Stripline bandpass filters with alternating coupling coefficients

This article shows the possibility in principle to design stripline comb filters with alternating signs of the coupling coefficients. The new feature of the stepped-impedance resonators of the quarterwave type was established. They provide the opposite sings of the electromagnetic coupling with adjacent resonators. Such resonators are asymmetric relative to the vertical axes, which is drawn through their middle part. The stripline passband filters with alternating signs of coupling coefficients have attenuation poles that are located to the left and to the right of the passband. Those poles improve the selectivity of such filters. The articles provide the measured characteristics of the stripline comb filter of the forth order with alternating coupling, which has the central frequency of f ₀ = 1835 MHz and the passband width of 90 MHz. The filter is constructed using a dielectric material with relative permittivity of ε_r = 92 and has the dimensions of 7.4×4.2×2 mm.     

Mixed Coupling on Stripline and Microstrip Bandpass Filters

The problems of designing stripline and microstrip bandpass filters with mixed coupling, including the magnetic and electric components of the interaction, are considered. It is shown that the transmission zeros corresponding to mixed coupling coefficients can be shifted along the frequency axis by changing the shape of the stepped-impedance resonators. It is confirmed that N-resonator planar filters can have (N–1) transmission zeros. Designs of microstrip filters with combined coupling, which include mixed coupling and the traditionally used magnetic and electric coupling, are proposed. It is shown that the number of transmission zeros of such filters is smaller than for filters with only mixed coupling, but their designing and tuning are less labor-consuming. The data of the experiment and computer simulation are presented.     

Influence of Geometric Parameters and Permittivity of Stripline Filters on Resonator Coupling Coefficients

It has been proved that electromagnetic coupling coefficients K of resonators in stripline filters with homogeneous dielectric depend only on geometric parameters of the filter designs and are independent of relative permittivity ε_r (if the dielectric is two-layer, coefficients K depend only on geometric parameters of the filter designs and ratio ε_r2/ε_r1). It has been shown that the revealed earlier influence of permittivity ε_r and the operating frequency on K is only a consequence of the influence of the length of stripline resonators on K: the lesser is the length, the larger is coefficient K. It has been found that these propositions enable consideration of frequency characteristics of the same design of the bandpass filter in different frequency bands by changing εr and performing slight changes in outermost resonators. The results of computer simulation of the transfer of frequency characteristics of a stripline bandpass filter from 3 GHz to 6 and 12 GHz with retaining the fractional bandwidth and selectivity are presented.     

Combline filters designed on symmetric stripline

Problems arising during the design of stripline combline filters, which until quite recently were considered as all-stop microwave structures, are considered. It has been shown that the electromagnetic coupling coefficient of quarter-wave stripline resonators increases with the value of material permittivity ε_r, the operating frequency, and the thickness of the filter resonators. For ε_r = 92 and a thickness of stripline resonators of 4 mm, it exceeds 12% at frequencies higher than 2.2 GHz. Two alternative versions of combline filters have been designed: a filter with a coupling strip and a filter without a coupling strip. Experimental data for a nine-resonator combline filter with a thickness of 4 mm, ε_r = 9.7, and the center frequency f ₀ = 2.4 GHz are presented. A method for increasing the selectivity of combline filters with the same number of resonators is proposed. It has been found that amplitude–frequency responses of stripline combline filters are near-symmetric, unlike the responses of microstrip combline filters.     

Microstrip Bandpass Filter with Left Transmission Zero Controlled by Parasitic Cross Coupling

A third-order microstrip filter is proposed and studied. It is characterized by a left-handed transmission zero f_z, caused by the parasitic cross-coupling between non-adjacent resonators. The filter contains a half-wave middle resonator and two quarter-wave resonators located from different sides, near the open ends of the middle resonator. The coupling between all resonators has magnetic character, and the zero of the filter transfer function f_z is located to the left of the center frequency of the passband f₀. Such filter is described by a modified coupling matrix, where one of the main coupling coefficients is artificially assigned a minus sign. In the proposed filter design, for a given value of the main coupling coefficients, it is possible to provide different values of the cross-coupling coefficient by appropriately selecting the design parameters. This allows adjusting the zero position of the transmission f_z for a given bandwidth of the filter, thereby changing the left slope of the amplitude-frequency characteristic. A sequence of steps is proposed for constructing such a filter. The measured and simulated frequency characteristics of the experimental filter are given.     

Thin stripline bandpass filters for the centimeter band

This article considers the design of thin stripline (1 mm) bandpass filters in the centimeter band, which contain dielectrics with different relative permittivity ε _r . This includes the choice of the resonators, the dielectric material, the preliminary assessment of resonators’ unloaded quality factors and taking into account the features of the frequency response curve of the filter. It was found, that the passband width of the thin comb filters with λ/4 resonators and array-type filters with λ/2 resonators cannot exceed 6% for any values of ε _r and the length of resonators of at least 2 mm. The array-type filters with resonators of half-wave type and with alternating signs of the coupling factors between resonators were proposed. Under certain additional conditions, the attenuation poles appear in such filters, resulting in improved selectivity. The results of computer modelling of the frequency response curve of thin filters of cm band are presented. They are compared to the frequency response of other filters. The data obtained from computer modelling showed good correspondence with the experimental data.     

Symmetric stripline duplexer

The compact duplexer using the symmetric stripline and containing the fifth-order comb filters in transmit channel TX (2300–2370 MHz) and receive channel RX (2510–2580 MHz) is constructed, and the characteristics of obtained duplexer are measured. This duplexer is built using dielectric material Al₂O₃ (Alumina, polikor) with high thermal conductivity that makes it possible to use the operating power of 10Wat small dimensions 57-11.8-4 mm. The losses in bandpass of TX and RX filters did not exceed 3 dB during the filter attenuation at adjacent channel frequencies of no less than 60 dB. It is shown that the selection of the width of metallized strip at the base of quarter-wave resonators makes it possible to change the duplexer width for attaining the required value. The circuit of coupling of resonators with loads used in this design made it possible to obtain a sufficiently high level of isolation from each other for RX and TX channels of duplexer. This level does not exceed 60 dB. The finite thickness of internal conductors of stripline amounting to 16 μm is taken into account while building the duplexer that results in good agreement between the simulation and measurement results.     

Millimiter-wave stripline bandpass filters

The possibility to use thin (1 mm or less) pseudocombline structures of λ/2 resonators made of sections of symmetric transmission strip lines from a dielectric material with ε _r = 2.2 as millimeter-wave bandpass filters is shown. It is established that the relative bandwidth of such filters can reach FBW = 0.1. Designs of stripline pseudocombline filters with alternating signs of the coupling coefficients, which are characterized by improved selectivity due to the attenuation poles located on both sides of the passband, are proposed; the filters contain stepped-impedance “half-wave” resonators with a new feature. The results of the computer simulation of the frequency characteristics of the filters in the frequency band of 31–122 GHz and the comparison of them with the characteristics of other filters are presented.     

Varicap-tuned narrowband filters with extended rejection band based on U-shaped microstrip Resonators

A resonance equation for the first unwanted resonant frequency of tunable microwave U-shaped loop-type resonator with variable capacitance has been derived. This frequency does not depend on the variable capacitance value; it is invariable and proportional to λ-type oscillations. The ascertained feature makes it possible to determine the ratio of the first unwanted resonant frequency to the frequency of the main resonance and control the rejection bandwidth of tunable filters with U-shaped resonators. A narrowband (2%) varicap-tuned filter with extended rejection band has been built and its experimental data are presented. The experimental four-resonator filter could be tuned in the frequency range 225–400 MHz. The filter rejection band in terms of the attenuation level of –40 dB was located in the frequency range 420–1290 MHz, i.e., f _max /f _min = 3.07. Varicap-tuned filters with microstrip U-shaped resonators are shown to have a good potential for their practical use.     

Real-Time Determination of Absolute Frequency in Continuous-Wave Terahertz Radiation with a Photocarrier Terahertz Frequency Comb Induced by an Unstabilized Femtosecond Laser

A practical method for the absolute frequency measurement of continuous-wave terahertz (CW-THz) radiation uses a photocarrier terahertz frequency comb (PC-THz comb) because of its ability to realize real-time, precise measurement without the need for cryogenic cooling. However, the requirement for precise stabilization of the repetition frequency (f _rep) and/or use of dual femtosecond lasers hinders its practical use. In this article, based on the fact that an equal interval between PC-THz comb modes is always maintained regardless of the fluctuation in f _rep, the PC-THz comb induced by an unstabilized laser was used to determine the absolute frequency f _THz of CW-THz radiation. Using an f _rep-free-running PC-THz comb, the f _THz of the frequency-fixed or frequency-fluctuated active frequency multiplier chain CW-THz source was determined at a measurement rate of 10 Hz with a relative accuracy of 8.2?×?10^?13 and a relative precision of 8.8?×?10^?12 to a rubidium frequency standard. Furthermore, f _THz was correctly determined even when fluctuating over a range of 20 GHz. The proposed method enables the use of any commercial femtosecond laser for the absolute frequency measurement of CW-THz radiation.     

Features of the coupling coefficients of planar stepped-impedance resonators at higher resonance frequencies and application of such resonators for suppression of spurious passbands

Features of the electromagnetic coupling coefficients between stepped-impedance resonators made of the sections of symmetric strip and microstrip transmission lines at higher resonance frequencies are investigated. It is found that, in stripline resonators, these coefficients are equal to zero at some coordinates of the jump of the characteristic impedance. A new method of expansion of the stopband of bandpass filters, which is based on suppression of the first spurious bandpass and frequency diversity of the main band and the second spurious bandpass is proposed. A Chebyshev bandpass filter with a center frequency of 2.45 Hz and a spurious band at 6.06 f ₀ is manufactured and tested to demonstrate the proposed method.     

Relaxation of excited donor states in silicon with emission of intervalley phonons

The process of low-temperature relaxation of excited states of Group V donors in silicon due to coupling of electrons bound at Coulomb centers with intervalley phonons is analyzed. The rate of transitions from the 2p ₀ state to the group of 1s(E, T ₂) states with emission of the intervalley acoustic phonons LA-g and TA-f is calculated for the phosphorus, antimony, arsenic, and bismuth donors. It is shown that the TA-f phonons make a substantial contribution to nonradiative decay of the 2p ₀ state that controls the stimulated infrared emission of the phosphorus and antimony donors in silicon.     

Stripe delay filters

There are considered constructions of microsized stripe delay filters, which are realized on a basis of ceramic materials with high dielectric permittivity. Delay time of non-minimal phase filters is 7–12 ns at frequencies of 1900 MHz with relative bandwidth of 3.6–3.85%. Filters dimensions are comparable with ones used in portable communication devices. Dimensions of researched three-resonator filter at frequency of 1900 MHz are 8.4×5×2mmwith material dielectric permittivity ε_r = 92, and 5-resonator filter ones are 9.2×8.6×2 mm. Filters are different from traditional delay filters. Two filters of considered ones contain odd resonator number and the third one contains four resonators and it has two cross couplings. The basis of the filters is amount of step-impedance stripe resonators pairs located close to each others whose electromagnetic coupling behavior is capacitive. There are represented the results of frequency characteristics simulation for different delay filters.     

Limiting ratios between symbol rate and minimal carrier frequency in ultra-wideband digital information transmission systems

Limiting ratios between symbol rate and minimal carrier frequency f ₀ in ultra-wideband digital information transmission systems, when using rectangular pulse as the message symbol and transmission efficiencies of radio signal’s energy of 90 and 99% in the frequency band [0–f ₀], are obtained. It is shown that modulation of sine and cosine oscillations by a rectangular pulse, in case of small number of carrier’s periods within the message symbol, gives different efficiency results of radio signal’s energy transmission in the provided frequency band. It is stated that, when using a rectangular pulse as message symbol and a requirement to transmit 99% of the radio signal’s energy in the frequency band[0 ? f ₀], the maximal symbol rate of information transmission should be 12 times less than the carrier frequency. However, if transmission of 90% of the rectangular radio signal’s energy in the frequency band[0 ? 2 f ₀] is acceptable, the symbol rate of information transmission may exceed the minimal carrier frequency f ₀, but no more than 1.45 times.     

Effect of copper doping on kinetic phenomena in <Emphasis Type="Italic">n</Emphasis>-Bi<Subscript>2</Subscript>Te<Subscript>2.85</Subscript>Se<Subscript>0.15</Subscript>

In single crystals of copper-doped and undoped Bi₂Te_2.85Se_0.15 solid solutions with an electron concentration close to 1 × 10¹⁹ cm^?3, the temperature dependences are investigated for the Hall (R ₁₂₃, R ₃₂₁) and Seebeck (S ₁₁) kinetic coefficients, the electrical-conductivity (σ ₁₁), Nernst-Ettingshausen (Q ₁₂₃), and thermalconductivity (k ₁₁) coefficients in the temperature range of 77–400 K. The absence of noticeable anomalies in the temperature dependences of the kinetic coefficients makes it possible to use the one-band model when analyzing the experimental results. Within the framework of the one-band model, the effective mass of density of states (m _d ≈ 0.8m ₀), the energy gap (ε_g ≈ 0.2 eV), and the effective scattering parameter (r _eff ≈ 0.2) are estimated. The obtained value of the parameter r _eff is indicative of the mixed electron-scattering mechanism with the dominant scattering by acoustic phonons. Data on the thermal conductivity and the lattice resistivity obtained by subtracting the electron contribution according to the Wiedemann-Franz law are presented.     

Microwave Dielectric Properties of BiCu<Subscript>2</Subscript>PO<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

A BiCu₂PO₆ microwave dielectric ceramic was prepared using a solid-state reaction method. As the sintering temperature increased from 800°C to 880°C, the bulk density of BiCu₂PO₆ ceramic increased from 6.299 g/cm³ to 6.366 g/cm³; the optimal temperature was 860°C. The best microwave dielectric properties [permittivity (? _r ) = ～16, a quality factor (Q × f) = ～39,110 GHz and a temperature coefficient of resonant frequency (τ _f ) = ～?59 ppm/°C] were obtained in the ceramic sintered at 860°C for 2 h. Then, TiO₂ with a positive τ _f (～+400 ppm/°C) was added to compensate the τ _f value. The composite material was found to have a near-zero τ _f (+2.7 ppm/°C) and desirable microwave properties (? _r  = 19.9, Q × f = 24,885 GHz) when synthesized at a sintering temperature of 880°C. This system could potentially be used for low-temperature co-fired ceramics technology applications.     

Fully Digitally Programmable Generalized Mixed Mode Universal Filter Configuration

This paper presents five feature-enriched hardware-efficient mixed mode universal filter (UF) biquads using digitally programmable (DP) current conveyors (CC). Common features of proposed UFs include use of only two grounded capacitors, operation in all the four modes, realization of all the filter functions, independently programmable filter parameters and cascadability (last three features, however, are partially present in last UF). Besides all these features, the first proposed UF, designated as Generalized DPUF provides additional features such as reconfigurability, use of minimum input terminals, no component matching constraint and lesser parasitic effects. Although Generalized DPUF encompasses almost all the desirable features of any filter, it uses eight CCs for obtaining these. The need of eight CCs is justified by introducing remaining four programmable/non-programmable UFs. These additional UFs are designated as Derived UFs as they are obtained by the deletion of CCs of the Generalized DPUF. Proportionate reduction in features of Derived UFs with number of CCs proves the reasonability of eight CCs in Generalized DPUF. To further strengthen this fact, all the proposed UFs are compared with reported filters. Better/comparable performance of Generalized and reduced-performance Derived filters again justifies the need of eight CCs in Generalized UF.     

The detection limit of curved InGaAs/AlGaAs/GaAs hall bars

The work is devoted to the study of noise characteristics of curved Hall bars based on InGaAs/AlGaAs/GaAs semiconductor heterostructures. The noise spectral density S_N(f) was investigated experimentally and the magnetic field detection limit B_N of a flat and similar Hall bar rolled in a tube was defined. The low-frequency spectra of 1/f noise were studied and the dimensionless Hooge noise parameter α_H was determined. The ability to use the curved Hall bars in the devices for measuring weak magnetic fields (<1 μT) was predicted.     

Improvement in the accuracy of determining impurity compensation in pure weakly compensated germanium from breakdown-field strength

It is shown that measurement of the electric-breakdown field E _br in a classically high magnetic field (H) at T = 4.2 K makes it possible to determine the value of the degree of compensation K in pure germanium with K < 50% much more precisely than at H = 0. The parameter S = E _br/H is introduced and its dependence S = f(K) is calculated; the obtained curve makes it possible to determine K if H and E _br are known. To decrease the resistance of the samples, it is recommended that measurements be carried out under “impurity” illumination. It is shown that the value of E _br is invariable at low intensities of such excitation.     

A New Type of Miniature Ultra-Wideband Band-Pass Filter with Coplanar Waveguide Fed

A novel miniature ultra-wideband (UWB) bandpass filter with coplanar waveguide (CPW) fed is proposed. The size of the filter is reduced largely because of combining the wideband couple gap and parallel-coupled CPW line (not cascading multiple resonator), and the length of realized filter is only 0.42 λ _g0 (λ _g0 is the guiding wavelength at central frequency). The measured insertion loss is less than 2.0 dB, and the group delay variation is less than 0.2 ns within the UWB passband. Basic agreement between the simulated and measured results has been achieved.