CHARACTERISTICS OF A SLOT-COUPED MICROSTRIP ANTENNA USING HIGH-PERMITTIVITY FEED SUBSTRATE

The slot-coupled microstrip antenna can be used for constructing a thi n and lightweight active antenna without a feed loss by electromagneti c coupling of such active circuits as MIC and MMIC on the back side di rectly with the radiating element via the slot. Hence, this structure is promising as a highly functional mobile communication antenna. In t his case, the feed substrate has a high dielectric constant as MIC and MMIC and are used while the antenna substrate has a low dielectric co nstant so that a large bandwidth and a high radiation efficiency can b e obtained. It is important for the design of active devices to unders tand various characteristics of the present antenna constructed from s ubstrates with different dielectric constants. In this paper, the effe ct of the dielectric constant of the feed substrate on various antenna characteristics is derived both by measurement and by computation usi ng the spatial network method. It is found that the resonant frequency changes if a high dielectric consant material is used, although the a mount of change is less than the relative bandwidth and that the relat ive bandwidth of the antenna does not depend on the dielectric constan t of the feed substrate. When an MIC or an MMIC is attached to the bac k side, the radiation from the feed line including the slot to the bac k side is coupled directly with the active device and causes intermodu lation. The effect of the dielectric constant of the feed substrate on the backside radiation is an indispensable item of investigation for development of active antennas. This investigation also is carried out in this paper which deals with the effect of the dielectric constant on the backside radiation.