a Study of Microstrip Antennas for Use in Millimeter Wave Phased Arrays
Several selected topics in microstrip antennas are investigated for potential use in millimeter wave phased array applications, namely the characterization of coupling between an isolated pair of microstrip antennas, and the characterization of three aperture coupled antennas incorporating thick ground planes and/or cavities. An asymptotic expansion of the microstrip Green's function is developed and employed to facilitate a study of mutual coupling between printed dipoles, and coupling versus element separation is presented for substrate parameters of practical interest. The asymptotic representation of the Green's function, which differentiates space wave terms from surface wave terms when source and observation points are largely separated, is used to characterize the behavior of mutual coupling in the principal planes. In particular, the asymptotic decay rates of E- and H-plane coupling are analytically determined. For certain substrate parameters, it has been unexpectedly found that the magnitude of mutual coupling may not decay monotonically with increasing element separation. Instead, the magnitude exhibits a quasi-periodic oscillation which can be attributed to the interference of surface and space waves. The presentation and discussion of this anomalous behavior, unreported in previous work, represents a major contribution of the above research. The feasibility of an aperture coupled microstrip patch antenna with a thick ground plane, an aperture coupled cavity fed microstrip patch antenna, and an aperture coupled cavity antenna are demonstrated using reciprocity and moment method analyses, followed with practical design examples. Each antenna incorporates a thick ground plane useful as a heat sink for active MMIC circuitry, and as structural support for thin substrates. Prototype antennas show good agreement with the analyses in each case. Design procedures and equivalent circuit models are developed for each antenna. The effect of ground plane thickness in the first antenna is shown to significantly reduce the level of coupling from the feed line to the patch. The resonators in the second antenna case can be optimized for larger bandwidth. The size of the third antenna geometry can be easily reduced for array applications via dielectric cavity filling.
- Pub Date:
- January 1995
- APERTURE COUPLED;
- Engineering: Electronics and Electrical; Physics: Electricity and Magnetism