Ultra-Wideband Vertically Polarized Circular Array for Passive Sensing Applications

We present an ultra-wideband (UWB) vertically polarized long-slot circular phased array with a compact design for passive sensing applications. Unlike conventional tightly coupled cylindrical systems that require multiple circular arrays, our quasi-magnetic current sheet array uses a single circular array while achieving similar radiated field properties. A 16-element prototype demonstrates azimuthally invariant radiation capabilities. Measurements indicate that the array offers wide impedance bandwidth, high cross-polarization discrimination (XPD), and significant compactness. In its omnidirectional mode, the array achieves a 107.07^% bandwidth (VSWR < 2.0) with XPD better than 19.5 dB. In its directional mode, it operates over 100% bandwidth with XPD better than 20.9 dB. The prototype also exhibits excellent azimuthal out-of-roundness (better than 1.3 dB in its omnidirectional mode) and scan-invariant radiation with a maximum deviation of only 0.8 dB in its directional mode.