A. A. Leksikov

Selective properties of microstrip filters designed on quarter-wave codirectional hairpin resonators

Selective properties of microstrip filters containing two to six codirectional irregular quarter-wave resonators with hairpin-shaped stripline conductors are studied. The dependence of the steepness of the slopes of the amplitude-frequency responses of such filters on the design parameters and the filter fractional bandwidth is studied in the quasi-static approximation in a wide range of operating frequencies. Possibilities for obtaining not only a symmetrical amplitude-frequency response but also a response with the maximum steepness of either the low-frequency or the high-frequency slope are demonstrated. The results of the numerical analysis of 1D models of these microstrip structures agree well with experimental data.

Miniature coaxial resonator and related bandpass filter with ultra-wide stopband

Resonator of a new type is described, which is formed by two coaxial conductors applied onto the internal and external surfaces of a ceramic tube arranged in a metal case. An equation for the resonant frequencies is derived. In comparison to a standard coaxial quarter-wave resonator, the proposed device has a shorter length and manifold increased ratio of frequencies of the second resonance to the first resonance. The new resonator can be used for the creation of bandpass filters with ultra-wide stopband. The frequency response of a working prototype four-resonator filter is presented, in which the stopband at a −90 dB level extends up to a frequency that is 47 times greater than the central frequency of the passband.

Bandpass filter with an ultra-wide stopband designed on miniaturized coaxial resonators

Characteristics of a new miniaturized coaxial resonator are theoretically investigated. It is shown that the first resonant frequency of the resonator can be significantly lowered relative to the second one and the resonator dimensions can be considerably decreased as compared to those of a traditional dielectric-filled quarter-wavelength coaxial resonator. Based on the investigated resonator, a fourth-order bandpass filter has been designed and fabricated. The filter stopband at a level of no worse than −90 dB extends to the frequency that exceeds the passband center frequency by a factor of 47. Calculated frequency responses are in good agreement with those measured on the fabricated filter prototypes.

Magnetically Tunable Resonant Phase Shifters for UHF Band

This paper presents a new type of magnetically tunable phase shifter. The shifter has the structure of microstrip bandpass filter on a substrate containing magnetic material whose magnetic permeability is controlled by magnetic field due to ferromagnetic resonance. The phase shifters operation is based on the fact that phase shift in a bandpass filter changes with tuning of its central frequency. Two types of devices were designed and fabricated for the UHF band. One of them has a five-layer NiFe film as an active medium and demonstrates a figure of merit of 40°/dB achieved already at 20 Oe of the controlling magnetic field in 10% of the relative operational bandwidth. The second device with YIG ferrite as an active medium gave 360° tunable phase shift in 5% operational bandwidth that corresponds to the figure of merit of 150°/dB (3.1°/dB·Oe).

Nonlinear Behavior of Plasma Antenna Vibrator

This paper presents the results of investigation of nonlinear properties for plasma antenna vibrator with a length of 330 mm and a diameter of 12.7 mm based on commercial luminescent lamp filled with argon gas. The investigation was carried out in the frequency range of 10 MHz-3 GHz. The vibrator was found to have a half-wave resonance at a frequency of about 280 MHz, that is, 1.6 times lower than that for half-wave resonance for a metal rod antenna of the same length. It is shown that inside the vibrator, a generation of second and third harmonics exists, whose power goes up as a second and third order of incoming power on the carrier frequency. For an incoming signal with level of +30 dBm, it was found that the second harmonic is -34.7 dBc, and the third is -45 dBc. The existence of higher harmonics as a feature of plasma medium can be a limitation for transmitter power when such a type of vibrator will be used as a transmitting antenna. In addition, the applied technique in the investigation, when the vibrator is connected with weak coupling in the measuring circuit, can be employed for the study of nonlinear properties for the plasma medium.

Miniature bandpass microwave filter with interference suppression by more than 100 dB in a wide rejection band

A new planar resonator design in which a single conductor is replaced by three parallel stripe conductors located one above the other on a suspended two-layer substrate is proposed. It is shown that the resonator longitudinal sizes can be significantly reduced and, at the same time, the resonator intrinsic Q factor and frequencies of higher oscillation modes can be increased. A fourth-order bandpass filter with a central frequency of the transmission band (relative width 5%) of 1 GHz has been developed and fabricated. This filter has a −100-dB rejection band up to frequencies exceeding 10 GHz. The filter is enclosed in a metallic case with an internal size of 38 × 12 × 7.5 mm. It is shown that a similar filter fabricated in accordance with low-temperature cofired ceramic (LTCC) technology has a −40-dB rejection band up to 30 GHz, with sizes reduced to 5.0 × 4.25 × 1.24 mm.

Analysis of the coupling coefficients of stripline resonators in the designs of suspended-substrate filters

Expressions for the frequency-dependent coupling coefficients of stripline resonators in miniature designs of suspended-substrate filters are obtained. The effect of the design parameters of such filters on the coupling coefficients of their resonators is theoretically studied and frequency-selective properties of the device are analyzed. It is shown that interaction between resonators at frequencies of the filter passband is predominantly inductive in the presence of small capacitive interaction and the attenuation poles of the amplitude-frequency response (AFR) observed beyond the passband are caused by the mutual cancellation of inductive and capacitive interactions. Frequency dependences of coupling coefficients can be used to explain features of the AFRs of suspended-substrate filters. It is shown that experimental AFRs agree well with theoretical AFRs calculated in quasi-static approximation with the use of 1D models.

A new design of a miniature microstrip resonator with interdigital structure

A microstrip resonator with a new design based on an interdigital structure has been studied, which is distinguished by its high degree of miniaturization. It is shown that the resonator length can be considerably decreased at a significant increase in the figure of merit (Q factor), provided that the number of microstrip conductors in the interdigital structure is increased without changing gaps between them. A prototype of the resonator manufactured on a ceramic substrate with dielectric permittivity ɛ = 80 has a resonance frequency of 817 MHz and Q = 100 for microstrip structure contour dimensions of 1 × 5.5 mm. It is shown theoretically and confirmed experimentally that the Q factor of the proposed resonator is higher than those of well-known microstrip analogs under otherwise equal conditions.

Frequency-selective properties of a microstrip filter with irregular dual-mode resonators

Frequency-selective properties of a microstrip filter containing dual-mode hairpin resonators with a stepwise change in the width of the stripline conductor whose one end is connected to the screen are studied. Dependences of the design parameters and the steepness of the slopes of the amplitude-frequency response of a two-resonator filter on the filter fractional bandwidth and the substrate permittivity are considered. A large domain of the anomalous behavior of the gaps between the resonator conductors, in which the gap increases with the width of the filter passband, is revealed. The domain of values of the fractional bandwidth and the frequency band in which the design parameters of the device are realizable are determined. Good agreement between the results of the quasi-static calculation and experimental results is demonstrated.

Controllable liquid-crystal microwave phase shifter

An electrically controlled phase shifter is described, which is based on a resonant microstrip structure with a nematic liquid crystal substrate. It is shown that the proposed device can operate in the centimeter and millimeter wavelength range.