Design of Low-cost Microstrip Antennas for Glonass Applications

Abstract

A new design procedure for low-cost circularly polarized microstrip antennas is proposed. Instead of the conventional truncated-corner square microstrip topology, a rectangular patch with four truncated corners and an equal number of stubs is utilized here. As an application, a Glonass receiver antenna is designed. Comparisons between experimental and simulated results are presented, revealing very good agreement. The design of microstrip antennas as low-cost radiators for mobile communications can be chal- lenging. Additional complexities are introduced into the conventional microstrip design when the FR4 laminate is used as the antenna substrate, due to its high loss tangent and inaccurate relative permittivity. The high losses in the antenna laminate have a direct efiect on its radiation e-ciency. Consequently, for higher e-ciency, thicker substrates must be used (1). In case, for instance, a probe-fed truncated-corner square microstrip antenna (TCSMA), frequently used for achieving cir- cular polarization (CP), is designed following the conventional procedure, an extra limitation is posed if the patch is printed on a thick substrate: its inherently inductive input impedance can not be properly matched to a 50-› SMA coaxial connector. In addition, the frequency where its axial ratio is best does not coincide with the frequency where its return loss is best (2). To overcome these limitations, a new design procedure is proposed here. Instead of the conven- tional topology (a square patch with two truncated corners), the new procedure utilizes a rectan- gular patch with four truncated corners. Besides, stubs are added to each corner to compensate for the inaccuracy of the FR4 relative permittivity. This new patch topology gives the antenna designer more ∞exibility and the ability to properly compensate for the undesirable reactive inductance.