characteristic impedance
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In this paper, a novel synthetization approach is proposed for filter-integrated wideband impedance transformers (ITs). The original topology consists of N cascaded coupled line sections (CLSs) with 2N characteristic impedance parameters. By analyzing these characteristic impedances, a Chebyshev response can be derived to consume N + 2 design conditions. To optimize the left N − 2 variable parameters, CLSs were newly substituted by transmission lines (TLs) to consume the remaining variable parameters and simplify the circuit topology. Therefore, there are totally 2N − N − 2 substituting possibilities. To verify the proposed approach, 25 cases are listed under the condition of N = 5, and 7 selected cases are compared and discussed in detail. Finally, a 75–50 Ω IT with 100% fractional bandwidth and 20 dB bandpass return loss (RL) is designed and fabricated. The measured results meet the circuit simulation and the EM simulation accurately.

The transmission and radiation of underground variable frequency electromagnetic waves will seriously interfere with the operation of the power cable and its surrounding environment. At present, the test methods for power cables basically require the impedance of the test system to match the characteristic impedance of the cable. The defect is that the process of designing and making the impedance matching impedance network is relatively complex and requires high manufacturing accuracy. In order to solve these problems, this paper puts forward the electromagnetic field fast detection formula and electromagnetic field shielding method of underground variable frequency power cable. The research method of this paper is the principle of shielding electromagnetic field materials and the suppression principle of shielding layer for electromagnetic coupling. The function of the two principles is to study the reflection, absorption, and multiple reflection of electromagnetic waves and to study the cut-off frequency of the nonmagnetic shielding layer. These two principles guide the experiment. In this paper, the measurement formula of the shielding performance of mismatched cables is derived through experiments. The results show that the error of the measurement formula is no more than 8 dB. Then, through the experiment of restraining the interference of magnetic materials on the electromagnetic field, it is concluded that the magnetic field shielding performance can reach 20 dB. Then, through the performance test of electromagnetic field shielding materials, the shielding efficiency of metal fiber antiradiation materials is the largest, and the average efficiency reaches 76.4 dB.

Through both backward (Pb) and forward (Pf) wave effects, a lower heart rate (HR) associates with increased central (PPc), beyond brachial pulse pressure (PP). However, the relative contribution to Pf of aortic flow (Q) versus re-reflection of Pb, has not been determined. Using central pressure, aortic velocity and diameter measurements in the outflow tract (echocardiography), we constructed central pressure waveforms that account for the relative contribution of Q versus re-reflection to Pf. We thus evaluated the mechanisms of HR-PPc relations in a community sample (n=824) and the impact of age thereon. Inverse HR-PPc ( P <0.0001), but not HR-brachial PP ( P =0.064) relations were noted. The slope of HR-PPc relation was increased in older adults ( P <0.005). HR was inversely associated with ventricular filling time, ejection duration, stroke volume, and peak Pf ( P <0.001 to P <0.0001). However, an increased Q and hence pressures generated by the product of aortic characteristic impedance and Q did not account for Pf effects. Age-dependent HR-PPc and Pf relations were both accounted for by enhanced Pb ( P <0.0001) with an increased Pf mediated by increments in wave re-reflection ( P <0.0001). The lack of impact of ejection duration on PPc was explained by an increased time to peak Pb ( P <0.0001). In conclusion, increases in PPc and Pf at a decreased HR are accounted for by an enhanced Pb rather than by a prolonged ejection or filling duration and hence flow (Q). These effects at a young-to-middle age are of little clinical significance, but at an older age, are of clinical importance.

Purpose of this work is to study modes and conditions that make it possible to excite the highest type of microwave oscillations, the frequency of which is a multiple of the frequency of the main type, in a monotron with a three-band resonator. Method of the investigation is a numerical 3D modeling, used to calculate the dimensions and electrodynamic parameters of the resonator (characteristic impedance, coupling coefficient, relative electronic conductivity); operation modes of the monotron are considered, which are characterized by excitation of oscillations in the highest type oscillations. Result. In the resonator under consideration, it is possible to achieve a multiple (equal to three) ratio between the frequency of the 25th highest type of oscillations and the frequency of the π/2-type. It was shown that in such resonator simultaneous excitation of electromagnetic field on those frequencies can be made. The maximum of an output power achieved at 100.22 GHz is 15.4 W with an accelerating voltage of 7825 V and an electronic beam microperveance 0.36 µA/V3/2 . The maximal efficiency on a third harmonic is 0.83% while the total efficiency (generating electromagnetic waves of the first and the third harmonics) is up to 17%. Conclusion. It was set that the described method of generation of terahertz range radiation is promising for further investigation, as it solves problem that orthodox microwave devices meet in the millimeter wavelength range, such as small linear dimensions of the components and critical current density of the electronic beam.

Introduction. The development of new amplifiers and generators of the Ku- and K-bands (12…27 GHz) for use in onboard equipment is increasingly attracting research interest. Low-voltage multi-beam klystrons (LMBK) can be a promising element base for such devices. Serious problems are associated with the need to suppress parasitic modes of oscillations in NMLK operating in the centimeter and millimeter range. A possible solution is to use double-gap photonic-crystal resonators (DPCR) in LMBK. Another promising direction for improving the characteristics of such resonators is to use resonant segments of strip lines with fractal elements. In this case, the strip lines are placed on a dielectric substrate in the interaction space. Such resonators exhibit new properties that are useful for klystrons (an increase in characteristic impedance, suppression of the spectrum of unwanted frequencies, a reduction in mass and dimensions).Aim. Determination of an optimal set of electrodynamic and electronic parameters of double-gap photonic-crystal resonance systems with fractal elements "Minkowski Island" when operated as part of the LMBK resonator system, excited on π- and 2π-modes of oscillation.Materials and methods. To calculate the electrodynamic parameters of resonators, the method of finite differences in the time domain was used. The well-known Wessel-Berg method was used to calculate electronic parameters, such as the Ge / G0 electronic conductivity and the coupling coefficient M.Results. The main electrodynamic parameters of the resonator – Q-factor, resonant frequency and characteristic impedance – were investigated. The electronic parameters of the resonator, the coefficient of coupling with the electron beam, and the relative electronic conductivity for π- and 2π-modes of oscillations were calculated. In this case, three variants of the resonator with zero, first and second iterations of the fractal element were investigated. The amplitude-frequency characteristics of the resonator were investigated with a change in the pitch of the photonic crystal lattice. An estimation of the inhomogeneity of the high-frequency field in the interaction spaces of the resonator was carried out. Operational conditions were determined simultaneously for two types of oscillations without self-excitation.Conclusion. The results can find application in the development of resonator systems for klystron-type devices in the centimeter and millimeter ranges.

Abstract This paper investigates the frequency response of load modulation networks for asymmetric Doherty power amplifiers (ADPA) with an output back-off power level larger than 6 dB and a power ratio of peak to main amplifier (N − 1) larger than 1. The influence of the main path impedance transformer (IT) on the Doherty impedances at main and peak path as well as on the ADPA's efficiency is analyzed. Scaling of the main IT's characteristic impedance via ξ indicates a maximum broadband matching for an input voltage Vin of ξ · Vin,max. By weighting the frequency- and ξ-dependent efficiency curves using a probability density function (PDF), an optimum is obtained for ξ = 1/N. To verify the theory, three ADPAs with different ξ-scaled ITs are designed, measured, and compared. For the design at 3.6 GHz, a gallium nitride (GaN) transistor is used. By means of the intrinsic node matching technique, matching at the current source plane is obtained. In laboratory measurements, the ADPA with ξ = 1/N achieves a power-added efficiency (PAE) of 63% at 42 dBm output power and a PDF-weighted average PAE of 38.8% within 400 MHz bandwidth for 8 dB peak-to-average power ratio. Comparison with similar state-of-the-art ADPAs in GaN technology shows highest PAE and operation power gain GP for center frequencies larger than 3.0 GHz.

Abstract Modern space communication systems often need high-power low-frequency (UHF, L-, S-, and C-band) low-pass filters (LPFs) with wide stopbands extending to Ka-band and beyond. Current design approaches frequently fail to meet these requirements completely. This paper proposes a new coaxial LPF concept and design methodology. The LPF consists of an array of cavity elements, which operate with transverse electromagnetic mode (TEM) and transverse magnetic (TM)-coupled resonances, and thus achieve a frequency response with a reflection zero at DC and transmission zeroes at targeted stopband locations. The design method is based on positioning the cavities in a quasi-periodic order, which efficiently spreads the transmission zeroes over the stopband, while keeping the characteristic impedance matched to the input/output interfaces over the passband. This design concept yields an ultra-wide, continuous and modal spurious-free stopband, while maintaining a low insertion loss, high peak power capacity, and low sensitivity to production tolerances.

Abstract A liquid-crystal (LC)-based floating electrode-free (FE-free) coplanar waveguide (CPW) phase shifter with an additional LC layer is demonstrated for the first time. An LC layer is overlain on the electrodes of the original model; this change increases the amount of electric flux that the proposed structure can confine in the tunable region, and thereby greatly increases the figure-of-merit (FoM) while maintaining the benefits of the simple coplanar structure. We simulated the variations in the phase shifter’s FoM, characteristic impedance, and driving voltage while sweeping the additional LC layer thickness up to 300 μm with each electrode condition at 28 GHz. In the case of electrode thickness variation, the FoM increased as electrode thickness increased, regardless of the presence of the additional LC layer. However, in the case of the signal electrode width variation, we obtained an opposite FoM tendency depending on the presence of the additional LC layer. This work shows the possibility of an efficient LC-based FE-free CPW phase shifter design for a given LC layer and electrode conditions.