An L- and C-Band Radiometer Utilizing Distributed Active Hot and Cold Loads With 156% Fractional Bandwidth

This article presents an
$L$
- and
$C$
-band radiometer with integrated wideband active hot and cold loads (AHCLs). By seamlessly integrating the distributed low noise amplifying unit and the wideband power-combining unit, the operational bandwidth of the conventional AHCL is significantly enhanced. The proposed distributed AHCL based on the reused noise-generation structure can realize a balanced calibration of the Dicke radiometer in 156% fractional bandwidth and, therefore, results in a significant reduction of noise equivalent temperature difference (NETD). The dual-band radiometer consists of a distributed AHCL, an SPDT switch, an LNA stage, a reflectionless bandpass filter, a diplexer,
$L$
- and
$C$
-band detectors, and backend analog circuits. Utilizing a distributed AHCL with 156% fractional bandwidth, the achieved NETDs in
$L$
- and
$C$
-bands are 1.39 K and 0.36 K, respectively. The implemented radiometer demonstrates an ability to make a balanced calibration automatically in an input range from around 225 K to 650 K. To the best of our knowledge, the proposed dual-band radiometer with a distributed AHCL demonstrates the ability to enhance the Dicke radiometer’s sensitivity effectively in the largest fractional bandwidth.