Abstract
A new model for the microstrip line interdigital capacitor is proposed. This model consists of calculating the 2N × 2N Y‐matrix of the N coupled lines using the multiple coupled line tool. Then, this matrix is reduced to a 2 × 2 matrix using simple circuit theory. The capacitance at the end of each finger is taken into consideration using closed‐form expression of the coplanar waveguide open‐end capacitance. This model can predict the resonances that might appear around the quarter‐wavelength frequency. These resonances are caused by the coupling between the fingers and exist only in capacitors with four fingers or more. Very good agreement is obtained between the results of our model and those obtained using the software HFSS and measurements.
Highlights
Interdigital capacitors (ICAPs) are frequently used in microstrip (MS) microwave integrated circuits
Fullwave analysis and=or measurements were used in Refs. [8, 12, 14, 15] to study the MS ICAP
An ICAP is usually used at frequencies well below the ®rst quarter-wavelength frequency, i.e., in the region where it behaves as a capacitor with negligible parasitics
Summary
Interdigital capacitors (ICAPs) are frequently used in microstrip (MS) microwave integrated circuits. A new model for the MS ICAP is proposed and tested In this model, all the coupling effects between the ®ngers are taken into account using the fast multiple coupled line (MCPL) tool in the CAD software Serenade [16]. All the coupling effects between the ®ngers are taken into account using the fast multiple coupled line (MCPL) tool in the CAD software Serenade [16] In this tool, the 2N 2 2N admittance matrix of the N-®ngers' section is obtained using the Spectral Domain technique, which is reduced to 2 2 2 matrix using simple circuit theory. It is shown that this model can predict the resonances that might appear due to coupling when long ®ngers are considered To our knowledge, these resonances occuring in ICAPs have not been reported in the literature before.
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