Low Noise, Tunable Non-Reciprocal RF Front-Ends Based on Time-Varying Transmission Lines (TVTL)

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A transmission line structure with its effective dielectric property modulated in space and time is proposed. Such a transmission line supports two-way propagation of electromagnetic waves on the same structure while keeping the electromagnetic waves propagating toward different directions separatable by shifting only the frequency of the wave that aligns with the direction of the space-time modulation. Leveraging both on the fundamental science of radio frequency circuits and the modern semiconductor technology, the proposed concept will find a broad range of applications in modern wireless systems by creating novel radio frequency devices and functional blocks that enables sensitive and interference resilient wireless front-ends. The proposed work fosters interactions among multiple engineering research fields. If successful, it will revolutionize the current way of transmitting and receiving electromagnetic waves in a challenging environment and lead to next generation communication or sensor electronics that are of low power consumption, high performance, compact and affordable. As the advancement of mobile communication technology is changing human lifestyle, a high performance wireless radio frequency front-end will provide a great thrust to this change.This proposal is to attack the noise and interference issues in the radio frequency front-end that fundamentally limits of the performance of a wireless system, by developing tunable, non-reciprocal front-ends with broad frequency tunability yet low noise. Such a front-end is only enabled through exploiting the unique property of Time-Varying Transmission Line. Time-varying transmission line consists of passive transmission lines whose inductance or capacitance is space-time modulated by another electromagnetic wave. It possesses a mixture of passive and active circuit characteristics. First, it is a transmission line that can be engineered and designed to have accurate impedance, phase and delay characteristics in both directions. Furthermore, it offers functions of active circuits such as amplifications and frequency conversions. Devices created out of this novel concept include resonators with accurately controlled resonating frequency yet allowing resonances across different frequencies to couple. This property can be utilized to create low noise, high-quality factor, tunable filtering capability even within miniaturized dimensions. The proposed effort will first establish a systematic theory of Time-Varying Transmission Line being used as a key building block to achieve superior performance in radio frequency front-ends. This includes various novel developments of functional blocks such as circulators, tunable filters with parametrically enhanced quality factors, low noise amplifiers, active frequency conversion and phase shifting circuits. Modern semiconductor technology will then be utilized for on-chip integration of the proposed devices. The performance bound on practical implementations of the radio frequency front-end will be derived based on these integrated circuit prototypes. Ultimately, new wireless system architectures and applications that fully leverage on the unique features of these devices will be explored for the purpose of meeting the need of emerging wireless communications.