Lumped Element Transmission Line Research Articles

Compact Distributed Phase Shifters at X-Band Using BST

A new type of distributed analog phase shifter is presented that utilizes the coplanar strip transmission line topology. This transmission line has several benefits for phase shifter design, resulting in decreased physical dimensions and potentially lower losses. A prototype was constructed using thin-film barium strontium titante (BST) varactor technology. The design achieved a 49°/dB figure of merit at 10 GHz. The performance and chip area of the coplanar strip circuit are compared with designs using coplanar waveguide and synthetic lumped element transmission lines.

High-pass lumped-element transmission lines

In this work the high-pass lumped-element transmission line is shown to have a number of useful advantages over the classic low-pass line including DC isolation between sections, lower loss per section, and a much higher maximum frequency of operation, far beyond the natural self-resonant frequencies of the passive components used.

Experimental measurements on a simulated lumped transmission line

A novel design for simulating a lumped element transmission line is described. Op-amp subcircuits replace discrete inductances—an approach which overcomes a number of disadvantages associated with conventional components. The apparatus models a lossy line which is free of amplitude and phase distortion. Experiments are described which demonstrate the design’s precise measurement capabilities with respect to determining frequency-dependent input impedance and phase shift, as well as the real and imaginary parts of the complex propagation function. Several pulse experiments are also discussed.

Use of transmission line analysis for multi-tuning of birdcage resonators

A general analysis for double-and higher order tuning of birdcage resonators is presented based on a lumped element transmission line model. Expressions were developed for the determination of the resonant frequencies of bandstop and bandpass birdcage coils and, with specified restrictions, for capacitor values required to obtain any two desired mode one resonant frequencies. Experimental measurements on three variants each of an eight-column bandstop and an eight-column bandpass were in excellent agreement with theory; the average absolute frequency difference and percent deviation were 1.51 ± 1.57 MHz and 2.61 ± 2.36%, respectively. In addition, 31P and 1H phantom images were obtained at 2.0 T using a representative bandstop coil.

Resonant steps in the characteristics of a Josephson junction coupled to a transmission line

A novel circuit is described which functions as an electronic analog of lumped element transmission line. The circuit requires only operational amplifiers, resistors, and capacitors. This module was coupled to a Josephson junction simulator and current voltage characteristics of the combined system were recorded. Steps were observed at voltages determined by the appropriate line resonances. When the transmission line was terminated with loads less than the characteristic impedance, chaos was seen in the lower steps. Similar results were obtained by numerical integration of the corresponding system of differential equations.

Generalized electrical analysis of low-pass and high-pass birdcage resonators

The radio-frequency ‘birdcage resonator’ has found wide use in MRI MRS for its field homogeneity and signalnoise characteristics. This paper presents a general analysis, derived from lumped element transmission line theory, of the electrical behavior of unloaded, N-column birdcage resonators applicable to several versions of the basic design including low-pass and high-pass coils. Analytic expressions and computer results are presented for both types of coil describing resonant frequencies, input and characteristic impedances, dispersion relations, pass-bands, resonant peak bandwidth and Q. Theoretical expressions for normalized resonant frequency difference ratios independent of element values and resonator geometry have been developed for generic low- and high-pass coils. Experimental measurements of resonant frequencies were made for six coils, and the average agreement with theoretical predictions was approximately 4%.