Time-varying Transmission Lines Research Articles

Monolithically Integrated Directly Pumped Time-Varying Transmission Lines

A novel directly pumped time-varying transmission line (DP-TVTL) is proposed here and implemented on gallium arsenide (GaAs) microwave monolithic integrated circuit (MMIC). Comparing to existing TVTL architectures where the pump wave is launched through the transmission line, the pump wave in the DP-TVTL is directly fed to the different parts of the transmission line through a parallel power division network. The impedance of TVTL is modulated by the pump through diode bridges that isolate the signal path from the pump path. The power division network creates a phase delay emulating that of a traveling-wave delay line yet without launching the physical pump wave on the TVTL. This avoids the loss of the pump energy propagating through the transmission line. It also adds more freedom in the design of the bandgap properties of TVTL and simplifies the combination/separation circuitry for waves at different frequencies in and out of the TVTL. The resulting MMIC TVTL offers exceptional, broadband conversion gain performance of up to 4.2 dB, a low noise figure of 3 dB, and input referred P1dB of 12 dBm when used as a parametric mixer. It may be used in an RF front end as a mixer first receiver or an RF correlator.

Monolithically Integrated Parametric Mixers With Time-Varying Transmission Lines (TVTLs)

Mixers are frequency conversion devices that are widely used in radio applications. This article presents an in-depth theoretical study on the parametric mixing and amplification performance of the time-varying transmission lines (TVTLs) and utilizes the concept to design two TVTL parametric mixers on a commercially available InGaP HBT process. Unlike traditional passive mixers, these parametric mixers can provide a mild conversion gain and achieve a relatively low-noise figure. For the traveling-wave TVTL, the theory of the parametric mixing with the single-sideband condition is reviewed and compared with the double-sideband mixing case. The noise performance analysis shows that the noise figure of the TVTL can be made arbitrarily low to the quantum noise limit through the input reactive termination. The theory serves as a guideline for the design of MMIC parametric mixers. Measurement results have shown that the MMIC traveling-wave TVTL can achieve a maximum of 2.1-dB conversion gain. The mean noise figure was 2.7 dB within the measured frequency band. For the reflective TVTL parametric mixer, the conversion gain and the pump power consumption can be significantly improved. The noise figure, however, is degraded due to the multiple reflections created in the matching circuit. These conclusions are supported by theoretical analyses, ADS harmonic balance simulations, and experiments in this article.

Magnetic-Free Isolators Based on Time-Varying Transmission Lines

Two magnetic-free reconfigurable isolators based on a doubly balanced gyrator (DBG) are designed in this paper. One of the isolators is a single-ended transmission isolator (STI), which uses two matching resistors to absorb the signal transmitted in the reverse direction. In theory, it has infinite isolation bandwidth, which is verified by simulation and an experiment. The other isolator is a differential transmission isolator (DTI) to improve the anti-interference performance, which consists of four Wilkinson power splitters (combiners) and two reciprocal transmission line segments. The DTI uses two pairs of differential signals to prevent the reverse signal. Compared to the STI, the DTI has higher power capacity. Furthermore, when the phases of the control signals acting on the switches are changed, the isolation directions of the two isolators will be changed, to obtain the reconfigurable property.

Energy Accumulation in Waves Propagating in Space- and Time-Varying Transmission Lines

This letter introduces a new principle of energy accumulation in transmission lines with the LC parameters varying in space and time-an effect emerging from the concept of dynamic materials. We consider a checkerboard material assembly created by a periodic temporal “flip over” of the properties of spatial laminates fabricated from two different substances. In some extended ranges of material and structural parameters, an exponential growth of energy is maintained in waves traveling through this assembly due to the work done by an external source at the moments of temporal property switching. The effect is numerically demonstrated for an equivalent LC circuit.

Time-varying wave digital filters for modeling analog systems

The theory of wave digital filters, which are well suited to model analog networks including those containing transmission lines, is extended to the time-varying case. This allows simulation of the moving vocal tract or parametric amplifiers. A representation consistent with the physics of time-varying reactances and transmission lines requires not only time-varying filter coefficients, but also structural modifications in the n-port adaptors and reactance one-ports of the filter. The number of coefficients in the adaptors is increased, and stability and pseudopassivity are not assured.

A method for the sensitivity improvement of radio astronomy receivers

The signal-to-noise ratio of radio astronomy receivers can be optimized and the sensitivity improved by reshaping the waveform of the signal received from the antenna by processing it through a transmission line in which the velocity of propagation can be made to vary as the signal enters or leaves the line. Presented here is the complete analysis of the determination of the minimum detectable temperature in the case of a total power radiometer incorporated with time-varying transmission lines. A comparison of the two sensitivity figures of the total power radiometers with and without such transmission lines is also given.

Digital Data Dynamic Transmission Systems

Digital data dynamic transmission systems which employ asynchronous time multiplexing are introduced with the experimental equipment of one of the systems. It is possible to attain dynamic matching between information sources even with time-varying parameters and transmission lines, by searching a time slot for each information signal block only when the subscriber has an information signal block ready to be transmitted. For the experimental system, the transmission delay time and the rate of channel busy time are derived by analytical methods and computer simulation under the specific conditions. By adding a priority transmission function to the experimental system, the system becomes capable of handling both on-line traffic and offline traffic. If proper sizes of buffer memories are chosen, it is possible to transmit various informations from various information sources being endurable against overload traffic.