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****Abstract.
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Local excitation
conditions of fundamental mode in the planar open ring resonators are studied.
Electrodynamic system is considered, which consists of planar interconnection
structure coupled with microstrip open ring resonator. Similar system was used
in previous works on frequency characterization of resonators and antennas by ac
Josephson effect in terahertz frequency range. Calculations are performed by
time domain finite difference method (TDFD). A real part of electrodynamic
structure admittance vs. frequency dependence Re*Y*(*f*) calculated,
which is a key factor in Josephson spectroscopy. It is shown, that
interconnection structure by itself has flat Re*Y*(*f*) dependence in
the frequency range of resonator fundamental mode excitation. When
interconnection structure interacts with the resonator, it’s Re*Y*(*f*)
dependence has a peculiarity, related to fundamental resonance mode excitation.
A form of the peculiarity depends on resonator layout. In particular Re*Y*(*f*)
shows local maximum or minimum. Basing on equivalent circuit representation of
the resonator, these peculiarity forms can be considered by serial or parallel
resonance circuit at frequencies in the vicinity of resonance frequency. These
cases correspond to different resonator excitation conditions. Resonator
fundamental mode can be excited by electric or magnetic field, which depends on
the arrangement of resonator and interconnection structure.

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****Key words:
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superconductivity,
Josephson junction, terahertz electronics.

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