100 GHz-1.0 THz) technology is expected to provide unprecedented data rates in future generations of wireless system such as the 6 th generation (6G) mobile communication system. Increasing the carrier frequencies from millimeter wave to THz is a potential solution to guarantee the transmission rate and channel capacity. Due to the large transmission loss of Low-THz wave in free space, it is particularly urgent to design high-gain antennas to compensate the additional path loss, and to overcome the power limitation of Low-THz source. Recently, with the continuous updating and progress of additive manufacturing (AM) and 3D printing (3DP) technology, antennas with complicated structures can now be easily manufactured with high precision and low cost. In the first part, this paper demonstrates different approaches of recent development on wideband and high gain sub-millimeter-wave and Low-THz antennas as well as their fabrication technologies. In addition, the performances of the state-of-the-art wideband and high-gain antennas are presented. A comparison among these reported antennas is summarized and discussed. In the second part, one case study of a broadband high-gain antenna at 300 GHz is introduced, which is an all-metal model based on the Fabry-Perot cavity (FPC) theory. The proposed FPC antenna is very suitable for manufacturing using AM technology, which provides a low-cost, reliable solution for emerging THz applications.INDEX TERMS Antennas, low-terahertz, additive manufacturing (AM), high gain, Fabry-Perot cavity (FPC), low-cost, three-dimensional printing (3DP). I. INTRODUCTIONA.

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This paper presents a 400 GHz CMOS TX and RX chip with two different chip-to-waveguide transitions. A first design is based on a coupled microstrip to waveguide coupler and is integrated together with a 400 GHz oscillator in 28 nm bulk CMOS. When this transmitter is combined with a micromachined horn antenna, it is capable of providing an EIRP of 1.26 dBm. In a second design, a folded dipole based coupler is utilized to make the transition between a waveguide and a 400 GHz mixer first receiver. This receiver fully integrates an on-chip LO, mixer and baseband circuits and achieves an effective conversion gain of 39 dB and a noise figure of 45 dB. Both chips are combined into a lensless active imaging setup with a spacial resolution of 2 mm.

Research in millimeter dielectric waveguides is experiencing a growing interest for data communication and sensor systems. This paper fully analyses the properties of the HE11 mode in hollow fibers. It will provide a theoretical background that can then be used to choose an appropriate channel for a dielectric waveguide system. The focus of this paper will primarily lay in linking properties like propagation constant, dispersion and attenuation with the geometry and frequency. Secondly due to the small cladding's allowed in practical millimeter wave fibers, evaluating power leaking out of the fiber by means of the evanescent field is addressed. Finally all theory is extensively verified with measurements and both agree very well.

This paper presents the design, implementation, and measurement of a 0.53-THz radiating source in a 28-nm bulk CMOS technology. An oscillator-tripler topology is employed to effectively generate and extract the third harmonic at 0.53 THz within a fully symmetrical layout. A dielectric lens is designed, fabricated, and mounted on top of the chip to enhance the antenna gain. During the design of the radiating source, a lumped model representing the transistor interconnect parasitics including the parasitic capacitances, resistances, and inductances is developed using a simulation-based modeling method. The accuracy of the developed model is validated by comparing the simulation and measurement of the 0.53-THz radiating source. The measured equivalent isotropically radiated power of the radiating source is-7.4 dBm at 527.6 GHz under 0.9-V supply voltage. According to the measured antenna directivity of 14.6 dBi, the radiated power and dc-to-THz efficiency of the radiating source are calculated as −22 dBm and 0.332%, respectively. By adjusting the supply voltage, the output frequency can be tuned from 524.7 to 555.8 GHz, indicating a 5.9% frequency tuning range.