Self and mutual admittance of slot antennas on a dielectric half-space

In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ _r =3.80), crystal quartz (∈ _r =4.53), silicon (∈ _r =11.9) and GaAs (∈ _r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies.     

Practical limitations of subwavelength resolution using negative-refractive-index transmission-line lenses

Previously, we have demonstrated both analytically and experimentally subwavelength imaging using a negative-refractive-index lens made of a periodically L, C loaded transmission line (TL) network. This loaded transmission line network has been referred to as the dual TL lens. Here, we consider the limitations on subwavelength imaging imposed by impedance mismatches and the component losses of a practical dual TL lens. Simple expressions for estimating the resolving capability of a dual TL lens are given. It is found that the resolution enhancement of the dual lens is proportional to the quality factor of the series loading capacitors divided by the electrical thickness of the lens. The effective material parameters of the dual TL lens are also derived so that these expressions can be directly related to those of previous studies considering uniform and isotropic left-handed lenses. Finally, the resolving capability of an experimental lens that achieves subwavelength imaging is theoretically predicted. These theoretical predictions are then directly compared to previously reported experimental results.     

Abnormal wave propagation in passive media

Abnormal velocities in passive structures such as one-dimensional (1-D) photonic crystals and a slab having a negative index of refraction are discussed. In the case of 1-D photonic crystal, the frequency- and time-domain experiments for waves tuned to the bandgap of the photonic crystal demonstrate a positive group velocity exceeding the speed of light in vacuum (superluminal). In the case of a medium with negative index of refraction, our theoretical studies show that such a medium can support positive group and negative phase velocities (backward waves), as well as negative group and negative phase velocities. The meaning of superluminal group velocity and negative group velocity, or equally, positive superluminal group delay and negative group delay, are discussed. It is shown that despite their counterintuitive meaning there are no contradictions with the requirements of relativistic causality (Einstein causality). To clearly demonstrate this, the important subject of the "front" is reintroduced.     

Design and analysis of quasi-integrated horn antennas formillimeter and submillimeter-wave applications

The authors present a systematic process for the design of multimode quasi-integrated horn antennas, and provide a full range of practical antenna designs for millimeter- and submillimeter-wave applications. The design methodology is based on the Gaussian beam approach and the structures are optimized for achieving maximum fundamental Gaussian coupling efficiency. For this purpose, a hybrid technique is used in which the integrated part of the antennas is treated using full-wave analysis, whereas the machined part is treated using an approximate model. This results in a simple and efficient design process. The design procedure has been applied to the design of 20-, 23-, and 25-dB quasi-integrated horn antennas, all with a Gaussian coupling efficiency exceeding 97%. The designed antennas have been tested and characterized using both full-wave analysis and 91/370-GHz measurements. The quasi-integrated horn antennas are also examined as feed elements for Cassegrain antenna systems and are proved to be comparable to the traditional machined corrugated horn feeds     

Antenna applications of negative-refractive-index transmission-line structures

A number of new antenna-related applications that have recently been developed at the University of Toronto based on the concept of negative-refractive-index transmission-line metamaterials are reviewed. These include non-radiating phase-shifting lines that can produce either a positive or a negative phase-shift while exhibiting a broadband linear phase response, as well as compact and broadband series power dividers and associated planar series-fed printed dipole arrays with reduced beam-squinting. Moreover, a fully printed electrically small ring antenna featuring vertical polarisation and good radiation efficiency is also described     

A Multilayer Negative-Refractive-Index Transmission-Line (NRI-TL) Metamaterial Free-Space Lens at X-Band

A volumetric free-space negative-refractive-index (NRI) transmission-line (TL) metamaterial lens is described that employs fully printed interdigitated capacitors and meandered inductors designed to exhibit NRI properties at X-band (8-12 GHz). The volumetric topology is realized in a layer-by-layer fashion without any vias, which facilitates easy and rapid fabrication. The fabricated lens was tested for its transmission and dispersion properties using a free-space X-band measurement system consisting of an Agilent network analyzer, standard gain horn antennas, and Rexolite dielectric lenses fabricated in-house, and showed good correspondence with simulations. The focusing ability of the multilayer NRI-TL lens was also verified using a free-space field probing system based on small shielded-loop antennas affixed to a computer-controlled xyz-translator apparatus. Arguably, these results represent the first experimental evidence of coupling between TL-based metamaterials and sources in free space.     

Wide-scan spherical-lens antennas for automotive radars

A new approach to wide scan-angle antennas at millimeter-wave frequencies is introduced with special focus on ease of manufacturing and reliability. The system is composed of planar feed antennas (tapered-slot antennas), which are positioned around a homogeneous spherical Teflon lens. Beam scanning can be achieved by switching between the antenna elements. The spherical-lens system is analyzed through a combined ray-optics/diffraction method. It is found that a maximum efficiency of 50%-55% can be achieved using Teflon, Rexolite, or quartz lenses. The efficiency includes taper, spillover, and reflection loss. Calculations also indicate that the maximum lens diameter is 30-40 λ₀, which results in a maximum directivity of 39.5-42 dB. Measurements done on a single-element feed and a 5-cm Teflon lens agree very well with theory and result in a 3-dB beamwidth of 5.5° and better than -20-dB sidelobe levels at 77 GHz. Absolute gain measurements show a system efficiency of 46%-48% (including dielectric loss). A 23- and 33-element antenna array with a scan angle of ±90° and a -3.5- and -6-dB crossover, respectively, in the far-field patterns was also demonstrated. The 23-element array resulted in virtually no gain loss over the entire 90° scan angle. This represents, to our knowledge, the first wide scan-angle antenna at millimeter-wave frequencies     

Miniaturized microwave components and antennas using negative-refractive-index transmission-line (NRI-TL) metamaterials

Negative-refractive-index transmission-line (NRI-TL) metamaterials comprise transmission lines loaded periodically with series capacitors and shunt inductors, such that the phase flow and power flow are contra-directional on the lines. These NRI-TL media exhibit properties that can be utilized for miniaturizing microwave components and antennas. In this mainly review paper, a compact antenna, power divider and branch-line coupler are presented to demonstrate the miniaturization techniques enabled by NRI-TLs. Furthermore, a generalized NRI-TL is described that exhibits two left-handed and two right-handed bands. This can be exploited for realizing compact dual-band and quad-band RF/microwave components. This generalized NRI-TL can be designed to exhibit two distinct frequencies where the corresponding propagation constants vanish.     

Metallo-dielectric electromagnetic bandgap structures for suppression and isolation of the parallel-plate noise in high-speed circuits

A novel approach for the suppression of the parallel-plate waveguide (PPW) noise in high-speed printed circuit boards is presented. In this approach, one of the two conductors forming the PPW is replaced by an electromagnetic bandgap (EBG) surface. The main advantage of the proposed approach over the commonly practiced methods is the omnidirectional noise suppression it provides. For this purpose, two EBG structures are initially designed by utilizing an approximate circuit model. Subsequently, the corresponding band structures are characterized by analytical solutions using the transverse resonance method, as well as full-wave finite-element simulations. The designed EBG surfaces were fabricated and employed in a number of PPW test boards. The corresponding frequency-domain measurements exhibited bandgaps of approximately 2.21 and 3.35 GHz in the frequency range below 6 GHz. More importantly, suppression of the PPW noise by 53% was achieved based on time-domain reflectometry experiments, while maintaining the signal transmission quality within the required specifications for common signaling standards.     

Time-domain measurement of negative group delay in negative-refractive-index transmission-line metamaterials

We have simulated and constructed a one-dimensional metamaterial composed of a periodically loaded transmission line that exhibits both negative and positive group velocities in a band of effective negative index of refraction. The negative group velocity or, equivalently, the negative group delay, is demonstrated theoretically and experimentally in the time domain using modulated Gaussian pulses. Due to this negative delay, we can show an output pulse peak emerging from the loaded transmission line prior to the input peak entering the line, i.e., the output pulse precedes the input pulse. The fact that this surprising behavior does not violate the requirements of relativistic causality is illustrated with time-domain simulations, which show that discontinuities in the pulse waveforms are traveling at exactly the speed of light in vacuum. The pulse-reshaping mechanism underlying this behavior is also illustrated using time-domain simulations.