A Gunn-Diode Active Leaky-Wave Frequency Scanning Antenna

A frequency tunable active leaky-wave scanning antenna using Gunn-diode voltage control oscillator (VCO) as source is developed. The frequency tuning controlled by changing either the varactor diode dc bias or the Gunn diode dc bias is demonstrated. The measured scanning angle of active antenna is close to 15 degree as the Gunn VCO frequency tuned from 12.58GHz to 12.98GHz. To excite the first higher order mode of the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the middle line of the microstrip leaky wave antenna. This is a prototype of frequency scanning antenna using two terminal device, which can be easily scaled up to millimeter wave frequency region.     

Varactor-tuned gunn diode voltage controlled oscillator antenna array

A simple varactor tuned X-band Gunn diode VCO antenna array which is strongly coupled has been demonstrated. These arrays have the advantages of simple biasing circuit, no resistors required to eliminate multimode problem and suitable for monolithic integration circuit. Preliminary results show a maximum tuning range of 47MHz for 1×1 array and 170MHz for 2×2 array. In order to solve power combining heating problem, we move the backside metal forward and it becomes a microstrip form. The measured frequency and radiation patterns of these grid arrays agree very well with theoretical calculations.     

Complementary electric-LC resonator antenna for WLAN applications

In this paper, a metamaterial antenna based on complementary electric-LC (CELC) resonator is proposed. The antenna consists of slot-loaded ELC on the ground plane as the main antennas radiating element and excited by a microstrip line. The CELC resonator is characterized by single-negative magnetic moment excited by coupling between the microstrip transmission line and slot-loaded CELC. The peak realized gain and efficiency of 2.63 dB and 86 % are obtained, respectively, at resonance frequency. Simulation and measurement results are presented to validate the design. The antenna is suitable for WLAN applications (2.39–2.48 GHz).     

基于超材料吸波体的低雷达散射截面微带天线设计

设计了一种高吸波率、宽入射角、无表面损耗层的超材料吸波体, 并将其用于微带天线的带内雷达散射截面(radar cross section, RCS)减缩.实验结果表明: 设计的吸波体的厚度为0.3 mm, 吸波率达99.9%, 相比普通微带天线, 加载该吸波体后的天线在工作频带内法向RCS减缩都在3 dB以上, 最大减缩16.7 dB, 单站RCS在-30°–+30° 角域、双站RCS在-90°–+90°角域减缩超过3 dB, 且天线辐射性能保持不变. 证实了该吸波体具有良好的吸波效果, 可以应用于微带天线的带内隐身. 关键词： 超材料吸波体 微带天线 雷达散射截面     

The U-Band Pattern Steerable Active Patch Antenna

Combing the active antenna concept with the reconfigurable antenna technique, a pattern steerable active patch antenna is presented and designed in this paper. A Gunn diode is used to generate the millimeter wave signal and loaded at the centre of the patch antenna. This antenna system has a stable oscillation frequency f : 44.0GHz and operates as a quasi-Yagi patch antenna. The radiation patterns of the antenna can scan in the whole horizontal plane with 3-db beam width by using four reconfigurable states and the radiation main beam of each state directs to the elevation angle 59° in the elevation-plane. The antenna can be applicable to the millimeter wave half-duplex communication and identification systems.     

A new double L-shaped multiband patch antenna on a polymer resin material substrate

The design and prototyping of a new double L-shaped patch antenna on substrate of available low cost polymer resin composite material is presented. The designed microstrip line fed compact antenna consists of a planar double L-shaped slotted radiating patch, 1.6 mm thick substrate and ground plane. The proposed small antenna was designed and analyzed using a finite-element method-based, commercially available, high frequency structure simulator, and fabricated on a printed circuit board. The measured ?10 dB return loss bandwidths were 220 MHz and 650 MHz at 4.85 GHz and 8.10 GHz center frequencies. The corresponding symmetric and almost steady radiation patterns have peak gains of 7.6 dBi and 4.1 dBi, making the proposed antenna suitable for C and × band wireless applications, especially for WLANs, mobiles and satellites. The radiation efficiency, input impedance and current distribution of the proposed antenna were also analyzed.     

Circular polarized electronically-controlled antenna array based on CRLH-TL

In this paper, a circular polarized electronically-controlled scanning microstrip antenna array is designed, which is based on composite right left-handed transmission line (CRLH TL) and is realized by varactor diodes. Proposed electronically-controlled antenna arrays till now are always linear-polarized as the axial ratio (AR) may be spoiled by the DC feed line, especially in the CRLH TL based case. A more separated CRLH TL integrated with active lumped elements is utilized to solve the problem. The antenna array is composed of the CRLH microstrip transmission line structure and circular polarized microstrip antenna. The direction of the main lobe varies from ?1° to ?20 ° by continuously modifying the varactor diodes bias voltages from 0 to 20 V with 5 V as a step. The AR remains below 3 dB in the scanning range. The simulation and experimental results show a good consistence.     

Highly efficient continuous-wave intracavity frequency-doubled Nd:YVO4-LBO laser at 457 nm under diode pumping into the emitting level 4F3/2

The continuous-wave high efficiency laser emission of Nd:YVO₄ at the fundamental wavelength of 914 nm and its 457 nm second harmonic obtained by intracavity frequency doubling with an LBO nonlinear crystal is investigated under pumping by diode laser at 880 nm into emitting level ⁴F_3/2. 6.5 W at 457 nm with M ²=1.8 was obtained from a 5-mm-thick 0.4 at.% Nd:YVO₄ laser medium and a 15-mm-long LBO nonlinear crystal in a Z-type cavity for 18.6 W absorbed pump power. An optical-to-optical efficiency with respect to the absorbed pump power was 0.35. Comparative results obtained for the pump with diode laser at 808 nm, into the highly-absorbing level ⁴F_5/2, are given in order to prove the advantages of the 880 nm wavelength pumping.     

35 GHz dielectric resonator stabilised gunn oscillator

A 35 GHz dielectric resonator oscillator(DRO) using GaAs Gunn diode in microstrip configuration has been designed and developed. The oscillator, with an integral waveguide-to-microstrip transition, delivered an output greater than 18 dBm. Phase noise of the oscillator is found to be better than –80 dBc/Hz at 100 KHz away from the carrier. A frequency drift of about ±25 MHz has been observed over the temperature range from –10 °C to 50 °C.     

Hot electron injector Gunn diode for advanced driver assistance systems

This paper reviews the main aspects of the design, fabrication and characterization of GaAs Gunn diodes intended to be used in advanced driver assistance systems. The corresponding Gunn diode based oscillators operate at the microwave frequency of 77 GHz and deliver an output power up to 19.2 dBm (83.2 mW). To fulfill the high demands of the automotive industry, temperature stability and a high grade of frequency purity, the Gunn diode structure includes a hot electron injector. This is based on the heteroepitaxy of a graded gap Al_xGa_1-xAs layer and an adjacent thin highly doped GaAs layer. The hot electron injector properties are investigated using dc and rf electrical measurements, including the temperature influence as well. Specific production related data of the cavity oscillators using our Gunn diodes are presented. New alternatives, such as the resonant tunneling emitter as a hot electron injector and the Gunn diode based MMIC as oscillator, are introduced. PACS 85.30.-z; 73.40.-c; 07.57.Hm; 84.30.Ng; 85.30.Fg     

Varactor Controlled Gunn Oscillator at W-Band

This paper describes the experimental circuit and measured performance of varactor tuned Gunn oscillator at W-band. The power output of 12.5 dBm has been achieved when packaged GaAs Gunn diode is used. Linear frequency excursion of 150 MHz with power variation of 1 dB has been observed when varactor was given reverse bias from 0 to 20 volts. GaAs hyperabrupt varactor is used in parallel to gunn diode at a distance of odd multiple of g/2 in waveguide channel.     

Radiation properties of microstrip patch antenna covered with an anisotropic dielectric layer and a plasma sheath

By using SO-FDTD method, radiation properties of microstrip patch antenna covered with an anisotropic dielectric layer and a plasma layer are investigated. Simulation results show that the resonant frequency of antenna covered with a plasma layer varies with different plasma parameters. It has been indicated that the frequency offset of antenna is as high as 120 MHz when plasma frequency changes from 1 GHz to 8 GHz. The effect on antenna covered with an anisotropic dielectric layer is analyzed, while altering the dielectric constant or thickness of dielectric layer. Finally, the peak gain of antenna in complex plasma environment is presented in detail.     

Thermistor controlled gunn oscillator at Ka-band

Frequency drift of Gunn oscillators is a major cause of concern in most of the Millimeter wave communication systems. This paper describes a simple and cost effective technique to arrest the frequency drift of a Ka band Gunn oscillator within 15 MHz for the operating temperature range of 0°C to 60°C as against a typical drift of about 50 to 100 MHz for free running Gunn oscillator for the same temperature range. At the ambient, the oscillator remains within ±1 MHz from switching on to stabilization. The temperature variation is sensed with a small thermistor bead placed close to the diode and a correction voltage is applied to the bias to compensate for the frequency drift. This compensation circuit also takes into account the non-linear behaviour of the thermistor and the Gunn oscillator with the temperature.     

Multiband metamaterial truncated square microstrip-based radiating structure design

We have reported multiband meandered truncated square microstrip patch antenna loaded with metamaterial in this paper. The patch is meandered at edges and truncated at corners. Metamaterials are composite materials that provide some unique characteristics, which are not available in nature. The inclusion of these structures allows simultaneous operation over several frequencies. The antenna is designed to function in multiple bands in the frequency range of 0.5–2.0 GHz. The antenna has five working frequency bands and its center frequencies are 660, 950, 1330, 1580, and 1750 MHz for design 1. We have obtained design 2 by changing the slit size and the design has five working frequency bands. Design results are obtained by a high frequency structure simulator which is used for simulating microwave passive components.     

Investigations on optically controlled millimeter wave Gunn oscillators

There is a growing interest in optically controlled millimeter wave oscillators. In this paper, we have investigated the external-circuit impedances of an optically controlled millimeter wave subharmonic Gunn diode oscillator, which is illuminated by GaAs/GaAlAs laser beam. The variation of the external-circuit impedances looking outward from the Gunn diode with respect to the optical injection plasma density are calculated based on a field analysis method. The results give some useful conclusions for optically controlled millimeter wave Gunn diode oscillator design. Experimentally an optical tuning frequency shift of 7MHz is achieved at W-band.     

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.     

一体化GPS磁窗天线的设计与实验研究

设计了一种用于减缓高超声速飞行器通信中断的、中心频率为1.575GHz、一体化GPS磁窗天线,并开展了静态验证实验。设计的磁窗天线由贴片微带天线和永磁体一体化组成,结构尺寸为100mm×100mm×75mm,并设计了防护结构。磁窗天线的贴片微带天线不会对永磁体磁场产生影响,而永磁体也不会改变贴片微带天线谐振频率;设计的磁场防护装置对天线轴向的磁场强度没有减弱,对非传播方向完全屏蔽,起到了保护作用。针对厚度为25.5mm、电子密度为6×1010~1×1011 cm-3的等离子体,设计的磁窗天线能将1.575GHz电磁波透射系数从-19~-23.5dB提高到-11~-16dB。研究结果表明:设计的一体化GPS磁窗天线能够一定程度减缓电子密度为6×1010~1×1011cm-3的等离子体对1.575GHz电磁波通信影响,且实现了磁窗天线的小型化,并提高了安全性。     

Effect of spiral left-handed material with near-zero index on rectangular microstrip antenna

In this paper, spirals are arranged periodically on the surface of the substrate, making a left-handed material (LHM) with a near-zero index of refraction. A radiation patch is etched on the surface of this substrate, making an antenna. The finite difference time domain method is used to study the effect of this LHM with a near-zero index of refraction on the microstrip. At f=13.78 GHz, the equivalent permittivity and permeability of the proposed spiral materials are both negative; at f=28.02 GHz, the equivalent permittivity and permeability are both negative and the refraction index is near zero. Compared with conventional microstrip antenna, the radiation gain of the antenna is much higher and the return loss is much lower due to the near-zero-index effect.     

An asymmetric feeding X-band active frequency-scanning leaky-wave antenna

An asymmetric feeding X-band active leaky-wave antennas is developed, to excite the first high order mode of the microstrip leaky wave antenna. One is the asymmetric feeding leaky-wave antenna which integrated with a HEMT oscillator, and the other is the frequency-tuned leaky-wave antenna which integrated with a varactortuned HEMT VCO. The microstrip leaky-wave antenna is operated in the first higher mode. To excite the first higher mode, the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the center of the microstrip leaky wave antenna. The design of these active leaky-wave antennas is discussed and the beam scanning phenomena of the antenna is presented. The HEMT oscillator frequency is controlled by tuning the varactor DC bias and the beam scanning is demonstrated. The measured scanning angle agree with prediction, it is close to 30° as the VCO frequency tuned from 8.06 GHz to 9GHz.     

A compact square loop patch antenna on high dielectric ceramic–PTFE composite material

Design and prototyping of a low profile, compact square loop microstrip line fed miniature patch antenna on 1.9 mm thick ceramic-polytetrafluoroethylene (PTFE) high dielectric composite material substrate is presented in this paper. The measured ?10 dB return loss bandwidths of the antenna are 300 MHz (0.75–1.05 GHz) and 800 MHz (2.4–3.2 GHz) with 3.4 dBi, 8.86 dBi and 7.42 dBi at 900 MHz, 2.5 GHz and 3.0 GHz, respectively. The measured symmetric and almost stable radiation pattern makes the proposed antenna suitable for RFID, GSM, ZIGBEE, WBAN, LR-WPAN etc. integrated mobile devices.