An Integrated Microwave and Millimeter-Wave Circularly Polarized Antenna with ISM Band Gain Suppression Performance

In this letter, an integrated microwave and millimeter-wave (mm-Wave) dual-band circularly polarized (CP) antenna using the structural reuse method is proposed. The mm-Wave CP antenna is a 2×2 array employing the sequential rotated array technique, in which the CP radiating element is constructed using two centrally symmetrical L-shaped patches that are excited via a substrate integrated coaxial line (SICL) feeding network. In terms of the microwave CP antenna, a slot-coupled square patch fed through a microstrip directional coupler incorporating stubs is developed. One microstrip stub is added to introduce a new coupling path with an opposite current, thus, forming an additional null in the upper sideband. The measured results demonstrate that the proposed CP antenna exhibits impressive impedance bandwidths of 27.91% (2.24∼2.91 GHz) in the microwave band and 23.53% (24.45∼31.04 GHz) in the mm-Wave band, respectively. The remarkable isolation between the two operating bands (over 45 dB) ensures independent operation. Moreover, the antenna demonstrates a notable out-of-band suppression level of 33 dB in the industrial scientific medical (ISM) band, indicating favorable gain filtering characteristics.