  We propose a new detection technique based on radio-frequency (RF) bias and
readout of an antenna-coupled superconducting nanobolometer. This approach is
suitable for Frequency-Division-Multiplexing (FDM) readout of large arrays
using broadband low-noise RF amplifier. We call this new detector RFTES. This
feasibility study was made on demonstrator devices which are made in all-Nb
technology and operate at 4.2 K. The studied RFTES devices consist of an
antenna-coupled superconducting nanobolometer made of ultrathin niobium films
with transition temperature Tc = 5.2 K. The 0.65-THz antenna and nanobolometer
are embedded as a load into a GHz-range coplanar niobium resonator (Tc = 8.9 K,
Q = 4000). To heat the superconducting Nb nanobolometer close to the Tc, the RF
power at resonator frequency f = 5.8 GHz is applied via a transmission line
which is weakly coupled (-11 dB) to the loaded resonator. The THz-antenna of
RFTES was placed in the focus of a sapphire immersion lens inside a
He4-cryostat equipped with an optical window and a semiconductor RF amplifier.
We have demonstrated optical response of the RFTES to THz radiation. The
demonstrator receiver system employing the RFTES device showed an optical
Noise-Equivalent Power (NEP) 1e-14 W/sqrt(Hz) at 4.2 K.
