Antenna for a radar apparatus
According to an example embodiment, an antenna assembly for a radar apparatus is provided, the antenna assembly comprising: a feed antenna arranged to radiate outbound radio waves that represent a transmitted RF signal supplied thereto and capture a received RF signal that represents inbound radio waves received thereat; and a focusing element arranged to collimate the outbound radio waves into a transmitter beam for transmission towards a monitoring direction and focus inbound radio waves of a receiver beam received at the focusing element from the monitoring direction for reception at the feed antenna, wherein the arrangement of the feed antenna and the focusing element is configured to transmit the transmitter beam as a sequence of substantially concave radio waves and receive the receiver beam as a sequence of substantially convex radio waves.
1 . A radar apparatus arranged for operation in meteorological and/or atmospheric studies to simultaneously detect and distinguish a plurality of targets at different distances from the radar apparatus, the apparatus comprising:
an antenna assembly comprising:
a feed antenna arranged to radiate outbound radio waves that represent a transmitted RF signal supplied thereto and capture a received RF signal that represents inbound radio waves received thereat; and
a single focusing element positioned with respect to the feed antenna such that the feed antenna is disposed further away from an antenna aperture of the antenna assembly than a phase center of the focusing element and such that the feed antenna is positioned on a plane that is offset from the phase center by a predefined distance along a center axis of the focusing element, thereby arranged to collimate the outbound radio waves originating from the feed antenna into respective concave radio waves of a transmitter beam for transmission towards a monitoring direction and focus convex inbound radio waves of a receiver beam received at the focusing element from the monitoring direction for reception at the feed antenna;
a transmitter arranged to supply the transmitted RF signal to the feed antenna and a receiver arranged to receive the received RF signal captured at the feed antenna; and
a processing unit arranged to determine, based on the received RF signal in consideration of the transmitted RF signal, respective characteristics of the plurality of targets at different distances from the antenna assembly in the monitoring direction, wherein said characteristics include at least one of the following:
respective locations of the plurality of targets,
respective velocities of the plurality of targets,
respective sizes of the plurality of targets,
respective shapes of the plurality of targets.
2 . The radar apparatus according to claim 1 , wherein the arrangement of the feed antenna and the focusing element is configured for measurements at distances closer than the Fraunhofer limit defined as
R F =2 d 2 /λ,
where d denotes a diameter of the antenna aperture of the antenna assembly and where λ denotes carrier wavelength applied for the transmitted RF signal.
3 . The radar apparatus according to claim 1 , wherein the focusing element comprises a substantially axially symmetric element.
4 . The radar apparatus according to claim 1 , wherein the predefined distance is defined as a predefined non-zero portion of the diameter of the cross-section of the focusing element.
5 . The radar apparatus according to claim 1 , wherein the focusing element comprises one of the following:
a lens element made of dielectric material arranged for refracting the outbound and inbound radio waves,
a reflector element arranged for reflecting the outbound and inbound radio waves.
6 . The radar apparatus according to claim 1 , wherein the focusing element comprises a lens element made of dielectric material arranged for refracting the outbound and inbound radio waves, where the lens element has a substantially circular cross-section and a convex front end that has a substantially ellipsoidal shape, where the front end or a portion thereof serves as the antenna aperture of the antenna assembly.
7 . The radar apparatus according to claim 6 , wherein the feed antenna comprises a single antenna element arranged for transmission and reception and disposed on said plane at the center axis of the lens element.
8 . The radar apparatus according to claim 6 , wherein the feed antenna comprises a first antenna element arranged for transmission and a second antenna element arranged for reception, disposed on said plane such that at least one of the first and second antenna elements is offset from the center axis of the lens element.
9 . The radar apparatus according to claim 1 , wherein the transmitter and the receiver are arranged to apply one of the following:
a frequency modulated continuous wave (FMCW) transmission and reception, or
a pulsed transmission and reception.
10 . The radar apparatus according to claim 9 , wherein the transmitter and the receiver are provided as a Doppler transceiver arranged to apply the FMCW transmission and reception.