Nahid Rahman

A Novel Modified Archimedean Polygonal Spiral Antenna

In this paper, we present a novel 2-18 GHz modified Archimedean polygonal spiral antenna that approximates a circular spiral in its highest frequencies and gradually transforms itself into a square spiral antenna at its lowest frequencies of operation. The design has successfully addressed the problem of high axial ratios associated with ultra-wideband (UWB) rectangular spiral antenna systems. A low-profile, cavity backed polygonal model and two variations of the original design are presented in this study. Our results demonstrate that the polygonal spiral antenna demonstrates excellent axial ratio and gain-bandwidth performance with ≤ 3 dB axial ratio over 97.5% of its operational bandwidth.

Millimeter Wave Complex Permittivity Measurements of High Dielectric Strength Thermoplastics

This paper presents for the first time the complex dielectric permittivity and loss tangent measurements for a selection of advanced polymer-based thermoplastics in the Q-band, V-band and W-band frequencies. These plastics are reported to have exceptional mechanical, thermal and electrical properties and are extensively used as electrical insulating materials, often operating at high voltages. With this view in mind, we have studied their dielectric properties with high-power sources in the millimeter wave range. The measurements have been performed using a broadband quasi-optical millimeter wave spectrometer with a backward wave oscillator (BWO) as a nondestructive high-power tunable source of coherent radiation. Values of real and imaginary parts of dielectric permittivity and loss tangent of the materials have been accurately calculated from the transmittance spectra.

Broadband absorbing material design and optimization of cavity-backed, two-arm Archimedean spiral antennas

In recent years, considerable interest has been placed on developing cavity-backed broadband antennas that retain their bandwidth performance despite having frequency-dependent lossy materials added to their cavities. Spiral antennas, especially Archimedean spiral antennas operating in the 2–18 GHz spectrum, are one of the most popular of these antennas, as they are very well-suited to a wide range of commercial, military and private applications where bandwidths of as much as 100:1 are desired. In most cases, a unidirectional pattern is preferred to detect reflections from or transmit towards one direction only. Therefore, a metallic cavity is added to absorb the back wave completely. Hence it becomes necessary to insert absorbing materials in the cavity that can effectively absorb EM energy over a wide range of desired frequencies.

Determination of negative permeability and permittivity of metal strip coated ferrite disks using the transmission and reflection technique

In this paper, a full band microwave isolator constructed from an array of metal wire-coated ferrite samples is presented. Here, the magnetic permeability of the metamaterialized structure is controlled by a relatively weak external magnetic field. The tunable permeability of the ferrites in this experiment allows us to create unidirectional wave propagation through the structure over the entire X-band frequency spectrum. The analysis presented here takes into account potential surface plasmon modes generated between the gaps of metal wires when the external magnetic field is applied. Here, we present a modification of the traditional transmission-reflection measurement method by normalizing the transmission and reflection coefficients. This modification removes the occurrence of atypical phenomena for negative imaginary components of permeability and permittivity that arises in the measurement of metamaterials. Our modified method precisely determines the refractive index, impedance, permittivity, and pe...

Beam-width control using a cavity-backed elliptical Archimedean spiral antenna

this paper presents the radiation characteristics and beam-width control features of a 2–18 GHz, cavity-backed, two-arm, elliptical Archimedean spiral antenna. 12We first discuss a precise microwave instrumentation and measurement technique to accurately characterize the frequency dependent complex permittivity and permeability of a wide variety of microwave materials. Using the method, we have designed a lightweight, multi-layer absorbing structure to be inserted in the cavity. For optimum performance, we have used a genetic algorithm approach to derive the optimal thickness of each layer. We then varied the ratio of the major axis to the minor axis of the spiral antenna to create an elliptical structure and observed changes in the radiation pattern. Our results show that by using an elliptical configuration, it is possible to regulate the beam-width in the two orthogonal planes by compromising to some extent the purity of the circular polarization.

Precise permittivty and permeability measurement of absorbers over broadband microwave frequency range

This paper presents complex permittivity and permeability measurements and reflection analysis of a selection of iron-loaded absorbing materials. A precise transmission-reflection based waveguide measurement technique was used to accurately characterize the materials in the 2 to 40 GHz frequency range. Based on the individual absorption spectra the materials were combined to form a composite structure that showed good absorption properties over a wide range of frequencies.

Broadband complex permittivity measurements of microwave interconnects and bonding materials

This paper presents a systematic study of the complex dielectric permittivity of two interconnect and bonding materials that are used in high frequency multi-chip modules. The materials are characterized in the Q-band, V-band and W-band frequency ranges using a broadband quasi-optical millimeter wave spectrometer with a backward wave oscillator (BWO) as a non-destructive high-power tunable source of coherent radiation. The real and imaginary parts of the dielectric permittivity and loss tangent have been accurately calculated from the transmittance spectra.

A novel polygonal spiral antenna

In this paper, we present a novel 2-18 GHz polygonal spiral antenna that approximates a circular spiral in its highest frequencies and gradually transforms itself into a square spiral antenna at its lowest frequencies of operation. The design has successfully addressed the problem of high axial ratios associated with UWB rectangular spiral antenna systems. Our results demonstrate that the polygonal spiral antenna demonstrates excellent axial ratio and gain-bandwidth performance with ≤3 dB axial ratio over 93.5% of its operational bandwidth.

Random and systematic error analysis in the complex permittivity measurements of high dielectric strength thermoplastics

This paper presents the complex dielectric permittivity and loss tangent measurements for a selection of advanced polymer-based thermoplastics in the Q-band, V-band and W-band frequencies and discusses in detail the random and systematic errors that arise in the experimental setup. These plastics are reported to have exceptional mechanical, thermal and electrical properties and are extensively used as electrical insulating materials, often operating at high voltages. With this view in mind, we have studied their dielectric properties with high-power sources in the millimeter wave range. The measurements have been performed using a broadband quasi-optical millimeter wave spectrometer with a backward wave oscillator (BWO) as a nondestructive high-power tunable source of coherent radiation. Values of real and imaginary parts of dielectric permittivity and loss tangent of the materials have been accurately calculated from the transmittance spectra.