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.

Articles you may be interested inMicrowave complex permittivity of voltage-tunable nematic liquid crystals measured in high resistivity silicon transducers Appl. Phys. Lett. 102, 102904 (2013); 10.1063/1.4795534 Microwave properties of semi-insulating silicon carbide between 10 and 40 GHz and at cryogenic temperaturesThe dielectric properties of a single crystal rutile (TiO 2 ) 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 10 4 , 10 5 , and 10 7 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.

No abstract

A microwave dielectric ceramic resonators based on BaCe2Ti5O15 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 X 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 (Tr) of BaCe2Ti5O15 and Ba5Nb4O15 have been measured accurately using different resonant modes and are + 41 and + 78 ppm/K, respectively.

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.