R.A. Woode

University of Western Australia, Perth City, Western Australia, Australia

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Publications (22)19.26 Total impact

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    ABSTRACT: A microwave dielectric ceramic resonators based on BaCe2Ti5015 and Ba5Nb4O15 have been prepared by conventional solid state ceramic route. The dielectric resonators (DRs) have high dielectric constant 32 and 40 for BaCe2Ti5O15 and Ba5Nb4O15, respectively. The whispering gallery mode (WGM) technique was employed for the accurate determination of the dielectric properties in the microwave frequency range. The BaCe2Ti5O15 and Ba5Nb4O15 have quality factors (Q×F) of 30,600 and 53,000 respectively. The quality factor is found to depend on the azimuthal mode numbers. The temperature coefficient of resonant frequency (τf) of BaCe2Ti5O15 and Ba5Nb4O15 have been measured accurately using different resonant modes and are +41 and +78 ppm/K, respectively.
    Materials Letters. 09/2000;
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    ABSTRACT: In this paper we show that it is possible to annul the frequency - temperature coefficient of a sapphire dielectric resonator using another dielectric with the opposite frequency - temperature dependence. We have successfully annulled the frequency - temperature coefficient of a composite sapphire - strontium titanate ( - ) microwave resonator at 108 K with a resulting Q factor of 20 000 - 50 000 below 150 K.
    Journal of Physics D Applied Physics 12/1998; 30(19):2770. · 2.53 Impact Factor
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    ABSTRACT: We report new microwave measurements of the anisotropic loss tangent and permittivity of rutile using well confined `whispering gallery' type modes of a shielded dielectric resonator. We report the first measurement of the two independent components of the loss tangent tensor, as well as the lowest measurement yet of the total loss tangent of parallel to the crystal c-axis and perpendicular to the c-axis, both measured at 3 K. We show that the mode frequency dependence possesses two stationary points in the temperature range 2-10 K and explain this dependence in terms of the competing effects of incidental paramagnetic impurities in the rutile, the variation of the rutile's permittivity with temperature and the thermal expansion of the material. We give the first measurements of the anisotropic permittivity of rutile at low temperatures.
    Journal of Physics D Applied Physics 12/1998; 31(11):1383. · 2.53 Impact Factor
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    R A Woode, E N Ivanov, M E Tobar
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    ABSTRACT: An ultrasensitive noise measurement system has been used to study the intrinsic fluctuations in microwave circulators and isolators. The key element of the measurement system is a carrier suppression interferometer which contains the device under test in one of its arms. The interferometer is used to cancel the carrier at the input of a low noise microwave amplifier in the readout system. Fluctuations in the device under test are then registered by the readout system which has an effective noise temperature of 360 K and is almost equal to its physical temperature. This corresponds to a phase noise of with 20 dBm of microwave power incident on the device under test. We show that this is sufficiently low to measure intrinsic fluctuations in low noise microwave components such as ferrite circulators and isolators. The noise of the microwave isolators was shown to be independent of both, microwave power and temperature in the region +10 to and -10 to . We have also measured the phase shift in microwave isolators as a function of external magnetic fields and temperature to determine the effects of environmental fluctuations.
    Measurement Science and Technology 12/1998; 9(9):1593. · 1.44 Impact Factor
  • E.N. Ivanov, M.E. Tobar, R.A. Woode
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    ABSTRACT: A concept of interferometric measurements has been applied to the development of ultra-sensitive microwave noise measurement systems. These systems are capable of reaching a noise performance limited only by the thermal fluctuations in their lossy components. The noise floor of a real time microwave measurement system has been measured to be equal to -193 dBc/Hz at Fourier frequencies above 1 kHz. This performance is 40 dB better than that of conventional systems and has allowed the first experimental evidence of the intrinsic phase fluctuations in microwave isolators and circulators. Microwave frequency discriminators with interferometric signal processing have proved to be extremely effective for measuring and cancelling the phase noise in oscillators. This technique has allowed the design of X-band microwave oscillators with a phase noise spectral density of order -150 dBc/Hz at 1 kHz Fourier frequency, without the use of cryogenics. Another possible application of the interferometric noise measurements systems include "flicker noise-free" microwave amplifiers and advanced two oscillator noise measurement systems.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 12/1998; · 1.82 Impact Factor
  • E.N. Ivanov, M.E. Tobar, R.A. Woode
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    ABSTRACT: To enhance the sensitivity of oscillator phase-noise measurements, an interferometric frequency-discriminator system may be implemented. Such systems consist of a microwave interferometer, incorporating a high-Q resonator and a phase-sensitive microwave readout. Suppressing the carrier at the output of the interferometer enables the microwave readout to operate in the small-signal regime with an effective noise temperature close to its physical temperature, When used as a sensor of a frequency-control system to lock the oscillator to a selected resonant mode of a high-Q resonator, the interferometric frequency discriminator has enabled more than two orders of magnitude improvement in oscillator phase-noise performance as compared with the state-of-the-art. Thus, the phase noise of an S-band oscillator was reduced to -150 dBc/Hz at 1-kHz Fourier frequency without the use of cryogenics, and was limited by the thermal noise in the microwave interferometer. To facilitate tuning and locking, an automatically balanced microwave frequency discriminator was developed using voltage-controlled attenuators and phase shifters. Rapid frequency tuning of the oscillator was achieved by varying the interferometer phase mismatch and automatically controlling the carrier suppression without tuning the high-Q resonator
    IEEE Transactions on Microwave Theory and Techniques 11/1998; · 2.23 Impact Factor
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    ABSTRACT: A sapphiro-rutile composite resonator was constructed from a cylindrical sapphire monocrystal with two thin disks of monocrystal rutile held tightly against the ends. Because rutile exhibits low loss and an opposite temperature coefficient of permittivity to sapphire, it is an ideal material for compensating the frequency-temperature dependence of a sapphire resonator. Most of the electromagnetic modes in the composite structure exhibited turning points (or compensation points) in the frequency-temperature characteristic. The temperatures of compensation for the WG quasi TM modes were measured to be below 90 K with Q-factors of the order of a few million depending on the mode. For WG quasi TE modes, the temperatures of compensation were measured to be between 100 to 160 K with Q-factors of the order of a few hundreds of thousands, depending on the mode. The second derivatives of the compensation points were measured to be of the order 0.1 ppm/K(2 ), which agreed well with the predicted values.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/1998; 45(3):830-6. · 1.82 Impact Factor
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    ABSTRACT: The dielectric properties of a single crystal rutile (TiO2) resonator have been measured using whispering gallery modes. Q factors and resonant frequencies were measured from 300 to 10 K. Q factors as high as 104, 105, and 107 were obtained at 300, 80, and 10 K, respectively. Using the whispering gallery mode technique we have determined accurately the loss tangent and dielectric constant of monocrystalline rutile and obtained much more sensitive measurements than previously reported. We show that rutile exhibits anisotropy in both the loss tangent and permittivity over the range from 10 to 300 K.
    Journal of Applied Physics 02/1998; 83(3). · 2.21 Impact Factor
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    ABSTRACT: A real time noise measurement technique has been developed which allows phase and amplitude noise measurements to be made with much higher sensitivity than previously possible. The technique is applicable at arbitrary operating frequency and can be used to measure the performance of wideband devices. The measurement system is based on an interferometer and a microwave implementation has been developed at X-band; using both connectorised `mechanical' components and a microstrip module. This paper reports the results of the microstrip implementation as both a noise measurement system and as part of a frequency discriminator in ultra-low noise oscillators
    Frequency Control Symposium, 1997., Proceedings of the 1997 IEEE International; 06/1997
  • E.N. Ivanov, M.E. Tobar, R.A. Woode
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    ABSTRACT: A low-phase noise 9 GHz oscillator with a tuning range of ±12 kHz has been developed. The SSB phase noise of the oscillator in the middle of the tuning range is of the order -145 dBc/Hz at 1 kHz Fourier frequency. The oscillator phase noise is suppressed by a frequency control system based on an ultra-sensitive frequency discriminator. The latter consists of a microwave interferometer with a high-Q resonator in one of the arms and a phase sensitive microwave readout system. Suppressing the carrier at the output of interferometer enables the small signal operation of the microwave readout system and effective cancellation of the oscillator phase noise. The frequency of the oscillator is tuned by varying the phase mismatch of microwave interferometer without affecting the high-Q resonator. To minimise the degradation of the oscillator phase noise during frequency tuning, an automatic carrier suppression system is introduced to keep the microwave interferometer balanced
    Frequency Control Symposium, 1997., Proceedings of the 1997 IEEE International; 06/1997
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    ABSTRACT: Using the Whispering Gallery (WG) mode method we report on the measured uniaxial anisotropy of both rutile and sapphire at microwave frequencies, and determine that the loss tangent as well as the permittivity exhibit anisotropy for both materials. The loss tangent of rutile below 40 K was measured to be significantly smaller than what was measured previously using other techniques. Because rutile exhibits low loss and an opposite temperature coefficient of permittivity to sapphire, it is an ideal material for compensating the frequency-temperature dependence of a sapphire resonator. A sapphire-rutile composite resonator was constructed from a cylindrical sapphire monocrystal with two thin disks of monocrystal rutile held tightly against the ends. Most of the electromagnetic modes exhibited turning points (or compensation points) in the frequency-temperature characteristic. The temperature of compensation for WG quasi TM modes was measured to be below 90 K with Q-factors of the order of a few million depending on the mode. For WG quasi TE modes the temperature of compensation was measured to be between 100 to 160 K with Q-factors of the order of a few hundreds of thousand depending on the mode. The second derivatives of the compensation points were of the order 0.1 ppm/K<sup>2</sup>, which agreed well with the predicted values
    Frequency Control Symposium, 1997., Proceedings of the 1997 IEEE International; 06/1997
  • E N Ivanov, M E Tobar, R A Woode
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    ABSTRACT: A novel 9 GHz measurement system with thermal noise limited sensitivity has been developed for studying the fluctuations in passive microwave components. The noise floor of the measurement system is flat at offset frequencies above 1 kHz and equal to -193 dBc/Hz. The developed system is capable of measuring the noise in the quietest microwave components in real time. We discuss the results of phase and amplitude noise measurements in precision voltage controlled phase shifters and attenuators. The first reliable experimental evidences regarding the intrinsic flicker phase noise in microwave isolators are also presented.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/1997; 44(1):161-3. · 1.82 Impact Factor
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    ABSTRACT: Two liquid nitrogen-cooled sapphire loaded cavities (SLC's) operating at about 80 K have been successfully constructed, Both cavities were designed to operate on the whispering gallery (WG) E/sub 12, 1, /spl delta// mode at a resonant frequency of 8.95 GHz. The first SLC was used as the frequency-determining element in a loop oscillator, while the second was used as a frequency discriminator to measure oscillator phase noise. The single sideband phase noise of a free running loop oscillator incorporating the first SLC was measured as -133 dBc/Hz at an offset frequency of 1 kHz, and was limited by the SLC Q-factor and the amplifier flicker phase noise. By using specially designed feedback electronics the oscillator phase noise was reduced to -156 dBc/Hz and -162 dBc/Hz at 1 and 10 kHz offset, respectively. This measurement was shown to be limited by the electronic flicker noise imposed by the phase detector in the feedback electronics, To our knowledge the phase noise and resonator Q-factor of 6/spl times/10/sup 7/ represent the best results ever measured at liquid nitrogen temperatures or above.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/1996; · 1.82 Impact Factor
  • E.N. Ivanov, M.E. Tobar, R.A. Woode
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    ABSTRACT: An advanced phase noise reduction technique has been developed to improve the short-term frequency stability of microwave oscillators. The technique is based upon an ultrasensitive microwave frequency discriminator with effective noise temperature close to its physical temperature. The phase noise spectral density of a 9 GHz microwave loop oscillator incorporating such a discriminator has been measured as -120 dBc/Hz and -150 dBc/Mz at offset frequencies of 100 Hz and 1 kHz, respectively. This performance is at least 25 dB better than current state of the art. The developed phase noise reduction technique is quite general and can have valuable implications for the design of various low phase noise microwave oscillators
    IEEE Microwave and Guided Wave Letters 10/1996;
  • E.N. Ivanov, M.E. Tobar, R.A. Woode
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel measurement system with thermal noise limited sensitivity has been developed for studying the fluctuations in passive microwave components. The developed system is capable of measuring the noise in the quietest microwave components in real time. The noise floor of a 9 GHz measurement system was measured to be -193 dB/Hz at offset frequencies above 1 kHz. We present the measurements of the phase and amplitude noise in precision voltage controlled phase shifters and attenuators, along with the first reliable experimental evidences regarding the intrinsic phase noise in microwave isolators. Also we discuss the possible applications of the developed noise measurement system for noise reduction in the microwave amplifiers and oscillators
    Frequency Control Symposium, 1996. 50th., Proceedings of the 1996 IEEE International.; 07/1996
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    ABSTRACT: We show that it is possible to obtain frequency-temperature compensation in a sapphire dielectric resonator using a dielectric with opposite permittivity-temperature coefficient. The compensating dielectric should have low loss and a temperature-frequency dependence of opposite sign to sapphire. For example, monocrystalline strontium titanate and rutile fulfil these requirements. We show that by using this technique it is feasible to construct a microwave resonator with zero frequency-temperature dependence and a curvature of order 0.1 ppm/K <sup>2</sup>. From the ratio of filling factors and the dielectric loss tangent we calculated that Q-factors of order 10<sup>7</sup> at 80 K and 10<sup>5</sup> near room temperature are possible, with good quality compensation materials. With a sapphire-SrTiO<sub>3</sub> composite structure we obtained frequency-temperature compensation with a Q-factor of about 50,000 below 150 K. The low Q-factor achieved was due to the losses in the compensating dielectric. Another problem was due to the excess spurious modes that exist due to the high permittivity of the compensating dielectric. This can cause the temperature dependence to markedly degrade the curvature of compensation. Ways of countering this problem are discussed
    Frequency Control Symposium, 1996. 50th., Proceedings of the 1996 IEEE International.; 07/1996
  • R.A. Woode, E.N. Ivanov, M.E. Tobar
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    ABSTRACT: The phase and amplitude noise in many microwave components has yet to be understood. This is because conventional measurement systems are not sensitive enough. We have been able to measure the phase and amplitude noise in components such isolators, power limiters and voltage controlled phase shifters and attenuators. This was possible due to the advent of the ultra-sensitive Ivanvov-Tobar-Woode (ITW) measurement system. For example, the phase noise in an isolator is shown to be flicker of phase noise with a level of -184 dBc/Hz at 1 kHz offset. The noise floor of the measuring system was also flicker of phase below 1 kHz, and flat at a level of -193 dBc/Hz above 1 kHz
    European Frequency and Time Forum, 1996. EFTF 96., Tenth (IEE Conf. Publ. 418); 04/1996
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    ABSTRACT: The authors report on an X-band microwave oscillator incorporating a room temperature thermoelectric stabilized sapphire resonator operating at 9.00000 GHz. With a Galani type stabilization scheme they have measured a reduced single sideband phase noise of about -124 dBc/Hz at 1 kHz with a f<sup>-3</sup> dependence. The measurement was limited by the flicker noise of the phase detector in the feedback electronics. The frequency stability was also measured; at an integration time of 0.1 seconds a δf/f of about 10<sup>-11</sup> with a τ<sup>0.7</sup> dependence was measured. The frequency drift strongly correlated with ambient temperature fluctuations
    IEEE Microwave and Guided Wave Letters 05/1995;
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    ABSTRACT: The use of whispering gallery modes allows the dielectric loss tangent of polycrystalline Al<sub>2</sub>O<sub>3</sub> (alumina) to be accurately determined at microwave frequencies without the use of a cavity. The dielectric loss tangent of alumina is shown to be strongly variable from sample to sample with a lowest measured value of 4.3×10<sup>-5</sup> observed at 9.0 GHz in a 99.5% alumina sample
    Electronics Letters 01/1995; · 1.04 Impact Factor
  • E.N. Ivanov, M.E. Tobar, R.A. Woode
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    ABSTRACT: In this paper we report an advanced phase noise reduction technique developed to improve the short term frequency stability of the microwave oscillators. The technique is based upon the ultra sensitive microwave frequency discriminator with the effective noise temperature close to its physical temperature. The frequency discriminator comprises a room temperature sapphire loaded cavity operating on a “whispering gallery” mode with an unloaded Q factor of 185000 at 9 GHz. The phase noise spectral density of the microwave loop oscillator, incorporating such a discriminator as a sensor for the frequency servo, has been measured to be equal to S<sub>φ</sub><sup>osc</sup>(F)&ap;-60-10log<sub>10</sub>(F<sup>3 </sup>) dBc/Hz at frequencies below a few kHz. This corresponds to a level of phase noise as low as -120 dBc/Hz and -150 dBc/Hz at offset frequencies 100 Hz and 1 kHz respectively
    Frequency Control Symposium, 1995. 49th., Proceedings of the 1995 IEEE International; 01/1995