Improvements in reverse breakdown characteristics of THz GaAs Schottky barrier varactor based on metal-brim structure

The excellent reverse breakdown characteristics of Schottky barrier varactor(SBV)are crucially required for the application of high power and high efficiency multipliers.The SBV with a novel Schottky structure named metal-brim is fabricated and systemically evaluated.Compared with normal structure,the reverse breakdown voltage of the new type SBV improves from-7.31 V to-8.75 V.The simulation of the Schottky metal-brim SBV is also proposed.Three factors,namely distribution of leakage current,the electric field,and the area of space charge region are mostly concerned to explain the physical mechanism.Schottky metal-brim structure is a promising approach to improve the reverse breakdown voltage and reduce leakage current by eliminating the accumulation of charge at Schottky electrode edge.

INDEPENDENTLY-TUNED CONCURRENT DUAL-BAND BRANCH-LINE COUPLER USING VARACTOR

This paper presents a concurrent dual-band branch-line coupler with an independently tunable center frequency. In the proposed architecture, the quarter-wavelength lines, which work at two separated bands concurrently and can be tuned in one of them, are key components. Based on the analysis of ABCD-matrix, a novel hybrid structure and a pair of varactors topology are utilized to achieve concurrent dual-band operation and independent tunability, respectively. Using this configuration, it is convenient to tune the center frequency of the upper band, while the responses of the lower band remain unaltered. To verify the proposed idea, a demonstration is implemented and the simulated results are presented.

A GaAs planar Schottky varactor diode for left-handed nonlinear transmission line applications

The left-handed nonlinear transmission line （LH-NLTL） based on monolithic microwave integrated circuit （MMIC） technology possesses significant advantages such as wide frequency band, high operating frequency, high conversion efficiency, and applications in millimeter and submillimeter wave frequency multiplier. The planar Schottky varactor diode （PSVD） is a major limitation to the performance of the LH-NLTL frequency multiplier as a nonlinear component. The design and the fabrication of the diode for such an application are presented. An accurate large-signal model of the diode is proposed. A 16 GHz-39,6 GHz LH NLTL frequency doubler using our large-signal model is reported for the first time. The measured maximum output powers of the 2nd harmonic are up to 8 dBm at 26.4 GHz, and above 0 dBm from 16 GHz to 39.6 GHz when the input power is 20 dBm. The application of the LH-NLTL frequency doubler furthermore validates the accuracy of the large-signal model of the PSVD.

Varactor-tunable frequency selective surface with an embedded bias network

A new technique for designing a varactor-tunable frequency selective surface （FSS） with an embedded bias network is proposed and experimentally verified. The proposed FSS is based on a square-ring slot FSS. The frequency tuning is achieved by inserting varactor diodes between the square mesh and each unattached square patch. The square mesh is divided into two parts for biasing the varactor diodes. Full-wave numerical simulations show that a wide tuning range can be achieved by changing the capacitances of these loaded varactors. Two homo-type samples using fixed lumped capacitors are fabricated and measured using a standard waveguide measurement setup. Excellent agreement between the measured and simulated results is demonstrated.

Design of a varactor-tunable metamaterial absorber

In this paper, we design a varactor-tunable metamaterial absorber （MA）. The tunable MA is based on a mushroom-type high impedance surface （HIS）, in which varactors are loaded between adjacent metal patches to adjust the capacitance and tune the resonance frequency, the primary ground plane is etched as the bias network to bias all of the varactors in parallel, and another ultra-thin grounded film is attached to the bottom. Its absorption characteristics are realized for electrically dielectric loss. The simulated values of a sample indicate that a tunable frequency range from 2.85 GHz to 2.22 GHz is achieved by adjusting the varactor capacitance from 0.1 pF to 2.0 pF, and better than 0.97 absorbance is realized; in addition, the tunable frequency range is expanded from 4.12 GHz to 1.70 GHz after optimization.

NOVEL ELECTRONIC TUNER USING VARACTORS FOR TUNABLE RF FRONT-ENDS

This paper presents a novel electronic tuner with high power handling capability utilizing varactors based on the asymmetric bilateral coupled microstrip transmission line. Through varying the bias voltage of the varactor at the Ultra High Frequency (UHF) band, the performance of the tuner is demonstrated according to simulated and measured results from several cases with the return loss (S11 ) below -20 dB and the insertion loss (S21 ) within ±0.5 dB. Compared with tuners using p and t network, electronic tuner of this paper shows superior frequency agility as well as wide impendence coverage. Advanced biasing structure has been developed to improve power handling for high power level applications. It is expected that the novel tuner would be part of intelligent Radio Frequency (RF) front-ends system and cognitive wireless system in the future.

Optimization of terahertz monolithic integrated frequency multiplier based on trap-assisted physics model of THz Schottky barrier varactor

The optimization of high power terahertz monolithic integrated circuit (TMIC) is systemically studied based on the physical model of the Schottky barrier varactor (SBV) with interface defects and tunneling effect. An ultra-thin dielectric layer is added to describe the extra tunneling effect and the damping of thermionic emission current induced by the interface defects. Power consumption of the dielectric layer results in the decrease of capacitance modulation ration (Cmax/Cmin), and thus leads to poor nonlinear C–V characteristics. The proposed Schottky metal-brim (SMB) terminal structure could improve the capacitance modulation ration by reducing the influence of the interface charge and eliminating the fringing capacitance effect. Finally, a 215 GHz tripler TMIC is fabricated based on the SMB terminal structure. The output power is above 5 mW at 210–218 GHz and the maximum could exceed 10 mW at 216 GHz, which could be widely used in terahertz imaging, radiometers, and so on. This paper also provides theoretical support for the SMB structure to optimize the TMIC performance.

基于阶跃阻抗谐振器的四阶频率可调滤波器设计

提出一种基于阶跃阻抗谐振器的紧凑型四阶四零点频率可调滤波器设计。滤波器使用变容二极管加载的阶跃阻抗谐振器(VL-SIR),有效拓宽了滤波器的调谐范围。在VL-SIR之间引入交叉耦合,从而在滤波器通带近端产生一对传输零点,显著提高了滤波器的选择性。同时,引入源和负载端的交叉耦合,在通带远端生成一对传输零点,以提高带外抑制。此外,采用基于VL-SIR的频变耦合结构来实现恒定绝对带宽。仿真结果与实测结果吻合良好。测量结果显示,可调滤波器频率调谐范围为0.78~1.15 GHz,3 dB绝对带宽约为55±3 MHz,滤波器的回波损耗大于10 dB,插入损耗约为2.8~3.3 dB。

基于变压器磁调谐的双模W波段VCO

提出了一种基于变压器的用于无变容管W波段压控振荡器(VCO)的磁调谐技术。通过控制变压器磁调谐线圈所连接MOS管的开关状态,引入了四个重叠的频率子带。所提出的可切换的六线圈变压器采用40 nm CMOS工艺的顶层厚金属设计,实现了较高的输出频率稳定性和谐振腔品质因数。所采用的技术在对相位噪声的不利影响最小的情况下扩展了调谐范围,实现了无变容管W波段VCO的宽调谐范围和低功耗。所设计的双模W波段VCO输出频率为84.2~107.5 GHz,频率调谐范围大于24%,在1 V电源电压下功耗仅6.1 mW,在10 MHz偏移处的相位噪声为-107.203~-97.875 dBc/Hz。

Planar Schottky varactor diode and corresponding large signal model for millimeterwave applications

A GaAs-based planar Schottky varactor diode （PSVD） is successfully developed to meet the demand of millimeter-wave harmonic generation. Based on the measured S-parameter, I-V and C-V characteristics, an accurate and reliable extraction method of the millimeter-wave large signal equivalent circuit model of the PSVD is proposed and used to extract the model parameters of two PSVDs with Schottky contact areas of 160 μm2 and 49 μm2, respectively. The simulated S-parameter, I-V and C-V performances of the proposed physics-based model are in good agreement with the measured one over the frequency range from 0.1 to 40 GHz for wide operation bias range from -10 to 0.6 V for these two PSVDs. The proposed equivalent large signal circuit model of this PSVD has been proven to be reliable and can potentially be used to design microwave circuits.

一种S频段反射型可调模拟移相器的设计

设计了一种应用于S频段卫星通信相控阵系统的反射型可调模拟移相器。该移相器利用三分支线定向耦合器扩展了带宽,改善了工作频段内驻波;采用传输线和变容二极管构成的L型反射负载扩大了相移量。测试结果表明,在上行频段1.98~2.01 GHz内,相移量达到191°±1°,在下行频段2.17~2.2 GHz内,相移量达到186°±0.1°;插入损耗优于3.3 dB且插入损耗波动小于1 dB,回波损耗在整个电压调谐范围内均大于20 dB。该移相器结构简单、便于调节且价格低廉,在卫星通信领域有一定的应用价值。

可重构微波滤波器研究现状及发展趋势

可重构滤波器是指在固定频率滤波器上加载调谐器件以实现滤波器中心频率、带宽等电性能灵活可重构的滤波器。基于可重构滤波器的射频前端能够灵活切换通信频段和带宽,显著提高频谱利用效率和抗干扰能力。综述了近年来可重构滤波器的研究进展,按照变容二极管、PIN二极管、微机电系统(Micro Electro Mechanjcal System,MEMS)器件、液晶材料、机械机构以及铁氧体器件的顺序进行梳理总结,同时对比了不同类型可重构滤波器的优缺点,总结了可重构滤波器可能的发展趋势。

一种角度与极化稳定的可调控电磁散射结构的设计与验证

通过调控成像雷达散射波的幅度、相位达到隐身伪装目的,是电子对抗领域发展的新方向.本文提出一种S波段角度与极化稳定的可调控电磁散射结构(electromagnetic scattering structure,ESS),该结构正面为加载变容二极管的金属网栅及方形金属贴片,背面为过孔连接的馈电网栅.利用二极管电容加载、等效电感加强、背面馈电电感等设计,实现了ESS的宽带小型化,其单元尺寸为λ0/10.通过改变外置调控电压,可实现1.98~3.91 GHz的连续调控,相对调控范围为69.5%.其中,在2.27~3.83 GHz反射波幅度调控深度大于15 dB,相位变化最大为269°.此外,整体性能在±60°入射、TE/TM极化下保持稳定,在雷达成像干扰领域具有良好应用前景.

一种低噪声C类LC压控振荡器的设计

为了改善压控振荡器相位噪声,基于40 nm CMOS工艺,设计一种低噪声C类LC压控振荡器。交叉耦合NMOS对管通过电流镜偏置作为电路的电流源,并采用共模反馈偏置电路使交叉耦合PMOS对管工作在饱和区,保证LC压控振荡器实现C类振荡。通过差分可变电容的设计,压控振荡器的增益减小,压控振荡器的相位噪声得到改善。设计了4组开关电容进行调节,增大压控振荡器的调谐范围。仿真结果表明,处于1.2 V的电压下,压控振荡器振荡频率范围在4.14~5.7 GHz,频率调谐范围变化率达到31.2%,相位噪声为-112.8 dBc/Hz。

基于中心对称结构的带宽可重构滤波器设计

为适应需求日益复杂的无线通信环境,充分利用紧缺的频谱资源,设计实现了基于中心对称结构及变容二极管的电可调微带带通滤波器。通过电磁仿真软件HFSS进行仿真实验,在加载枝节的开口环谐振器结构上,引入叉指结构和马刺线型耦合馈线完成滤波器的原型设计。在原有的基础上加入可调节电容值的变容二极管,调节低频传输零点,实现通带带宽可重构,从而达到灵活控制滤波性能的目的。实际测试表明该滤波器的初始相对带宽为5.1%,初始绝对带宽为170 MHz,变容二极管调节绝对带宽在140~200 MHz范围内,即82.4%~117.6%,中心频率在2.70~2.76 GHz,传输零点调谐范围在2.57~2.63 GHz,通带内插入损耗在0.9~1.5 dB,回波损耗在10~35 dB,测试结果与仿真基本相符,在S波段的带宽精密控制方向具有一定应用前景。

基于感性传输线的可调有源滤波器

论文采用电容加载传输线结构实现了一个可调谐的有源带通滤波器。该滤波器主要由感性微带线与三极管极间电容产生并联谐振提供频率选择性。通过在微带线后加载一个可变电容改变该感性微带线的等效输入阻抗,从而改变谐振频率,同时产生一个传输零点,以提高阻带抑制性,可变电容同样可以改变传输零点的频率。输出匹配采用多节传输线达成宽带匹配以确保调谐过程中输出端始终保持良好的回波损耗。该有源滤波器的中心频率在1.5GHz~2.5GHz频段范围内可调,中心频率处增益大于5dB,回波大于10dB。

基于短路λ/4谐振器对的双通带可调滤波器

为了实现动态的频率控制,设计了一款双通带可调滤波器。通过改变变容二极管电容,使通带的中心频率发生移动,并且该滤波器的2个通带在调谐过程中相互独立。通过在源与负载之间引入容性耦合,在靠近滤波器每一个通带的两侧各产生1个传输零点,共有4个传输零点,从而提高了带外抑制性。最终制备并测试的双通带滤波器低频通带中心频率在1.40~1.49 GHz之间连续可调,高频通带中心频率在2.10~2.24 GHz之间连续可调,2个通带的插入损耗均低于2.6 dB,回波损耗均高于10 dB,能够满足目前对滤波器小型化、多频段、高性能的要求。

耦合式非线性谐振的WPT系统研究

无线电能传输(WPT)系统在实际的应用场景中往往会产生移动或发生偏移,这种位置的变化会显著降低WPT系统的工作效率,造成能量的严重衰减。针对这个问题,提出了一种基于反向串联变容二极管的非线性WPT系统,通过调整变容二极管的反向偏压,对系统传输性能衰减进行补偿,推导了反向串联变容二极管的数理方程,并对平面螺旋电感线圈进行了分析研究。通过搭建的实验平台,完成了基于反向串联变容二极管的非线性WPT系统性能实验,通过与ADS 2017软件仿真结果进行对比分析,去除两者之间无法避免的差异性,该非线性WPT系统提高了收发线圈轴向距离的自由度,降低了线圈精确定位的要求,实验结果验证了理论分析和设计的正确性。

一种适用于2.4GHz ISM射频波段的全集成C MOS压控振荡器

提出了一种频率可调范围约 2 30MHz的全集成LC压控振荡器 (VCO) .该压控振荡器是用 6层金属、0 18μm的标准CMOS工艺制造完成 .采用MOS晶体管和电容组合来实现等效变容管 ,为降低芯片面积仅使用一个片上螺旋电感 ,并实施了低电压、低功耗的措施 .测试结果表明 ,该压控振荡器在电源电压为 1 8V的情况下功耗约为10mW ,在振荡器中心频率为 2 46GHz时的单边带相位噪声为 - 10 5 89dBc/Hz @6 0 0kHz .该压控振荡器可以应用于锁相环电路或频率综合器中 .

225 GHz三倍频器实用设计方法

结合国内现有的加工工艺水平,提出自偏置条件下的反向并联二极管对电路结构.不但解决了三倍频器偏置电路加工的难题,而且可以有效实现奇次倍频.同时,利用HFSS和ADS软件,以场路结合的方式准确模拟三倍频器的电特性,考虑到寄生参数引入的影响.设计完成以后,器件加工以及电装过程均在国内完成.测试结果表明在221 GHz处,有最大输出功率3.1 m W,在219~227 GHz频率范围内输出功率均大于2 m W.以上研究为今后设计高效率亚毫米波倍频器提供重要的参考价值.