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A simple printed monopole antenna using parasitic loops and defective ground plane is presented for broadband circular polarized (CP) radiation. For this purpose, two square open loops, which install air gaps at the corner and close to the monopole, are printed on both sides for achieving broadband CP radiation with three minimum axial ratio (AR) points. By using a defective ground plane with a vertical slot and a horizontal slot, additional AR points can be excited to further broaden the AR bandwidth. This design was fabricated, and the measured results show that the antenna with a simple structure achieves both wide impedance bandwidth of 87.2% (2.62‐6.67 GHz) and AR bandwidth of 83.9% (2.6‐6.36 GHz).

A simple broadband circularly polarised (CP) crossed‐dipole antenna is proposed. The antenna is composed of two crossed‐strip dipoles with two stepped sections, which are connected by vacant‐quarter rings to realise CP radiation, and a parasitic cross‐slotted square patch (CSSP) consisting of a modified square‐ring patch and a cross‐slot, which surrounds the crossed dipoles. By controlling the width ratio of the two strip sections, the stepped dipole can provide proper amplitude between two orthogonal modes to achieve wide axial ratio (AR) bandwidth. The CSSP can generate two minimum AR points simultaneously: one point is from the ring‐patch mode, while the other is generated based on the mode from the combination of the crossed dipole and the cross‐slot, which can be equivalent to a magneto‐electric dipole. An antenna prototype is fabricated and measured for design verification. The experimental results show that the proposed antenna with its simple structure has a wide −10 dB impedance bandwidth of more than 80% (3.38–7.97 GHz) and a 3 dB AR bandwidth of 59.1% (4.17–7.67 GHz). The proposed antenna also demonstrates excellent features including high gain, good stability, and symmetrical radiation pattern.

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A low-profile broadband circularly polarized (CP) crossed-dipole antenna is proposed. In this antenna, the dipole uses a fractal-based structure with multiple similar patches for obtaining broadband CP radiation and impedance matching. The incorporation of the crossed-dipole antenna with four triangular parasitic patches improves both the impedance and axial ratio (AR) bandwidths. Four parasitic inverted-L metal plates are loaded on the ground plane to significantly enhance the AR bandwidth and reduce the antenna profile. The measured results are in agreement with the simulations, which demonstrates that the proposed antenna has a low profile of 0.18 λ0, a -10 dB impedance bandwidth of 91% (2.78~7.42 GHz), a 3 dB AR bandwidth of 81.5% (2.99~7.1 GHz), and a good right hand circular polarization (RHCP) radiation pattern with an average gain of 7.9 dBi over the whole operating band.

A low-profile broadband circularly polarized (CP) crossed-dipole antenna is proposed. In this antenna, the dipole uses a fractal-based structure with multiple similar patches for obtaining broadband CP radiation and impedance matching. The incorporation of the crossed-dipole antenna with four triangular parasitic patches improves both the impedance and axial ratio (AR) bandwidths. Four parasitic coupled inverted-L metal plates are loaded on the ground plane to significantly enhance the AR bandwidth and reduce the antenna profile. The measured results are in agreement with the simulations, which demonstrates that the proposed antenna has a low profile of 0.18 λ0, a − 10 dB impedance bandwidth of 91% (2.78–7.42 GHz), a 3 dB AR bandwidth of 81.5% (2.99–7.1 GHz), and a good right hand circular polarization (RHCP) radiation pattern with an average gain of 7.9 dBi over the whole operating band.

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