接收机的寄生带对系统性能的影响

主要论述接收机的寄生带是客观存在的,它的存在使系统灵敏度降低,噪声系数变坏,甚至使雷达的测距和测角精度降低,因此在设计接收机时应对寄生带的抑制度提出一定的要求.由于测量方法上的原因,寄生带的存在在测量系统噪声系数时,一般并不直接反映出来,在这种情况下,应以灵敏度来评价系统的性能才正确.

带寄生单元宽带单极子天线研究

提出并设计了一种带寄生单元宽带单极子天线,该天线由一个单极子天线附加两个寄生振子组成。仿真及实验结果证明:天线在保持单极子天线特性的同时,实现了其宽带特性。该天线在750～2240 MHz的频带内反射损耗小于-10 dB,具有水平全向的方向图、稳定的增益。天线的结构和电特性决定了天线有广阔的应用前景,非常适用于移动通信终端设备,作为手持终端天线和车载天线将大有可为。

一种单极子超宽带四陷波天线设计

超宽带(Ultra Wide Band,UWB)天线在通信领域至关重要,但由于超宽带频段和窄带通信频段互有交叉,为了消除某些窄带信号的干扰,设计了一种微带馈电的单极子四陷波超宽带天线。该天线由矩形金属贴片作为辐射贴片获得超宽带特性,通过在辐射贴片上刻蚀两个不同尺寸的矩形开环谐振器,以及把相互嵌套的U形寄生带耦合在微带馈线附近来获得天线的陷波特性。HFSS电磁仿真和实际测量表明:该天线的工作范围为3.1~11.1 GHz,有效滤除了全球微波接入互联(World Interoperability for Microwave Access,WiMAX)波段(3.54~3.82 GHz)、印度国家卫星系统(Indian National Satellite System,INSAT)波段(4.45~4.62 GHz)、无线局域网(Wireless Local Area Network,WLAN)波段(5.38~5.76 GHz)和X波段下行频(6.87~7.26 GHz)。天线结构简单,易于加工,陷波频段可单独调节,天线实物和模拟吻合度较好,具有一定的工程价值。

Risk factors connected to gastrointestinal parasites in mantled Alouatta palliata mexicana and black howler monkeys Alouatta pigra living in continuous and in fragmented rainforests in Mexico

In this study we document the prevalence of gastrointestinal parasites （helminths and protozoans） found in fecal samples of populations of Alouatta palliata mexicana and ofA. pigra in Los Tuxtlas and in Palenque, southeast Mexico, and its re- lation to habitat condition, sex/age and season. Nineteen parasite morphotypes were detected in the fecal samples from populations of the two howler monkeys, of which 58% were shared by both species. When considering all parasite species, populations of the two howler species were more likely to be parasitized in fragmented habitat compared to continuous habitat. Individuals of both howler monkey species that lived in fragmented habitat had a higher prevalence of Controrchis biliophilus. A. p. mexicana individuals had a higher prevalence of Trypanoxyuris minutus than A. pigra, probably the result of the larger group sizes found in the former species, and T. minutus was more likely to be found in A. palliata individuals that lived in fragmented habitat. Adult A. p. mexicana males had a higher risk of being parasitized compared to adult females, but these differences were not detected in A. pigra, Parasite species such as Entamoeba sp., Nematoda sp. 28, Nematoda sp. B and Parabronema sp. where only found during the wet season in both howler monkey species. Populations of both howler monkey species had a higher prevalence of Nematoda sp. A in the wet season and Ascaridae eggs were only detected during the wet season in A. pigra. Other parasites detected displayed no clear seasonal pattern [Current Zoology 58 （3）： 375-383, 2012].

Experimental demonstration of λ/8 DFB semiconductor laser array for 1.3 μm CWDM system

In this article,we report the first experimental demonstration of an eight-wavelength λ/8 phased-shifted laser array based on the REC technique in the 1.3 μm wavelength domain.Measurement results exhibit good linearity of lasing wavelength with+/-0.35 nm wavelength residual.The SLM property was ensured with SMSRs all larger than 38 dB.Moreover,the directmodulation performance was also tested.The experimental results show that the modulation bandwidth can reach up to 13GHz even at the small injection current of 40 mA and the measured spurious-free dynamic range(SFDR)is up to 87 dB/Hz2/3,which shows good linearity.These measurements show that REC-based λ/8 phased-shifted laser array has good modulation performance and it may find potential application in actual fiber-optic systems.