Numerical Simulation of the Base Impedance of Long Wire Whisker Antennas

With increasing frequencies the whisker structures used to contact honeycomb Schottky diodes remain no longer thin compared to wavelength. Whereas the finite thickness and the detailed tip shape do not influence the antenna pattern very much the antenna base impedance depends on these parameters to a great extent. A good impedance matching between Schottky diode and whisker antenna is necessary to optimise mixer or detector performance and can only be achieved if the antenna impedance is known.Antenna base impedances have been simulated numerically and checked by means of scaled model measurements for several whisker shapes. The influence of further parts of the antenna environment, as for example reflectors, has also been investigated. Simulation results have been discussed and compared to theory. Simulation has been found out to be a reliable tool for the determination of base impedances of almost arbitrarily shaped whisker antennas.     

0.38 THz混频器关键器件设计和仿真优化北大核心CSCD

太赫兹混频器是太赫兹波收发系统中的关键器件,是将信号频率从一个量值变换为另一个量值的电路器件,其中肖特基二极管是太赫兹混频器中的核心器件,除了肖特基二极管以外,低频滤波器、本振端口等也属于太赫兹混频器中的关键器件。对0.38THz混频器中的关键组件包括波导管、肖特基二极管、滤波器等在HFSS中进行了建模、仿真,最后通过对仿真结果的分析,实现了可以满足0.38THz太赫兹混频器的各个关键模块的模型,通过这些模型实现了混频器整体的优化。     

GaAs Schottky devices for submillimeter wavelengths

Conclusion The above analyses assume the absence of excess noise in the Schottky barrier mixer diode. Achievement of such a condition is dependent not only on the absence of interfacial stress in the device structure, but also on device surface properties. Reduction of excess noise caused by these two mechanisms is discussed by Sherrill, et al.,⁽¹⁰⁾ and Kattman, et al.⁽¹¹⁾ Minimum conversion loss in the THz range occurs for mixer diode with the smallest possible junction capacitance. This capacitance can be reduced along with the R_s, C_j(0) product by decreasing the device area and increasing the active layer impurity concentration. It was shown above that this impurity concentration increase will (a) permit higher frequency of operation, (b) cause a lower intrinsic conversion loss, and (c) be responsible for an increase in mixer diode I–V slope parameter, V₀. The only potentially negative effect comes from (c), but the analysis reviewed in the last section shows that an increase in V₀ has a minimal effect on mixer noise temperature for terahertz range operation. Experimental results of Dr. H. P. Röser⁽¹²⁾ to frequencies as high as 2.5 THz are in agreement with these predictions.It is thus concluded on the basis of the above four analyses of device mixer noise temperature and conversion loss that reasonable Schottky barrier mixer diode operation can be expected to at least 10 THz.This work was supported in part by the National Science Foundation under Grant ECS-8412477     

Antenna patterns of an open structure mixer at a submillimeter wavelength and of its scaled model

To verify the enhancement in sensitivity of a Schottky barrier diode using a 90° corner reflector at submillimeter wavelength a 651 scaled model of the open structure mixer was constructed and investigated at 2.8 cm wavelength.The results show clearly the advantage of a 90° corner reflector, the reality of the deviations for 45° and 60° corner reflectors found for submillimeter wavelengths, and the equality of the antenna patterns for a 90° corner reflector and a cat-eye (corner cube) reflector.     

183 GHz double diode subharmonically pumped mixer

A double diode subharmonically pumped mixer is described. A diode-whisker contacting arrangement has been developed which avoids many of the problems associated with whisker contacts. Early tests indicate that the circuit structure is rugged and capable of good electrical performance.     

A corner-reflector mixer mount for far infrared wavelengths

A new type of corner-reflector mixer mount, which has the advantages of ease of fabrication and assembly as well as frequency versatility, has been designed and constructed. The mixer works with arbitrary antenna lengths > or = 4 lambda with the reflector to antenna spacing adjusted to give a strong and symmetric central lobe. The predicted response patterns have been experimentally verified for various antenna lengths and operating frequencies between 800 and 2000 GHz. An important design feature is the incorporation of a microstrip matching network which eliminates IF impedance mismatch and provides mechanical isolation of the whisker antenna.     

Measured mixer noise temperature and conversion loss of a cryogenic Schottky diode mixer near 800 GHz

We accurately measured the noise temperature and conversion loss of a cryogenically cooled Schottky diode operating near 800 GHz, using the UCB/MPE Submillimeter Receiver at the James Clerk Maxwell Telescope. The receiver temperature was in the range of the best we now routinely measure, 3150 K (DSB). Without correcting for optical loss or IF mismatch, the raw measurements set upper limits ofT _M=2850 K andL _M=9.1 dB (DSB), constant over at least a 1 GHz IF band centered at 6.4 GHz with an LO frequency of 803 GHz. Correction for estimated optical coupling and mismatch effects yieldsT _M=1600 K andL _M=5.5 dB (DSB) for the mixer diode itself. These values indicate that our receiver noise temperature is dominated by the corner cube antenna's optical efficiency and by mixer noise, but not by conversion loss or IF mismatch. The small fractional IF bandwidth, measured mixer IF band flatness from 2 to 8 GHz, and similarly good receiver temperatures at other IF frequencies imply that these values are representative over a range of frequencies near 800 GHz.     

Simulated performance and model measurements of an SIS waveguide mixer using integrated tuning structures

A three-port approximation of the quantum mixer theory is employed to perform mixer gain calculations at 230 GHz for SIS junctions with integrated tuning structures. In addition, the embedding impedance range of a waveguide mixer mount has been obtained from model measurements and has been included in the gain calculations. The results show that even moderately small junctions can perform well in a waveguide environment when an integrated tuning structure is used. A three-element tuning circuit is presented that would allow broad band operation with a fixed embedding impedance which is important for applications using a planar antenna structure.     

The use of antenna theory to calculate the electric fields in a thermal field emission metal whisker diode

In recent years, research groups have used metal-metal point contact diodes for frequency mixing and detection of infrared laser radiation. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is the tunneling of electrons through an intermediate oxide film from the whisker tip to the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunneling junction. Several features of the diodes' operation create considerable doubt concerning the applicability of the MOM tunneling mechanism. Analysis of the available data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunneling. In an earlier paper, we calculated the power absorbed by the cylindrical shank of a point contact diode in an infrared radiation field. Using the absorbed power as a source, detailed calculations were made of the laser induced temperature distributions on the diode; more approximate treatments were used to obtain the electric fields developed on the tip. Values of the computed temperature and field parameters for tungsten were found to be consistent with a thermal field emission process. In this paper we present a more rigorous calculation of the voltages and fields induced on different metal whisker tips by the incident laser radiation. Linear antenna theory is used to describe the receiving properties of the diode. The actual pointed geometry of the diode tip has been taken into account using Schelkunoff's theory of the conical antenna. The electric fields at the tip are found to be comparable with those necessary for field emission. The highest fields are established on gold tips, consistent with the experiments of Green et al. who found the best responsivity occurs with gold-gold contacts. Finally we discuss the significance of the experimental results of Young et al. on metal-vacuum-metal tunneling characteristics to the MOM tunneling hypothesis.     

A Broad-Band Low-Noise Schottky Diode Full-Height Waveguide Mixer from 80 to 115 GHz

The RF matching problem in the input circuit of the mm-wavelength whisker contacted Schottky diode mixer is studied. The experimental results, obtained on the 3mm wavelength mixer mounts in the broad band of frequencies from 80 to 115 GHz are presented. It is shown that advantage in the receiver noise temperature may be realized by the use of a full-height instead of 1/4-reduced-height waveguide because of reduction loss in the mixer input circuit even beginning from the 3mm-wavelength. With a full-height waveguide mixer the double sideband (DSB) receiver noise temperature is 300 divided by 350K over the 85 to 110 GHz band. Input bandwidth of the fullheight waveguide mixer (cap delta f _S/f _SO greater than 30%) is equal to 1/2-and close to 1/4-reduced-height waveguide mixers.     

Generation of phase-locked and tunable continuous-wave radiation in the terahertz regime

Broadly tunable phase-stable single-frequency terahertz radiation is generated with an optical heterodyne photomixer. The photomixer is excited by two near-infrared CW diode lasers that are phase locked to the stabilized optical frequency comb of a femtosecond titanium:sapphire laser. The terahertz radiation emitted by the photomixer is downconverted into RF frequencies with a waveguide harmonic mixer and measurement-limited linewidths at the Hertz level are demonstrated.     

角锥棱镜阵列谐振腔的输出特性

 角锥棱镜阵列具有溯源反射和准相位共轭两大特点,可在一定程度上补偿高平均功率固体激光器的热畸变。但由于这种角锥棱镜阵列自身的缺陷和由它构成的谐振腔输出激光模式众多的特点,限制了其在谐振腔中的应用。分析了角锥棱镜阵列谐振腔产生多模输出的原因,提出了采用腔内滤波的方法实现单模输出。理论模拟和实验研究结果表明：利用该方法可较好地改善阵列角锥棱镜谐振腔的输出特性,获得了近5倍衍射极限的输出。     

Thermal and field emission effects of laser radiation on metal whisker diodes: Application to infrared detection devices

In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region of the spectrum (λ ? 10 μm) using a metal point contact diode for generation, frequency mixing and detection. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is tunnelling of electrons through an intermediate oxide film from the whisker into the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunnelling junction. Several features of the diode's operation create considerable doubt concerning the applicability of the MOM tunnelling mechanism. Analysis of the available experimental data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker tip in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunnelling by field emission. In this paper we calculate rigorously the power absorbed in the metal whisker from the incident radiation. From the power absorbed, the heat conduction equation is solved for model geometries to obtain the laser induced temperature distribution at the whisker surface. Estimates of the electric field are obtained and combined with temperature calculations to obtain the nonlinear I–V characteristics of the thermally enhanced field emission model. Finally some simple experiments are proposed to test the thermal field emission hypothesis as a possible mechanism to explain the nonlinear characteristics of the metal whisker point contact diode.     

Measurements of the sideband conversion gain ratio of a millimeter-wave heterodyne sub-harmonic mixer using a fourier transform spectrometer

A Fourier transform spectrometer, based on a Martin-Puplett polarisation rotation interferometer and using broad-band blackbody noise sources, has been used to study the sideband response i.e., conversion gain, of a room temperature Schottky diode sub-harmonic mixer operating at 300 GHz. The technique enables the response of the mixer to be characterised and preferentially tuned to one sideband, thereby improving the rejection of unwanted spectral components which can be present in the mixer image sideband.     

Excellent stability of laser passively Q-switched with a retroreflecting corner cube prism

A miniature Cr⁴⁺:YAG Q-switched, repetitive operation, conductive cooling Nd:YAG laser with a retroreflecting corner cube prism is demonstrated. The corner cube prism which is insensitive to misalignment in any direction makes it useful for the laser to adapt to the violent change of ambient temperature and also makes the laser cavity insensitive to the variation of thermal lens of the crystal. The laser has excellent stability of the average output pulse energy and the threshold voltage under different ambient temperature of −40, 25, and 55°C.     

机载角反射器阵列设计

 低轨目标目前流行的类半球状布阵方式的远程角偏小,测距盲区较大。对角锥棱镜进行研究分析,依据角反射器光束入射角度允许变化范围,合理分布角反射器,设计了一机载激光反射器装置,外形尺寸为119 mm×88.8 mm,共有15个角锥棱镜,底面切割成正六边形,底面边长为15.5 mm,底面对边距为26.87 mm,有效通光口径为25 mm,高为19 mm。考虑到角反射器的速差效应及其补偿要求,角锥棱镜最大角误差为5″,面形最大误差为5″。通过合理设计,比较单层角反射器,增加了入射光允许的角度范围,大大减小了低轨目标的测试盲区。     

Broadband IF matching for quasioptical mixers

Everyone recognizes the need to drive symmetric quasioptical antennas in a symmetric way to maintain clean antenna patterns; in this note we report on the advantages of bringing out the IF in a symmetric (balanced) way as well. The main difference in IF circuits between waveguide and open structure mixers is that the quasioptical mixers are usually also open at IF wavelengths, so IF currents can flow on the outside of the mixer mounting structures. We measured these surface currents and their associated resonances on a scale model of our mixer block for a 690 GHz SIS mixer. Bringing the IF off the mixer with a balanced circuit solves the surface current problems, yielding a broad bandwidth with predictable impedances. We successfully tested an octave bandwidth IF matching circuit for open structure mixers that incorporates a commercial 180° hybrid at cryogenic temperatures. We also found that surface currents are not significant for corner cube mixers because they generate their own balancing currents.     

基于二极管精确电路模型的183GHz分谐波混频器设计

针对亚毫米波混频二极管管对电路模型不够精确的问题,采用场路结合协同分析,将进出二极管的频率信号分类处理,建立了一种应用于亚毫米波分谐波混频器电路的反向并联二极管对精确电路模型。基于获取的管对精确电路模型,建立了全局性的分谐波混频器电路的集总元件等效电路模型,设计并实现了一款183GHz分谐波混频器。测试结果表明混频器在本振频率为92GHz、功率为2mW,射频频率176~192GHz范围内,双边带变频损耗小于6.8dB,等效噪声温度小于800K,在182GHz测得最小双边带变频损耗为4.9dB,与仿真数据吻合较好。     

Output polarization states of a corner cube reflector irradiated at non-normal incidence

A method has been developed for determining the polarization state of the retro-reflected beam from a corner cube irradiated with an input beam of arbitrary polarization state and of arbitrary tilt angle to the cube. Experimentally, the output beam consists of six distinct beamlets of different polarization states that are focused into six non-overlapping regions in the active area of the detector. The overall polarization state of the beam as measured by the photodetector can thus be represented by the incoherent superposition of the polarization states of the six beamlets. Experiments have been performed that verify the theory for a linearly polarized input beam irradiating the corner cube.     

Linewidth and tuning characteristics of terahertz quantum cascade lasers

We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.