Abstract
A new approach to controlling cross-polarization (XP), for either suppressing XP or exciting circular polarization (CP), in single-fed microstrip antennas using novel grid defected ground structures (GDGSs) is proposed. The key idea of GDGS is to construct defected ground structures (DGSs) from a grid of etched slots on a ground plane. The properties of each slot can be directly set by using either an open or short with fixed hardwires. The overall fixed hardwire configuration of the GDGS can be found straightforwardly by optimization of the XP or CP characteristics of the microstrip antenna. The importance of the approach is demonstrated by the results achieved. Results from two experimental prototypes are provided that demonstrate XP can be suppressed by 15 dB and CP can be excited with 78 MHz (2.2%) 3-dB axial ratio (AR) bandwidth and 6.6 dBic gain respectively on single-fed microstrip patch antennas.
Highlights
M ICROSTRIP patch antennas resonating with TMm,n mode are primarily linearly polarized
XP becomes significant for probe-fed microstrip antennas when the thickness of the substrate is large [3], [4]
Inspired by the results of grid defected ground structures (GDGSs) for suppressing the XP level in the last sub-section, we study it for increasing XP levels and meeting the circular polarization (CP) phase requirement for CP excitation
Summary
M ICROSTRIP patch antennas resonating with TMm,n mode are primarily linearly polarized. Some orthogonal modes exist and create cross-polarization (XP) [1], [2]. XP becomes significant for probe-fed microstrip antennas when the thickness of the substrate is large [3], [4]. Controlling XP is important, when frequency increases and substrate thickness remains fixed. Controlling XP can be leveraged to provide microstrip patch antennas with circular polarization (CP) and these have important applications [5], [6]. For a rectangular patch antenna, the dominant mode is TM0,1 and the main contribution of XP comes from TM2,0 [3]. The radiating orthogonal TM2,0 mode mainly causes XP in the H-plane and the overall electric fields are not symmetric [7].
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