In this paper, a broadband and tunable terahertz absorber based on a graphene metasurface in a sandwiched structure is introduced. A single-layered graphene patterned with hollow-out squares is applied in this design, which is continuously connected to provide convenience for electrical tuning and fabrication. Plasmonic coupling and hybridization inside the graphene pattern can significantly enhance the absorption bandwidth. Moreover, polarization-insensitive and omnidirectional performances are also guaranteed by the symmetrical design. Full wave simulations demonstrate that the absorber exhibits over 90% absorbance within 1.14∼3.31 THz with a fractional bandwidth up to 97.5%. The device reveals tunable absorbance from 14% to almost 100% by manipulating the graphene chemical potential from 0 to 0.9 eV. When the incident angle sweeps up to 55°, the absorbance remains more than 90% from 1.77 to 3.42 THz for TE polarization, while over 90% absorbance maintains around 3.3 THz for TM polarization. These superior abilities guarantee the applicability of the presented absorber in THz cloaking, tunable sensor and photovoltaic devices.

The analysis and design methods of a broadband coplanar Wilkinson power divider are proposed in this paper. The novelty is that cascaded two sections of coupled asymmetrical coplanar strips (ACPSs) are utilized to obtain broadband performance over X‐band and two resistors are used for isolation. The design equations are derived using even‐ and odd‐mode analysis. The specific structure parameters for broadband performance over X‐band are obtained through electronic design simulation tool and quasi‐static conformal mapping technique. The power divider is fabricated on GaAs substrate and is compatible with GaAs MMIC process. The measured results of the power divider show close agreement with the simulation. The measured return loss S11 is better than −15 dB across the entire X‐band, 8–12 GHz. Good dividing and high isolation properties are also revealed through measurements. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:307–312, 2017

This letter presents the design, fabrication, and measurement of a broadband MEMS microwave phase detector for X-band, 8-12 GHz. In order to realize the broadband performance, a two-section power combiner is designed and utilized for the configuration of the phase detector. Stable sensitivities of phase detection are revealed by measurements within the bandwidth 8-12 GHz. The sensitivities are all better than 7.1, 22.1, 33.4, 42.0, and 51.2 mV/mW at 10, 50, 100, 150, and 200 mW input power, respectively. Moreover, the discrepancies are less than 1. 8, 5.1, 7.3, 9.3, and 10.9 mV/mW at the above powers for different frequencies. The measured output voltage versus the phase difference at 200 mW, 10 GHz is normalized and compared to the theoretical value. The relative error is less than 8.5%. The response times of this presented phase detector are also obtained by measurement. . However, they suffer from small dynamic range, large power consumption, and difficulties to fabricate as an IC, respectively. The MEMS technology provides a solution to these problems. A MEMS microwave phase detector fabricated by micromachining processes have been presented by our group [5]. It consists of a power combiner operator based on vector combination and a thermoelectric power sensor based on Seebeck effect. However, this phase detector was designed and optimized at the center frequency of 10 GHz and suffers from performance degradation at the other frequencies of X-band. Thus, it cannot satisfy the urge for broadband phase detection components in modern communication systems.For these reasons, this paper presents the design, fabrication, and measurement verification of a MEMS microwave phase detector with broadband detection range for the whole X-band, 8-12 GHz. The novelty of this phase detector is that, a twosection power combiner is designed and utilized in order to realize the broadband performance. The fabrication process is completely compatible with the GaAs MMIC technology. Measurements are performed for this phase detector over 8-12 GHz. The output responses of phase detection show cosine relationship versus the phase differences, which is in accordance with the theory. The phase detection sensitivities within the measured bandwidth are rather stable at low frequencies and show slight variation when the frequency increases. Moreover, this letter presents an experimental study of the response time at different input powers. DESIGN AND FABRICATIONA MEMS microwave phase detector is composed of a power combiner and a thermoelectric power sensor, among which the power combiner is the factor element in determining the phase detection bandwidth. Thus, it is essential to adopt a power combiner that can maintain good performance over X-band instead of the traditional power combiner which is matched and optimized at one signal center frequency [6]. According to the study in Ref. 7, the bandwidth of a power combiner can be broadened by cascading multi-section matching networks.Thus, the basic idea for the architecture of...

This paper presents a 0.1–40 GHz broadband MEMS capacitive power sensor based on GaAs technology. An impedance compensation method utilizing a T-matching network is proposed to expand bandwidth. A lumped parameter model is established, the reflection coefficient, the voltage on the membrane and the sensitivity of RF-power detection are derived based on the multi-reflection transmission line theory. Performances of different up-states before pull-in are analysed when the membrane is electrostatic actuated. The proposed capacitive power sensor has been fabricated using GaAs process and MEMS technology. A controllable lateral etching technique is used to improve the sensitivity of RF-power detection and a low-spring-constant membrane is obtained. Measurement results show that return and insertion losses (S11 and S21) are less than −20.31 and 0.29 dB up to 40 GHz, respectively. DC voltage measurement indicates a low pull-in voltage of 10 V. Sensitivities of different operating frequencies are measured to be 11.6 aF mW−1 at 5 GHz, 11.3 aF mW−1 at 15 GHz, 10.8 aF mW−1 at 25 GHz and 10.4 aF mW−1 at 35 GHz. Frequency dependence measurements show a decreasing trend of sensitivity with the increase of frequency.

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