sub-


infl ection point which will continue with the development of similar architecture at 285GHz. T e team is also exploring whether dual-frequency, dual-polarisation signals could eventually be combined into a single spatial path, eff ectively quadrupling throughput. T at goal remains theoretical for now, but it is on their radar. In the near future, the most immediate


applications are in fi xed wireless systems that demand extreme capacity, particularly for backhaul and infrastructure links where fi bre may be impractical. High-speed, low-latency interconnects in data centres are another target, especially in modular or reconfi gurable environments where over- the-air links off er fl exibility. Looking ahead, joint communication


and sensing systems, next-generation automotive radar and high-resolution imaging all stand to benefi t as well, if the hardware continues to advance in step with system demands. With each leap forward, demonstrations like this are helping to defi ne not just what is possible at sub-THz frequencies but how close it is to becoming practical.


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