
Source Available from: John Gideon Hartnett
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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; 45(545):279285. DOI:10.1016/S0167577X(00)00118X · 2.49 Impact Factor

Source Available from: Michael 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. DOI:10.1088/09570233/9/9/032 · 1.43 Impact Factor

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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. DOI:10.1088/00223727/30/19/016 · 2.72 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 caxis and perpendicular to the caxis, both measured at 3 K. We show that the mode frequency dependence possesses two stationary points in the temperature range 210 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. DOI:10.1088/00223727/31/11/013 · 2.72 Impact Factor

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ABSTRACT: A concept of interferometric measurements has been applied to the development of ultrasensitive 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 Xband 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 noisefree" microwave amplifiers and advanced two oscillator noise measurement systems. IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 12/1998; 45(645):1526  1536. DOI:10.1109/58.738292 · 1.51 Impact Factor

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ABSTRACT: To enhance the sensitivity of oscillator phasenoise measurements,
an interferometric frequencydiscriminator system may be implemented.
Such systems consist of a microwave interferometer, incorporating a
highQ resonator and a phasesensitive microwave readout. Suppressing
the carrier at the output of the interferometer enables the microwave
readout to operate in the smallsignal regime with an effective noise
temperature close to its physical temperature, When used as a sensor of
a frequencycontrol system to lock the oscillator to a selected resonant
mode of a highQ resonator, the interferometric frequency discriminator
has enabled more than two orders of magnitude improvement in oscillator
phasenoise performance as compared with the stateoftheart. Thus, the
phase noise of an Sband oscillator was reduced to 150 dBc/Hz at 1kHz
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 voltagecontrolled 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 highQ resonator IEEE Transactions on Microwave Theory and Techniques 11/1998; 46(1046):1537  1545. DOI:10.1109/22.721162 · 2.24 Impact Factor

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ABSTRACT: A sapphirorutile 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 frequencytemperature dependence of a sapphire resonator. Most of the electromagnetic modes in the composite structure exhibited turning points (or compensation points) in the frequencytemperature characteristic. The temperatures of compensation for the WG quasi TM modes were measured to be below 90 K with Qfactors 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 Qfactors 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):8306. DOI:10.1109/58.677747 · 1.51 Impact Factor

Source Available from: Jerzy Antoni Krupka
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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). DOI:10.1063/1.366871 · 2.18 Impact Factor

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ABSTRACT: A lowphase 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 ultrasensitive frequency
discriminator. The latter consists of a microwave interferometer with a
highQ 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 highQ 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
frequencytemperature dependence of a sapphire resonator. A
sapphirerutile 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 frequencytemperature
characteristic. The temperature of compensation for WG quasi TM modes
was measured to be below 90 K with Qfactors 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 Qfactors 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

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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
Xband; 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 ultralow noise oscillators Frequency Control Symposium, 1997., Proceedings of the 1997 IEEE International; 06/1997

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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):1613. DOI:10.1109/58.585211 · 1.51 Impact Factor

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ABSTRACT: An advanced phase noise reduction technique has been developed to
improve the shortterm 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; 6(96):312  314. DOI:10.1109/75.535829

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ABSTRACT: Two liquid nitrogencooled 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 frequencydetermining 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 Qfactor 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 Qfactor 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; 43(543):936  941. DOI:10.1109/58.535497 · 1.51 Impact Factor

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ABSTRACT: We show that it is possible to obtain frequencytemperature
compensation in a sapphire dielectric resonator using a dielectric with
opposite permittivitytemperature coefficient. The compensating
dielectric should have low loss and a temperaturefrequency 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 frequencytemperature 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 Qfactors 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 sapphireSrTiO<sub>3</sub> composite
structure we obtained frequencytemperature compensation with a Qfactor
of about 50,000 below 150 K. The low Qfactor 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

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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: 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 ultrasensitive IvanvovTobarWoode (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 Xband 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; 5(45):108  110. DOI:10.1109/75.372807

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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; 30(2530):2120  2122. DOI:10.1049/el:19941470 · 0.93 Impact Factor

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ABSTRACT: Two liquid nitrogen cooled Sapphire Loaded Cavities (SLC) operating at about 80 K have been successfully constructed. Both resonators were designed to operate on the Whispering Gallery (WG)E<sub>12, 1, δ</sub> mode at a resonant frequency of 8.95 GHz. The highest unloaded Qfactor measured was approximately 60 million for the first SLC and 40 million for the second. The first 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 Qfactor and the amplifier flicker phase noise. By using specially designed feedback electronics the oscillator phase noise: was reduced to 156 dBc/Hz at 1 kHz. This measurement was shown to be limited by the electronic flicker noise imposed by the phase detector in the feedback electronics. Optimising the oscillator further, we measured by self discrimination a phase noise of 162 dBc/Hz at kHz. Further analysis reveals that this type of liquid nitrogen cooled oscillator has the potential to reach 177 dBc/Hz at 1 kHz Frequency Control Symposium, 1995. 49th., Proceedings of the 1995 IEEE International; 01/1995