Abstract
Analysis and design of an ultra-wideband microstrip-to-slotline transition on a low permittivity substrate is presented. Cross-sectional structures along the proposed transition are analyzed using conformal mapping assuming quasi-TEM modes, attaining one analytical line impedance formula with varying design parameters. Although the slotline is a non-TEM transmission line, the transitional structures are configured to have quasi-TEM modes before forming into the slotline. The line impedance is optimally tapered using the Klopfenstein taper, and the electric field shapes are smoothly transformed from microstrip line to slotline. The analytical formula is accurate within 5% difference, and the final transition configuration can be designed without parameter tuning. The implemented microstrip-to-slotline transition possesses insertion loss of less than 1.5 dB per transition and return loss of more than 10 dB from 4.4 to over 40 GHz.
Highlights
With the advent of the 4th industrial revolution and the 5th generation mobile communication, the amount of data tends to increase rapidly, requiring various microwave components with wide bandwidth
In order to design a good-performing ultra-wideband transition from microstrip line to slotline, the line impedance along the stretch of the transition should be optimally matched, and the electric field line shapes should be smoothly transformed to conform the change of line modes
The slotline, with wide-width conductors separated by a slot gap, has horizontally dominated field distributions similar to the coplanar stripline (CPS) line, but it the transition can be divided into four sections
Summary
With the advent of the 4th industrial revolution and the 5th generation mobile communication, the amount of data tends to increase rapidly, requiring various microwave components with wide bandwidth. In order to design a good-performing ultra-wideband transition from microstrip line to slotline, the line impedance along the stretch of the transition should be optimally matched, and the electric field line shapes should be smoothly transformed to conform the change of line modes. For use as a compact balun of an antenna, several transition designs were attempted with a slotted microstrip structure or a novel shape stub [9,10] Another type of transition was designed with bifurcated microstrip lines, and used a half-wave-delayed microstrip line to feed the slotline [11]. In order to obtain a wider bandwidth, a type of transition having a continuous signal line has been studied These transitions were designed with low-permittivity substrates [12,13,14], but had difficulties in operating at over 30 GHz due to parasitic modes at high frequencies. The design parameters for optimal impedance matching are obtained efficiently with the analytical formula without parameter tuning
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