Ajay Chakrabarty

Low Insertion-Loss, Sharp-Rejection and Compact Microstrip Low-Pass Filters

Complementary split ring resonators are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. A prototype filter implementing area is 0.23 lambda_gtimes0.09lambda _g, lambda_g being the guided wavelength at 3-dB cut-off frequency (f_c) 1.887GHz. Maximum IL is within 0.5dB up to 1.717GHz and 20-dB stopband extends up to 3.4f_c

Ultrawideband Performance of Dielectric Loaded T-Shaped Monopole Transmit and Receive Antenna/EMI Sensor

This letter presents the performance of a T-shaped monopole antenna loaded with an annular dielectric resonator as an ultrawideband transmitting/receiving antenna. By adjusting the length of the monopole and load arm, a 10-dB bandwidth of 110% is achieved while maintaining monopole-like radiation pattern. The antenna factor of the same antenna, while used as electromagnetic interference (EMI) sensor is also presented for the desired and cross-polarized component of incident electric field. The results for antenna factor show an ultrawide bandwidth with the cross-polarization isolation better than 86 dB/m for the T-monopole/DRA as EMI sensor. The simulated result for return loss is verified with the measured data from a prototype antenna.

Compact Ultra-Wideband Bandpass Filter With Improved Upper Stopband

In this letter, a design of a compact bandpass filter with wide upper stopband is presented for the ultra-wideband communication systems. The filter structure is composed of a modified square slot-line resonator with parallel microstrip feed lines. Improved upper stopband is obtained by exploiting the frequency dispersive coupling behavior between the feed lines and the resonator. Measurements show that the 20.9 dB upper stopband extends at least up to 20 GHz. Filter occupying area is 0.26lambdag times 0.28g, lambdag being the microstrip line guided wavelength at 6.85 GHz.

Slotted Waveguide Antenna With Two Radiation Nulls

A design of a linear array antenna having two radiation nulls and otherwise omnidirectional radiation pattern is reported. A new configuration of a waveguide broad wall longitudinal slot doublet with positive and negative offsets with respect to the waveguide center line is used to design the array. This type of doublet produces two radiation nulls. Each of the null directions can be shifted at least up to plusmn25deg by proper choice of slot offset. Resonance and radiation characteristics of the proposed doublet are also presented. Finally, one linear array antenna consisting of seven doublets has been fabricated. Measurements show that the 15 dB null widths are 14.2deg and the null depths are at least 24.8 dB. Maximum gain ripple in the omnidirectional region is 1.75 dB.

Compact Wideband Bandpass Filters With Wide Upper Stopband

In this letter, a T-shaped microstrip feeding arrangement is proposed to design wideband bandpass filter (BPF) using shorted slot-line resonators. This feed line produces frequency selective external coupling which is utilized to suppress unwanted harmonics. Up to sixth order harmonics are suppressed. Other advantages are low passband group delay variation, ease of fabrication, low insertion loss (IL), and compact size. A fabricated BPF of fractional bandwidth 56.3% at midband frequency 2.3 GHz has a maximum IL of 1.2 dB in its passband and 30-dB upper stopband extends over 11.53 GHz

Estimation of equivalent circuit of loaded trans-receive antenna system and its time domain studies

The time domain studies of different reduced-height loaded wire antennas (e.g., inverted L, T, I and C-shaped antennas) when used in trans-receive system is presented. Due to the reduced height of the loaded antennas, these antennas have found wide application as transmitting and receiving antenna/sensors for electromagnetic interference (EMI) measurements. However, while using these antennas in trans-receive system for wideband application, the time domain characterization of both the transmit and receive antenna is required and investigation on this has not yet been performed. This paper presents the results of the initial investigation on the time-domain performance of these loaded trans-receive systems. An optimized transmit antenna generator waveform is used to maximize receive antenna voltage amplitude (with bounded input energy), as presented in the recent literature. The frequency domain Method of Moments with Pulse basis function and Point-matching technique has been used to evaluate the current distribution on the antenna surface and hence the radiated electric field at the position of the receiving antenna. The same technique has been extended for receiving wire antenna to evaluate the Complex Antenna Factor (CAF) of these antennas. The CAF versus frequency data has been used to evaluate the input and output voltage waveform of the trans-receive system. The results have been verified with theoretical and experimental data available in reported works.

Single-Layer Wideband Microwave Absorber Using Array of Crossed Dipoles

In this letter, a single-layer wideband absorber with compact thickness is proposed, and its ability to reduce the radar cross section (RCS) is investigated. The absorber consists of two-dimensional array of conductive crossed dipoles with lumped resistor elements on the top of a single-layer FR4 substrate, backed by continuous metallic layer. Simple methodologies for design and analysis of the absorber are presented. The thickness of the fabricated sample is less than 0.077λL. (wavelength at the lowest cutoff frequency). It offers the 10-dB reflection reduction bandwidth of 70.7% (5.3-11.2 GHz) and full width at half-maximum (FWHM) absorption bandwidth of 104.76% (3.75-12 GHz). The experimentally demonstrated performance of the absorber shows good agreement with the numerical simulations.

Miniaturized Dual-Mode Circular Patch Bandpass Filters With Wide Harmonic Separation

Two slots oriented orthogonal to each other are cut on a circular patch resonator. The slots bring down the fundamental resonance frequency of the patch. The second higher order mode, however, remains unaffected. This effectively miniaturizes the patch by 57.8% at the same time increases the harmonic separation by 2.51 times. By adding two more slots parallel to and on both the sides of each arm of the crossed slot, fundamental frequency can be further brought down resulting in a filter which is 87.4% smaller compared to a circular patch. The second passband appears at a frequency which is 4.66 times that of the first passband center frequency.

Estimation of Antenna Factor of Wire Antenna as Emi Sensor

The ratio of incident electric field at the surface of receiving antenna to the received voltage at the antenna terminal when terminated in 50 ohms load is known as the antenna factor. It is an important parameter of a sensor used for EMI measurements. To determine electromagnetic radiation from an electronic component it is required to evaluate the field strength at a certain distance from it using the sensor. If the antenna factor of the receiver and the received voltage are known then the field can be found out applying simple relations. In this paper a simple and useful Method of Moment-based theoretical technique is described to evaluate the antenna factor of wire antenna. The wire is considered as perfectly conducting with radius much less compared to the wavelength of operation. The wire is divided in large number of small segments. A point matching technique is applied to evaluate the surface current distribution due to the incident electric field. The output impedance is found out from the short circuit current and the open circuit voltage of the wire. The received voltage and hence the antenna factor is evaluated from the equivalent circuit diagram of the antenna. The data for current distribution on the antenna in receiving and transmitting mode and input impedance for transmitting mode are well comparable to the results available in literature. Studies have been extended for off-centered antenna and for oblique incidence of electric field.

Incorporation of Anti-Jamming Techniques in a GPS Receiver

GPS guidance uses low power signals from satellites which are 11000 NMI away. The satellite transmitter power is modest nearly 10 W orders of magnitude. Neither satellite nor receivers have the luxury of very high antenna gain since both entities have significant field of view requirements. These factors result in a very low power density incident on a GPS receiver antenna. The signal received is generally 165 dB down than the thermal noise level. Such signals are notoriously easy to jam either by intentional noise sources (Jammer) or unintentionally from harmonics of broadcasting stations or other out of band sources. Here in this paper we will show how a nulling antenna or controlled reception pattern antenna with adaptive spatial filtering technique efficiently mitigate the intentional and non intentional interferences.