Tunable Loss Reflectionless Filtering Attenuator With Ultrawide Bandwidth and Extended Tunable Attenuation Range

In this letter, a novel tunable loss reflectionless filtering attenuator with ultrawide bandwidth and extended tunable attenuation range is proposed for the first time. The ultrawide bandwidth benefits from the application of unequal-width three-coupled line structures. In order to achieve both in-band and out-of-band reflectionless performance, a pair of absorptive sections are loaded at both ports to eliminate out-of-band reflections. Moreover, the unequal-width three-coupled line structure loaded by p-i-n diodes is utilized to realize a wide tunable attenuation range. For demonstration, an ultrawideband (UWB) reflectionless filtering attenuator prototype is fabricated, where the measured results agree well with the corresponding simulations. The measured results show that the reflectionless filtering attenuator features a fractional bandwidth of 104.9% and can realize the attenuation of 2.5–26.4 dB.