Analysis and simulation of a cylindrical microstrip antenna for spin-stabilized satellites.

Lubab Ali Salman
Dr. Abbas A. Al-Shalchi

Abstract: An omni-directional antenna for telemetry, tracking and command (TT&C) com- munications is required for spin-stabilized geostationary satellites whether in the launching phase or once in orbit. The need for a despun platform can even be reduced by implementing a conformal microstrip antenna array °ush mounted on the cylindrical surface of the satellite for that purpose. The analysis and design of this kind of antennas is quite complicated and a powerful simulation software proves indispensable to achieve this goal. In this work a cylindrical microstrip antenna array (CMSArr) for the aforemen- tioned purpose has been investigated using rigorous full wave analytical techniques in conjunction with the numerical method of moments (MoM). The rigorous full wave analysis involves the solution of Maxwell's equations in a cylindrically strati-¯ed linear isotropic medium. The solution has been formulated into the form of an eigenfunction expansion with cylindrical wave functions as the kernel of expansion. The dyadic Green's functions then are formulated in the spectral domain for an elec-trical current point source radiating in the vicinity of the structure. The microstrip patch elements are considered to be of in¯nitesimal thickness, hence reducing the complexity of the problem, as well as being a valid approximation for microwave and millimeter wave applications. These microstrip elements are replaced with current sheets along the interfaces including them and the whole problem is formulated as an integral equation problem whose unknowns are those surface currents by enforcing the boundary conditions along these structures in the spatial domain. The Galerkin approach for the method of moments is employed to approximate these currents. The formulation leads to the solution of an eigenvalue problem whose eigenvalue is the operating frequency and the eigenvector is the coe±cient vector of the cur- rent approximating series. In the intermediate formulation the associated surface wave phenomenon that plays a crucial role in the characterization of the cylindrical microstrip antenna has been analyzed in detail. Using MATLAB R2008a as a programming language and a development environ- ment a set of simulation routines has been written and run to characterize the associated surface wave phenomena, resonance characteristics and radiation pat-terns of the proposed device. It has been shown that basically there at least two surface wave modes propagating with approximately zero cuto® frequency which can a®ect the whole e±ciency of the antenna. In addition, the role of the substrate's permittivity on the radiation pattern has been investigated showing broadened ra-diation patterns in the elevation plane with larger permittivities while maintaining the required omni-directional coverage in the azimuthal plane.