Tunable microwave resonators and oscillators using magnetostatic waves

The status of magnetostatic wave (MSW) straight-edge resonators (SERs) and their applications in tunable oscillator circuits are reviewed. The resonators are based on magnetostatic waves propagating in high-Q cavities fabricated in thin ferrimagnetic yttrium iron garnet (YIG) films. The resonance frequency of these resonators can be tuned using a bias magnetic field. The theory of operation and design criteria for the straight-edge resonators are described with emphasis on the effect of the resonator parameters on the tuning range, power handling, and phase noise performance. The use of the SER as the frequency-selective element in oscillator circuits is reported. Examples of tunable oscillators are included.     

A hybrid superconductor/GaAs-MESFET microwave oscillator at 10.6 GHz

A 10.6 GHz hybrid superconducting film/GaAs-MESFET microwave oscillator has been designed, fabricated and characterized on a 10 mm × 15 mm LaAlO₃ substrate. The oscillator was a reflection mode type using a GaAs MESFET (NE72084) as the active device and a superconducting microstrip resonator as the frequency stabilizing element. By improving the unloaded quality factor of the superconducting microstrip resonator and adjusting coupling coefficient between the resonator and the MESFET, the phase noise of the oscillator was decreased. At 77 K, the phase noise of the oscillator at 10 KHz offset from carrier was −87 dBc/Hz.     

Planar ferrite-piezoelectric composite microwave resonator with electric and magnetic frequency tuning

A planar composite microwave resonator based on a bilayer structure comprising a single-crystal yttrium iron garnet (YIG) ferrite film on a lead magnesium niobate-lead titanate (PMN-PT) piezoelectric plate has been studied. The possibility of electric and magnetic tuning of the resonance frequency in this structure is demonstrated. The magnetic tuning in the frequency range of 2–18 GHz is effected by varying the magnetic bias field and the electric tuning within a 20 MHz bandwidth is achieved by applying a dc bias voltage to the piezoelectric layer. An increase in the central frequency of a YIG/PMN-PT composite resonator is accompanied by a growth in the resonator Q from 110 to 990, while the electric tuning bandwidth remains unchanged     

Application of RF varactor using Ba(x)Sr(1-x)TiO3/TiO2/HR-Si substrate for reconfigurable radio

In this paper, the potential feasibility of integrating Ba_xSr_1-xTiO₃ (BST) films into Si wafer by adopting tunable interdigital capacitor (IDC) with TiO₂ thin film buffer layer and a RF tunable active bandpass filter (BPF) using BST based capacitor are proposed. TiO₂ as a buffer layer is grown onto Si substrate by atomic layer deposition (ALD) and the interdigital capacitor on BST(500 nm)/TiO₂(50 nm)/HR-Si is fabricated. BST interdigital tunable capacitor integrated on HR-Si substrate with high tunability and low loss tangent are characterized for their microwave performances. BST/TiO₂/HR-Si IDC shows much enhanced tunability values of 40% and commutation quality factor (CQF) of 56.71. A resonator consists of an active capacitance circuit together with a BST varactor. The active capacitor is made of a field effect transistor (FET) that exhibits negative resistance as well as capacitance. The measured second order active BPF shows bandwidth of 110 MHz, insertion loss of about 1 dB at the 1.81 GHz center frequency and tuning frequency of 230 MHz (1.81-2.04 GHz).     

Reduced transposed flicker noise in microwave oscillators using gaas-based feedforward amplifiers

Transposed flicker noise reduction and removal is demonstrated in 7.6 GHz microwave oscillators for offsets greater than 10 kHz. This is achieved by using a GaAs-based feedforward power amplifier as the oscillation-sustaining stage and incorporating a limiter and resonator elsewhere in the loop. 20 dB noise suppression is demonstrated at 12.5 kHz offset when the error correcting amplifier is switched on. Three oscillator pairs have been built. A transmission line feedback oscillator with a Qo of 180 and two sapphire-based, dielectric resonator oscillators (DROs) with a Qo of 44,500. The difference between the two DROs is a change in the limiter threshold power level of 10 dB. The phase noise rolls-off at (1/f)(2) for offsets greater than 10 kHz for the transmission line oscillator and is set by the thermal noise to within 0-1 dB of the theoretical minimum. The noise performance of the DROs is within 6-12 dB of the theory. Possible reasons for this discrepancy are presented.     

Characterization technique of optical whispering gallery mode resonators in the microwave frequency domain for optoelectronic oscillators

Optical Q factor measurements are performed on a whispering gallery mode (WGM) disk resonator using a microwave frequency domain approach instead of using an optical domain approach. An absence of hysteretic behavior and a better linearity are obtained when performing linewidth measurements by using a microwave modulation for scanning the resonances instead of the piezoelectric-based frequency tuning capability of the laser. The WGM resonator is then used to stabilize a microwave optoelectronic oscillator. The microwave output of this system generates a 12.48 GHz signal with -94 dBc/Hz phase noise at 10 kHz offset.     

Broadband spin-wave delay lines with slot antennas

A planar spin-wave delay line with slot antennas based on an yttrium iron garnet (YIG) film has been experimentally studied. A specific feature of the proposed device is a relatively large (about 1.8 GHz) microwave bandwidth. Within this band, the signal delay time can be smoothly controlled from 4 to 18 ns. The central frequency can be tuned by an external magnetic field within 5–9 GHz. It is demonstrated that, using slot antennas and relatively thick ferromagnetic films, it is possible to achieve a significant increase in the microwave bandwidth of spin-wave devices.     

Design of an Ultra Broad Band YIG-Tuned FET Oscillator Operating within -45～＋65℃

In this paper, the design of an ultra broad band YIG-Tuned FET oscillator is briefly presented. These performances of the superior linearity, the pure spectrum and the ultra broad band tuned oscillation have been realized by a common source circuit topology and a dual coupling YIG resonator. Using a BeO substrate and a buffering amplification stage made up of monolithic MIC traveling wave amplifier, the RF output power has been obtained above 13 dBm in the range from 4 to 16.5 GHz; By means of YIG heater and the temperature compensation of the magnetic circuit, the broad temperature operation performance of YTO has been realized within -45～+65℃.     

Tunable magnetostatic waves bandpass filters with scandium doped yttrium iron garnet films

This paper reports results of theoretical and experimental studies of microwave bandpass tuned filters based on magnetostatic surface wave (MSSW) propagation in yttrium iron garnet (YIG) films. Filter transmission and input impedance characteristics for saturation magnetization 139 kAm^–1 of YIG films and 32 kAm^–1 of scandium-doped YIG films have been calculated and measured experimentally. Structures of a planar, multilayer metal-dielectric-YIG geometry are used to model the filters. Parameters of the structures have been optimized with the help of a computer. Scandium-doped YIG films of thickness near 100 m and saturation magnetization 32 kAm^–1 have been found potentially useful in the manufacture of tunable bandpass filters.     

Ka-band oscillator integrating a high-Q low-temperature co-fired ceramic circular resonator using zigzagged via posts and a λ/4 short stub

A Ka-band oscillator with a high-Q low-temperature co-fired ceramic circular resonator is presented. The resonator, including zigzagged dual-row via posts for tightly confined electromagnetic power as a metallic boundary wall, is presented. The unloaded-Q of the proposed resonator is improved by 22.1% compared to that of a conventional one with vertical via posts. Another resonator is fed with a lambda/4 short stub on a feeding via post in the circular resonator for effectively power transmission in the resonator to the output load without radiation loss. The measured unloaded-Q of the proposed resonator with zigzagged dual-row via posts and a lambda/4 short stub is improved by 45.1% compared with that of a conventional one. Approaches for enhancing Q-factors using two techniques are demonstrated. The Ka-band oscillator integrating a negative resistance generator monolithic microwave integrated circuit and the resonator with zigzagged dual-row via posts and the lambda/4 short stub shows an output power of 19.34 dBm at 26.98 GHz and phase noise of -102.17 dBc/Hz at 1 MHz offset. The figure-of-merit is -164.1 dBc/Hz, and the DC-to-RF conversion efficiency is 18.28%. It can be easily implemented without any additional processes to achieve the high resonator Q-factor. At the same time, it is also very suitable to implement in high-integrated systems for millimeter-wave applications.     

Electric switching in bistable ferrite-piezoelectric microwave resonator

The electric switching in a bistable ferrite-piezoelectric microwave resonator comprising a mechanically coupled yttrium iron garnet (YIG) ferrite film on a lead zirconate titanate (PZT) piezoelectric plate has been studied. The YIG/PZT resonator exhibits switching between stable states with small and large reflectance for a time on the order of a microsecond.     

YIG rod ferrite limiter with extended dynamic range

Analytical and experimental results obtained on aC-band ferrite limiter which utilizes a YIG rod inserted down the center of a coupled dielectric resonator bandpass structure are described. This device is aimed at providing receiver protection for communication systems operating in a dense, high signal power environment. By utilizing a long thin single-crystal YIG rod instead of YIG spheres, the dynamic range has been extended from 20 dB to 35 dB. The threshold power varies from 5 dBm at 4.4 GHz to 15 dBm at 5 GHz with an insertion loss of less than 1 dB.     

Circuit co-simulation and measurement techniques applied to voltage-controlled oscillator design

A voltage-controlled oscillator (VCO) was designed for operation in C-band for use in a microwave pointto- point radio system. Microstrip technology was chosen for resonator implementation since it offers ease of manufacturing and frequency adjustment. The design was performed using an electromagnetic harmonic balance co-design technique in conjunction with linear analysis in order to achieve first pass success. Emphasis in this work is the ability to use multiple design approaches and test techniques while validating in advance with co-simulation. The measured frequency against tune voltage data shows excellent agreement with simulation. Maximum deviation of 2% between the two was observed. The VCO tuned from 4.3 to 5.4 GHz as the tuning voltage was varied from 0 to 9 V representing a tuning bandwidth in excess of 20%. Power dissipation is 150 mW. Phase noise over the tune range was better than 2108 dBc/Hz at 100 kHz offset. The oscillator design efficiency, applicable to wider tune range designs, is greater than 2%. The hybrid oscillator figure-of-merit functions evaluated in this work exceeded comparable silicon-integrated implementations.     

Oxide superconductors and ferroelectrics—Materials for a new generation of tunable microwave devices

We describe materials deposition and characterization for a broad class of tunable microwave devices using high-temperature oxide superconductor and voltage-tunable oxide ferroelectric thin-film multilayer structures. Tl-Ba-Ca-Cu-O thin films deposited by sputtering ore-beam evaporation were patterned into microwave resonators, each consisting of two colinear microstrip line sections separated by a 5–20μm gap. A Ba_0.1Sr_0.9TiO₃ (BST) layer was then over-coated to fill the gap. The relative dielectric constant of the BST films deposited by physical vapor or chemical techniques was measured at 77 K in the 1–10 MHz range and found to vary by up to a factor of 2 or more with voltage bias in test capacitor structures using Pt electrodes. In the BST (variable capacitor)-HTSC microwave resonator structures, the change of the relative dielectric constant of the BST under voltage bias has allowed variation of the fundamental frequency of up to 80 MHz in the 5–10 GHz range at 4 K. Film deposition by various techniques and associated structural, morphological, and electronic properties, as well as materials compatibility issues, are discussed.     

Dielectric constant measurement of low loss liquids using stacked multi ring resonator

The concept of dielectric constant measurement has been extended and applied in agriculture, pharmaceutical and food industry for quality control of liquids. Dielectric analysis of material at microwave frequencies can be done using novel shielded stacked multi-ring resonator (SMRR). The dielectric constant of liquids and paste has been calculated using SMRR with greater accuracy than the planar resonator, boxed resonator and stacked resonator. SMRR contains a ring resonator with fed patch and parasitic patch with different numbers and sizes of rings. The dimensions of rings on the parasitic patch are optimized to achieve Quality factor Q greater than 100 and return loss less than ?2 dB. Due to dual resonance in novel SMRR, structure losses are reduced by 50% than planar resonator structure. The behavior of SMRR structure at the 2.45 GHz frequency is studied with E field and H field. 3D model is designed in Computer Simulation Technology Microwave Studio (CST MWS) using TLM (Transmission Line Modeling) solver. Electromagnetic field analysis as well as impedance bandwidth of SMRR using CST MWS 3D model prove that electromagnetic coupling in SMRR structure increases thus improves quality factor. In SMRR quality factor increases and losses reduce help us to predict the complex permittivity of material for quality analysis.     

Single- and dual-passband microwave planar filters with coupled double-transmission-line resonators

A type of planar double-transmission-line resonator, consisting of two open-ended half-wavelength transmission-line segments edge inter-coupled along their entire length, is proposed. This microwave resonator, because of the generation of double resonances, allows coupled-line bandpass filters with reduced longitudinal length to be implemented. This is the main contribution of this work. Furthermore, as an added feature of the aforementioned resonator, its two-line geometry makes it suitable for dual-band bandpass filter design. To prove the concept experimentally, two different examples of single- and one dual-passband microstrip filter prototypes within the 1-1.5 GHz range are synthesised, constructed and tested. The major advantages of these filter solutions are emphasised. A complementary section dealing with the analysis of the split-type double-transmission-line resonator is also reported. Here, as a result of this study, formulas for its exact design are provided for the first time.     

The use of thermosensitive quartz sensor for thermal regulation at cryogenic temperatures: application to microwave sapphire resonator references

We demonstrated the use of thermosensitive quartz resonator oscillator as a thermal sensor for temperature control at the liquid nitrogen temperature. The high sensitivity of the quartz enables an efficient thermal regulation at ambient temperature as well as liquid nitrogen temperature. LC-cut quartz oscillator phase noise measurements show that the temperature measurement resolution is not limited by the intrinsic noise of the sensor and that a resolution of 10 muK can be achieved. This thermal regulation is applied to control a microwave temperature-compensated sapphire resonator oscillator at a temperature above 77 K, enabling the achievement of a flicker floor of 9.10(-13 ) at 9 GHz.     

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.     

High-temperature superconducting resonators

Preliminary measurements on high-T(c) superconducting resonators are reported and why they are attractive candidates for incorporation in low-noise oscillators is discussed. Some of the important contributions to oscillator noise are reviewed and how they depend on the resonator parameters is shown. A preliminary YBaCu (3)O(7)/LaAlO(3) resonator with a Q of 9x10(4) at 6.9 GHz and 7x10(4) at 3.5 GHz has been fabricated. The temperature sensitivity, power dependence, and residual phase noise are discussed. An upper-limit on the coefficient of the 1/f component of fractional-frequency fluctuations has been measured to be -204 dB at 60 K.