Dhanesh G. Kurup

Synthesis of uniform amplitude unequally spaced antenna arrays using the differential evolution algorithm

A computationally efficient global optimization method, the differential evolution algorithm (DEA), is proposed for the synthesis of uniform amplitude arrays of two classes, i.e., unequally spaced arrays with equal phases and unequal phases. Phase-only synthesis and the synthesis of uniformly exited unequally spaced arrays (position only synthesis) are compared and it is seen that, by using the unequal spacing, the number of array elements can be significantly reduced for attaining reduced sidelobe levels. From the DEA-based synthesis of unequally spaced arrays with uniform amplitudes and unequal phases, it is found that a tradeoff exists between the size of the unequally spaced arrays and the range of phases for the same radiation characteristics. The proposed synthesis technique using uniform amplitudes, unequal spacing, and unequal phases (position-phase synthesis) not only decreases the size of the array for the same sidelobe level compared to both the phase-only synthesis and position-only synthesis but also retains their advantages.

Design of an unequally spaced reflectarray

We present the design and experimental results of an X-band unequally spaced reflectarray of microstrip patch elements. For a given number of elements, it is shown that reduced sidelobe levels can be attained for unequally spaced reflectarrays compared to that of equally spaced reflectarrays with no significant change in directivity and array size. The synthesis tool used for deriving the element positions is a variant of the genetic algorithm, namely the differential evolution algorithm.

Amplifying active reflect-antenna using a microstrip-T coupled patch /sub e/sign and measurement

A compact design of an amplifying active reflect-antenna using a novel microstrip-T coupled-patch antenna is proposed. The dual-polarized ports of the microstrip-T coupled-patch antenna provide excellent RF isolation as well as dc isolation. The dc isolation helps in avoiding additional coupling capacitors in the RF path, thereby achieving reduced layout size and cross-polarization levels for the active reflect-antenna. The gain and monostatic radar cross section (RCS) measurement of the active reflect-antenna has been carried out using a time-domain technique based on a single dual-polarized antenna and vector network analyzer. The measured monostatic RCS and gains are then compared with the calculated ones using two different modeling approaches.

Spatial Domain Green's Functions of Layered Media Using a New Method for Sommerfeld Integrals

A simplified approach for accurate and efficient computation of infinite domain Sommerfeld integrals (SI) associated with spatial domain Greens functions of layered media is described in this article. Integrand in SI excluding Bessel function is expressed as sum of complex exponentials using the matrix pencil method (MPM) which requires fewer terms than when we include oscillating Bessel functions. By using a novel three term representation for small arguments and classical large argument formulas of Bessel functions, analytical expressions for computing integrals along infinite domain SI tails are derived. The newly derived analytical formulas use the same MPM expansions for any given set of radial distance parameter ρ, enabling us to efficiently solve closed form Greens functions in layered media.

Analytical Expressions for Spatial-Domain Green’s Functions in Layered Media

Accurate and efficient formulas for computing spatial-domain Greens functions are presented in this paper. To apply the formulas, we only require a set of sample points of the spectral-domain Greens function (SDGF) on an integration path avoiding its singularities and an infinite domain tail path. Since the sampling is carried out for the integrand excluding the Bessel function, the number of sample points required is much smaller than the numerical integration method. This aspect of the proposed method proves to be very advantageous for evaluating closed-form Greens functions at large source observer distances. It is shown that the proposed formulas provide accurate results for both the near- and far-field regions as well as a wide range of material parameters such as lossless, lossy, left-handed materials as well as multilayered substrates.

DIELECTRIC CONNECTORS FOR MULTILAYERED RF INTEGRATION

Using an array synthesis tool based on a modified differential evolution algorithm, it is shown that the position-phase synthesis exhibits improved pattern characteristics compared to both the phase only and position only synthesis of uniform amplitude antenna arrays. The design of an unequally spaced planar reflect-array and an active power combining reflect-array are presented. The unit cell of the active reflect-array consists of an amplifying active reflect-antenna designed using a novel dual polarized microstrip-T coupled patch antenna. Two modelling approaches are proposed for the active reflect-antenna and the modelling methods are compared with the experiments.A computationally efficient analysis of an H-slot in the ground plane of a microstripline is carried out using a transmission line model. To improve the accuracy in the resonant region of the H-slot and retaining the computational efficiency, an artificial neural network is combined with an efficient spectral domain method. An efficient analysis tool for a silicon micromachined H-slot coupled antenna is developed by combining the transmission line models of the H-slot and an aperture coupled antenna. The experimental results are compared with the theory showing good agreement.The analysis and design of a microwave amplifier based on non-resonant slot matching is carried out. It is seen that the designed slot matched amplifier has decreased layout size, improved gain and noise figure characteristics compared to a stub matched amplifier. An efficient method for the analysis of non-resonant slots is compared with other approaches showing good agreement. This points to the fact that non-resonant slot matched circuits can be designed with the same speed and efficiency as we design the traditional stub based matching circuits.To address the problem of bandwidth and performance of reflect-arrays we propose a dielectric resonator antenna with slotline stubs. As a preliminary step we design a dielectric resonator antenna with slotline feed and the experimental results are compared with those of a commercial CAD tool. Design and analysis of 3D interconnects based on non-radiative dielectric waveguides is carried out. At millimeterwave, these interconnects are useful for hybrid and multilayer integration techniques.

Design and analysis of a 6 Watt GaN based X-band power amplifier

This paper, deals with the design of a class AB, Gallium Nitride (GaN) transistor based High Power Amplifier (HPA) for Monolithic Microwave Integrated Circuits (MMICs). GaN transistor is selected because of its rugged nature and its capability to work in extreme conditions. The designed HPA is intended to be housed in a Quad Trans-Receive Module (QTRM) of an Active Phased Array RADAR system. The HPA delivers a gain of 10.2 dB and an output power of 37 dBm, as well as high efficiency over many octaves of bandwidth.

Implementation aspects of a new RFID anti-collision algorithm

In this article, we propose a new RFID anti-collision algorithm which increases the throughput as well as system efficiency when compared to the Dynamic Frame Slotted Aloha (DFSA) algorithm in EPC-global standard. The proposed algorithm is synthesized in 180nm technology for studying its power consumption and on-chip area.

Combined amplitude and phase noise effects in QAM direct conversion receivers

This paper deals with the modelling and simulation of combined phase and amplitude noise for QAM direct conversion receivers (DCR). We show that, due to phase noise, there is a cross coupling of quadrature component of the signal as well as quadrature component of amplitude noise to in-phase component of signal. Similarly, there is a cross coupling of in-phase component of signal as well as in-phase component of amplitude noise to quadrature component of the signal. Based on the analysis, the symbol error rate (SER) for different levels of amplitude noise as well as phase noise values are presented for M-ary QAM modulation schemes. It is seen that for small phase noise, the SER approaches theoretical SER for only amplitude noise case and increases to large values for large phase noise.

Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation

In recent research, microwave sensors have been used to follow up the recovery of lower extremity trauma patients. This is done mainly by monitoring the changes of dielectric properties of lower limb tissues such as skin, fat, muscle, and bone. As part of the characterization of the microwave sensor, it is crucial to assess the signal penetration in in vivo tissues. This work presents a new approach for investigating the penetration depth of planar microwave sensors based on the Split-Ring Resonator in the in vivo context of the femoral area. This approach is based on the optimization of a 3D simulation model using the platform of CST Microwave Studio and consisting of a sensor of the considered type and a multilayered material representing the femoral area. The geometry of the layered material is built based on information from ultrasound images and includes mainly the thicknesses of skin, fat, and muscle tissues. The optimization target is the measured S11 parameters at the sensor connector and the fitting parameters are the permittivity of each layer of the material. Four positions in the femoral area (two at distal and two at thigh) in four volunteers are considered for the in vivo study. The penetration depths are finally calculated with the help of the electric field distribution in simulations of the optimized model for each one of the 16 considered positions. The numerical results show that positions at the thigh contribute the highest penetration values of up to 17.5 mm. This finding has a high significance in planning in vitro penetration depth measurements and other tests that are going to be performed in the future.