The paper contains an introduction, formulation of the problem, the implementation of the antenna and discussion of the results. The introduction discusses some approximate models, based on circuit theory, the development of effective equivalent circuit of antennas. Radiation characteristics of the slot are explained by an experimentally determined resistance and modeled microstrip-slotline junction by employing an ideal transformer. Section "Formulation of the problem" considers analysis and design of rectangular slot antenna excited by stripline in the cavity filled with air (Fig .1). A detailed explanation of parameters of equivalent circuit of stripline slot antenna (Fig.2) is provided. Parameters of emitters depend on exciting circuit device. In particular, the resonant frequency, quality factor and the input conductance of the input transducer with in-phase and antiphase excitation are usually much different. In section "Implementation of antenna and discussion of results" the results of experimental research are presented. To verify effectiveness of equivalent circuit, an experimental rectangular slot antenna shown in fig. 3 is excited by the strip-line. Fig. 5,a presents the results of calculation of the reflection coefficient in the frequency band using proposed equivalent circuit. Fig. 5,b shows the results of experimental measurements which were made with Rohde & Schwarz FSH8 spectrum analyzer. The results of calculation are in a good agreement with measurement data as well as with calculations following known theories. Thus, due to its simplicity and effectiveness, proposed equivalent circuit is convenient in analysis and design of slot antennas with a strip-line excitation, which are under high requirements of matching and reactivity of the input resistance, particularly in analysis of small-element antenna array with dielectric coating.