Progress In Electromagnetics Research C, Vol. 110, 197–212, 2021 Dynamically Switched Dual-Band Dual-Polarized Dual-Sense Low-Profile Compact Slot Circularly Polarized Antenna Assisted with High Gain Reflector for Sub-6 GHz and X-Band Applications Asutosh Mohanty 1, * and Bikash R. Behera 2 Abstract—A low-profile compact uni-planar slot antenna design of size 26 mm × 26 mm is proposed, assisted with a metallic bottom reflector at a height of λ 6 (λ is the lowest CP frequency). The dual- band dual-polarization is observed at 6.2 GHz and 9.3 GHz, and polarization sense (LHCP and RHCP) is dynamically switched by introducing a pair of RF p-i-n diodes mounted at the confluence of right-slot (RS) and left-slot (LS). A metallic reflector of size 60 mm × 60 mm helps to improve overall impedance matching, enhance antenna gain and assertsq uni-directional dual-polarized radiation with good back- lobe suppression. The proposed antenna operates at dual bands (5.46–6.76 GHz) with 21.27% IBW and (8.18–10.48 GHz) with 24.65% IBW for S 11 < -10 dB. The antenna gain reaches (7.82–8.75 dBi) for D1-OFF, D2-ON state with (9.2%, 15.63%) axial bandwidths and (6.42–7.0 dBi) for D1-ON, D2-OFF state with (7.53%, 16.04%) axial bandwidths with radiation efficiency ranging (75%–87%). A prototype antenna is fabricated and measured, which shows good agreements with simulated performances and can be used for sub-6 GHz in 5G applications and X-band radar systems. 1. INTRODUCTION In present scenario, circularly polarized (CP) antennas are often considered as an important part for highly demanded sub-6 GHz band for 5G applications and X-band radar systems [1, 2]. To satisfy such a requirement, dynamically switched CP antennas are adopted for improving polarization attributes, bringing system and wireless diversity to a platform, where system capacity can be improved with compensation to fast fading effects in radio channels. To provide improved wireless link at relatively low cost, dual-band dual-polarized dual-sense antennas have superior performances in terms of polarization purity in which orthogonal E-field components boost the overall RF performance by compensating polarization mismatch losses. Moreover, the polarization characteristics can be dynamically switched, depending on users’ RF requirements [3, 4]. In [5], a dual-sense CP patch antenna is designed using a dual-coupled line, with gains 5.3/5.7 dBi. Utilizing a capacitive-probe method, a dual-band dual-mode dual-polarized patch antenna is achieved in [6], with two mode antenna gains 1.1/8.4 dBi. For BeiDou navigation satellite applications, [7] designs a dual-band dual-polarized annular-ring CP antenna with gain variation of 4.3/6.4 dBi at dual bands. A bow-tie shaped dual-band dual-polarized antenna with integrated electric dipole and metal cavity as a magnetic dipole connected to an array resonator is designed in [8], with dual band gains of 4.2/6.3 dBi. A cross dipole structure CP antenna with dual-band dual-sense characteristics is achieved in [9] for WLAN/Wi-MAX applications with dual band gains of 7.7/7.4 dBi. In [10], a dual-band dual-polarized antenna with less radiating layers, only one layer radiating patch, is achieved with a dual band gains Received 5 January 2021, Accepted 23 February 2021, Scheduled 3 March 2021 * Corresponding author: Asutosh Mohanty (asutoshmohanty.kiit0409@gmail.com). 1 School of Electronics Engineering, KIIT Deemed to be University Bhubaneswar, Odisha 751024, India. 2 Advanced RF and Microwave Lab, Department of Electronics and Telecommunication Engineering, IIIT Bhubaneswar, Odisha 751003, India.