Abstract:
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This paper presents the design and implementation of
uniplanar bandpass filters that use end-coupled slotline resonators
and a new kind of multimodal immitance inverter. These inverters
are based on an asymmetric shunt-short-circuit coplanar waveguide
(CPW) transition, and are modeled using a multimodal circuit
model, which takes into account both fundamental modes of
the CPW (the even and the odd modes). From this model, analytical
design expressions for the inverters are obtained. These structures
are used as input/output inverters of a new class of compact
low-loss arbitrary-order easily reconfigurable uniplanar filters featuring
half-wavelength and quarter-wavelength end-coupled resonators.
A multimodal model is obtained for these filters, which allows
an accurate analysis, design, and prediction of their behavior.
By using these multimodal tools, three second- and fourth-order
prototypes, and a second-order frequency-tunable prototype, were
designed and implemented. The fourth-order filter has an insertion
loss of 2.2 dB at 2 GHz with an out-of-band rejection better than
20 dB in an extremelywide frequency band. The frequency-tunable
filter features a tuning range from 1 to 1.37 GHz with quasi-constant
3-dB bandwidth from 121 to 135 MHz. The measurements
show a good agreement with the proposed multimodal model, thus
validating the model and the design methodology. |