An Active Ka-Band Shared-Aperture Antenna With 50 dB Isolation for Satellite Communication

Anactive hybrid shared-aperture concept (employing both active and passive circuits) is presented. This active shared aperture realizes the required isolation level of 48 dB between transmit (TX) (30 GHz) and receive (RX) (20 GHz) channels of a ground terminal for two-way satellite communication. It can be applied in very small aperture terminals. The dual-frequency shared aperture can be used as a building block for a linearly or circularly polarized phased-array feed in a focal-plane array system. It includes a 20-GHz low-noise amplifier with on-chip notch filtering realized in a 0.25-mu m SiGe:C BiCMOS technology. The on-chip filter achieves 30 dB of attenuation at 30 GHz with only 0.4 dB noise figure degradation. The isolation is further enhanced by a novel dual-frequency shared-aperture concept based on defected ground structures in the printed circuit board. Experimental results from the prototype show an overall isolation between TX and RX channel of more than 50 dB at 30 GHz.