A. M. Serzhantov

DUAL-MODE SPLIT MICROSTRIP RESONATOR FOR COMPACT NARROWBAND BANDPASS FILTERS

A straight split dual-mode microstrip resonator is proposed. The frequencies of the two flrst oscillation modes in the resonator may be brought closer together by adjusting a split parameter whereas the frequency of the third mode remains approximately equal to the doubled average frequency of the flrst and the second modes. It is shown that formulas derived within 1D model give qualitatively true relations between the resonant frequencies and the structure parameters of the resonator. Examples of narrowband bandpass fllters of the fourth and the sixth order are described. Transmission zeros below and above the passband substantially improve the fllters performance. The simulated frequency response of the three-resonator dual-mode fllter is compared with the measured response of the fabricated fllter.

Highly Selective Suspended Stripline Dual-Mode Filter

Miniature bandpass fllter constructions based on a novel dual-mode suspended stripline resonator are proposed. Because of a special structure of the resonator, the frequencies of two flrst oscillation modes may be brought closer together. That allows realizing narrowband fllters with the wide upper stopband. The fllters have low insertion loss in the passband at small dimensions. Several transmission zeros substantially improve the fllter performance. The derived coupling coe-cients account for some features in the frequency response of the fllter. The second-order and fourth-order fllters with transmission zeros have been fabricated and measured.

Miniature Suspended-Substrate Bandpass Filter

A new quasi-lumped suspended-substrate stripline structure admitting implementation of miniature highly selective narrowband filters is studied. Appreciable improvement of the device selectivity is achieved with supplementary strip conductors introduced between the resonators, which induce attenuation poles near both passband edges. Furthermore, these supplementary conductors reducing the coupling between the resonators allow diminishing the interresonator spacing and the total size. A four-resonator filter is synthesized using the intelligence optimization method. Experimental results of the manufactured filter are presented. Received 6 July 2010, Accepted 11 August 2010, Scheduled 16 August 2010 Corresponding author: V. V. Tyurnev (tyurnev@iph.krasn.ru).

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).

Features of the coupling coefficients of microstrip irregular quarter-wavelength resonators

In the present work on the base of modified energy approach a behavior of the frequency-dependent coupling coefficient of pair microstrip stepped-impedance quarter-wavelength resonators was investigated. It is revealed that at a certain gap between the resonators the total coefficient of coupling becomes zero due to mutual compensation of coefficients describing inductive and capacitive interactions between the resonators.

Tunable resonant microstrip phase shifter with the magneto dielectric substrate

The new design of a tunable microstrip phase shifter is proposed. It is based on the resonant microstrip structure in which a magnetodielectric is used as a substrate with controlled electromagnetic characteristics. The design of the phase shifter is characterized by a high degree of diminutiveness and high figure of merit. The manufactured breadboard of a five-resonator phase shifter demonstrated a controllable phase shift of 360° with a figure of merit of 150 °/dB.

Investigation of a liquid crystal tunable phase shifter

An electrically controlled phase shifter is investigated, 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.

A METHOD OF STOPBAND WIDENING IN BPF BASED ON TWO-CONDUCTOR SUSPENDED-SUBSTRATE RESONATORS

A method aiming to widen the upper stopband in a microwave bandpass filter based on two-conductor suspended-substrate stripline resonators is described in this letter. Applicability of the method is illustrated by simulating and fabricating fourth-order filter that has a very wide upper stopband: Δfstop/f0 = 7.92 measured at a level −50 dB, which is achieved because the widths of the inner resonators in the structure are 1.4 times greater than that of the outer ones.

High-Quality Compact Interdigital Microstrip Resonator and its Application to Bandpass Filter

A compact microstrip resonator based on the interdigital structure is proposed. The resonator has several times higher unloaded quality factor compared to similar resonators presented previously and can even reach the Q-factor of a regular λ/4 resonator. The size of the resonator can be significantly reduced with a substantial increase in quality factor by incrementing the number of fingers in the interdigital structure. In addition, for each gap between the fingers, there exist an optimal number of fingers that correspond to the maximum Q-factor. An extension of the upper stopband for a bandpass filter designed using the resonator can be achieved by the interconnection of the fingers in each of the comb structures. The simulation results are proven by fabricated resonators and a fourpole bandpass filter. For the central frequency of 2000 MHz and 16.2% fractional bandwidth, the lateral size of the filter is only 11.5mm × 3.8 mm for alumina substrate (eps = 9.8). The filter has an upper stopband up to 5.8f0 at the level −40 dB.

Miniature suspended-substrate stripline filter

A new suspended-substrate stripline structure admitting implementation of miniature highly selective narrowband filters is studied. The diminutiveness of the structure is achieved due to introducing supplementary strip conductors, which considerably reduce the coupling between the resonators. Furthermore, in this case attenuation poles arise on both sides of the passband appreciably improving the device selectivity. Experimental results of the manufactured four-resonator filter are presented.