A compact wide band filter based on the left handed material theory

A novel micro CRLH (composite right/left-handed) wide band filter based on Left handed material (LHM) theory was designed and fabricated. As a promising design, the length of the main part is only 1/20 compared to the working wavelength. It can be used to eliminate the noise in RF interconnect and other area. The phase shift in LHM is negative. This characteristic can decrease the phase delay. And also, the absolute value of phase constant will increase when frequency decrease at the left handed band (LH-band), which contribute to minimize the design. The other advantage of the LHM is that the phase constant will changed to the opposite direction, when the wavelength changed with the working frequency. This provides a negative feedback to the electric length, so the left handed region has a wider band width. Measurements results show that relative bandwidth (3 dB) of 8 cells is 71.42%. The relative bandwidth (3 dB) of 4 cells is 58.46%.     

The DIGILATOR, a New Broadband Microwave Frequency Translator

Frequency translation of an RF wave can be accomplished by subjecting it to a constant rate of phase shift or by applying an ideal repetitive sawtooth phase function which snaps to zero at 360 degrees (serrodyne modulation). The DIGILATOR is a new type of frequeucy translator which employs a multibit latching ferrite phase shifter with a suitable digital switching driver to obtain a multiple-step approximation to the serrodyne phase function. This paper reviews the theory of an N-step DIGILATOR and describes the design of a 16-step, X-band device. Experiments showed that performance is independent of microwave frequency over the design frequency band of the phase shifter. The carrier and close-in sidebands were suppressed by 39 dB and predicted far-out sidebands were within 1 dB of theoretical amplitudes.     

Unity-gain frequency-independent precision phase-shifter

The letter describes an operational amplifier circuit which gives a constant (±0.1°) phase shift and a constant (±0.1%) unity gain to a sinusoidal signal, over a frequency band of range ±2%. The circuit incorporates two standard phase-shifters with different characteristics, deployed so that their phase errors mutually cancel as the frequency deviates from its central value. The device has been used as a phase-shifter in a precise negative phase sequence current measurement circuit in a power system.     

常模盲均衡算法：消除常相位偏移和多普勒频移引起的相位模糊

多滞后高阶瞬时量(Multi-Lag High-order Instantaneous Moment,ML-HIM)作为一种纠正相位模糊的编码方法,不仅能消除传输中的常相位偏移,还能消除多普勒频移的影响.虽然差分编码可消除常相位偏移,却无法纠正多普勒频移,而多普勒频移无法在盲常模(Constant Modulus,CM)均衡中消除.为此,该文将ML-HIM方法应用于常模盲均衡算法中能够很好纠正信道产生的相位模糊问题.实验结果表明,修改后的常模算法较之迄今为止文献中其他消除相位模糊的算法效果更理想,ML-HIM方法完全适用于盲均衡算法.     

太赫兹液晶反射阵列移相单元的设计与分析

为了满足高增益天线大的移相度和可工作在太赫兹频段,设计了一种基于液晶的双偶极子反射移相单元结构。采用液晶的等效介电常数模型,在频率为335~345 GHz频段均产生360o以上的相移,在342 GHz实现最大相移390o。为了减小液晶不均匀性对相移产生的影响,建立了单元的精确模型,该模型在频率范围为330~338 GHz时均产生了250o以上的相移,在336 GHz实现最大相移285o。与均匀液晶等效介电常数模型相比,产生最大相移的频率点发生了变化,并且产生了最大为105o的移相差值,这在相控反射阵列天线的设计中是不可忽略的。     

A 500 kW X-Band Air-Cooled Ferrite Latching Switch

The design of a high-power air-cooled microwave SPDT switch which is capable of operation at peak and average power levels of 500 kW and 666 watts, respectively, is described. The unit is of a differential phase shift circulator design employing 90/spl deg/ nonreciprocal phase shift elements which are forced air cooled. The phase shifter design employs dual ferrite toroids, "floating" in reduced height RG-51 waveguide. Two approaches are compared for heat sinking the phase shifter; namely the "H-beam" and the "I-beam" configurations. The results obtained indicate that the I-beam configuration is superior to the "H-beam" configuration. The switch exhibits an insertion loss of 0.6 dB maximum and isolation greater than 20 dB over a 100 MHz bandwidth centered at 9.375 GHz. The input VSWR of the switch over the frequency band is less than 1.28:1.     

基于相移光纤光栅的单光源毫米波生成研究

利用相移光纤光栅中不同的相移量可以在光栅传输阻带中的不同位置打开透射窗口这一特性,给出了用光外差法将单一光源形成两个差频再经拍频后生成毫米波的方案.理论分析和数值计算结果表明,采用单个光源产生毫米波所引入的激光随机相位噪声低于双光源系统,能够产生波长稳定、相位噪声低、频率调整方便、耦合效果好的毫米波,可为光纤无线通信系统实际应用提供参考.     

Frequency invariant interferometry

The authors discuss frequency-independent phase comparison interferometry as a method of direction finding. Theoretical relationships are derived that show the electrical phase between two elements of an array can remain approximately constant over frequency. The theory is developed for log-periodic dipole arrays. Design and fabrication of a two-element interferometer using log-periodic antennas are discussed. Experimental results are presented which show that this array remains frequency independent over a three-octave bandwidth     

Parametric four-photon mixing followed by stimulated Ramanscattering with optical pulses in birefringent optical fibers

An analysis into the phase matching condition of four-photon mixing in birefringent optical fibers is presented. The analysis yields six independent parametric processes. Some of the associated frequency shifts show a dependence on the fiber birefringence, allowing the authors to obtain constraints under which the parametric Stokes pulse will fall within the Raman gain band to undergo subsequent Raman amplifications. Both polarizations of the pump contribute to the Stokes gain through the stimulated Raman effect. Emphasis is placed on short optical pulses with tradeoffs among frequency shift, pulse walk-off length, and fiber attenuation to yield maximum power conversion to the Stokes frequency. Numerical simulation with a highly birefringent germania-doped silica fiber is used to illustrate the conditions for maximum gain of the Stokes signal     

Broad-Band Active Phase Shifter Using Dual-Gate MESFET

This paper describes a broad-band, dual-gate MESFET phase shifter (vector generator), operating over the 4- 8-GHz frequency band and capable of a continuous phase shift and multiplicity of modulations including digital phase shift and amplitude modulation directly, and indirectly (with additional information processing circuits), single sideband modulation, frequency modulation, and phase modulation, etc. A dual-gate FET is used as a variable gain amplifier and phase shift is obtained by complex addition of two orthogonal variable vectors. The principle of the phase shifter and the experimental results are presented.     

On the correlation between wide-band arrays and array simulators

A ninety-six element scanning array, which operates over an octave bandwidth, has been built and tested. The array beam is steered with digital latching ferrite phase shifters, which have low insertion loss and essentially constant phase shift over considerably more than an octave. A reasonable match has been achieved through the use of dielectric transformers at both the input and radiating apertures. The array performs properly over nearly an octave bandwidth for scan angles up to 60°, but at the upper end of the frequency band, the thick dielectric transformers caused a surface wave-type phenomenon and a subsequent loss of the main beam. An examination of the occurrence of `lost beams' at scan angles of 60° showed that these effects could be predicted from simulator measurements performed at higher frequencies and smaller scan angles     

The relationship between optical guiding and the relative phase infree-electron lasers

The relative phase in this case is defined as the shift in the wavenumber from the vacuum value integrated over the interaction length. The relative phase is studied from the standpoint of the linear stability analysis in both the high- and low-gain regimes, and the qualitative implications in each of these regimes of the relative phase on the refractive guiding of the signal are identical. Specifically, the relative phase is found to be negative at the low-frequency end of the gain band. The relative phase increases with increasing frequency over this band until it turns positive at a frequency approximately 10% below the frequency of peak gain. Thus optical guiding is indicated over a large portion, but not all, of the gain band. The specific example of interest involves the low-gain regime prior to saturation. In this case, it is shown that the analytic result is in substantial agreement with the calculation of the relative phase     

A Dual-Mode Latching Reciprocal Ferrite Phase Shifter

A ferrite phase shifter has been developed to provide latching reciprocal phase shift over a moderate frequency band. The principle of operation is based on the use of dual-mode circularly polarized waves in the active ferrite with nonreciprocal polarizers to select modes that provide reciprocal transmission phase. The physical structure of the phase shifter consists of a metallized assembly of ferrite and ceramic dielectric. A ferrite yoke is fitted over a portion of this assembly to permit latching operation. The completed phase shifter has a very simple geometry that can be produced at low cost and has relatively low insertion loss. The maximum cross-sectional dimensions are small and are consequently compatible with application in two-dimensional electronically scanned arrays. Experimental results are presented for an X-band design having a 10-percent bandwidth centered near 9 GHz.     

Investigation into the Effect of Dielectric Loss on RF Characteristics of Helical SWS

A general theory has been developed to account for the effect of the dielectric loss of discrete rods on the performance characteristics of an actual helical slow wave structure (SWS). The effect of the lossy dielectric rods has been studied on various propagation parameters, namely, phase propagation constant, interaction impedance and attenuation constant at different operating frequency. It is clearly shown that the influence of dielectric loss on RF characteristics is much larger at the millimeter frequency band than that at the microwave frequency band, especially on interaction impedance and attenuation constant. The general theory developed here has been further confirmed by comparing the results with those obtained elsewhere for some special cases.     

Asymmetric Coupled-Transmission-Line Magic-T

A Magic-T was designed using a 3-db asymmetric coupled-transmission-line directional coupler and a schiffman phase shift network. Expressions for the coupling and phase difference of the outputs of the basic coupler were obtained. Two phase shift networks for compensating the phase variation in the coupled outputs were investigated. The Schiffman phase shift network was shown to provide the best compensation over a given bandwidth. One unit designed in strip transmission line to operate from 2 to 4 Gc showed good agreement with the theory. The maximum difference in output power was 0.4 db, and the phase deviation was less than 4/spl deg/. The isolation between the input ports was greater than 25 db, while the isolation between output ports was greater than 21db throughout the entire band. Levy's design equations for a two-section asymmetric coupler with optimum coupling distribution are given for completeness.     

A limiting amplifier with low phase deviation using an AlGaAs/GaAsHBT

The design and performance of an AlGaAs/GaAs HBT limiting amplifier are presented. It is revealed that the main cause of phase shift deviation in a limiting amplifier is the bias dependence of the input capacitance, which is the dominant nonlinear factor in a transistor. A circuit design featuring a differential configuration with an emitter peaking technique lowers phase deviation and widens the frequency band. The device achieves high-frequency operation of 15 GHz with a low phase shift deviation of 3° over a 15-dB input dynamic range     

The phase shift of the light output in sinusoidally modulated semiconductor lasers

The dependence of the phase shift of the light output from sinusoidally modulated semiconductor lasers was investigated as a function of the modulation current. This measurement is effective in accurately determining the short damping time constant associated with the relaxation oscillation. The frequency half width of this phase shiftDelta fwas found to be inversely proportional to the damping time constant. For narrow stripe lasers, the phase shift occurs more gradually, which corresponds to the fact that the narrow stripe lasers have shorter damping time constants. To analyze the narrow stripe effect, the recently developed time-dependent self-consistent theory was applied, considering the transverse distribution of both optical field and carrier density and including the carrier diffusion term. This theory can explain the shorter damping time constant for narrow stripe lasers compared with broader stripe lasers.     

A Method of Producing Broad-Band Circular Polarization Employing an Anisotropic Dielectric

A procedure is described whereby it is possible to design circular polarizers for both waveguides and in window form to be used over a broad band of frequencies. The difference in phase constants for two mutually orthogonal E fields while propagating in an anisotropic dielectric is combined with the effect due to guide wall spacing to obtain a reasonably constant differential phase constant for the two fields over a broad frequency band. By properly choosing the length of the anisotropic dielectric in the direction of propagation, and orienting this dielectric properly with respect to an incident linearily-polarized wave, the transmitted wave is circularly polarized over a correspondingly broad band of frequencies.     

A 360/spl deg/ Reflection-Type Diode Phase Modulator (Correspondence)

A 360/spl deg/ phase modulator using two series-tuned varactors in a parallel connection is described. The design minimizes the change in total phase shfit with frequency and gives a small attenuation ripple. The modulator is centered at 2 GHz and gives a total phase shift at 360/spl deg/ at the center frequency, an attenuation ripple of 1.3 dB over a 10-percent bandwidth and a 7/spl deg/ decrease of phase shift at the band edges.     

Phase Shift by Periodic Loading of Waveguide and Its Application to Broad-Band Circular Polarization

A rectangular or square waveguide may be loaded periodically by thin capacitive or inductive irises in order to produce phase delay or phase advance, respectively. The amount of phase shift may be calculated with accuracy by making use of available theoretical values of iris susceptance and of transmission line theory. The phase shifting sections maybe designed for low voltage standing-wave ratio (vswr) over a considerable bandwidth. When a square waveguide capable of supporting two fundamental modes is loaded periodically, the irises act inductively for one mode and capacitively for the other, thus introducing a differential phase shift. This differential phase shift may be made equal to 90°, in order to convert linear to circular polarization. Furthermore such a device may be made, by proper choice of parameters, to yield near-circular polarization over a bandwidth of 1.65:1, because the variation in phase delay for one mode and phase advance for the other tend to compensate each other as the frequency is varied. Several of these circular polarizers have been built and tested at X band and the measured results of ellipticity and vswr, as well as broad-band performance check with theoretical values quite closely.