Double circularly polarized on-chip antenna for a 120–130 GHz amplitude monopulse radar

In this paper two closely spaced circularly polarized on-chip antennas each fed by a differential 90° branchline coupler are investigated. The antennas are radiating by the principle of an integrated lens antenna and can be used as antennas of an amplitude monopulse radar with two separated receivers. The common broadside radiation of both antennas feeding the transmit path is superposed by the beam tilted receivers radiation patterns thus enabling an amplitude comparison for the receive channels. For measurement purposes of the antenna itself without connected radar the transmit path and both receive paths are connected to 50 Ω CPW pads. Adequate power-splitters and branchline couplers are investigated and presented in this work. Finally calibrated gain measurements are used for verifying the antennas operation.