INTRODUCTION. Onboard equipment (OE) of spacecrafts consists of numerous modules having both analog and digital parts. The present day trend is to ...
ISSN 00204412, Instruments and Experimental Techniques, 2012, Vol. 55, No. 2, pp. 231–237. © Pleiades Publishing, Ltd., 2012. Original Russian Text © I.F. Kalimulin, T.R. Gazizov, A.M. Zabolotsky, 2012, published in Pribory i Tekhnika Eksperimenta, 2012, No. 2, pp. 91–97.
ELECTRONICS AND RADIO ENGINEERING
Impedance of LowFrequency Passive Components of Spaceborne Equipment at Frequencies Ranging to 20 GHz I. F. Kalimulin, T. R. Gazizov, and A. M. Zabolotsky Tomsk State University of Control Systems and Radioelectronics, pr. Lenina 40, Tomsk, 634050 Russia Received September 27, 2011
Abstract—The paramount importance of studying the impedance of lowfrequency passive components of spaceborne equipment at frequencies ranging to tens of gigahertz is shown. The preliminary results of mea surements of the resistor and capacitor impedances at 100 V/m in the range of up to 10 GHz and stretches to 100 GHz. Therefore, highfrequency interference may also be induced in lowfrequency circuits. These factors complicate the problem of electromagnetic compatibility (EMC)—the ability to operate properly, without interfering into the performance of the other systems under the defined electromagnetic environ ment. To ensure EMC, spacecrafts are subjected to com prehensive testing under severe conditions [2]. It is recommended that EMC tests be performed in the fre quency ranges of up to 1, 18, 40, and 100 GHz [3, 4]. However, as the frequency increases, the expenses on the equipment for such tests grow sharply, thus increasing the cost of the spacecraft development. Shielding is the traditional designer’s approach to the provision of EMC, but its efficiency rapidly deterio rates with increasing frequency due to the resonances of the slots and the casing [5]. In addition, it increases the mass of the spacecraft and, hence, the cost of its injection into orbit. It is expedient to solve the above problems by sim ulating both the routine operating mode of the onboard spacecraft equipment and the EMC tests. For the results of this simulation to be in agreement with the actual values, the models of the components must
be adequate and take into account their behavior at the predetermined frequencies. Foreign manufacturers often present models of components on their web sites. Automated design systems often incorporate libraries containing not only the circuitry symbols and foot print for components of the printed circuit boards, but also their electric models. Such a support facilitates simulation of OE com prising import components. However, in many cases, only domestic circuitry components must be used, for which models, particularly for the above frequency ranges, are usually absent. In addition, as the fre quency goes up, passive components (resistors, capac itors, and inductors) cannot be adequately described by single ideal components and must be represented by equivalent circuits composed of several ideal ele ments.
231
Electric field strength, V/m 103
102
101
100 –1 10
100
101 102 Frequency f, GHz
Fig. 1. Electric field strength measured by the satellite at a distance of 200 nautical miles (~360 km) from the Earth’s surface [1].
232
KALIMULIN et al. R
(a)
L (d)
R
C
(a)
C
(d) R
L
C |Z | |Z |
|Z | (b)
|Z | (b)
(e)
(e) C
R
R
R
C
L
Arg(Z) Arg(Z)
Arg(Z) (c)
Arg(Z) (c)
L
(f) +90
(f)
+90
0 0
0 –90
–90 –90 1 1 2πRC 2π LC
1 2π LC
f
f
Fig. 2. Diagrams of the equivalent circuit, magnitude, and phase of the impedance (a–c) of the ideal and (d–f) actual resistors.
Fig. 3. Diagrams of the equivalent circuit, magnitude, and phase of the impedance (a–c) of the ideal and (d–f) actual capacitors.
Examples of the equivalent circuits, as well as the generalized graphs of the impedance module and phase for the ideal and actual resistors and capacitors are shown in Figs. 2 and 3 [5]. It is apparent that taking into account parasitic inductances and capacitances of actual components causes the frequency dependence of the impedance to substantially differ from the dependence for the ideal components. In particular, it exhibits a resonant frequency for a component, in the region of which its impedance abruptly changes. For standard components, this resonance is, as a rule, in the region of low frequencies (hundreds and even tens of megahertz), and the behavior of these compo nents at frequencies as high as 1 GHz and, moreover, 18 GHz has not yet been clarified. Therefore, develop ment of models capable of adequately describing the behavior of lowfrequency passive components in a wide frequency range is an urgent task. One of the approaches [6] to creating the model of a passive component consists in measuring complex reflectance S11 in the predetermined frequency range and forming the equivalent circuit of this component based on the obtained results. The second part of this work generally requires structural and parametric optimization by the criterion of the maximum close
ness of the circuit’s frequency characteristic to the measured response and is beyond the scope of this paper. Meanwhile, measuring the S11 value is the ini tial part of this study; it frequently helps to obtain models at
