Anomalous mutual coupling between microstrip antennas

Abstract

An asymptotic expansion of the microstrip Green's function is used to facilitate a study of mutual coupling between two printed antennas, and coupling versus element separation is presented for substrate parameters of practical interest. For certain substrate parameters, it is found that the magnitude of mutual coupling does 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, heretofore unreported in previous work, is the purpose of this paper. 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.

Highly decoupled planar dipoles in an air waveguide backed by a perfect‐magnetic‐conductor plate above the earth

“…[1,2]. For example, a world-record f MAX of ϳ800 GHz has been reported [3]; an InP HBT with a low-noise figure of 0.46 dB at 2 GHz has also been demonstrated [4]. However, InP-based HBTs have several device and substrate-processing limitations such as difficulties in substrate handling, smaller wafer size, and higher cost.…”

“…The analysis of the microstrip patch antennas in a free space [4,5] shows that the coupling between the patch antenna elements are identified as the contributions of the space and the leaky waves in addition to the dominant surface waves. Although the structure may be similar to the separated aperture sensor, the mutual coupling between the patches is very high and does not meet the large decoupling requirement for CW ground-penetration radar.…”

Green's functions in lossy layered media: integration along the imaginary axis and asymptotic behavior

“…More recently, these results have been used in the study of the coupling between two dipole antennas in [12]. In that work the analytical formulation of the Green's functions in surface and space waves allowed to get insight into the coupling mechanisms occurring between two printed dipoles, when the basic substrate parameters (thickness and dielectric constant) are varied.…”

“…In this paper, a thorough discussion on this asymptotic behavior is included together with the numerical results obtained for the Green's functions using the developed approach. A very interesting and somewhat complementary discussion on the asymptotic behavior of Green's functions can be found in [12], but derived in the specific context of the mutual coupling between two printed dipole antennas.…”

“…However, many current practical problems involve distances of several tens or even hundreds of wavelengths. This is the case when computing mutual coupling inside large arrays [11], [12], or when modeling cavity backed antennas by using space images respect to the cavity's lateral walls [13].…”