Low-loss Microwave Research Articles

Microstrip resonators and filters using high-T/sub c/ superconducting thin films on LaAlO/sub 3/

Very low microwave losses have been measured in YBa/sub 2/Cu/sub 3/O/sub 7/ linear resonators, ring resonators, and bandpass filters. The stoichiometric 1-2-3 compound was deposited on LaAlO/sub 3/ substrates, patterned microwave circuits, and overcoated with a passivating LaAlO/sub 3/ layer. HTS (high T/sub c/ superconductor) linear microstrip resonators demonstrated Q values greater than 1200 at 10 GHz, corresponding to surface resistances less than 300 mu Omega . Identical silver resonators showed Q values of 60 and surface resistance of 15 m Omega . The high-frequency transition temperature for these HTS films was greater than 83 K. Q values of 240 were measured in ring resonators at 15 GHz. Finally, the authors designed, fabricated, and tested a two-pole, Chebyshev narrow-bandwidth bandpass filter. The HTS filter was designed to be a 1% bandwidth with 0.2-dB ripple. Insertion loss was 2 dB at 4 K, rising to 3 dB at 77 K. The authors observed a temperature dependence in the filter center frequency which they attribute to kinetic inductance effects. The proposed HTS filters outperform similar cryogenic silver filters, indicating that practical levels of HTS performance have been achieved.

High-T/sub c/ thin films on low microwave loss alkaline-rare-earth-aluminate crystals

It is demonstrated that the alkaline-rare-earth aluminates (K/sub 2/NiF/sub 4/-type perovskites) are an excellent choice as the substrate material for the growth of high-T/sub c/ thin films suitable for microwave and far-infrared applications. The CaNdAlO/sub 4/ and SrLaAlO/sub 4/ single crystals have been grown by Czochralski pulling and fabricated into the form of

Polycrystalline hexaferrites for millimetre wave applications

Polycrystalline M-type hexaferrites have been prepared with low microwave losses and high coercive fields. Standard ceramic techniques were employed in the preparation, with the milling method and pressing and sintering conditions being optimized to obtain the desired characteristics. The magnetic and dielectric losses at 94 GHz have been compared with those measured for single crystals, with the aim of evaluating whether polycrystalline materials could be used in nonreciprocal millimetre wave devices.

Investigations on ceramic materials for fusion technology

Abstract Thermophysical and mechanical properties were measured on SiC as an irradiation-resistant First Wall (FW) protection material and on various low loss microwave window materials. An evaluation shows that SiC may not to be excluded from use for FW protection, but only moderate plasma disruption impacts could be tolerated. For the HF window development several grades of alumina, A1N, and spinel were extensively tested for their thermal and mechanical properties and with respect to HF absorption at ≈ 145 GHz. Alumina and particularly sapphire are superior in dielectric properties, but if thermal stresses are taken into account, the best grades of A1N are preferable. This could be demonstrated by parametric lifetime calculations for windows of a given design. The tolerable HF power densities are, however, still unsatisfactory. Irradiations deteriorate both thermal conductivity and dielectric loss.

Ba(Zn 1/3 Ta 2/3 )O 3 –Ba(Cd 1/3 Nb 2/3 )O 3 dielectric ceramics with low microwave loss

Microwave dielectric properties of Ba(Zn1/3Ta2/3)O3–Ba(Cd1/3Nb2/3)O3 ceramics are presented. Sintering of Ba(Zn1/3Ta2/3)O3 was accelerated by the addition of Ba(Cd1/3Nb2/3)O3, and the microwave Q value was also improved. As ZnO volatilises from the sample, the crystallographic distortion was compensated, and the improved microwave loss quality, Q, was explained.

Electrical properties of spinel ferrite films grown by spin-spray plating (abstract)

The spin-spray plating (SSP) is an equilibrium chemical process with which spinel ferrite films can be grown on a variety of substrate materials at temperatures as low as 100 °C. The process is particularly attractive for the monolithic integration of microwave magnetic and electronic GaAs devices. The study of the electrical characteristics of these films is part of an effort aimed at achieving this integration. Low-loss microwave magnetic devices require that the materials used have dielectric loss tangents (tan δ) on the order of 0.001 or lower, and dc resistivities greater than 107 Ω cm. In the SSP process, control of the chemical composition of the films is limited by an incompatibility of desirable transition metal ions (e.g., Fe,Ni,Zn,Mn) with the tetrahedral and octahedral cation sites available in the spinel structure. Therefore, the substitution of a specific cation modifies the site distribution of other ions in the spinel lattice. The overall distribution of the metallic cations determines the electrical and magnetic properties of the ferrite films. Specifically, low resistivity is due to the mixtures of high- and low-valence cations of a metal element in the same lattice site. In this study Ni-Zn ferrite films were produced with resistivities ranging from 10 to 106 Ω cm. Dielectric loss tangents measured, however, were several orders of magnitude higher than desired. Predictably, the loss tangent decreases monotonically with increasing resistivity; however, its values are much higher than the literature values for ceramic ferrites and semiconducting materials for the same range of dc resistivities. The reasons for this are presently being investigated.

Developments in HTS devices

Rather than taking a long-term, speculative approach this review attempts to identify a limited number of application areas where HTS devices operated at 77 K are already competitive with those of other technologies. The devices described are novel magnetometers, electromagnetic shielding, SQUIDS and passive low-loss microwave components.

DK-Messung durch Auswertung der 7E011-Resonanz geschirmter dielektrischer Zylinder

It is a commun practice to determine the dielectric losses of low-loss microwave ceramic materials by measuring the quality factor of the TE 011 -resonance of shielded disc-resonators, because the influence of the shield is negligible as long as its dimension is chosen appropriately. To determine the material's permittivity with the same setup we establish a field-theoretical relationship between the resonance-frequency and the permittivity of the dielectric resonator using a mode-matching technique.

Electron nuclear double resonance near the phase transitions of the KH2PO4-type of ferroelectrics

Using high rf fields, a low-loss microwave cavity/ENDOR coil system, and the AsO4- 4 centre as a probe, we have detected ENDOR signals from 1H. 39K, 31P, 85Rb, 87Rb and 133Cs in the close vicinity of paraelectric-ferroelectric transitions of the KH2PO4-type of compounds. This methodology enhances E.P.R. spectral resolution and motional sensitivity by almost two orders of magnitude, and appears to be a valuable complement to spin-echo techniques, even for samples exhibiting high dielectric losses.

The microwave power dependence of low field microwave loss and flux trapping in Hf doped YBa2Cu3O7

The Hafnium doped YBaCuO ceramics are studied by EPR and low field microwave loss measurements. Microwave loss (ML) signal saturates at very low microwave power as compared to EPR signal of Cu2+. It is shown that the amount of the trapped flux is proportional to the amount of impurity phase in the material. The lower critical field, Hc1, is found to be 7mT at 77K from these studies. Diminishing microwave loss with increasing impurity phases is attributed to the increasing Jc in these samples.

Temperature dependence of the low field microwave loss in hafnium doped YBaCuO superconductor

Temperature dependence of the microwave loss at low fields is presented for Hafnium doped YBaCuO system with Tc = 88K. The peak to peak height, peak position and the area under the hysteresis loop of this lossy signal are observed to decrease with increasing temperature up to Tc and vanish at Tc. Results are interpreted in terms of Josephson weak links between the superconducting grains.

Processing of thick-film dielectrics compatible with thin-film superconductors for analog signal processing devices

The authors demonstrate the feasibility of integrating thick-film dielectrics with thin-film superconductors in the fabrication of signal processing devices. Thin films of Nb and NbN are deposited by RF sputtering and patterned photolithographically. Thick film dielectrics can be spun on to a controlled thickness of 10 to 25 mu m, which is an optimum range for high-density, low-loss microwave delay lines. After an organic-binder burnout step at 450 degrees C in air, the ceramic dielectrics are sintered onto the NbN thin films at 850 degrees C in vacuum. The transition temperature of the NbN changes from 15 K as sputtered to 9 K after sintering, but superconductivity is preserved by the presence of thin-film MgO and SiO/sub 2/ barrier layers. Lumped-element resonators, in which the inductor and the capacitor electrodes are made of NbN and the dielectric of thick-film ceramic, have been successfully fabricated for measuring the dielectric properties of the ceramics at 4.2 K and 10 MHz. Preliminary results indicate a dielectric constant of 6-8 and tan delta of 10/sup -2/. >

Six-port and four-port reflectometers for complex permittivity measurements at submillimeter wavelengths

The frequency range of six-port reflectometry is extended into the submillimeter wavelength range. The complex permittivity of low-loss microwave materials is determined using novel six-port and four-port reflectometers. These either consist of quasi-optical components or utilize oversized waveguide techniques. Permittivity measurements of materials possessing a wide range of values of epsilon ' (2 to 7) and of the loss tangent (0.0003 to 0.03) were carried out at frequencies of about 380 GHz to 390 GHz. Good agreement with published permittivity data is shown. Moreover, the equivalance of the simple waveguide four-port reflectometer (which is preferred because of its easy handling and high stability against temperature fluctuations) to the quasi-optical reflectometers is shown. >

Cryogenic vacuum window

A procedure is described for assembly of an inexpensive, easy to assemble waveguide window that has both low microwave losses and small reflectivity. This window is vacuum, superfluid-helium-tight, and withstands repeated thermal cycling to helium temperatures.

Measurements of high- T c superconductivity in a microwave cavity

Measurements on a cylindrical microwave cavity with yttrium barium copper oxide end-plates show that this new class of superconductor has low loss at microwave frequencies. Low-loss microwave components operating at liquid nitrogen temperatures could be built using this compound.

Ba(Zn1/3Nb2/3)O3–Sr(Zn1/3Nb2/3)O3 Solid Solution Ceramics with Temperature-Stable High Dielectric Constant and Low Microwave Loss

Solid solution ceramics in the Ba(Zn1/3Nb2/3)O3(BZN)–Sr(Zn1/3Nb2/3)O3 (SZN) system have been studied with a view to finding materials for use as dielectric resonators at microwave frequency. The relative dielectric constant and the unloaded Q at 10 GHz are respectively 41 and 5400 for BZN, and 40 and 2000 for SZN. The temperature coefficient of the resonant frequency is estimated as 30 ppm/°C for BZN and -38 ppm/°C for SZN. The dielectric constant of 0.3 BZN–0.7 SZN ceramic is nearly independent of temperature, which gives a very small estimated temperature coefficient of the resonant frequency of -5 ppm/°C.

The complex permittivity of six n-alkanes; measurements in the far infrared

The optical absorption of six n-alkanes (n-pentane to n-decane) has been measured in the far infrared using the Grubb-Parsons Mark III interferometer. The results are related to low frequency permittivity, microwave loss, and refractive index measurements using the Kramers-Kronig relation.

A new electroless method for low-loss microwave integrated circuits: S. Mahapatra and S. N. Prasad IEEE Trans. Components, Hybrids, Mfg Technol. Chmt.-1, (4) 428 (December 1978)

A new electroless method for low-loss microwave integrated circuits: S. Mahapatra and S. N. Prasad IEEE Trans. Components, Hybrids, Mfg Technol. Chmt.-1, (4) 428 (December 1978)

A new electroless method for low-loss microwave integrated circuits : S. Mahapatra and S. N. Prasad. IEEE Trans. Components, Hybrids, Mfg Technol.Chmt.-1, (4) 428 (December 1978)

A new electroless method for low-loss microwave integrated circuits : S. Mahapatra and S. N. Prasad. IEEE Trans. Components, Hybrids, Mfg Technol.Chmt.-1, (4) 428 (December 1978)

A New Electroless Method for Low-Loss Microwave Integrated Circuits

A new method of depositing copper on alumina substrates is described. This results in less attenuation and better adhesion than that obtained by the prior method. The measured attenuation of microstriplines made by conventional vacuum evaporation of chromegold and by electroless copper deposition methods is compared in the range of 2-10 GHz. It is found that classical chrome-gold metallization gives higher attenuation. The experimental data for this new method are in good agreement with the theoretically predicted values. The superiority of the new method over the prior methods is discussed.