V.N. Mitrokhin - Dr. Sc. (Eng.), Professor of Bauman Moscow State University, Senior Research Worker at Bauman Moscow State University Research Institute
N. Yu. Fadeeva  Post-graduate Student, Bauman Moscow State University, Junior Research Worker at Bauman Moscow State University Research Institute. E-mail: fadeeva.n.u@gmail.com

The paper describes the influence of effective feed location on circular microstrip radiator efficiency. The influence of effective feed location and antenna parameters on radiator and route match was studied. The location of offective feed of microstrip antenna is determined on the basis of results obtained within the process of research of radial line feed by coaxial probe[8]. Antenna may be analized with the help of resonant element (Fig. 1). Field components are determined through magnetic vector potential (7). Maximal values of polar pattern of circular printed antenna are studied according to location of coaxial probe. The result of the study shows that polar pattern maximum is reached within coaxial probe location kb=2,0 and coincides with coaxial probe location within effective feed of radial line (Fig. 2). Results are proved by finite elements method which is more unified as well as more expensive method from the point of view of resourses. It should be noted that suggested method allows to estimate polar pattern of the antenna but not the quality of its match with route. VSWR is calculated with the help of finite elements method. It is shown that VSWR does not reach its highest point in frequency bandwidth within antenna effective feed. (Fig. 3). It is also noted that the match becomes better when antenna size is enlarged. There is such a value for radiator radius for which minimal VSWR has maximal power radiated in the direction of normal (Fig. 5). Antenna size is important for wireless mobile gadgets, that is why it is important to compensate current reactivity of coaxial probe to reduce radiator radius.