Afshin S. Daryoush

A 2.5-GHz InGaP/GaAs differential cross-coupled self-oscillating mixer (SOM) IC

This letter presents a monolithic differential cross-coupled self-oscillating mixer (SOM). The SOM chip is fabricated using an InGaP/GaAs heterojunction bipolar transistor (HBT) foundry process and operates at 2.5 GHz. The chip provides voltage controlled oscillator (VCO) operation, up- and down-conversion mixing, and injection locking functionalities. The voltage down-conversion gain and the power up-conversion gain of up to 15 and 11.5 dB, respectively, are measured for the circuit. There is a compromise between obtaining a high conversion gain, and the oscillator power (-0.3 dBm for a 5-V supply) and phase noise (-84 dBc/Hz at 100 kHz). However, phase noise improvement of 32dB is observed by injection of a -30-dBm stable reference.

Characterization of the complex permittivity of brain tissues up to 50 GHz utilizing a two-port microstrip test fixture

Broad-band complex-permittivity values of biological tissues above 20 GHz obtained from direct measurements have not been reported in the literature. This paper presents for the first time the measurement results of complex permittivity of brain grey and white matters from 15 to 50 GHz utilizing a two-port microstrip test fixture. Test fixture S-parameters are simulated employing the finite-element method. To apply the data obtained from the simulation in complex-permittivity extraction, an efficient procedure, using the linear least square technique, is introduced to fit the modeling results to a rational function of complex permittivity, which is similar to the transfer function for a linear system. This fitting procedure is computationally more efficient than the previously developed fitting methods. Measurements are performed on slices of brain sample using a calibrated network analyzer utilizing custom designed through-reflect-line (TRL) calibration standards. The measurements are corrected for the residual errors observed in the measurement results due to the lack of performance repeatability of coaxial-to-microstrip launchers utilized in the TRL calibration standards. Finally, the measured results for brain matters are fitted to a single term Cole-Cole relation representing the dispersion characteristics of white and grey matters up to 50 GHz.

Comparison of two post-calibration correction methods for complex permittivity measurement of biological tissues up to 50 GHz

Two correction methods are discussed in this paper to remove residual errors due to the lack of repeatability of coaxial-to-microstrip launchers as part of the TRL calibration procedure. These methods are applied for accurate insertion loss measurement of biological tissues embedded in a two-port microstrip test fixture, from which the tissues complex permittivity values are extracted for frequencies between 15 and 50 GHz. In the first method, distilled water is used as a calibration standard as part of a two-port calibration procedure. The second method identifies an error transfer function using the difference between simulated and measured insertion loss for distilled water, and then applies it as a correction factor to the measurement results for biological tissues. Both methods are compared in terms of extracting the accurate complex permittivity of brain matter.

Biological Tissue Complex Permittivity Measured From

Our analysis and measurements of a custom-designed two-port microstrip test fixture for biological tissue characterization at microwave and millimeter-wave frequencies demonstrated that the transmission parameter S 21 would provide a better sensitivity to the complex permittivity change than the reflection coefficient S 11. However, the standard through-reflect-line (TRL) calibration method employed for the extraction of the tissue complex permittivity did not fully remove the coaxial-to-microstrip adaptors induced errors, which were manifested by ripple artifacts on the measured two-port S parameters. A simple deconvolution method was demonstrated wherein these errors were removed by postcalibration correction of the measured S 21 of the tissue under test (TUT) by using water as a reference material. This paper provides a theoretical analysis of this method based on a model presented for postcalibration adaptors. Our detailed analysis shows that the error for S 21 using the deconvolution method linearly depends on the difference between the S 11 of the TUT and the reference material. Measurement and error estimation are also provided for various biological tissues and are consistent with analytical expectations. Our analysis provides support that systematic errors of numerically modeled S 21 utilized for complex permittivity extraction can significantly be reduced by the deconvolution method. On the other hand, the analysis also shows that the S 21 numerical modeling errors and the postcalibration adaptors error terms have a similar impact on the extracted complex permittivity using the standard time-gating technique and are irreducible, unless the deconvolution method is used. Our analysis also identifies water as a better reference sample than methanol for accurate extraction of the complex permittivity of tissues in the range of epsiv > 9 and epsiv > 7 at 30 GHz.

S_{21}

Various design aspects of a two-port test fixture are presented to measure permittivity of biological tissues. Dimensions of this fixture are optimized using a commercial finite element method package. High measurement sensitivity to the tissue parameters is obtained up to 45 GHz by careful design of the microstrip feed line and aperture dimensions. Material inhomogeneity with millimeter spatial resolution is predicted using this optimized fixture.

—Error Analysis and Error Reduction by Reference Measurements

Experimental results of the exposure of neurological cells to radio frequency are presented. The exposure is quantified by the mean of the complex permittivity of cell solutions as a function of frequency. A set-up is used for measurement of complex permittivity of live and dead neurological cell cultures from 20 to 40 GHz. Differences are observed between the two cultures and are compared against the expected measurement error. The statistical significance of these differences is also studied and reported in this paper.

Characterization of biological tissues up to millimeter wave: test fixture design

Digital receivers are pursued as part of future civilian and military communication applications. Design and implementation of a broadband receiver is presented that operates for 4G wireless communications. Performance of the realized hardware is evaluated in terms of system parameters.

Study of the activity of neurological cell solutions using complex permittivity measurement

This paper presents the experimental results of a push-pull Self-Oscillating Mixer (SOM) tunable in a range of 421-463 MHz operating in PLL and Injection Locked PLL (ILPLL) regimes. By careful selection of the oscillator feedback resistor, an excellent down-conversion gain of up to 24.3 dB is observed. As a result, for the first time, the phase detection is performed as part of the SOM without the need for an external phase detector and gain stages. Issues such as tuning voltage-frequency variation, SOM phase-frequency variation, tracking range, pull in range, phase noise, and SOM phase controllability are discussed in the paper.

IC based broadband digital receiver for 4G wireless communications

The electronic information transfer revolutionizes the flow of information in a similar manner as the print material did over 400 years ago. The opportunity for mass production of the written knowledge has transformed the classical methods of teachings. Electronic publishing, with its free flow of knowledge, has already reshaped the structure of our libraries, and it is posed to influence not only the physical structure of the classroom but also the style and methods of teaching. Even the technical publications distributed by the Institute of Electrical and Electronics Engineers (IEEE) as journals or symposia digests are gradually moving to the electronic format. It is not too far off mark that, in a short time, the technical papers are going to merely be a movie clip of the actual experiments or numerical models of the reported paper. The IEEE Microwave Theory and Techniques (MTT) Society has led this campaign and is poised to provide the information-age benefits to its members. Since one of the primary responsibilities of any professional society is the continuing education of its members, it is natural to expect the MTT Society to initiate educational initiatives. As a result of advances in telecommunication and the popularity of the Internet, electronic multimedia now could augment the traditional teaching methods. Hence, the Education Committee initiated the Microwave Multimedia Module (M4) project, in addition to many other efforts. The Drexel University team of Mohammed-Reza Tofighi, a Ph.D. student, and myself has responded to the M4 project challenge. Our goal is to develop an E-book that covers various topics in passive and active microwave circuits in the hope of assisting MTT Society members in their continuing education efforts. This product is developed as standard “post page” and will be completed in mid-2001. The copyrighted material will then be delivered to IEEE as an electronic book.

PLL and injection locked PLL (ILPLL) operations of a push-pull self oscillating mixer (SOM)

This work presents the measurement results of a 2.5 GHz push-pull self-oscillating mixer (SOM) circuit with internal and external LC resonators. This SOM is used for injection locked phase locked loop (ILPLL) applications, where a separate phase detector (PD) circuit is not required. This SOM design was fabricated using an InGaP/GaAs HBT foundry process. Output power of about 0 dBm is attained over a large frequency tuning range. The power consumption of the SOM is typically about 60 mW using a 5 V supply. The voltage down-conversion gain and power up-conversion gain of up to 15 and 11.5 dB are measured for the circuit. It is also observed that there is a compromise between obtaining a high conversion gain and low close-in to carrier phase noise. It is demonstrated that a phase noise improvement of up to 6 dB can be achieved by implementing an external LC resonator.