Sayantan Dhar

A Wideband Minkowski Fractal Dielectric Resonator Antenna

A CPW slot loop fed Minkowski shaped fractal dielectric resonator antenna is proposed. Self similar property of fractal geometry is utilized to bring higher order modes close together to realize a wide impedance bandwidth. A comparative study of the resonant frequency behavior between the well established fractal electrical boundary antennas and fractal magnetic boundary antennas is presented to provide insight into the functionality of the proposed antenna. The comparison highlights the fact that electrical boundary lowers resonance frequency, whereas fractal magnetic boundary increases the resonant frequency. Minkowski fractal is also compared with Koch fractal and Sierpinski curve geometries. It is observed that the Minkowski fractal DRA yields the widest impedance bandwidth along with stable gain amongst the three proposed geometries. The proposed antenna exhibits a fractional bandwidth of 64% (5.52 -10.72 GHz) and a maximum gain of 4.9 dBi.

Development of wearable and implantable antennas in the last decade: A review

Utilization of wearable textile materials as antenna substrate has been rapid due to the recent miniaturization of wireless devices. A wearable antenna is meant to be a part of the clothing used for communication purposes, which includes tracking and navigation, mobile computing and public safety. This article portrays research on wearable and body mounted antennas designed and developed for various applications at different frequency bands over the last decade. A section is also devoted to describe the developmental scenario of implantable antennas for medical applications.

A Dielectric Resonator-Loaded Minkowski Fractal-Shaped Slot Loop Heptaband Antenna

A multiband fractal co-planar waveguide (CPW)-fed slot antenna loaded with a dielectric resonator conforming to multiple wireless standards is presented in this paper. The Minkowski fractal geometry is utilized to generate multiple frequency bands as well as to provide a miniaturized design compared to its Euclidean counterpart. The idea behind placing the dielectric load is to serve a dual purpose of enhancing the impedance bandwidth of the antenna at the upper frequency band as well as improving the overall gain of the antenna. The slot loop acts as a hybrid antenna performing the task of both an antenna as well as a feed mechanism for the dielectric slab to radiate. Design guidelines involving closed form formulae and equivalent model consisting of lumped resonators, distributed resonators and impedance transformers of the dielectric-loaded fractal slot antenna are provided to present an insight into the functioning of the antenna. The reflection coefficient parameters of the antenna yield a close match between the circuit model and those obtained from full wave simulator. The proposed antenna exhibits a heptaband performance with a maximum gain of 3.1 dBi.

Lumped circuit model analysis of meander line antennas

The past decade has seen phenomenal advances in portable electronics technology like mobile phones, RFID tags and MP3 players. This has led to the development of System in Package (SiP) which combines all the necessary components into a single package. Miniaturization of RF circuit technology has resulted in the need for miniaturized antennas. Meander line antennas are widely used in applications where compactness and miniaturization are key objectives. Although this antenna has been widely used, yet no simple analytical model except those using complicated numerical techniques is available. In this paper, we present a simple analytical model to calculate the resonant frequency of the antenna employing a lumped equivalent circuit model. Circuit response of a typical meander line antenna using our model has been compared with simulated antenna response using Method of Moments based simulator IE3D with good agreement, thereby validating our approach.

Compact K-band distributed RF MEMS phase shifter based on high-speed switched capacitors

A high-speed switched capacitor based distributed MEMS phase shifter has been presented. Miniaturization of the conventional MEMS capacitor dimensions has been done to achieve sub-microsecond switching, lower actuation voltage and a compact structure. Conventional design approach of such high-speed MEMS capacitor based phase shifter employs cascading the capacitors on a linear coplanar transmission line. Compactness of the device is achieved by employing space filling curves like i) Meander line CPW and ii) Modified Hilbert curve CPW. Simulations conducted reveal that the modified Hilbert Curve based phase shifter provides the most compact structure and yields a phase shift of ∼180° at 22GHz (K-band). The modified Hilbert Curve occupies an area of (820×820) µm2 only. Electromechanical simulations indicate that the switched capacitors require an actuation voltage of 14V and a switching time of 220ns.

Miniaturization of wearable electro-textile antennas using Minkowski fractal geometry

This paper deals with miniaturization of wearable electro-textile antennas by the use of Minkowski fractal geometries. Two electro-textile materials namely Flectron and Zelt are considered for the design of flexible microstrip antennas. In both cases, polyester fabric material has been employed as dielectric medium. In the basic design both the antennas are designed for WLAN applications. The Flectron antenna provides a gain of 6.54 dB with an impedance bandwidth of 132 MHz whereas, the Zelt antenna offers a gain of 7.4 dB and an impedance bandwidth of 104 MHz. By applying Minkowski fractal geometry to the antennas, miniaturization is achieved. In its first iteration, antenna designs are optimized and tuned to WiBro band and in the second iteration, antennas are further miniaturized in order to make them suitable for GSM 1900 applications. In these two bands, the gain and efficiency of both Flectron and Zelt antennas conform to their respective wireless standards. The simulation studies reveal that Zelt antenna yields better results compared to Flectron antenna.

Novel compact CPW filter for MICs using metamaterial structures

A band pass filter for Q-band MIC application is presented using two sets of resonator of different dimensions on Silicon substrate. The two resonators are implemented with the help of metamaterial structures and compactness is achieved by placing the resonators on both signal and ground planes of a Co Planar Waveguide (CPW). The resonators are realized using Complementary Split Ring Resonators (CSRRs). An equivalent circuit of the proposed design is presented along with the fabricated structures. Extraction of the LCR parameters of the proposed equivalent circuit is demonstrated. Further, it is seen that changing the metamaterial structure geometry from CSRR to Complementary U-shaped Split Resonators (CUSRs) tailoring of the pass-band can be achieved. By using different combinations of these two resonators, it is possible to tailor the bandwidth of the filter.

A CPW fed slot loop Minkowski fractal antenna with enhanced channel selectivity

A Minkowski fractal shaped CPW fed slot antenna is proposed in this article. The primary objective of this paper is to obtain multiband characteristics with narrow bandwidth. The proposed antenna radiates with an omnidirectional pattern and may be utilized for wireless applications.

A reconfigurable dielectric resonator antenna for polarization diversity applications

A circularly polarized rectangular dielectric resonator antenna is presented. Circular polarization is obtained by introducing a cross slot to generate two near orthogonal degenerate modes having similar amplitudes and 900 phase difference. Four pin diodes are placed across the slots to switch between two polarization states namely, Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP). The antenna yields a measured impedance bandwidth of 26.3% in case of LHCP and 28.2% in case of RHCP. The antenna radiates with a gain of 4.21 dB exhibiting an axial ratio bandwidth of radiate with an acceptable gain over the entire band.

Preliminary studies on performance of a 2.45 GHz wearable antenna in the vicinity of human body

Impedance and radiation characteristics of 2.45 GHz wearable antennas in close proximity to a human body are studied in this paper. Three rectangular microstrip antennas namely wash cotton antenna, polyester antenna and polyester combined cotton antenna are considered in this preliminary study. Each of these three antennas is assumed to be placed in the vicinity of human torso with an air gap of 1 mm between torso and antenna. In this study, the human torso has been modeled as a lossy medium of fluid with permittivity and conductivity close to human torso at a frequency of 2.45 GHz. The results obtained indicate that the wearable antenna can provide required impedance and radiation characteristics even when it is placed in the vicinity of human body.