Comparatve Study of Radiation Characteristics of Various Microstrip Mic Elements

1. Introduction Monolithic-type microwave integrated circuits used in various communication devices have many microstrip discontinuities such as ends, bends, gaps, and width changes. Such circuits are usually designed assuming no radiation from these discontinuities. However, radiation always occurs more or less because the structure is theoretically of open type. Recent trend of use of higher frequency and densely compacted circuits necessitates careful consideration of influence of such radiation on circuit characteristics and surrounding environment. Nevertheless, little work has been done on how radiation characteristics differ by the difference of discontinuities, or by frequency change[1]. The reason is that no pertinent means have been available to evaluate accurately radiation properties, both radiation patterns and radiated powers. The authors have developed a new method combining FD-TD method and radiation mode theory, which makes it possible to calculate radiation patterns and radiated powers in both space region and substrate region [2],[3]. In the present paper, by using this new method, radiation properties are analyzed very accurately, and comparative studies of radiation characteristics are undertaken by taking several typical microstrip-type circuit elements as examples. Summarized results are presented by putting these elements together into four groups, each group including elements with similar shape and similar radiation characteristics: bends and mitered bends are put in group 1, ends, gaps, and steps are collected in group 2, stubs are put in group3, and double-beam couplers and parallel line couplers are in group 4. 2. Common features to all examples All numerical examples are given for the element structures of which straight line parts are consisted of 50 microstrip lines with substrate thickness h being 0.6mm, relative permittivity r