Phased array feeds (PAF) are playing an increasingly important role in low-frequency radio astronomy, but less explored at THz wavelengths. Here we present the design of a 0.35-THz planar array antenna, which consists of an array of twinslot antennas, a coplanar waveguide (CPW) feed network and airbridges. The planar array antenna is based on a silicon substrate without any lens as well as anti-reflection coating. The airbridges are used to improve the performance of the CPW T-junctions and the transmission efficiency of the feed network. Simulation results show that the substrate thickness can change the power distribution on both sides of the substrate. With an appropriate substrate thickness and some airbridges, the total gain of a 16-element array can reach 15.3 dB and the main-beam efficiency is about 54%. This kind of planar array antenna can be easily integrated with a terahertz detector such as hot electron bolometer (HEB) and kinetic inductance detector (KID), based on photolithographic fabrication.
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