Siamak Ebadi

A Microstrip Patch Electronically Steerable Parasitic Array Radiator (ESPAR) Antenna With Reactance-Tuned Coupling and Maintained Resonance

A new approach to parasitic phased-array antennas is presented. A symmetric two-layer, single-input inexpensive three-element array at 1-GHz employing varactors as tuning mechanisms are designed, fabricated, and measured. The driven element is mutually coupled to two parasitic elements in the H-plane. The varactors are used to control the mutual coupling and beam scanning and to maintain resonance at 1 GHz. A continuous scanning range of -15 + 15° is measured with maintained impedance matching and radiation pattern integrity. The low cost of diode varactors, used in place of expensive phase shifters, allows for more economic fabrication. This is advantageous to applications in point-to-point communication systems, weather, and target tracking radar systems.

A Low-Profile Wireless Passive Temperature Sensor Using Resonator/Antenna Integration Up to 1000

A novel wireless temperature sensor is presented herein for high-temperature applications. This sensor is robust in harsh environments using stable materials and purely passive structures. The resonant frequency of the sensor is determined by the temperature-dependent dielectric constant of the substrate material. The temperature can be wirelessly detected by sensing the resonant frequency of the sensor. The integration of the resonator and antenna enables realization of low-profile and compact sensors. Measured resonant frequency of the sensor decreases from 5.12 to 4.74 GHz when the temperature increases from 50°C to 1000°C. This corresponds to a variation of dielectric constant from 9.7 to 11.2 for the alumina substrate. The presented sensor structure is scalable in size or frequency based on the design requirements.

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In this paper, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under metallic-waveguide incidence. Using this theory, effects of different physical parameters on reflection properties of unit cells can be thoroughly studied without the need of full-wave simulations. It is shown that the reflectarray unit cell falls into three coupling regions depending on its physical dimensions and substrate properties, which lead to either well-behaved or inadequate reflection phase. Detailed analysis is performed for Ka -band reflectarray unit cells and verified by full-wave simulations. Reflectarray unit cells with different substrate thicknesses, patch widths, and dielectric constants are fabricated and measured. The measurement data closely matches both the theory and full-wave simulations. The presented theory provides valuable physical insight and guidelines for optimization of reflectarray unit cells.

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This letter introduces a new class of miniaturized reflectarray unit cells with increased phase swing employing Minkowski fractal-shaped patch-slot elements. Square, 1st Minkowski, and 2nd Minkowski fractal patches are designed as a reflectarray unit cell. A slot with variable lengths of 0 <; Ls <; 6 mm is used in the ground plane to perform the phase variation function. The resonant frequency corresponding to the maximum phase swing is reduced from 10.6 GHz for the square patch down to 8.8 and 8.3 GHz for the first- and second-order Minkowski fractal patches, respectively, which is equivalent to 17% and 22% size reduction. Unit cells with different patch type and slot length are fabricated, and close agreement is observed between the measured and simulated results. As it has been proven for conventional phased array antennas, this size reduction can lead to a decrease in mutual coupling in reflectarray antennas. Alternatively, it allows for smaller distance between reflectarray antenna elements, which renders a wider beam-scanning range.

Theoretical Analysis on Reflection Properties of Reflectarray Unit Cells Using Quality Factors

A novel method is presented in this paper to precisely characterize the dielectric properties of silicon carbon nitride (SiCN) ceramic materials at high temperatures for wireless passive sensing applications. This technique is based on a high quality factor (Q) dielectrically loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent. The dielectric properties of SiCN ceramics are characterized from 25 °C to 1000 °C. Two different metallization processes are implemented for the measurements with the highest temperatures of 500 °C and 1000 °C, respectively. A custom-made thru-reflect-line calibration kit is used to maximize the measurement accuracy at every temperature point. It is observed that the dielectric constant and loss tangent of the SiCN sample without Boron doping increase from 3.707 to 3.883 and from 0.0038 to 0.0213, respectively, when the temperature is raised from 25 °C to 500 °C, and for the SiCN with Boron doping (SiBCN), the dielectric constant and loss tangent increase from 4.817 to 5.132 and from 0.0020 to 0.0186, respectively, corresponding to the temperature ranging from 25 °C to 1000 °C. Experimental uncertainties for extracted εr and tanδ are no more than 0.0004 and 0.0001, respectively. The temperature dependency of Si(B)CN dielectric properties, as well as the dielectrically loaded cavity resonator structure, provides the basis for the development of wireless passive temperature sensors for high-temperature applications.

Miniaturized Reflectarray Unit Cell Using Fractal-Shaped Patch-Slot Configuration

In this paper, a new wireless sensing mechanism is proposed based on the integration of a cavity resonator and a slot antenna. A compact structure can be achieved since this integration eliminates additional volume of the antenna and transition structure between the resonator and antenna. A resonator/antenna is demonstrated to verify the proposed technique. The resonator/antenna size is 14 by 13 by 3 mm. The resonant frequency of the resonator, i.e. 10.13 GHz, can be wirelessly detected at distances up to 55 mm. This approach can be useful in high-temperature wireless sensing applications where only passive sensors can survive.

Characterization of SiCN Ceramic Material Dielectric Properties at High Temperatures for Harsh Environment Sensing Applications

Wireless passive temperature sensors for harsh-environment applications based on cylindrical microwave cavity resonators are presented herein. Slot antennas are integrated with sensors with zero additional volume. The resonant frequencies of the sensors are determined by the dielectric constants of the ceramic materials, which monotonically increase versus temperature. Silicoboron carbonitride (SiBCN) ceramic materials, which are very robust inside harsh environments featuring high temperatures and corrosive gases, are optimized in this paper to reduce dielectric losses and increase sensing ranges and accuracies. A robust interrogation antenna is developed to wirelessly measure the sensors up to 1300 °C. Two sensors based on Si6B1 and Si4B1 ceramics are measured up to 1050 °C and 1300 °C, respectively, with a sensitivity of ~0.78 MHz/°C at 1050 °C. This type of wireless, passive, and robust sensor can be used for many harsh-environment applications, such as gas turbines.

A compact wireless passive sensing mechanism based on a seamlessly integrated resonator/antenna

A low-cost electrically scanned phased array utilizing microstrip patch electrically steerable parasitic array radiator (ESPAR) subarray cells is presented for the first time. Four single-layer three-element ESPAR subarray cells at one-wavelength spacing are uniformly illuminated by a corporate feed network consisting of microstrip Wilkinson power dividers and ring hybrids. The array is scanned using a combination of ESPAR capacitive mutual coupling control and microstrip switched delay line phase shifters at the subarray level to achieve a scanning range from -20° to +20° while maintaining high return loss. The ESPAR coupling technique allows a 50% reduction in the number of phase shifters used by utilizing a full wavelength subcell spacing, resulting in excellent performance with inexpensive fabrication. The fabricated prototype exhibits boresight gain of 12.1 dBi with low scan loss and 7.0-dB worst case sidelobe level. The array is compared quantitatively to thinned arrays with and without parasitic elements to illustrate this advantageous technique. A functional prototype is fabricated and measured and is aptly predicted by the full-wave model.

Wireless Passive Temperature Sensors Using Integrated Cylindrical Resonator/Antenna for Harsh-Environment Applications

Tunable reflectarray unit cells operating at Ka- and X-bands are presented in this paper using barium strontium titanate (BST) technology. A patch antenna is capacitively loaded with a narrow gap in the middle and a thin-film BST layer is deposited under the patch. By tuning the dc-bias voltage across the gap, the dielectric properties of the BST layer are changed and then an integrated tunable capacitor is realized. The proposed design is evaluated using both full-wave simulations and measurements. Due to the monolithic integration of the tuning mechanism with the unit cell, the antenna element can be applied at millimeter-wave frequencies without suffering from packaging and bonding problems. The effects of substrate thickness, system pressure, and operating frequency on the performance of the BST-integrated unit cell are presented. An overall phase range of 298° and 263° with maximum reflection losses of 16 and 8.8 dB at Ka- and X-bands, respectively, are measured when the unit cells are operated for maximum phase range. By judiciously selecting the frequency of operation, a phase range of 250° with maximum reflection losses of 5.6 and 5.8 dB at 30.7 and 10.27 GHz are achieved. The presented analysis provides guidelines for optimizing the unit cells performance required for efficient beam-scanning reflectarray antennas.

A Low-Cost 2

A novel technique is presented in this paper to precisely characterize silicon carbonitride (SiCN) ceramic materials at high temperatures for wireless passive sensing applications. This technique is based on a high quality (Q) factor resonator method, which allows accurate characterization of both dielectric constant and loss tangent. SiCN ceramic materials are measured from 50°C up to 500°C. It is observed that the dielectric constant of SiCN increases from 3.71 to 3.87, corresponding to a temperature range between 50 and 500°C. This temperature-dependent dielectric constant behavior provides the basis for the development of wireless passive temperature sensors in high-temperature applications.