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ABSTRACT In this paper, the bandwidth limitations of frequency multipliers are analyzed theoretically in terms of maximum power transmission. The analysis shows that due to conjugate with the impedance of the diode itself, the optimum embedded impedance of the diode possesses a counterclockwise impedance trajectory versus frequency on the Smith chart, whereas the matching circuit exhibits a clockwise impedance trajectory versus frequency on the Smith chart. Under this constraint, an impedance compression matching technique (ICMT) is proposed to realize broadband design for terahertz frequency multipliers. Based on the proposed design method, a 170‐ to 260‐GHz full‐band frequency doubler was designed, fabricated, and measured. The measured results show that the doubler achieves an output power of 4–7.5 mW in the entire frequency band under 140‐mW input power, corresponding to a conversion loss of 12.5–15.4 dB. [ABSTRACT FROM AUTHOR]

In this paper, a novel full waveguide matching method (FWMM) is proposed to improve design efficiency and verify the feasibility of full waveguide matching for terahertz frequency doubler. In the proposed method, the frequency doubler is divided into three parts: packaging diode, input matching waveguide, and output matching waveguide, each of which realizes different functions. The most important diode embedding impedance matching part is transferred from the microstrip to the input and output matching waveguide. The impedance matching of the waveguide is realized by the structure called quasi-coupled resonator. These quasi-coupled resonators are implemented by inserting irises at the broadside of the waveguide and function as a capacitive load for the circuit. Using this method, a compact and efficient frequency doubler was designed and characterized. Measured results show that the peak efficiency of the doubler is 25.8% at 215 GHz with 50 mW input power. The good output performance of the 220 GHz doubler verifies the effectiveness of the proposed full waveguide matching method. [ABSTRACT FROM AUTHOR]

This paper summarizes the development of novel Schottky-diode-based terahertz frequency multipliers. The basic structure and manufacturing process of planar Schottky barrier diodes (SBDs) are reviewed, along with other diode structures that have been proposed in the literature. A numerical modeling method for the novel diodes in the context of terahertz frequency multipliers is presented, which includes 3D electromagnetic (EM) modeling, electro-thermal modeling and modeling of physical non-ideal effects. Furthermore, a general design methodology for developing terahertz frequency multipliers is introduced, involving a sub-division design method (SDM), a global design method (GDM) and a half-sub-division and half-global design method (HS-HGDM). These methods are summarized and compared for 110 GHz and 220 GHz frequency multipliers in the context of communication and imaging applications. Laboratory measurements of these multipliers show good agreement with numerical simulations. Finally, several classic terahertz remote sensing systems are reviewed, and a 220 GHz remote sensing system established using novel frequency multipliers for security inspection purposes is presented along with associated imaging results. [ABSTRACT FROM AUTHOR]

In this paper, a new terahertz solid-state frequency doubler design method named function-based harmonic impedance optimization method (FHIOM) is reported to improve the simulation iteration speed and accuracy of terahertz solid-state circuit design. Obtaining the matching impedance of the diode part in the optimal operating condition and realizing this impedance through the input-output matching structure are the two main steps in the design of the terahertz doubler. In this design method, harmonic impedance optimization and function-based impedance optimization are applied to quickly obtain the best input and output embedded impedance of the broadband frequency doubler device, which reduces the blindness of tentative optimization. This method innovatively estimates the impedance of the matching structure through the formula, which strengthens the connection between impedance optimization and matching structure realization. Based on the function-based harmonic impedance optimization method, a 220 GHz doubler is designed, processed, and measured. Measured results show that the doubler exhibits a bandwidth from 212 GHz to 230 GHz, with a conversion efficiency of above 15.0% a mean output power of 9.12 mW when supplied with up to 32 mW of input power. A 16 mW peak output power with a 16.4% efficiency was measured at 228 GHz when the input power was 97.55 mW. The frequency doubler design method presented in this work has the advantages of high efficiency and accuracy, which makes it very attractive for practical broadband terahertz applications. [ABSTRACT FROM AUTHOR]

In this paper, a 500 GHz frequency tripler with an idle harmonic control technique is proposed, in which the 3rd-harmonic wave at the input port and the fundamental-wave at the output port are recycled with simple control circuitry. Especially for the output fundamental-wave, it is controlled by a carefully designed function-combined probe. Besides, both of input and output probes adopted an inline waveguide-to-microstrip transition using a wedge-waveguide iris to realize an inline input-output configuration. The designed tripler was fabricated, and measured. The measured maximum efficiency is 3% under 20 mW input power with a peak output power of 0.55 mW at 500 GHz, and the available bandwidth convers a range of 460-540 GHz. With the proposed harmonic-wave control technique, the conversion efficiency of the tripler was improved. The good output performance of the 500 GHz tripler verifies the effectiveness of the proposed idle harmonic control technique and function-combined design concept. [ABSTRACT FROM AUTHOR]

This paper describes the design and demonstration of a 135–190 GHz self-biased broadband frequency doubler based on planar Schottky diodes. Unlike traditional bias schemes, the diodes are biased in resistive mode by a self-bias resistor; thus, no additional bias voltage is needed for the doubler. The Schottky diodes in this verification are micron-scaled devices with an anode area of 6.6 μm2 and an epitaxial layer thickness of 0.26 μm. For accurate design of the doubler, the 3D-EM model of the Schottky diode is built up to extract the parasitic parameters induced by the diode package when frequency rises up to the terahertz band. In order to implement broadband working, input waveguide steps, output suspended microstrip steps, and output probe with bias filter are all used as matching elements for impedance matching. Measured results show that the doubler exhibits a 3 dB bandwidth of 34% from 135 GHz to 190 GHz, with a conversion efficiency of above 4% when supplied with 100 mW of input power. A 17.8 mW peak output power with a 10.2% efficiency was measured at 166 GHz when the input power was 174 mW. The measured results agree well with the simulated results, which indicates that the self-bias scheme for Schottky diode-based frequency multipliers is feasible and effective. [ABSTRACT FROM AUTHOR]

A high-performance terahertz InP Schottky Barrier Diode (SBD) with a submicron T-shaped contact structure featuring a high theoretical cut-off frequency of 9.0 THz is reported in this paper. The Schottky contact with a minimum diameter of 0.2 μm was achieved by photoresist laminate and gradient exposure process, exhibiting a minimum zero-bias junction capacitance is 0.15 fF. The quality of Schottky contact was improved by surface treatment of particles and high-temperature passivation of the edge with a polymer film, with an ideal factor of between 1.2 and 1.4. The high-frequency performance of the diode is further improved due to the small parasitic capacitance contributed by the polymer film dielectric bridge. The terahertz monolithic integration circuit based on this T-shaped contact submicron Schottky has better performance in reducing the circuit dielectric loss, exhibiting a remarkable potential for high-frequency applications. [ABSTRACT FROM AUTHOR]