Abstract
This paper presents branch line couplers with compact size and harmonic suppression based on non-periodic reactively loaded artificial lines. The reactive loading elements of the lines are step impedance shunt stubs (SISSs). Such elements provide transmission zeros, which are useful to efficiently suppressing the harmonic content of the device. Moreover, by virtue of reactive loading, the reported artificial lines exhibit a slow wave effect of interest for device miniaturization. The combination of size, harmonic suppression efficiency, and design simplicity (with a clear design methodology) is of interest within the framework of artificial transmission lines and their application to the optimization of microwave passive components.
Highlights
Slow wave transmission lines are artificial lines, typically consisting of a host line loaded with reactive elements, exhibiting a small phase velocity, as compared to the one of ordinary lines [1], [2]
Most slow wave transmission lines are implemented by periodic reactive loading [3]–[37], and it has been argued that periodicity generates stop bands, useful for harmonic suppression, or for the implementation of devices with filtering capability
We have considered as a first step two different transmission zeros, one of them located at 3f0, and the other one positioned at 7f0
Summary
Slow wave transmission lines are artificial lines, typically consisting of a host line loaded with reactive elements (either quasi-lumped or distributed), exhibiting a small phase velocity, as compared to the one of ordinary lines [1], [2]. It is shown in this paper that by loading the constitutive host lines of the branch line coupler with SISSs resonating at different frequencies, a set of transmission zeros can be generated This represents a further degree of freedom in the design, and it is possible to achieve an efficient harmonic suppression. The capacitor patches are wide capacitive lines open-ended at the extreme The width of these capacitive lines determines their length (according to the required capacitance value), and such width has been tuned in order to generate roughly square patches for the capacitances of the different SISSs. Previously to the generation of the layout of the whole branch line coupler, we have compared the lossless electromagnetic response of the four designed cells (including the host line and the SISS) with the circuit response. With regard to amplitude balance, the bandwidth has been found to be 0.159 GHz (or 15.9%), where, in this case, the maximum considered variation has been considered to be ±1 dB
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