There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This paper gives a basic review and a summary of recent developments for leaky-wave antennas (LWAs). An LWA uses a guiding structure that supports wave propagation along the length of the structure, with the wave radiating or “leaking” continuously along the structure. Such antennas may be uniform, quasi-uniform, or periodic. After reviewing the basic physics and operating principles, a summary of some recent advances for these types of structures is given. Recent advances include structures that can scan to endfire, structures that can scan through broadside, structures that are conformal to surfaces, and structures that incorporate power recycling or include active elements. Some of these novel structures are inspired by recent advances in the metamaterials area.

Leaky-Wave Antennas

Introduction to Electromagnetic Compatibility

In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.

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Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

Ultra Wideband Signals and Systems in Communication Engineering

In this letter, frequency selective surface (FSS) properties of a uniplanar electromagnetic band-gap (EBG) unit cell are studied. The unit cell consists of meander-line inductor and interdigital capacitors on one side of a substrate. Simulation results indicate that the unit cell exhibits passband characteristics centered at 10.04 GHz. FSS property of the structure is verified by measurement using X-band waveguides. The measured results show passband characteristics at 9.45 GHz. A 13 × 13 array of these unit cells (FSS screen) is used as a superstrate at a distance ≈ 0.5λ
 0
 over a patch antenna operating at 10.8 GHz, offset from center frequency of the FSS passband. Directivity improvement of 6.95 dB is observed along 0° in the measurements of patch antenna with FSS superstrate as compared to the patch antenna without superstrate.

FSS Properties of a Uniplanar EBG and Its Application in Directivity Enhancement of a Microstrip Antenna

In this study, theory of EMI shielding and research conducted on textile fabrics to impart conductivity for attenuating the electromagnetic (EM) radiation by means of different techniques have been reviewed in detail. Shielding of the EM waves can be done by means of reflection, multiple reflection and absorption by the shield. Different metals with their alloys and polymeric materials are initially used as shielding materials with some limitations. However, the recent developments in conductive fabrics and composites replace the conventional shielding materials. The composites with better conductivity and light weight could be a promising barrier material for protecting electronic circuits from the EM radiation and mechanical damage. Materials with high absorption co-efficient could impart shielding effectiveness of 80 dB for the frequency of 18 GHz. This paper mainly focuses on the necessity of conductive textile fabric and composites used as hybrid electromagnetic shields.

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Electromagnetic shielding behaviour of conductive filler composites and conductive fabrics – A review

A broadband and compact stacked microstrip patch antenna has been developed using stacked configuration. The antenna comprises two parasitic patches stacked above the driven patch fed by shifted microstrip feed and a step transformer between feed and patch to achieve broadband coupling. Cross polarization has been improved by inserting a vertical slot in the direction of feed. The antenna occupies very low volume of ${\mathbf{0}}.{\mathbf{36}}{\lambda _{{\mathbf{o}}}}\,\times\,{\mathbf{0}}.{\mathbf{39}}{\lambda _{{\mathbf{o}}}}\,\times\,{\mathbf{0}}.{\mathbf{096}}{\lambda _{\mathbf{o}}}$ (radiating elements volume), while overall dimensions with ground plane are ${\mathbf{0}}.{\mathbf{7}}{\lambda _{{\mathbf{o}}}}\,\times\,{\mathbf{0}}.{\mathbf{7}}{\lambda _{{\mathbf{o}}}}\,\times\,{\mathbf{0}}.{\mathbf{096}}{\lambda _{\mathbf{o}}}$ . The overall bandwidth achieved is 35% (4.9–7.05 GHz) and a peak gain of 8.2 dBi with average gain of 6 dBi. Antenna radiation patterns are quite unidirectional with ${\mathbf{F}}\text{/}{\mathbf{B}} > {\mathbf{21}}$ dB and significantly low cross-polarization levels, suitable for target scanning applications. In the class of printed broadband antennas with unbroken ground plane, the proposed antenna achieves minimum volume with good bandwidth and radiation properties.

Compact and Broadband Stacked Microstrip Patch Antenna for Target Scanning Applications

A simple technique to reconfigure a notch filter employing a 1-D electromagnetic bandgap (EBG) structure, which is capacitively coupled to a microstrip line, is presented in this letter. The resonant nature of the EBG creates a notch in the transmission band. The notch filter is made reconfigurable/tunable by introducing an additional capacitive structure to change the size (geometry) of the EBG unit cell. The structure is connected or disconnected to the main structure (unit cell) by means of a PIN diode or varactor diode. Its application in notched-band ultra wideband (UWB) filter is demonstrated. A 450 MHz change in notch frequency is observed using PIN diode, and 340 MHz tuning range is observed using varactor diode.

Switchable and Tunable Notch in Ultra-Wideband Filter Using Electromagnetic Bandgap Structure

A series of monolithic tunable microwave band-stop filters and phase shifters have been designed, fabricated, and characterized on arrays of ferromagnetic nanowires (FMNWs) constituted of Ni, Co, CoFeB, and NiFe alloy embedded in anodic alumina templates (AAO). The aim of the present investigation is to significantly boost the operating frequency of devices in very low applied magnetic field. The stop-band response can cover from 8 to 40 GHz with an applied magnetic field up to 5 kOe using these materials. In addition, we observed a substantial increase in frequency tunability (>110%) for Ni and NiFe alloy based filter. Frequency bandwidth/linewidth can be tuned with the proper choice of magnetic material, broad band for Co nanowires to narrow band for CoFeB nanowires. The amorphous nature of CoFeB reduces linewidth considerably and hence increases resonance absorption. It is also observed that the frequency linewidth (Δf) decreases with increasing applied magnetic field. The same filter can be used as a tunable phase shifter. For Ni nanowire based phase shifter, a maximum shift of 75°/cm at 4 kOe was observed.

Ananjan Basu

Papers

FSS Properties of a Uniplanar EBG and Its Application in Directivity Enhancement of a Microstrip Antenna

Electromagnetic shielding behaviour of conductive filler composites and conductive fabrics – A review

Compact and Broadband Stacked Microstrip Patch Antenna for Target Scanning Applications

Switchable and Tunable Notch in Ultra-Wideband Filter Using Electromagnetic Bandgap Structure

New opportunities in microwave electronics with ferromagnetic nanowires