RF HBT oscillators with low-phase noise and high-power performance utilizing a (/spl lambda//4/spl plusmn//spl delta/) open-stubs resonator

This paper presents a new type of transmission-line resonator and its application to RF (microwave and millimeter-wave) heterojunction bipolar transistor (HBT) oscillators. The resonator is a parallel combination of two open stubs having length of /spl lambda//4/spl plusmn//spl delta/(/spl delta//spl Lt//spl lambda/), where /spl lambda/ is a wavelength at a resonant frequency. The most important feature of this resonator is that the coupling coefficient (/spl beta//sub C/) can be controlled by changing /spl delta/ while maintaining unloaded Q-factor (Q/sub u/) constant. Choosing a small value of /spl delta/ allows us to reduce /spl beta//sub C/ or equivalently to increase loaded Q-factor (Q/sub L/). Since coupling elements such as capacitors or electromagnetic gaps are not needed, /spl beta//sub C/ and Q/sub L/ can be precisely controlled based on mature lithography technology. This feature of the resonator proves useful in reducing phase noise and also in enhancing output power of microwave oscillators. The proposed resonator is applied to 18-GHz and 38-GHz HBT oscillators, leading to the phase noise of -96-dBc/Hz at 100-kHz offset with 10.3-dBm output power (18-GHz oscillator) and -104-dBc/Hz at 1-MHz offset with 11.9 dBm (38-GHz oscillator). These performances are comparable to or better than state-of-the-art values for GaAs- or InP-based planar-circuit fundamental-frequency oscillators at the same frequency bands.     

Unloaded Q of Single Crystal Yttrium-Iron-Garnet Resonator as a Function of Frequency (Correspondence)

The practical feasibility of constructing magnetically tunable broad-tuning range microwave filters using single crystal yttriumiron-garnet resonators was demonstrated in a recent paper. Experimental results were presented on one- and two- resonator filters which can be tuned by varying a dc magnetic field bias over a full waveguide bandwidth and greater, at the same time maintaining an insertion loss performance which is comparable to mechanically-tuned cavity filters. The crucial parameter of the resonant elements in a band-pass filter is the unloaded Q, Q/sub u/. With a spherical single crystal of yttrium-iron-garnet the Q/sub u/ decreases with frequency below X-band frequencies reaching very low values at frequencies around 2000 Mc.     

Exploratory Study of a Millimeter Resonance Isolator for the Circular Electric Waveguide Mode

A feasibility study was made on a TE/sub 01/ mode circular waveguide resonance isolator at frequencies near 35 Gc. A design was developed which utilized circumferentially oriented and magnetized thin rings of hexagonal ferrite material in contact with the inner or outer surface of a ring of alumina ceramic mounted concentrically in the waveguide. Approximate experimental measurements indicated that appreciable nonreciprocal attenuation could be obtained without severe degradation of the mode purity. Expressions are given for the field distributions in the dielectric ring loaded wave guide and for the ellipticity of the magnetic fields at the surfaces of the ring. Magnetic field ellipticity is computed as a function of a "slow-wave mode" cutoff constant for an experimental ring configuration. For sufficiently large values of this constant, the magnetic fields at the boundary are almost circularly polarized and are relatively independent of mean ring radius. The analytical results tend to support the experimental findings.     

Some Effects of Field Perturbation Upon Cavity-Resonance and Dispersion Measurements on MIC Dielectrics

An analysis is presented of field perturbations in MIC resonators in order to examine the errors which occur in permittivity measurements made by cavity-resonance methods: Q factor, coupling effects, fringing fields, crystal misalignment (for anisotropic materials), changes in ambient temperature are all considered. Analysis of a cavity with mixed boundary conditions shows that the resonant-mode frequencies depend to the first order on that part of Q/sub 0/ associated with imperfect electric (metal) walls, but to the second order on that part associated with imperfect magnetic (open-circuit) walls. A new expression is given for the Q of an open-ended microstrip resonator when surface waves are excited in the dielectric, and it is shown that the unloaded Q (Q/sub 0/) can be dominated by this phenomenon. It is further shown that these Q-related effects, together with reactive perturbations arising from fringing, coupling structures, are the principal source of error in measurements for epsilon or epsilon/sub eff/. Such reactive effects may be treated semiquantitatively by applying Slater's perturbation theorem to the affected region. These procedures lead to the following revised values for the crystal permittivity of sapphire (monocrystalline Al/sub 2/0/sub 3/) in the microwave region: epsilon/sub ||/ (parallel to the c axis) = 11.6; epsilon/sub /spl perp// (base-plane) = 9.4.     

A Nonreciprocal Circular Polarizer

A nonreciprocal circular polarizer has been developed. This ferrite device converts linear polarization propagating in rectangular waveguide into circular polarization propagating in circular waveguide. The sense, right- or left-hand, of the circular polarization is determined by the direction of a longitudinal magnetic field applied to the ferrite. If one sense of circular polarization, e.g., right-hand, is transmitted, then only left-hand circuIar polarization can be received. Performance data indicate good ellipticity with reasonable loss and VSWR for two models of the circular polarizer, and for two devices--a circulator and a nonreciprocal antenna element--based on the polarizer. The antenna element permits one antenna to be used both to transmit and to receive the reflected circularly polarized signals from a target.     

A hybrid ferrimagnetic-dielectric microwave filter

This paper describes a low-loss tunable dielectric resonator band bandpass filter for the frequency range 1 to 12 GHz. The filters are mechanically and/or magnetically tuned. Mode splitting, due to coupling between dimensional dielectric resonances with ferrimagnetic modes, and heat sinking techniques significantly improve the power-handling capabilities.     

A Study on Circular Disk Resonators on a Ferrite Substrate

In this paper, an exact analysis of a circular disk resonator on a magnetized ferrite substrate which can be used for tunable filters and circular polarizing radiators is presented. The method makes use of Galerkin's method applied in the Hankel transform domain and is quite suitable for numerical calculation. The calculated values of the resonant frequencies and unloaded Q's are shown to be in good agreement with the measured data and the validity of the present theory is confirmed. Furthermore, the characteristics of the traveling wave filters are investigated theoretically and experimentally, and their advantages over the standing wave filters are demonstrated in terms of reflection and sensitivity of the Q/sub L/ on the coupling strength.     

Modeling ferrimagnetic resonators

The impedance matrix for an arbitrary n-port ferrimagnetic resonator is derived by applying Poynting's theorem to a region of space surrounding the resonator. Simplifications to the impedance matrix for low-loss (Q>≈100) ferrite material make it possible to obtain an equivalent circuit model for the resonator, which can be used with most computer-based circuit simulation programs. The circuit model for the general-case polymodal ferrimagnetic resonator consists of a network of single-pole resonators, each of which has a possible non-frequency-dependent, nonreciprocal phase shift. The components of the circuit model are described in terms of the properties of the ferrite material, and the coupling strength of the microwave circuit to the magnetostatic modes of the ferrimagnet. The method is demonstrated in three simple examples, including a one- and two-port loop coupled filter, and a ferrimagnet in a waveguide     

YIG-tuned Gunn effect oscillator

A mechanical cavity of coaxial or waveguide type is generally used as a resonator of a Gunn oscillator. Reported here is the use of a resonator consisting of a ferrimagnetic sample instead of the mechanical cavity to obtain the electrically tunable Gun oscillator. The coupling between the Gunn diode and the the ferrimagnetic resonator was experimentally observed and oscillation frequency from 3.2 GHz to 2.4 GHz was obtained proportionally to the applied dc magnetic field.     

Broadband quasi-Chebyshev bandpass filters with multimode stepped-impedance resonators (SIRs)

Planar broadband bandpass filters of order up to 9 are synthesized based on the multimode property of stepped-impedance resonators (SIRs). Based on the transmission line theory, the modal frequencies of the SIRs are calculated based on the impedance and length ratios of its hi- and low-Z segments. In the synthesis, the SIR coupling schemes are determined by the split mode graphs. Using one, two, two, three, and three dual- or triple-mode SIRs, quasi-Chebyshev filters with four, six, six, eight, and nine transmission poles, respectively, are synthesized with a fractional bandwidth (BW) /spl Delta/=50%. Emphasis is placed not only on designing the I/O coupling structures for matching the external Q (Q/sub ext/) and the circuit BW, but also on matching the resonant peaks of the circuit with the nominal Chebyshev poles. Measured results of experimental circuits show good agreement with simulated responses.     

On-chip solenoid inductors with high quality factor for high frequency magnetic integrated circuits

On-chip solenoid inductors for high frequency magnetic integrated circuits are proposed. The eddy current loss was reduced by dividing the inductor into three consecutive inductors connected in series. The inductor has an inductance of 1.1nH and the maximum quality factor (Q/sub max/) of 50.5. The self-resonant frequency and the operating frequency at Q/sub max/ are greater than 17.5GHz and 16.7GHz, respectively.     

Precise Design of a Bandpass Filter Using High-Q Dielectric Ring Resonators

A precise design is presented for a bandpass filter constructed by placing TE/sub 01delta/ dielectric ring resonators coaxially in a TE/sub 01/ cutoff circular waveguide. On the basis of a rigorous analysis by the mode- matching technique, the interresonator coupling coefficients are determined accurately from the calculation of two resonant frequencies f/sub sh/ and f/sub op/ when the structurally symmetric plane is short- and open-circuited. For the TE/sub 01delta/ ring resonator,the resonant frequency f/sub 0/, the temperature coefficient tau/sub f/, the unloaded Q(Q/sub u/), and the other resonances are also calculated accurately in a similar way. From the calculations, the optimum dimensions are determined to obtain the maximum Q/sub u/, as F/sub r/ = f/sub r/ /f/sub 0/ is kept constant, where f/sub r/ is the next higher resonant frequency the ring resonator using low-loss ceramics (epsilon/sub r/ = 24.3, tan delta = 5 x 10/sup -5/) has Q/sub u/ = 16800 at 12 GHz and tau/sub f/ = 0.1+-0.5 ppm/° C, while the rod one has Q/sub u/ = 14700. A four-stage Chebyshev filter having ripple of 0.04 dB and equiripple bandwidth of 27.3 MHz at f/sub 0/ =11.958 GHz is fabricated using these resonator; the measured frequency responses agree well with theory. The insertion loss is 0.9 dB, which corresponds to Q/sub u/ = 9800.     

A miniature 2.1-GHz low loss microstrip filter with independent electric and magnetic coupling

A miniature planar two-pole microstrip filter with independent electric and magnetic coupling has been developed at 2.1 GHz. The independent coupling allows separate control of two transmission zeroes and result in a sharp filter skirt. The two-pole filter occupies an area of 6.6/spl times/4.6 mm/sup 2/ (30 mm/sup 2/) on an /spl epsi//sub r/=10.2 substrate, and shows a 5% bandwidth (100 MHz) and an insertion loss of 1.4 dB. The filter unloaded Q is 150 at 2.1 GHz which is much better than compatible filters done in LTCC technology.     

A field theoretic foundation for the representation of quality factor in terms of reactance-slope parameters for electrically large three-dimensional arbitrarily shaped resonators

The use of reactance-slope parameters for the design of RF and microwave filters was drawn from lumped-element circuit representations. This paper provides a field-theoretic foundation for reactance-slope parameters based upon the treatment of arbitrarily shaped electrically large resonators comprised of electric and magnetic conducting enclosures. Traditional representations for these parameters in terms of the reactance for series-connected network elements and susceptance for parallel-connected network elements are related to electromagnetic fields. The resulting generalized expressions for reactance-slope parameters with utility for evaluating quality (Q) factor are developed for both electric and magnetic conducting resonators using strictly surface electromagnetic fields and sources. The generalized expressions are used to evaluate the unloaded Q for TE/sub 101/-mode rectangular resonators comprised of silver, copper, aluminum, and brass based upon two different standard rectangular waveguides with enclosed ends. Q results are also presented for TM/sub 011/-mode circular cylindrical resonators comprised of the same conducting materials. Results from the method here are compared to well-established results published in the literature. These expressions are useful for either analytically or numerically evaluating the reactance-slope parameter and Q factor.     

Metal-insulator-metal RF bypass capacitor using niobium oxide (Nb/sub 2/O/sub 5/) with HfO/sub 2//Al/sub 2/O/sub 3/ barriers

A high capacitance density (C/sub density/) metal-insulator-metal (MIM) capacitor with niobium pentoxide (Nb/sub 2/O/sub 5/) whose k value is higher than 40, is developed for integrated RF bypass or decoupling capacitor application. Nb/sub 2/O/sub 5/ MIM with HfO/sub 2//Al/sub 2/O/sub 3/ barriers delivers a high C/sub density/ of >17 fF//spl mu/m/sup 2/ with excellent RF properties, while maintaining comparable leakage current and reliability properties with other high-k dielectrics. The capacitance from the dielectric is shown to be stable up to 20 GHz, and resonant frequency of 4.2 GHz and Q of 50 (at 1 GHz) is demonstrated when the capacitor is integrated using Cu-BEOL process.     

A microstrip nonreciprocal tunable YIG filter

A nonreciprocal tunable YIG filter in a microstrip configuration has been constructed which makes use of a novel method of generating a circularly, polarized field in the plane of a microstrip circuit. Nonreciprocities in excess of 40 dB have been obtained atXband with relatively low insertion loss and VSWR.     

Nonreciprocal transmission in a fiber Fabry-Perot resonatorcontaining a magnetooptic material

A fiber Fabry-Perot resonator containing a Faraday-active medium and measured nonreciprocal resonance-enhanced transmission for circularly polarized light was built. The results show that an 18-μm length of material producing only 2.1° of Faraday rotation could achieve an optical isolation of 10 dB. The isolation would be larger for interferometers with higher finesse or more single-pass Faraday rotation. The device could also serve as a nonreciprocal wavelength filter transmitting different sets of wavelengths in the two directions     

Circularly Polarized Microwave Cavity Filters

A new group of circularly polarized microwave cavity filters is described. With a single circularly polarized cavity, a reflectionless filter is achieved that couples nearly 100 per cent of the energy from the main waveguide at the cavity resonant frequency. Two degenerate cavity modes may be excited, to produce a circularly polarized field, by coupling to the transverse and longitudinal waveguide magnetic fields or to the transverse electric and magnetic waveguide fields. A theoretical analysis is presented as well as experimental results. The loss between the band-pass terminals of the reflectionless circularly polarized filter is identical with the loss in a conventional reflectiontype band-pass filter with the same bandwidth and cavity-wall losses. The null at resonance between the band-elimination terminals of the reflectionless circularly polarized filter is limited only by the asymmetries of the cavity and not by the cavity-wall losses. Design equations and curves are given for eight of the lower order, circularly cylindrical, degenerate cavity modes that are coupled to a rectangular waveguide at the point of circularly polarized waveguide magnetic fields.     

Tunable microwave and millimeter-wave band-pass filters

The authors present an overview of tunable microwave and millimeter-wave bandpass filters realized in different technologies. Some general design principles are described. Recent progress in the performance of various tunable filters is reported. The authors survey magnetically tunable filters (ferrimagnetic resonance filters, magnetostatic-wave filters, evanescent waveguide filters, E-plane printed circuit filters), electronically tunable filters, and mechanically tunable filters. The typical performance parameters are summarized. This comparison shown that none of these devices can simultaneously satisfy all requirements for perfect tunable filters. For microwave systems where multioctave tuning is essential, a YIG filter is an obvious choice. In systems where the requirement of high power handling capability combined with low insertion loss, predominates, mechanically tunable filters and magnetically tunable E-plane filters are recommended. If the tuning speed is a crucial requirement, varactor-tuned filters or E-plane filters with ferrite toroids are devices of choice. For millimeter-wave design, the most promising structures are ferrimagnetic resonance filters utilizing hexagonal ferrite resonators or, up to 60 GHz, magnetically tunable E-plane printed circuit filters     

Insertion loss function synthesis of maximally flat parallel-coupled line bandpass filters

Insertion loss (IL) functions are derived for synthesis of microstrip parallel-coupled line bandpass filters with maximally flat responses. The derivation is performed by successively multiplying the ABCD matrices of all coupled stages. Simultaneous equations for determining linewidth and line spacing of the coupled stages are established by total Q (Q/sub T/) of the filter specification and comparing the IL function with the canonical form. The results are provided for filters of order N/spl les/6. Two filters with fractional bandwidths /spl Delta/=30% are synthesized and demonstrated by simulation using a full-wave software package. In addition, two filters with /spl Delta/=40% and 50% are fabricated. Tapped line inputs are employed to these two circuits since some linewidths or gaps are beyond the fabrication resolution. The measured results show very good agreement with the theoretical responses.