Ramesh Garg

Edge feeding of microstrip ring antennas

We have achieved 50 /spl Omega/ input impedance for edge-fed narrow microstrip square-ring antennas by using the circumferential variation of current on the ring. The reference point for the current distribution has been fixed by loading the ring. The antenna has been modeled as a lossy transmission line to determine the variation of resonant frequency and input impedance with load. This model has been validated using the mixed potential integral equation approach. The agreement between the two approaches is found to be good. The concept and the model used here can be applied to any type of ring antenna including loop antennas.

Position Mutated Hierarchical Particle Swarm Optimization and its Application in Synthesis of Unequally Spaced Antenna Arrays

A family of position mutated hierarchical particle swarm optimization algorithms with time varying acceleration coefficients (viz. PM_nHPSO-TVAC, n = 1, 2, 3, 4) is introduced in this paper. The proposed position mutation schemes help the swarm to get out of local optima traps and the hierarchical nature of the swarm prevents premature convergence. One distinct advantage of the proposed algorithms over the existing mutated PSO algorithms is that PM_nHPSO-TVAC do not involve any controlling parameter. Performance of the proposed algorithms is evaluated on standard benchmark functions. Comparative study shows that PM_4HPSO-TVAC performs better than the other PM_n HPSO-TVAC, HPSO-TVAC, comprehensive learning PSO (CLPSO), adaptive-CLPSO (A-CLSPO), PSO with time-varying inertia weight (PSO-TVIW), and constriction factor PSO (CFPSO) for the benchmark functions considered. We apply the proposed algorithm to the synthesis of uniformly excited, unequally dpaced linear array to minimize sidelobe level (SLL) and to control first-null-beamwidth (FNBW) and null locations. Further, we apply the proposed algorithm to the synthesis of unequally spaced sparse planar array to minimize SLL.

Characterization of V-groove coupled microshield line

A new membrane supported air-filled V-groove coupled microshield has been investigated using finite element method. The even- and odd-mode characteristic impedances and the effective dielectric constants have been computed. The dependence on various dimensions has been studied. The crosstalk levels between adjacent lines have been compared with that in coupled microstrip lines, coupled microstrip lines with lateral ground planes, and V-groove structures with and without metallization in the groove.

A broad-band coupled-strips microstrip antenna

A coupled-strip microstrip antenna with increased bandwidth and increased polarization purity is presented. We have demonstrated the underlying principle of its operation using even/odd modes of the coupled strips. An optimized parameter set for three coupled strips is obtained. The VSWR=2, impedance bandwidth of this antenna is 23% for antenna thickness of 0.083/spl lambda//sub 0/.

Design of a PIFA-Driven Compact Yagi-Type Pattern Diversity Antenna for Handheld Devices

This letter presents a compact folded-strip printed inverted-F antenna (FS-PIFA) having dipole-like radiation pattern. The designed antenna operates at 2.45-GHz band and offers 5.75% bandwidth. A parametric study of the FS-PIFA is presented to show the effect of symmetry on the quality factor. Next, an FS-PIFA-driven compact Yagi-Uda antenna is designed by using folded strips as passive elements. The dimension of the Yagi antenna is optimized using mutated particle swarm optimization (PSO) algorithm. The designed Yagi-Uda antenna operates in the 2.45-GHz band with front-to-back (F/B) ratio of 17 dB and gain of 4.6 dBi. Finally, a pattern diversity antenna is realized by placing two such Yagi-Uda antennas back to back with a common reflector. The diversity antenna is very compact, and it occupies approximately 41 ×68 ×5 mm3 volume. The port isolation is about 24 dB. The signal envelope correlation coefficient of the diversity antenna is found to be as low as 0.074.

A Compact Yagi-Uda Type Pattern Diversity Antenna Driven by CPW-Fed Pseudomonopole

This paper presents two end-fed compact Yagi-Udatype pattern diversity antennas, which use a coplanar-waveguide (CPW)-fed printed pseudomonopole antenna (PPMA) as the driver element. The balun-less driver PPMA behaves like a folded strip dipole and adds to its compactness. A common mode/differential mode (CM/DM) decomposition of antenna current on PPMA is carried out to show that the CM current distribution is similar to the current distribution of an asymmetrically fed dipole. The designed three-element Yagi-Uda antenna operates in the 2.4-GHz band with F/B ratio of about 23 dB and gain of 7.3 dBi. The compact pattern diversity antennas are realized by using two Yagi-Uda antennas separated by a common reflector. Two diversity antennas are realized using two different arrangements of Yagi-Uda antennas. The separation between the constituent PPMAs is varied to study its effect on the isolation and element embedded efficiency. The better of the two diversity antennas has overall footprint area of 65 × 58 mm2 and the separation between two radiating elements is only 34 mm or 0.272 λo. The simulated and measured port isolation (|S12|) between two diversity branches is about 35 and 27 dB, respectively. The signal envelope correlation is 0.018 and the embedded efficiency is about 93%.

Physics-based compact lumped circuit model of PIFA using a retarded partial element equivalent circuit

This paper presents a physics based approach of developing a compact lumped circuit model of a narrow-strip printed inverted-F antenna (PIFA) using retarded partial element equivalent circuit (rPEEC) technique. The reduction in the rPEEC model size is achieved by assuming the potential to be uniform along the strip width, which is approximately λ/25, and by using non-uniform sub-gridding of capacitive and inductive cells to capture the charge and current discontinuity near the strip edge. In the proposed approach, the total number of lumped circuit elements is reduced by around 90% and the total number of nodes is reduced by nearly 65% at the cost of 1.037% change in the resonance frequency. Measurements show good agreement with rPEEC results.

Use of TSK type fuzzy system based fitness function approximation for efficient optimization of low-profile wideband diversity PIFA by PSO

This paper presents a computer aided design (CAD) framework for efficient optimization of antennas. Generally complicated antenna structure is directly optimized using evolutionary algorithm (EA) where each fitness function evaluation requires a full-wave electromagnetic (EM) simulation [1]–[2] and the whole design process requires thousands of full-wave simulations. In the proposed method, a Takagi-Sugeno-Kang (TSK) type fuzzy system is used to approximate the fitness function from fewer full-wave EM simulations. This approximated fitness function is used to optimize an antenna structure using particle swarm optimization (PSO) algorithm. In this paper, a low-profile selection-combining diversity printed-inverted-F-antenna (PIFA) structure is proposed and its geometry is optimized in the proposed CAD framework. It is found that the PSO in conjunction with TSK type fuzzy system forms an effective CAD framework which requires 100 times less number of full-wave EM simulations than the number of EM simulations required for direct PSO based optimization of the proposed diversity PIFA.

FINITE DIFFERENCE TIME DOMAIN (FDTD) ANALYSIS OF MICROWAVE CIRCUITS : A REVIEW WITH EXAMPLES

Finite Difference Time Domain (FDTD) technique is used extensively in the analysis and design of microwave problems. This technique is reviewed here in a tutorial fashion. The various aspects of FDTD dealt with are: stability criteria, numerical dispersion, various types of absorbing boundary conditions, excitation schemes and source modeling. A number of examples are worked out to describe the application of FDTD to microwave circuits and transmission lines. These include: modes in a waveguide cavity, propagation constant of parallel plate waveguide and microstrip line, characteristic impedance of microstrip line, S-parameters of microstrip patch antenna and microstrip low pass filter. Extraction of propagation constant in case of multimode propagation is also discussed. To bring out the real time animation display characteristic of this technique, the propagation of time domain pulse in a microstrip patch antenna is plotted in 3-D.

Design of power amplifiers at 2.4 GHz/900 MHz and implementation of on-chip linearization technique in 0.18/0.25/spl mu/m CMOS

This paper presents a step by step design of power amplifiers at 2.4 GHz (for WLAN applications) and on-chip linearization of these amplifiers. CMOS power amplifiers are designed at 2.4 GHz with output power ranging from 30 mW to 100 mW with efficiency varying from 20%-40%. Two or three stages are cascaded according to the gain and efficiency requirements. The topology used for 2.4 GHz amplifier is also verified as a part of an FM transmitter at 900 MHz. All these integrated power amplifiers are not intended to have a very good linearity. At the later part of this work, feedforward technique is used for linearization of a 2.4 GHz two-stage power amplifier in 0.25 /spl mu/m CMOS8 process. The power output of the linear amplifier (in push-pull configuration) is 17 dBm with 20% efficiency. The in-band non-linearity (from two-tone simulations) is given by 3/sup rd/ order inter-modulation product and is about 40 dBc. For on-chip combining, transformers and baluns are used. All the circuits are simulated using CADENCE tools (ICFB). Inductors, transformers and baluns are designed and simulated using ASITIC tools. The power amplifiers are currently under fabrication in CMOS8 (0.25 /spl mu/m) and CMOS9 (0.18 /spl mu/m) processes.