一种应用于微波探测的双频天线的设计

为增加火灾探测天线频带范围,基于微带贴片天线,采用凹槽加载技术,设计了中心频率在Ku(12.4～18.0 GHz)波段的双频微带单元天线.利用HFSS软件对其建模、仿真及优化,结果表明,该单元天线在14.8 GHz和16.1 GHz时回波损失达到最小值,且回波损失小于-10 dB的带宽分别为600MHz和390 MHz.利用该单元天线,进而设计了一款2×2阵列天线,实测结果表明:该阵列天线具有很好的双频谐振特性,在14.3～14.9 GHz和15.7 ～16.1 GHz频带内既保留了原单元天线好的回波损耗特性,又提高了增益,使两个频段最大增益分别达到13.7 dBi和11.3 dBi.     

一种双频段有源频率选择表面的设计

在频率选择表面问题的研究中,当传统FSS结构成型后,其工作带宽和谐振频率等参数固定,不能适应外部电磁环境的变化.为解决上述问题,设计了一种有源FSS结构,在传统FSS中加载PIN管或变容二极管等有源器件,通过调节器件的偏置电压或电流来改变FSS的电磁特性;运用等效电路法分析了有源FSS结构的传输线模型,利用有限元软件HFSS研究了不同加载方式下,该结构的电磁响应变化;通过有源FSS结构单元与传统FSS结构单元的交替排列,实现了具有双频性质的FSS结构.研究结果表明FSS加载电容时,谐振频率降低,且加载电容值越大,谐振频率越低,带宽越小;FSS加载电感时,谐振频率增大,且加载电感值越小,谐振频率越高,带宽越大.结果表明,为在实际应用中达到带宽优化的效果,应尽可能加载较小的电容与电感.     

基于深度学习的单层双阻带频率选择表面设计

为了满足FR1频段与Ku频段电磁干扰的屏蔽需求，提出一种双阻带、具有良好角度稳定性和极化稳定性的频率选择表面(FSS)结构。所设计的FSS单元结构由覆盖在FR4介质表面的金属方环与四个弯折金属臂共同组成。该结构的低频阻带覆盖0～5.5 GHz，高频阻带可根据金属臂长度进行调节。为快速获得高频阻带结构，构建了反向传播深度神经网络(BP-DNN)模型。该模型以FSS单元结构的五个参数作为输入，以高频阻带的中心频点与15 dB屏蔽效能(SE)带宽作为输出。训练后的深度网络模型可快速获得12～21 GHz范围内指定高频阻带中心频点及15 dB屏蔽效能带宽的FSS单元结构参数。利用训练后的BP-DNN网络模型快速获得了高频阻带中心频点在16 GHz，|S₂₁|≤-15 dB带宽为1.86 GHz的FSS结构，全波分析仿真结果表明该设计达到预期效果。     

用于卫星通信的Ku波段宽带双频双极化微带天线阵

利用口径耦合馈电、错位倒相馈网技术和单层微带贴片结构设计出一种用于卫星通信的Ku波段宽带双频双极化微带四元天线阵。用电磁仿真软件CST2008对天线阵的电特性进行了仿真和优化。四元天线阵实测结果表明:水平极化端口在11.21GHz～13.47GHz频率范围内VSWR燮1.5,相对阻抗带宽为18.3%;垂直极化端口在13.43GHz～14.88GHz频率范围内VSWR燮1.5,相对阻抗带宽为10.24%。工作频带内两端口隔离度<-35dB,最大增益为13.2dB,与仿真结果一致。     

具有匹配反馈环的微波段RFID标签天线设计

针对标签天线在RFID系统中的重要性,基于微带天线设计和电磁散射理论,设计和分析了一种具有匹配反馈环的微波段RFID标签天线。谐振频率为2.45 GHz和2.41 GHz天线的尺寸为54 mm×33 mm左右,天线显示近线性相位特性,在电压驻波比小于2的条件下天线的阻抗带宽为300 MHz。可以通过调整匹配反馈环的长度来调整天线的谐振频率,天线的增益为2.4~2.7 dBi。谐振频率为5.8 GHz的天线阻抗带宽为7%,增益为2.8~3.2 dBi,尺寸大小为20 mm×12 mm。通过仿真和测量可知,这种天线能较好地满足RFID微波段标签的要求。     

基于CRLH—TL及CSRR的带通滤波器

首次提出一种复合左右手传输线零阶谐振器及互补谐振环的新型带通滤波器.设计方法利用左右手复合传输线的独有特性,即零阶谐振器中心频率与谐振器长度无关,能在特定非零频率上得到无限波长的特点,来构造环形滤波器,并且地板蚀刻了长方形互补谐振环结构.设计过程中使用了AnsoftHFSS软件进行全波仿真,经过多次仿真,通过调节参数大小优化设计,最终结果得到中心频率为1.85GHz、带宽为0.1GHz的新型带通滤波器.在达到同样效果的前提下,减小尺寸,单个谐振器与传统相比体积减少了近80%,长方形CSBR还提高了传输特性.上述结构的实现对于左手材料在微波器件中的发展有一定的促进作用,进一步扩大了左手材料的应用范围.     

Ku宽带正交模耦合器仿真设计

正交模耦合器(OMT)是实现天线馈源系统双极化工作的关键器件.为实现Ku宽带频率复用馈源网络,设计了一种宽带双脊OMT,由双脊波导、轴向阻抗变换器和功率合成器组成.用HFSS仿真设计了一个Ku全频段的OMT,工作带宽10.7GHz～ 14.5GHz,根据仿真优化后的尺寸,加工了实物样机,测试驻波小于1.16,隔离大于40dB,传输损耗小于0.15dB.结果表明,宽带双脊OMT具有频带宽、高性能的特点,能够满足需求.     

L/C双频共口面微带天线阵列设计研究

介绍了一种新的双频共口面微带天线阵列的设计.天线工作在L波段和C渡段,采用共口面结构实现复合双频工作,适用于机载合成孔径雷达.L波段(1.275GHz)采用带扇形头的微带线耦合馈电的蝶形缝隙天线,达到10%的阻抗带宽.C波段(5.3GHz)采用缝隙耦合馈电的矩形贴片天线,4×4阵列仿真带宽达到6%左右.此高低波段单元结构组合形式可以实现高频比,且在物理结构上没有相互遮挡.用Ansoft Hfss和Cst对设计进行了对比仿真优化,得到了较好的双频辐射特性.     

基于同向开口双环的双通带左手材料研究

为了改进传统的开口谐振环-导线（ SRRs-wire）结构电磁特性,利用不同大小的开口谐振环所产生不同负磁谐振频率点的特点,设计了同向开口双环的SRRs-wire结构,并给出了其等效电磁参数反演结果。通过增加其单元结构的金属短线的个数实现了双通带左手特性;同时通过改变外环为U型环降低了内外环的相互耦合。利用内外谐振环间具有弱耦合的特性,提高了高频左手通带的带宽,同时可以较方便地调节双通带工作频率点,具有很好的可调性。     

基于互补结构的有源FSS传输特性

研究了由方型缝隙单元和十字贴片组成的互补结构有源频率选择表面(Frequency-selective surface,FSS)的传输特性.通过HFSS仿真和实物测试,给出了PIN管不同工作状态下的插入损耗和插入相移,研究了该结构的角度稳定性.数据结果表明,通过改变PIN管的工作状态,在谐振点处插损有17 dB的动态变化范围,从而为有源FSS天线罩的设计提供参考和借鉴.     

High gain CPW‐fed UWB planar monopole antenna‐based compact uniplanar frequency selective surface for microwave imaging

In this article, a novel uniplanar ultra‐wideband (UWB) stop frequency selective surface (FSS) was miniaturized to maximize the gain of a compact UWB monopole antenna for microwave imaging applications. The single‐plane FSS unit cell size was only 0.095λ × 0.095λ for a lower‐operating frequency had been introduced, which was miniaturized by combining a square‐loop with a cross‐dipole on FR4 substrate. The proposed hexagonal antenna was printed on FR4 substrate with coplanar waveguide feed, which was further backed at 21.6 mm by 3 × 3 FSS array. The unit cell was modeled with an equivalent circuit, while the measured characteristics of fabricated FSS array and the antenna prototypes were validated with the simulation outcomes. The FSS displayed transmission magnitude below ?10 dB and linear reflection phase over the bandwidth of 2.6 to 11.1 GHz. The proposed antenna prototype achieved excellent gain improvement about 3.5 dBi, unidirectional radiation, and bandwidth of 3.8 to 10.6 GHz. Exceptional agreements were observed between the simulation and the measured outcomes. Hence, a new UWB baggage scanner system was developed to assess the short distance imaging of simulated small metallic objects in handbag model. The system based on the proposed antenna displayed a higher resolution image than the antenna without FSS.     

Polarization independent quad‐bandpass frequency selective surfaces with wide‐band ratio

A single layer polarization independent quad‐bandpass frequency selective surface (FSS) with wide‐band ratio is demonstrated theoretically as well as experimentally. The proposed structure passes four frequency bands with wide band ratio. The proposed FSS design is implemented by incorporating alternate arrangement of four units which are rotated 90° clockwise to form a unit cell of metal over a FR4 substrate. The geometrical dimensions of proposed unit cell are optimized and arranged in such a way that the structure possesses the quad bandpass characteristic and aspect dimensions of one unit is 0.11λ × 0.11λ with respect to first resonant frequency. This FSS provides stable response for different angle of incidence in transverse electric (TE) mode and transverse magnetic (TM) mode. To validate the results proposed FSS array has been fabricated and measured in free space environment. The measured results are in good agreement with the simulated results. Excellent stability is also observed for different incident angle.     

GSM filtering of horn antennas using modified double square frequency selective surface

In this work, a dual‐band frequency selective surface (FSS) is proposed to be placed perpendicularly into the apertures of horn antennas for prefiltering 900 and 1800 MHz GSM signals interfering during the signal reception, with the enhanced return loss, gain, and directivity at the desired frequencies. For this purpose, the microstrip double square loop MDSL is modified in the first stage. As for the second stage, an FSS array (2 × 2) is built up arranging the unit MDSLs in a periodic structure and finally these FSS unit arrays are fixed perpendicularly covering the aperture of a ridged horn antenna which is a part of the available radar system operating between 0.5 and 3 GHz in our laboratory, to construct an integrated module having both bandstop prefilter and horn antenna called “filtenna.” The simulated and experimental results are agreed that the proposed FSS structure attenuates GSM signals at the 900 and 1800 MHz through the high reflection and very poor transmission mechanisms meanwhile enhances return loss characteristics, radiation pattern, and gain of the horn antenna in the desired band. Thus, it can be concluded that these simple microstrip FSS structure can be effectively adapted to the horn antennas which need the GSM prefiltering.     

Frequency‐selective rasorber with two low insertion loss transmission bands

A frequency‐selective rasorber (FSR) with two low insertion loss transmission bands is proposed. The FSR is composed of the resistive sheet layer at the top and bandpass FSS layer at the bottom, and separated by air spacer. Full‐wave simulation results show that the FSR realize two transmission bands at frequencies 8.5 GHz and 10.8 GHz with 0.45 dB and 0.77 dB insertion loss. Meanwhile, the band with |S₁₁| < ?10 dB is over 4.2‐8.8 GHz and 9.2‐17.4 GHz. Compared with the reported FSR with two transmission bands, the proposed FSR in this article achieves two transmission bands with lower insertion loss and wide absorption band at high frequencies. To validate the performance of the proposed FSR, the samples are fabricated and measured, reasonable agreement between simulated and measured results is achieved.     

A spatial power limiter using a nonlinear frequency selective surface

A novel spatial power limiter based on nonlinear frequency selective surface (FSS) is presented for high power electromagnetic (HPEM) wave protection. Embedded with Schottky diodes, the nonlinear FSS not only reflects out‐of‐band electromagnetic incidence like a filter, but also exhibits a power‐limiting characteristic, allowing low‐loss transmission for an in‐band low‐power incidence while rejecting a high‐power one. Such a FSS with 4 × 4 unit cells is designed, fabricated and measured. Results demonstrate its pass‐band centering at 2.5 GHz, power density threshold of about 0.27 W/m² and shielding effectiveness (SE) up to 20 dB at 2.5 GHz.     

Both transversal negative permeability and backward‐wave propagation in X‐Band waveguide with double‐side SRR metamaterials

In this article X‐band rectangular waveguides partially filled with the double‐side single ring resonator (DSRR) array are investigated for miniaturization, stop‐band, and multi‐band filters applications. Several rectangular waveguides loaded with the DSRR array in 2–10 GHz frequency band have been studied and optimized. We observe both the transversal negative permeability presented above the cutoff frequency and the backward‐wave located below the cutoff frequency with the DSRR array in X‐band waveguide. Both simulation and measurement results of DSRR array are with good agreement. The DSRR array provides better performance of the transversal negative permeability and the backward‐wave than the split‐ring resonator array. The physical explanation of backward‐wave is presented. The power loss distributions are clearly presented for the negative permeability attenuation and the backward‐wave propagation. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:240–246, 2016.     

A compact uniplanar ultra‐wideband frequency selective surface for antenna gain improvement and ground penetrating radar application

A simple structured single layered frequency selective surface (FSS) that has unit cell size of 11 × 11 mm², substrate thickness of 0.8 mm only and capable to work in a very widespread band from 0.001 to more than 17 GHz is proposed in this article. The FSS is competent to augment the gain of a UWB monopole antenna by 2 to 3.5 dBi when integrated at the back of antenna. The performances of “antenna‐FSS” structure is evaluated by simulation and experimental measurement where good correlations are obtained. The integrated structure provides wide impedance band (S₁₁ < ?10 dB) from 2.82 to 19.94 GHz (more than 150%) with improved broadside radiation and high radiation efficiency profile. The transient and frequency domain characteristics of “antenna‐FSS” composite structure are also evaluated in close proximity of diverse sub‐surfaces such as dry sand, wet sand, wood and concrete where an almost unaltered impedance band profile, linear transfer function response and non‐varying group delay responses are achieved which establishes the applicability of the composite structure in ground penetrating radar for low depth sub‐surface scanning applications.     

Spoof surface plasmon polariton band‐stop filter with single‐loop split ring resonators

A novel band‐stop filter with single‐loop split ring resonators (SRRs) is proposed for spoof surface plasmon polaritons (SPPs) at millimeter wave frequencies, achieving a miniaturized size of 0.052λ₀ × 0.278λ₀ at its resonant frequency. The SRRs provide both a low‐pass response as the rectangular corrugations used in the conventional SPPs and an additional band‐stop response induced by the resonance of SRRs. To verify this design, a back‐to‐back device with two coplanar waveguides as the input and output feeding was fabricated and characterized, the measured S‐parameters of which agree well with the simulation. The measured stop band is centered at 49 GHz with a ?10‐dB bandwidth of 4.1 GHz and a high Q‐factor of 93, in which the maximum attenuation is 31 dB. The filter has a low insertion loss of less than 2.8 dB in the pass band. Such approaches may find many applications to achieve compact millimeter wave circuits.     

Dual‐band rotary standing‐wave voltage‐controlled oscillator

In this article, a dual‐band rotary standing‐wave oscillator (RSWO) is introduced that generates sinusoidal signals by the formation of a standing wave on a ring (closed‐loop)‐distributed composite right/left‐handed (CRL) Inductor‐Capacitor (LC) transmission line network. The LC network consists of four unit cells of CRL LC resonator stacked in series, and two pairs of cross‐coupled transistors are used to compensate for the loss of LC resonator. Varactors are used as the control to switch on/off the high‐ or low‐frequency bands. In the fundamental mode, the RSWO operates at the high‐frequency band. In the harmonic mode, the oscillator provides low‐frequency band outputs. The dual‐band function exploits the multiple oscillation modes of the CRL RSWO. The proposed RSWO has been implemented with the Taiwan Semiconductor Manufacturing Company, Limited (TSMC) 0.18‐μm SiGe BiCMOS technology. It can generate differential signals in the high‐band frequency range of 6.73–8.60 GHz and in the low‐band frequency range of 3.68–3.73 GHz. The die area of the RSWO is 1.123 × 1.123 mm². © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:536–543, 2014.