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Problems of Modeling HF-band Feed Devices Using Quasi-Distributed Elements

Keywords:

V.A. Braznikov, V.V. Yudin


This article is about modeling HF-band feed devices (for example, matching devices) using quasi-distributed elements. Modern tendencies in HF-band are being analyzed. The most important one is automation of adjustable feed devices (matching devices mostly) to ease real-time adaptive modes for transmitters without preceding adjustment to foreseen frequencies, bearing with transient loads and so on. That leads to a problem of creating more complex (compared to the ones already in use) models for the feed device elements, mainly the ones that address quasi-distributed inductive elements. Problems of modeling capacitors are being addressed shortly, as those solve relatively easy due to small electrical size. Inductive elements model based on coupled lines where elements are described using four frequency-independent parameters is explained. Based on inphase and antiphase excitation of coupled lines system analysis of equivalent scheme of inductive element is held. Equations for input admittance and impedance are derived for short-circuit and no-load on output poles, enough to determine all parameters of inductive element as a four-pole. Conditions that enable modeling second resonance on a frequency which is not a multiple of base one are discussed. The problems of synthesizing of inductive element equivalent scheme are discussed. The approach that scheme is synthesized after few conditions are met: the appearance of second resonance on a given frequency and the condition of inductive equivalence in low frequency band. Then two out of four parameters of equivalent scheme are independent ones and could be used to fine-tune characteristics of inductive element in first resonance band and on lower frequencies. Results of calculation of frequency characteristics reactive part of iductive element impedance (single coil solenoid) acquired by different methods - electrodynamical modeling, generalized equivalent schemes method, earlier model based on regular line segment and suggested method based on coupled lines. Results show that suggested model achieves higher accuracy (compared to the earlier model) on low frequencies (below first resonance) and behaves well on higher frequencies (up to second resonance).
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