An antenna assembly for a frequency modulated continuous wave, FMCW, radar apparatus for meteorological and/or atmospheric studies, the antenna assembly comprising: a first feed antenna arranged to transmit outbound radio waves of a transmitter beam based on a transmitted RF signal supplied thereto and a second feed antenna arranged to capture a received RF signal based on inbound radio waves of a receiver beam received thereat; and an axially symmetric lens element arranged to collimate the transmitter beam obtained via a back end of the lens element for transmission from a front end of the lens element to a monitoring direction and to focus the receiver beam received at the front end of the lens element from the monitoring direction for reception via the back end of the lens element at the second feed antenna, where a center axis of the lens element also serves as its symmetry axis, wherein the first and second feed antennas (111a, 111b) are disposed on a conductive ground plane that is perpendicular to the center axis of the lens element such that the conductive ground plane and each of the first and second feed antennas (111a, 111b) are offset from the back end of the lens element by a predefined distance (k) in direction of the center axis of the lens element and wherein a volume between the back end of the lens element and the conductive ground plane comprises material that has a refractive index that is smaller than that of the lens element for converging the outbound and inbound RF beams between the back end of the lens element and the first and second feed antennas (111a, 111b), wherein the predefined distance (k) is defined as k = 0.5 λ ε rc, where λ denotes a carrier wavelength applied for the transmitted and received RF signals and ε rc denotes relative dielectric constant of the material applied in the volume between the conductive ground plane and the back end of the lens element, wherein the first feed antenna is offset from the center axis of the lens element to a first direction by a first distance (r 1) and the second feed antenna is offset from the center axis to a second direction by the second distance (r 2), where the second direction is different from the first direction, and wherein the first feed antenna is arranged to transmit the outbound radio waves with an orientation of polarization where the direction of E component of the electromagnetic field vectors of the transmitter beam are substantially aligned with a conceptual line connecting respective positions of the first feed antenna and the second feed antenna. a first feed antenna arranged to transmit outbound radio waves of a transmitter beam based on a transmitted RF signal supplied thereto and a second feed antenna arranged to capture a received RF signal based on inbound radio waves of a receiver beam received thereat; and an axially symmetric lens element arranged to collimate the transmitter beam obtained via a back end of the lens element for transmission from a front end of the lens element to a monitoring direction and to focus the receiver beam received at the front end of the lens element from the monitoring direction for reception via the back end of the lens element at the second feed antenna, where a center axis of the lens element also serves as its symmetry axis, wherein the first and second feed antennas (111a, 111b) are disposed on a conductive ground plane that is perpendicular to the center axis of the lens element such that the conductive ground plane and each of the first and second feed antennas (111a, 111b) are offset from the back end of the lens element by a predefined distance (k) in direction of the center axis of the lens element and wherein a volume between the back end of the lens element and the conductive ground plane comprises material that has a refractive index that is smaller than that of the lens element for converging the outbound and inbound RF beams between the back end of the lens element and the first and second feed antennas (111a, 111b), wherein the predefined distance (k) is defined as k = 0.5 λ ε rc, where λ denotes a carrier wavelength applied for the transmitted and received RF signals and ε rc denotes relative dielectric constant of the material applied in the volume between the conductive ground plane and the back end of the lens element, wherein the first feed antenna is offset from the center axis of the lens element to a first direction by a first distance (r 1) and the second feed antenna is offset from the center axis to a second direction by the second distance (r 2), where the second direction is different from the first direction, and wherein the first feed antenna is arranged to transmit the outbound radio waves with an orientation of polarization where the direction of E component of the electromagnetic field vectors of the transmitter beam are substantially aligned with a conceptual line connecting respective positions of the first feed antenna and the second feed antenna.