Meander-Line and Hybrid Meander-Line Transformers

The application of meander lines to impedance transformers is described. Meander-line transformers have less bandwidth than stepped-impedance transformers for a given passband VSWR, but can have greatly superior shape factors in stripline and microwave-integrated-circuit (MIC) realizations. Hybrid meander-line transformers allow circuit designers greatly increased flexibility in choosing transformer shape factors, while allowing (basically) the same electrical performance as with either stepped-impedance or meander-line transformers. Experimental confirmations of a trial three-turn meander-line transformer and a fourth-order hybrid meander-line transformer are presented. A comprehensive design table of nearly equal-ripple meander-line transformers of from two to six turns, incorporating a wide range of bandwidths and impedance transformations has been deposited with the ASIS National Auxiliary Publications Service.     

A novel shunt hybrid active power filter based on magnetic flux compensation

In this article, the principle of a novel shunt hybrid active power filter (APF) based on magnetic flux compensation is proposed. The parallel transformer can exhibit nearly zero impedance to harmonic current whereas the zero magnetic flux condition is satisfied for harmonics, which leads harmonic current to flow into the transformer branch. Meanwhile, the transformer can exhibit continuously adjustable impedance to the fundamental current based on fundamental magnetic flux compensation, which works together with the passive power filter to compensate for reactive power. A mathematical model is established for system stability analysis and steady state estimation. The experimental results verify that the performance of the proposed APF is satisfactory in harmonic suppression as well as reactive power compensation.     

Broad-banding technique for in-phase hybrid ring equal powerdivider

A broad-banding technique for in-phase equal power divider is described. Detailed comparisons between the proposed variants of power dividers and the conventional in-phase power divider are also performed. Based on the 15-dB input and output return losses criteria, it is noted that a maximum impedance bandwidth of 44.3% for an amplitude error of ±0.9 dB and a phase error of ±1.8° can be achieved, for the first time, for divider with length more than 3λ/2 ring impedance transformer. A systematic design technique that relaxes some of the conventional constraint in in-phase hybrid ring equal power divider design, is also described     

扫频仪测圆环天线输入阻抗值的可行性研究

用扫频仪测量天线的输入阻抗时，在同轴传输线与天线间应按平衡—不平衡变换器。针对圆环天线的输入阻抗为复阻抗，提出了一种新的四分之一波长平衡一不平衡变换器，得到了实验结果，并进行了讨论。     

A novel principle of magnetic flux compensation and its application in power systems

A novel principle of magnetic flux compensation of a linear transformer is proposed. The current of the primary winding is detected and multiplied by a compensation coefficient to get a reference current, which is tracked by a voltage source inverter to produce a compensation current. This compensation current is injected inversely in phase into the secondary winding. According to the law of superposition and the transformer's voltage equations, the main magnetic flux in the transformer and the equivalent impedance of the primary winding correlate linearly with the current compensation coefficient, and this equivalent impedance varies linearly with the current compensation coefficient. This new principle can be widely applied in power systems, such as series hybrid active power filter, fault current limiter, continuously controllable reactor, arc suppression coil and power system load flow control, and many FACTS devices can be implemented in terms of the new principle. A current control scheme is analysed. The theory is validated by experimental results, and some new devices based on the principle are discussed.     

Design of an ultra compact electronically tunable microwave impedance transformer

A novel ultra compact microwave tuneable impedance transformer topology is proposed. It consists of a classical /spl pi/ CLC network where an equivalent tuneable inductance is realised with a high impedance transmission line in series with fixed inductance and a diode's varactors. The realised hybrid prototype at 900 MHz operating frequency is only 0.06/spl lambda/-long. Impedance loads from 16.5 to 280 /spl Omega/ can be matched with a return loss better than -20 dB, and the relative bandwidth equals /spl plusmn/36% for a fixed 50 /spl Omega/ load.     

On the design of unilateral dual-loop feedback low-noise amplifiers with simultaneous noise, impedance, and IIP3 match

This work describes the theory and design of a nonenergetic dual-loop feedback low-noise amplifier (LNA) that provides maximum unilateral gain and simultaneous noise and impedance matching conditions. The dual-loop feedback is implemented in the form of transformer current-feedback and inductive series feedback (emitter degeneration). The current-feedback transformer is also used to neutralize the base-collector capacitance (C/sub bc/), by combining it with a properly dimensioned shunt admittance at the collector output. The result is a single-transistor unilateral-gain amplifier with high isolation and good stability, eliminating the need for a cascode stage and thus enableing the use of a lower dc-supply voltage. For the complete LNA, simple design equations are derived for the unilateralization, noise, and impedance matching requirements. Finally, second-harmonic tuning at the source improves the linearity without compromising the simultaneous noise and impedance match. To verify the presented theory, a 900-MHz hybrid Si BJT LNA has been implemented, which achieves 1.3-dB noise figure, 15-dB gain, -55dB isolation, and +10dBm IIP3 using a conventional double poly transistor, consuming I/sub C/=2.5 mA at V/sub CE/=1.5 V.     

径向振动压电变压器的等效电路模型及特性研究

本文使用线性压电方程并结合相关的弹性理论对目前国际上刚刚出现的径向振动压电变压器进行了分析和研究,导出了该压电变压器的等效电路模型,并根据电路模型得出径向振动压电变压器的输入阻抗、输出阻抗、升压比、输出功率及效率等特性的数学表达式.文中通过实验对上述特性加以验证,实验结果与理论计算值基本一致,说明本文给出的径向振动压电变压器等效电路模型及其各种特性的数学表达式是正确的.     

T形双波段阻抗变换器设计

阻抗匹配技术在微波工程中十分重要。分析了四分之一波长阻抗变换器的T形等效电路,从而得到了双波段阻抗变换器的设计公式。利用该等效电路,将单频工作方式的四分之一波长阻抗变换器转变为双波段工作方式,以实现2个任意的频率点对任意电阻性负载实现理想的阻抗匹配。对该方法设计的阻抗变换器性能进行了仿真分析,结果显示该方法适用于工程应用。     

一种新的广义阻抗变换器模型及应用

本文在微波网络综合理论中，提出一种新的广义阻抗变换器模型，它是Ｋ，Ｊ变换器的最一般推广，可应用于带任意复杂不连续性的微波滤波器，阻抗变换器和耦合器的设计，并能解决对称和反对称网络两种情况，文中给出了设计实例。     

A broad-band quarter-wavelength impedance transformer with three reflection zeros within passband

A new impedance transformer employing a transmission line and a coupled-line section is presented in this paper. It is physically a quarter-wavelength long, but can achieve three reflection zeros within the passband. Therefore, broad bandwidths can be obtained for a wide range of impedance ratios. The location of the reflection zeros can be synthesized through the transmission line and coupled-line parameters. Design curves for the transformer synthesis have been obtained by solving the design equations directly. Using these results, a stripline impedance transformer has been implemented. This 50-110-/spl Omega/ impedance transformer achieved over 25-dB return loss from 0.6 to 1.6 GHz.     

Synthesis of Mixed Lumped and Distributed Impedance-Transforming Filters

The design of a class of impedance-transforming filters in the form of very compact and convenient mixed lumped and distributed ladder networks is presented. The synthesis utilizes the distributed prototype technique introduced in a previous paper, but here a new approximation function appropriate to the impedance transformer problem is derived. In addition to combining the properties of an impedance transformer and a low-pass filter, the new circuit represents a solution to the problem of short-line matching to an extreme impedance value without using extreme impedance values in the transformer. Broad-band designs are tabulated for a wide range of parameters. A discussion of the application of the technique in the design of mixed lumped and distributed broad-band matching networks is included. A 50-10-/spl Omega/ transformer was designed for the band 3.5-7.0 GHz, having a voltage standing-wave ratio of 1.15 and giving an attenuation >20 dB in the band 10.5-21.0 GHz. The length of this transformer is 0.875 in, and the experimental results showed excellent agreement with theory.     

Tunable Impedance Transformer Using a Transmission Line With Variable Characteristic Impedance

This paper proposes a new structure for a tunable impedance transformer. The proposed transformer consists of a quarter-wavelength transmission line with variable characteristic impedance. The operating principle of the variable characteristic impedance is based on the use of parallel combinations of multiple transmission lines and by controlling the line connection with RF switches. Multiple switches are inserted at the in/out terminals of each transmission line. Since a parallel microstrip transmission line has a unique structure that involves a partially removed ground plane under the conductor line, it is possible to realize a high characteristic impedance line with a wide linewidth.     

Impedance Transformations For The Generalized Reflection Modulator

A procedure is given for obtaining the impedance transformer which will produce a prescribed pair of phasor reflection coefficients by transformation from a given pair of impedance states terminating the transformer. The transformer may be used in a general two-state reflection modulator: as a phase shifter with phase change at constant amplitude or as an amplitude modulator with level shift at constant or variable phase. The condition governing the reflection coefficients available from a given pair of impedance states is given. Examples and limitations are discussed.     

Miniaturised broadband on-chip transformer employing PPGM on MMIC for application to low impedance transformation

Using a microstrip line employing periodically perforated ground metal (PPGM) on a GaAs monolithic microwave integrated circuit (MMIC), a highly miniaturised and broadband impedance transformer was developed for application to low impedance matching in broadband. Its size was 0.132 mm/sup 2/ on GaAs substrate, which was 2.3% of the one fabricated by a conventional microstrip line. The transformer showed good RF performance over a broadband including ultra-wideband. This is the first report of an on-chip broadband impedance transformer fabricated on MMIC.     

The behavior of the wide-band transmission-line transformer for nonoptimum line impedance

The transmission-line transformer can perfectly match at a single frequency any resistance ratio greater than or equal to four. This requires an optimum choice for the impedance and length of the line. For short lines, the transformer behavior is insensitive to small variations from optimum of the line impedance. A simple easily applied theory predicts the transformer behavior as a function of line length, the ratio of resistances to be matched, and the departure of line impedance from the optimum value.     

实际变压器适用理想化变压器模型的条件

本文从一般的电感耦合电路出发，讨论了实际变压器电压、电流变比在不同条件下随负载阻抗的变化关系，提出了将实际变压器看作理想变压器所需要满足的条件：一个实际变压器，如果满足①紧耦合，即耦合系数 ；②损耗电阻及漏抗远小于负载阻抗；③线圈感抗远大于负载阻抗，它就可以被视为理想变压器。如果只满足①和②，可以实现理想的电压变比；如果只满足①和③，可以实现理想的电流变比。     

Comments on "Transmission-Line Transformation Between Arbitrary Impedances" (Letters)

The solution given by the author of the above letter, for the characteristic impedance of the line transformer, has been given before (see H. Jasik, Antenna Engineering Handbook, McGraw-Hill, 1961, paragraph 31.3, p. 9). Jasik also gives the correct length of the transformer whereas Milligan and also apparently Day (IEEE Trans. Microwave Theory Tech., vol. MTT-23, p. 772, 1975) give the distance between load and source impedance along the impedance circle, which is not the length of the desired transformer since the transformer should produce at the source the conjugate of the source impedance if matching, which presumably means power matching is desired. Thus in the expression given by Milligan for length, X/sub 2/should be given as -X/sub 2/, which will now agree with Jasik's expression.     

A New Type of VF Repeater for Two-Wire Transmission Loops

Power loss at voice frequencies in two-wire telephone lines is presently overcome by employing electronic repeaters which produce bidirectional amplification without undue interaction between the outgoing and incoming paths. This isolation between the directional gain elements is achieved by employing balanced transformer windings or negative impedance transformations. Both methods rely heavily on complex line matching circuits to minimize the chance of instability or "singing." This paper describes a simple repeater that achieves bidirectional amplification while using conventional 1:1 line transformers. The obtainable return loss against fixed terminal impedances is only limited by the quality of these transformers. The new device reproduces the action of a hybrid transformer using very simple electronic circuitry and has a potentially wide application both in two-wire systems and in two to four wire conversions.     

A Three-Section Dual-Band Transformer for Frequency-Dependent Complex Load Impedance

In this letter, we propose a practical three-section dual-band transformer, which can terminate frequency-dependent complex load impedance at two arbitrary bands simultaneously. Analytical equations are derived to achieve the exact closed-form solutions. Numerical examples are examined to verify the validity. This three-section transformer can be utilized to match the complex load impedance with unequal values at two different frequencies, such as microwave amplifiers based on transistors, mixers, various kinds of antennas, and so forth.