Feature: RF and microwave


Figure 4: Phase noise power spectral densities (PSD) for the free running RTD (top trace), DWBL (bottom trace) and injected RTD and several injection powers


extremely narrow bandwidths, stringent manufacturing tolerances and material limitations. Te broadband hybrid circulator IMRA applied was developed by Micro Harmonics; see Figure 3. Te design combines a Faraday rotator with an orthomode transducer (OMT): both components are inherently broadband and, when properly configured, enable low-loss signal routing across the entire band.


Beyond 260GHz Although the proof of concept centred on 260GHz, the IMRA team states that the architecture is scaleable to 1THz and beyond. Fundamentally, nothing limits the research to 260GHz. Te RTD, the photomixed source and the waveguide infrastructure can all support operation well above that frequency. If a 1THz circulator existed today, IMRA could run the same experiment at 1THz. Te RTD itself, fabricated by Rohm


Semiconductor, spans a tuning range of 240-260GHz and produces up to 40µW of power in free-running mode. Once injection locked, the team achieved a


34 April 2026 www.electronicsworld.co.uk


spectral linewidth narrowing from 5MHz to below 1Hz, enabling precise control over the frequency output. Tis kind of tunability is vital for


real-time signal processing and opens up architectures like tracking oscillators, where noisy or driſting signals can be amplified, filtered and stabilised inside the same waveguide loop.


First-ever residual phase noise characterisation In addition to demonstrating signal amplification, the IMRA team performed the first ever residual phase noise characterisation of an injection- locked RTD at THz frequencies. Te results confirmed key trade-offs


between gain and bandwidth; see Figure 4. As injection power increased, the phase noise dropped by up to 90dB at 100Hz offset. But the effective locking range narrowed accordingly. Te study quantifies this behaviour using theoretical modelling based on the Adler-type injection locking and the oscillator’s quality factor (Q ≈ 165). Tis level of detail enables researchers


to treat the RTD amplifier as a “resonant amplifier”, one that is narrowband but extremely quiet within its range.


Why it matters Reliable THz sources have applications across a wide range of industries. In wireless communications, they can unlock ultra- high-speed links or reduce congestion via parallel channelisation. In sensing, they’re essential for rotational spectroscopy, molecular clocks and narrow linewidth radar. Until now, the tools to generate these signals, with both high power and low noise, have been lacking. Tis shows that with the right architecture, researchers can have both. Looking forward, the IMRA team is


exploring ways to push the technology even further via RTD arrays, integrated amplifier designs and extended frequency operation. As high-frequency systems inch closer


to mainstream adoption – especially in the context of 6G, compact atomic clocks, or THz imaging – the ability to produce clean, tunable and powerful THz signals will be essential. With this work, IMRA has provided a concrete step in that direction.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48