Equivalent Input Impedance Research Articles

An Analysis of Base Bias Current and Intrinsic Base Resistance Effects on InP–InGaAs, InGaP–GaAs, and SiGe Heterojunction Bipolar Transistors

An analysis of the effects of base bias current (IB) and small-signal intrinsic base resistance (Rbin) on the RF performances of various HBTs, including InP–InGaAs, InGaP–GaAs, and SiGe HBTs, are demonstrated. It was found that for these HBTs, both the real part of the equivalent input impedance [Re(Zin)] and the equivalent output impedance [Re(Zout)] increase with the increase of Rbin. Therefore, an increase of Rbin (i.e., reducing the base doping, reducing the base width, and increasing the equivalent distance between the emitter–base junction and the base contact) makes the kink phenomena of both the scattering parameters S11 and S22 of these HBTs more prominent. These phenomena can be explained by our derived analytical expressions of Zin and Zout. In addition, for relatively smaller Rbin, it was found that under constant collector–emitter voltage (VCE), an increase of IB [which corresponds to a decrease of base–emitter resistance (rπ) and an increase of trans-conductance (gm)] enhances the anomalous dip. However, for relatively larger Rbin, it was found that under constant VCE, an increase of IB obscures the anomalous dip. These phenomena can also be explained by our proposed theory.

Calculation of the wave reflecting characteristics of magnetized plasma surface

The total wave energy reflectance of the interface between the magnetized plasma before a conductor plate and the atmosphere or vacuum can be calculated by usin g the equivalent input impedance method. The result is that the reflection chara cteristics can be affected by electron numerical density, magnetized plasma thic kness, incidence wave frequency and magnetic intensity. Magnetic field can reduc e wave energy reflectance obviously only when the electron numerical density is of an appropriate value. The increased frequency of the incident wave must accom pany the augmented magnetic intensity, which is the condition that magnetized pl asma will absorb more energy of the electromagnetic wave.

Calculation and analysis on the wave reflected characteristics of plasma before the conductor plate

Regarding the nonuniform plasma plate as uniform multilayer slabs, the total wave energy reflectance of the interface between the plasma before a conductor plate and the atmosphere or vacuum can be calculated by applying the equivalent input impedance method. The result obtained is that the reflection characteristics are affected by electron number density, plasma thickness, frequency and transmitting direction of the incident wave. Changing any factor of them, the total wave energy reflectance can be reduced greatly. In the low frequency band, the d istribution of electron number density almost does not affect the reflectance. B ut in the high frequency band, it will affect the reflectance. The effect of pla sma thickness, wave frequency, electron number density distribution on it is alm ost independent of the wave polarizing direction.

Electrical properties of oilshale rocks

The characterization of electric properties of oilshale deposit is reported. The scanning electron microscopy and the results of the dielectric constants show that the deposit is a heterogeneous composite material containing some conducting and insulating microstructural units. The components of the equivalent input impedance measured at microwave frequencies (8 to 12 GHz) and the impedance at low frequencies (0.5 Hz to 30 kHz) showed frequency dependence. The real and imaginary components of the permittivity determined from the impedance data obtained at low frequencies showed an exponential decrease with frequency. The observed frequency dependence of the rock permittivity is ascribed generally to a Maxwell-Wagner type of mechanism. Also it was observed that the conductivity is almost independent of the frequency below 1 kHz and increases with frequency above this range. The values obtained for the conductivity at low frequencies indicate that the rock has an intermediate electrical conduction due to some mineralized metallic complexes and carbon content.

Microwave measurements on oilshale rocks

Characterization of some structural and electrical properties of oilshale deposit are studied in the X-band (8 to 12 GHz) through measuring the insertion loss (IL), return loss (RL), and the material equivalent input impedance, Zm. X-ray diffraction and scanning electron microscopy show that the deposit contains a number of minerals and oil pores. Measurements at microwave frequency show that the IL for the rock specimen of 5.1 mm thickness ranges between 2 and 4.5 dB; and the value of the RL for the same specimen ranges between 2 and 5.8 dB over the whole X-band. A particular surface deposit specimen of thickness 7.15 mm shows a high value of RL of about 38 dB at around 11.2 GHz, which seems almost transparent at this frequency. The overall behaviour of the measured impedance as a function of frequency shows a relatively strong dependence on the specimen thickness and weak dependence on both deposit depth and composition. Analysis of the obtained data of impedance indicates that the deposit has an inductive behaviour.

Electrical characterization of some materials in the X-band

Three classes of materials, i.e. dielectric, semiconducting and conducting materials are considered, where some of their electrical properties are measured at microwave frequencies, i.e. in the X-band (8 to 12 GHz). These include the insertion loss, return loss, shielding effectiveness and the equivalent input impedance. Comparison between these different parameters is made using a set of curves as a function of frequency. The results obtained indicate virtually no unusual behaviour. A maximum shielding efficiency of about 34 dB is found for GaAs limit and lower values are found for the silicon, flexible carbon and dielectric materials. The equivalent input impedance was found to be roughly constant over the X-band for the dielectric and conducting materials while it exhibits a high dependence on frequency for semi-conducting material oscillating between inductive and capacitive.

Some properties of nickel-coated carbon fibre-polypropylene composite at microwave frequencies

Some properties of nickel-coated carbon fibre-polypropylene composite are considered at microwave frequencies in the range 8 to 12 GHz. The paper presents the measured values of the insertion and return losses and the equivalent input impedance in the above frequency band. Measurements were performed on composite material for different nickel-coated fibre concentrations of 0, 5, 10, 16 and 28 wt%. The filler effects shows a transition region and identifies the dependency of the electrical properties on these concentrations. Furthermore, shielding effectiveness is calculated for the given concentrations and it is found that its value could reach more than 30 dB over the whole frequency band for a specimen of 2.6 mm thickness and with 28 wt% concentration.

EMP Response of Aircraft Antennas

The responses of aircraft antennas to a broad-band electromagnetic wave such as the nuclear electromagnetic pulse (EMP) are analyzed. For convenience of analysis the antennas are divided into five classes: blades, loops, slots, bowls, and long wires. From each class a few specific antennas are selected as examples for detailed discussion. For each exemplary antenna the detailed equivalent circuit, input impedance, and effective height at the antenna's connector are given. Measurements of input impedance on some antennas are compared with the corresponding calculated results.

EMP response of aircraft antennas

The responses of aircraft antennas to a broad-band electromagnetic wave such as the nuclear electromagnetic pulse (EMP) are analyzed. For convenience of analysis the antennas are divided into five classes: blades, loops, slots, bowls, and long wires. From each class a few specific antennas are selected as examples for detailed discussion. For each exemplary antenna the detailed equivalent circuit, input impedance, and effective height at the antenna's connector are given. Measurements of input impedance on some antennas are compared with the corresponding calculated results.