C. K. Aanandan

ACTIVE MICROWAVE IMAGING FOR BREAST CANCER DETECTION

Active microwave imaging is explored as an imaging modality for early detection of breast cancer. When exposed to microwaves, breast tumor exhibits electrical properties that are significantly different from that of healthy breast tissues. The two approaches of active microwave imaging — confocal microwave technique with measured reflected signals and microwave tomographic imaging with measured scattered signals are addressed here. Normal and malignant breast tissue samples of same person are subjected to study within 30 minutes of mastectomy. Corn syrup is used as coupling medium, as its dielectric parameters show good match with that of the normal breast tissue samples. As bandwidth of the transmitter is an important aspect in the time domain confocal microwave imaging approach, wideband bowtie antenna having 2:1 VSWR bandwidth of 46% is designed for the transmission and reception of microwave signals. Same antenna is used for microwave tomographic imaging too at the frequency of 3000 MHz. Experimentally obtained time domain results are substantiated by finite difference time domain (FDTD) analysis. 2-D tomographic images are reconstructed with the collected scattered data using distorted Born iterative method. Variations of dielectric permittivity in breast samples are distinguishable from the obtained permittivity profiles.

A New Compact Microstrip-Fed Dual-Band Coplanar Antenna for WLAN Applications

A novel compact microstrip fed dual-band coplanar antenna for wireless local area network is presented. The antenna comprises of a rectangular center strip and two lateral strips printed on a dielectric substrate and excited using a 50 Omega microstrip transmission line. The antenna generates two separate resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. Lower resonant mode of the antenna has an impedance bandwidth (2:1 VSWR) of 330 MHz (2190-2520 MHz), which easily covers the required bandwidth of the 2.4 GHz WLAN, and the upper resonant mode has a bandwidth of 1.23 GHz (4849-6070 MHz), covering 5.2/5.8 GHz WLAN bands. The proposed antenna occupy an area of 217 mm2 when printed on FR4 substrate (epsivr=4.7). A rigorous experimental study has been conducted to confirm the characteristics of the antenna. Design equations for the proposed antenna are also developed

DESIGN OF COMPACT RECONFIGURABLE DUAL FREQUENCY MICROSTRIP ANTENNAS USING VARACTOR DIODES

The design of a compact, single feed, dual frequency dual polarized and electronically reconfigurable microstrip antenna is presented in this paper. A square patch loaded with a hexagonal slot having extended slot arms constitutes the fundamental structure of the antenna. The tuning of the two resonant frequencies is realized by varying the effective electrical length of the slot arms by embedding varactor diodes across the slots. A high tuning range of 34.43% (1.037–1.394 GHz) and 9.27% (1.359–1.485 GHz) is achieved for the two operating frequencies respectively, when the bias voltage is varied from 0 to −30 V. The salient feature of this design is that it uses no matching networks even though the resonant frequencies are tuned in a wide range with good matching below −10 dB. The antenna has an added advantage of size reduction up to 80.11% and 65.69% for the two operating frequencies compared to conventional rectangular patches.

An Electronically Reconfigurable Microstrip Antenna With Switchable Slots for Polarization Diversity

An electronically reconfigurable microstrip antenna with circular and linear polarization switching is presented. The prototype fabricated on a substrate of dielectric constant (εr) 4.4 and height (h) 1.6 mm is fed by a proximity feed fabricated using the same substrate. By controlling the bias voltage of two PIN diodes, the polarization of the antenna can be switched between three states; two states for linear polarization (horizontal and vertical) and one state for circular polarization (RHCP). Simulation and experimental results show that the proposed antenna has a cross polar level better than 10 dB in the linear polarization state and 18 MHz axial ratio bandwidth in the circular polarization state. The frequency and polarization diversities of this design could potentially improve the reliability of wireless communication systems.

Compact dual band slot loaded circular microstrip antenna with a superstrate

Design of a compact dual frequency microstrip antenna is presented. The structure consists of a slotted circular patch with a dielectric superstrate. The superstrate,not only acts as a radome, but improves the bandwidth and lowers the resonant frequency also. The proposed design provides an overall size reduction of about 60% compared to an unslotted patch along with good efficiency,gain and bandwidth. The polarization planes at the two resonances are orthogonal and can be simultaneously excited using a coaxial feed. Parametric study of this configuration showed that the frequency ratio of the two resonances can be varied from 1.17 to 1.7 enabling its applications in the major wireless communication bands like AWS, DECT,PHS,Wi.Bro,ISM,and DMB. Design equations are also deduced for the proposed antenna and validated.

A Compact Dual-Band Planar Antenna for DCS-1900/PCS/PHS, WCDMA/IMT-2000, and WLAN Applications

A compact dual-band planar antenna developed for DCS-1900/PCS/PHS, WCDMA/IMT-2000, and WLAN applications is presented. The proposed antenna consists of a flared monopole with an additional sleeve for dual-band applications. The overall size of the antenna is 40 mm times 25 mm times 1.6 mm including the Finite Ground CPW feeding mechanism. The antenna operates in two frequency bands from 1.83 to 2.34 GHz and 3.23 to 5.76 GHz covering DCS-1900/PCS/PHS, WCDMA/IMT-2000, and WLAN bands. Simulation results along with measurements of the prototyped antenna are presented and discussed.

Dielectric Studies of Corn Syrup for Applications in Microwave Breast Imaging

Permittivity and conductivity studies of corn syrup in various concentrations are performed using coaxial cavity perturbation technique over a frequency range of 250 MHz-3000 MHz. The results are utilized to estimate relaxation time and dipole moments of the samples. The stability of the material over the variations of time is studied. The measured specific absorption rate of the material complies with the microwave power absorption rate of biological tissues. This suggests the feasibility of using corn syrup as a suitable, cost effective coupling medium for microwave breast imaging. The material can also be used as an efficient breast phantom in microwave breast imaging studies.

SQUARE MONOPOLE ANTENNA FOR ULTRA WIDE BAND COMMUNICATION APPLICATIONS

In this paper, we present a detailed study of a printed square monopole antenna for Ultra Wide Band (UWB) communication applications. The 2:1 VSWR bandwidth of the proposed antenna is from 2.87–14 GHz. The antenna can be made to reject particular frequency bands by introducing narrow slits on the patch. In addition, the rejection band can be easily tuned for centre frequency, VSWR and rejection bandwidth by adjusting the slit parameters. In the proposed antenna, slits are introduced to reject the IEEE802.11a and HIPERLAN/2 bands used for WLAN applications. The antenna is analyzed in both frequency and time domains. Radiation patterns of the antenna are omnidirectional with appreciable gain throughout the band. Transient analysis indicates linear phase response and minimum pulse distortion.

Wideband Printed Microstrip Antenna for Wireless Communications

A simple electromagnetically coupled wideband printed microstrip antenna having a 2:1 VSWR bandwidth of 38% covering the 5.2/5.8-GHz WLAN, HIPERLAN2, and HiSWANa communication bands is presented. The large bandwidth is obtained by adding a rectangular metal strip on a slotted square microstrip antenna. The antenna occupies an overall dimension of 42 times 55 times 3.2 mm3 when printed on a substrate of dielectric constant 4. It exhibits good radiation characteristics and moderate gain in the entire operating band. Details of the design along with experimental and simulation results are presented and discussed.

Analysis of a new compact microstrip antenna

A new compact microstrip antenna element is analyzed. The analysis can accurately predict the resonant frequency, input impedance, and radiation patterns. The predicted results are compared with experimental results and excellent agreement is observed. These antenna elements are more suitable in applications where limited antenna real estate is available.