LTCC基P波段90°功分器的制作

文章以LTCC基P波段90°功分器的设计和制作为例,从无源设计仿真和LTCC工艺阐述了P波段功分器的研制过程。选用了承受功率大、尺寸相对较小的宽边耦合器结构。设计的宽边耦合器采用多层结构,有利于发挥LTCC基板多层、高集成度等优点。其电路物理模型为Broadside-coupled symmetric stripline（BCL）,采用的介质为LTCC,介电常数为5．9,每层介质厚度为0．1mm,导体采用Ag浆。在实物制作过程中,TOP层和Bottom层是采用灌银通孔实现的。最终测试结果与仿真结果吻合较好,在225MHz～400MHz频段内隔离23dB,插损0．5dB,驻波1．1,相平衡度±2．5,功率250W．     

A 500-600 MHz GaN power amplifier with RC-LC stability network

A 500-600 MHz high-efficiency, high-power GaN power amplifier is designed and realized on the basis of the push-pull structure. The RC-LC stability network is proposed and applied to the power amplifier circuit for the first time. The RC-LC stability network can significantly reduce the high gain out the band, which eliminates the instability of the power amplifier circuit. The developed power amplifier exhibits 58.5 dBm (700 W) output power with a 17 dB gain and 85% PAE at 500-600 MHz, 300 μs, 20% duty cycle. It has the highest PAE in P-band among the products at home and abroad.     

星载P波段SAR电离层效应的双频校正方法

对于高分辨星载P波段SAR系统,电离层效应对P波段SAR会带来一系列较为严重误差,包括时间延迟、法拉第旋转和色散等,这些误差与电波频率和电离层TEC值关系密切,并使得图像质量下降。如何测量与校正电离层效应误差是星载P波段SAR面临的重要问题。根据SAR系统自身的宽带特点,借鉴GPS系统采用的电离层双频测量校正方法,提出了一种基于双频SAR距离像相关的延迟误差测量方法,计算机仿真结果表明,该方法有效提高了双频回波信号的电离层延迟误差测量精度,适于低频段星载SAR系统的电离层效应测量与校正应用。     

Cu2+掺杂调控NiZn铁氧体的P波段吸波性能

目的 研究离子掺杂对NiZn铁氧体电磁特性的影响,提高NiZn铁氧体的P波段吸波性能。方法 以NiO、ZnO、Fe2O3、CuO等为原料,采用高温固相反应法,通过球磨、预烧、造粒以及烧结等工艺,制备Cu²⁺掺杂的Ni0.22Zn0.66CuxMn0.04Co0.08–xFe2O4(x=0.04、0.05、0.06、0.07)铁氧体样品。通过XRD、VSM和SEM分别表征样品的晶格特征、磁学特性和微观形貌,利用阻抗分析仪对样品的电磁特性进行测量。结果 Cu²⁺掺杂量的增加引起NiZn铁氧体的A-B超交换作用减弱和磁晶各向异性降低,样品的Ms、Hc和Mr都呈现出减小的趋势。样品的复磁导率与其磁特性关系密切,随着Cu²⁺的增加,实部μ?减小,而虚部μ?增大。此外,Cu²⁺掺杂量的增加对Fe²⁺与Fe³⁺之间的电子迁移率产生影响,使得复介电常数实部ε?增大,而ε?增大的主要原因是Cu²⁺掺杂量的增加导致铁氧体内部产生了晶格缺陷。Cu²⁺的掺杂量对样品的P波段吸波性能影响显著,随着Cu²⁺掺杂量的增加,NiZn铁氧体的阻抗匹配特性明显改善,电磁衰减能力显著提高,这进一步降低了样品的最佳吸波匹配厚度。掺杂量x=0.07的NiZn铁氧体样品,在厚度为6.6 mm时,实现了有效吸波带宽完全覆盖P波段。结论 通过调节Cu²⁺的掺杂量可以调控NiZn铁氧体的P波段吸波性能,增加Cu²⁺掺杂量对于降低样品的P波段吸波匹配厚度有积极作用。     

L- and P-band backscatter intensity for biomass retrieval in hemiboreal forest

At present, the greatest source of uncertainty in the global carbon cycle is in the terrestrial ecosystems. In order to reduce these uncertainties it is necessary to provide consistent and accurate global estimates of the world forest biomass. One of the most promising methods for obtaining such estimates is through polarimetric SAR backscatter measurements at low frequencies. In this paper, the relation between polarimetric SAR backscatter at L- and P-bands and forest biomass is investigated using data acquired within the BioSAR-I campaign in southern Sweden during 2007. Methods for estimating biomass on stand level using these data are developed and evaluated, and the results for the two frequency bands are compared. For L-band data, the best results were obtained using HV-polarized backscatter only, giving estimation errors in terms of root mean square errors (RMSE) between 31% and 46% of the mean biomass for stands with biomass ranging from 10 to 290 t/ha, and an (adjusted) coefficient of determination (R²) between 0.4 and 0.6. For P-band data, the results are better than for L-band. Models using HV- or HH-polarized P-band backscatter give similar results, as does a model including both HV and HH. The RMSEs were between 18 and 27%, and the R² values were between 0.7 and 0.8.     

Airborne P-band SAR applied to the aboveground biomass studies in the Brazilian tropical rainforest

The objective of this study is to evaluate the relationship between the response (σ°) of airborne P-band Synthetic Aperture Radar (SAR) polarimetric data versus biomass values of primary forest and secondary succession. To ensure that different landscapes of “Terra firme” tropical forest of the Brazilian Amazon were represented, a test-site was selected in the lower Tapajós river region (Pará State). The microwave signals from the P-band polarimetric images were related to the aboveground biomass data by statistical regression models (logarithmic and polynomial functions). In the field survey, physiognomic and structural aspects of primary forest and regrowth were collected and afterwards the biomass was estimated using allometric equations based on dendrometric parameters. As an example of the potential use of P-band polarimetric images, they were classified by a contextual classifier (ICM), whose thematic stratification of land use/land cover was associated with biomass class intervals for mapping purposes. The main objective of this P-band experiment is to improve this tool for regional mapping of Amazon landscape changes, due to the growing rate of land use occupation.     

P波段3kW GaN功率器件的研制

介绍了一款高压高功率GaN功率器件及其匹配电路。基于国内高压GaN高电子迁移率晶体管(HEMT)的研究基础,选取了GaN HEMT芯片,确定了器件的总栅宽。根据GaN HEMT芯片阻抗,器件内部进行了LC谐振匹配设计,外部采用双边平衡同轴巴伦进行推挽匹配设计。散热方面通过改善封装管壳热沉材料提高热导率。最终成功研制出高压、3 kW的GaN功率器件,该器件在工作电压为60 V、工作频率为0.35~0.45 GHz、脉宽为300μs、占空比为10%条件下,频带内输出功率大于3 kW、功率增益大于16 dB、功率附加效率大于71%、抗负载失配能力不小于10∶1。     

一种轻量化高效率P频段数字阵列模块设计

为了满足未来大型相控阵天基雷达对低剖面、轻量化有源天线阵面的需求,设计了一种P频段14通道数字阵列模块(Digital Array Module,DAM).通过精简的系统架构设计、高密度集成的电路设计和紧凑的结构设计一系列技术方法,克服了DAM小型化和轻量化的设计难点,同时又获得了高效率和其他优良的电性能.最终研制得到样机,质量低至2.23 kg,效率达到45％(10％工作比),在天基雷达领域具有很好的应用前景.     

室内P波段后向散射测量系统

在微波暗室内构建了一种实用的P波段后向散射测试系统。利用矢量网络分析仪发射步进频率信号,通过傅里叶变换得到目标高分辨率时域响应,然后采用多种信号处理技术消除目标区外的杂波干扰;经过处于非光学区的金属球定标后,获得了P波段的高精度雷达散射截面（RCS）测试数据。实验通过多个目标的对比分析,验证了系统的精度可优于1 dB。     

一种低剖面宽带宽角扫描阵列天线的设计

基于超材料技术理念,在考虑阵元间互耦效应下,优化设计了一种低剖面宽带宽角扫描阵列天线,使该阵列剖面为最低工作频率的四分之一波长,相对带宽达55%下,工作频段内中心阵元的平均工作效率高达87%以上,30o扫描角范围内的平均有源驻波系数小于2.0,其阵元方向图E面、H面的半功率波瓣宽度大于60o。研制的6伊8阵列样机测试结果说明了阵列天线具有良好的宽带宽角扫描特性,同时该天线具有结构紧凑、重量轻和易于实现的特点,在相控阵雷达天线中有很大的应用价值。