Circular-Polarization Mushroom EBG Antenna Module for 122 GHz Monostatic Radar Sensor in LTCC Technology

This paper presents a circular-polarization Mushroom electromagnetic bandgap (EBG) antenna module for realizing a 122 GHz monostatic radar sensor. The module consists of the following components: an aperture-coupled antenna, using a 4 × 4 matrix of Mushroom EBG unit cells as radiating elements, a novel stripline patch-based quadrature hybrid and two stripline-to-grounded coplanar waveguide (GCPW) signal transitions. The quadrature hybrid provides two orthogonal stripline feeds to the Mushroom EBG antenna, thus generating circular-polarization radiation characteristics. The stripline-to- GCPW signal transitions are required for probe-based measurement of the antenna module as well as for integrating the antenna module with a radar transceiver chip. The module is designed and fabricated in low temperature co-fired ceramic technology and its overall dimensions are 4.5 mm × 6.5 mm × 0.32 mm. Simulation results of the novel stripline patch-based quadrature hybrid demonstrate an amplitude imbalance of less than 1.5 dB and a phase imabalance of less than ±5° over a broadband operating range of 110 to 155 GHz. Simulation and probe-based measurement results of the antenna module demonstrate that the reflection coefficients, isolation between the transmitter and receiver paths, the radiation patterns and the axial ratio are suitable for realizing a 122 GHz monostatic radar sensor.