A modular Ka-band front-end receiver for passive imaging system

The two-dimensional synthetic aperture interferometric radiometer (SAIR) technique is being extensively employed in passive imaging systems. Compared to the other techniques, SAIR offers distinct advantages such as larger field of view (FOV) and high imaging rate. In this work, a modular front-end receiver is proposed for a SAIR based passive imager. In the design of millimeter wave heterodyne front-end receivers, one of the key components is the image rejection filter. The fabrication of image rejection filter on laminated substrates with conventional photolithography process lacks in reproducibility of such filters in terms of electrical performance. The proposed modular design mitigates the manufacturing tolerance issue of image rejection filters as well as gives a flexibility to adopt desired correlation bandwidth, receiver gain, noise figure and image rejection suppression. The proposed modular receiver comprises of three modules namely, a) antipodal finline low noise amplifier, b) waveguide band-pass filter and c) Mutichip module (MCM). The complete MCM is realized on a single substrate (E_r: 6.2, 254 μm thickness) and a two-layer planar technology is adopted for compact realization. The measured receiver gain, noise figure and image rejection is 42 dB, 4.1 dB and 60 dB respectively with excellent spurious free response.