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Omni-directional Microstrip Antenna for GBAS

The ground-based augmentation system (GBAS) is a system for receiving supplementary information directly from a ground-based transmitter using the global navigation satellite system (GNSS). The GBAS is also used for precise approach and landing of aircraft. The antenna used for transmission and reception exhibits the quadrangular array structure of a dipole antenna having linear polarization with VHF data broadcast (VDB). However, in the case of a VDB antenna, signal cancellation and interference among individual elements may occur.In this paper, we describe an omni-directional microstrip antenna that can replace the VDB antenna used in GBAS. The proposed design reduces the ground plane in a λ/4 folded microstrip antenna in order to have omni-directional characteristics and to radiate without affecting the ground plane itself. To miniaturize the physical size of the antenna, a metal plate is added between the openings using a perturbing effect.The designed antenna is verified through simulation. The size of the radiating element is 318 mm (0.12λ) × 100 mm (0.038λ) × 221 mm (0.083λ), whereas the size of the radiating element of a λ/4 folded microstrip antenna is 568 mm (0.214λ) × 100 mm (0.038λ) × 608 mm (0.23λ). Thus, the size of the radiating element is reduced by 79.7%. As a result of the electrical characteristics of the designed antenna, S11 is −37.1 dB, the −10-dB bandwidth is 0.56 MHz, and its gain is 1.09 dBi at a center frequency of 113 MHz. The radiation pattern shows the desired omni-directional characteristic. It is thus confirmed that the proposed antenna can replace the existing VDB antenna used in GBAS.