Enhanced broadband performance of thick CP patch antennas: A novel annular gap capacitor design

Traditional probe-fed CP patch antennas are attractive design candidates due to their simplicity and intuitive design strategy, but unfortunately they suffer from narrow axial ratio (AR) and S₁₁ bandwidths (<;2%). In this paper, we enhance the AR-S₁₁ bandwidth through the utilization of thick substrates in combination with a novel annular gap capacitor to compensate for the feed reactance. Without the annular gap, thick substrates can increase the AR bandwidth, but the impedance matching within this band is severely degraded due to the inductive feed reactance. This paper demonstrates the annular gap design on the popular truncated corner patch antenna, although the annular gap concept can be easily applied to other traditional CP patch designs. A design prototype is demonstrated, with a measured AR-S₁₁ bandwidth of 5% for a substrate height of 0.08λ₀. To the authors´ best knowledge, this is the first time that an annular gap in conjunction with thick substrates has been used to enhance the AR-S₁₁ bandwidth of CP patches.