Quasi TEM Research Articles

Extremely Low-Profile Periodic 2-D Leaky-Wave Antenna: An Optimal Solution for Antenna-Frontend Integration

We investigate and present a very low-profile, high-efficiency, and high-gain 2-D leaky-wave antenna (2DLWA) implemented on a high permittivity substrate operating in the millimeter-wave range, paving the way for the seamless integration of a high-gain and high-efficiency antenna with a frontend. In contrast to the typical air-filled 2DLWA, where a perturbation of the first higher-order mode (TE1/TM1) results in highly directed broadside radiation, in the proposed antenna, the propagation and leakage of a quasi-TEM (Q-TEM) mode results in an extremely low-profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.065\lambda _{0}$ </tex-math></inline-formula> ), high-gain (~15 dBi) antenna. In this scenario, the transverse resonance condition for a Q-TEM mode is established by employing a capacitive partially reflective surface (PRS) in a thin ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.065\lambda _{0}$ </tex-math></inline-formula> ) substrate with a relative permittivity of 10.2. The proposed periodic 2DLWA, unlike the conventional uniform/quasi-uniform air-filled counterparts, radiates based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {n}=-\mathbf {1}$ </tex-math></inline-formula> space harmonic operation. Due to a strong mutual interaction between the PRS and ground plane, conventional design and analysis approaches are no longer relevant in this low-profile architecture. Instead, we employ the Floquet modal expansion theory to create an equivalent circuit model (ECM) for the PRS that takes into account the contributions and mutual interactions of the Floquet harmonics as well as the ground plane effect. By employing reflecting boundaries realized with edge truncation (air trenches) in a high permittivity substrate, we show that the aperture efficiency is enhanced by 15% compared to conventional counterpart.

Ferroelectric phase transition and crystal asymmetry monitoring of SrTiO3 using quasi TE m,1,1 and quasi TM m,1,1 modes

Dielectric spectroscopy of a SrTiO3 single crystal over a broad range of microwave frequency using quasi TEm,1,1 and quasi TMm,1,1 modes reveals crystal asymmetry from typical measurement of Q-factor, transmission, or frequency characteristics in continuous cooling down to a few Kelvin. The properties of the modes due to the crystal asymmetry are validated by implementing a quasiharmonic phonon approximation. The observed ferroelectric phase transition temperature is around 51 K, and quantum-mechanical stabilization of the paraelectric phase arises below 5 K with very high permittivity. Also, an antiferrodistortive transition was indicated at 105 K. Landau’s theory of correlation length supports the observation of an extra-loss term so the transition may be identified near the Q-factor maxima or transmission maxima depending on the other loss terms present in the cavity. Thus, the ferroelectric phase transition with respect to temperature is identified when its extra-loss term causes a discontinuity or deviation in the derivative of the temperature characteristic near the minimum of total cavity loss (maximum Q-factor or maximum transmission temperature characteristic). This temperature is confirmed by transmission amplitude variation of quasi TE2,1,1 under 200 V dc electric field showing the existence of the soft-mode. These measurements support a typical polarization model and explicit temperature dependency of the soft-mode incorporating an imaginary frequency.

Design and Characterization of Ultra-Wideband Horn Antenna in Quasi-TEM Mode

This paper describes the ultra-wideband horn antenna design operating in quasi TEM mode. The antenna consist of a triangular plate with an inclination angle above a ground plane and directly feed by a coaxial cable. Broadband characteristics, radiation pattern, high gain and small reflection coefficient were achieved. Its performance analysis and main parameters effects were obtained by using ANSYS HFSS software. In the numerical analysis, an optimized model was obtained in 1.57 to 12.85 GHz bandwidth a 11 to 14 dBi gain. The proposed antenna was manufactured and the measured reflection coefficient results show an operation frequency range between 1.48 and 10.12 GHz, agreeing very well with simulations.

Effective and accurate modelling of multiconductor transmission lines in multilayer dielectric media

Development of very high speed integrated circuits is currently of great interest for today's technologies. This paper presents the quasi–TEM approach for accurate parameter extraction of multiconductor transmission line interconnects in single–, two– and three–layered dielectric regions using the Finite Element Method (FEM). We illustrate that FEM is accurate and effective for modelling multilayered multiconductor transmission lines in strongly inhomogeneous media. We mainly focus on designing of five transmission lines embedded in single–, two– and three–layered dielectric media. We compute the capacitance matrices for these configurations. We also determine the quasi–TEM spectral for the potential distribution of the multiconductor transmission lines in multilayer dielectric media.

On switching behavior of ferrite substrate with magnetostatic and spin wave exchange term

Due to the generation of magnetostatic and spin waves, switching phenomena of ferrite substrate with a normal magnetic biasing field is presented. Generally below the X-band of microwave range, the Pozar’s quasi TEM waves (extraordinary waves) were studied, but for the study of X-band there should be an inclusion of spin wave exchange term (ωr) in the magnetostatic wave analysis which depends upon the static internal field (Hex). This term is included in analysis because the wavelength of microwave approach is the inter-atomic distance of ferrite material. In this work we synthesize LiTi ferrite through Solid State Reaction Technique (SSRT) and obtained electric and magnetic properties for the analysis. Absorbing and transmission power coefficients have been calculated to obtain the power loss and transmitted power through the substrate, respectively. The absorbing power coefficient verifies the switching behavior of substrate for certain range of applied external magnetic field (H o) which depends on the resonance line width parameter (ΔH) of ferrite material.

Influence of MSL Substrate Semiconductor Specific Resistivity on Electrodynamical Characteristics

In this paper the electrodynamical characteristics of open microstrip lines (MSLs) with semiconductor n–Si substrates were investigated using the method of singular integral equations (SIE) in the quasi–TEM approximation. Our algorithm allows anyone to consider in their calculations the real geometry and sizes of MSLs. There is an agreement between our numerical and experimental results. The dependences of a complex wave impedance, a wavelength, and an attenuation constant of a MSL were analyzed on the frequency f until f = 70 GHz. Our calculations were fulfilled for MSLs with low ohmic semiconductor substrates and for several specific resistivities of the substrate material. We specified the dependences of electrodynamical characteristics on frequencies when they became constant at the start of a certain frequency and then they remained constant at higher frequencies. These frequency values were dependent on the substrate specific resistivity.

THE PROPER CURRENT SPECTRA OF AN OPEN INTEGRATED MICROSTRIP WAVEGUIDE - Abstract

Continuous current spectrum of an integrated open waveguide structure is identified as the branch cut contribution to singularity expansion of those currents in the complex axial transform plane. Those singularities in that plane include poles associated with the guiding structure and branch points contributed by layered background environments. The manner in which singularities in background environments manifest themselves as branch points in the complex axial transform plane is reviewed. Based on spectral integral equation formulation, approximate and analytical expression for spatial microstrip current is obtained. That approximation is based on Maxwellian distribution for the transverse current profile. This result is the representation of currents in terms of proper propagation mode spectrum. During the integration around branch cuts, singularities in the transverse transform plane migrate in a complicated manner. The trajectories of this migration are identified and suitably accommodated during the real axis integration in that plane. This overall procedure leads to a decomposition of the total currents into bound modes and continuous spectrum contributions. This representation is validated by real axis integration in the axial transform plane. The quasi TEM characteristic impedance of bound mode is calculated and validated by comparison with well-known empirical formula.

Electromagnetic waves: microwave components and devices

Part 1 Electromagnetic waves: Maxwell's equations electromagnetic waves in non-conducting media energy flow in an electromagnetic wave electromagnetic waves in conducting materials propagation of waves in plasmas polarization of waves propagation in gyromagnetic media boundary conditions. Part 2 Waves guided by perfectly conducting boundaries: TEM transmission lines reflection of waves by a conducting plane transverse electric waves transverse magnetic waves propagation in a rectangular waveguide power flow in rectangular waveguide higher-order modes in a rectangular waveguide other waveguides. Part 3 Waves with dielectric boundaries: reflection of waves by a dielectric boundary total internal reflection the Brewster angle dielectric waveguides mono-mode and multi-mode optical fibres radomes, windows and optical blooming quasi TEM waveguides non-TEM waveguides. Part 4 Waves with imperfectly conducting boundaries: waves incident normally on a conducting surface transmission through a thin conducting sheet electromagnetic screening waves incident obliquely on a conducting surface losses in transmission lines and waveguides microwave attenuators microwave loads. Part 5 Antennas: magnetic vector potential retarded potentials small electric dipole the reciprocity theorem small magnetic dipole half-wave dipole dipole arrays radiation from apertures slot antennas phased array antennas. Part 6 Coupling between wave-guiding systems: discontinuities broadband matching techniques coupling without change of mode coupling with change of mode coupling by apertures effect of holes in screens on screening effectiveness waveguide directional couplers distributed coupling. Part 7 Electromagnetic resonators and filters: transmission-line resonators cavity resonators effect of resonance on screened enclosures dielectric resonators Fabry-Perot resonators filter theory transmission-line filters waveguide filters optical filters. Part 8 Ferrite devices: microwave properties of ferrites resonance isolators phase shifters and circulators junction circulators Faraday rotation devices edge mode devices YIG filters. Part 9 Solid state microwave devices: semiconductor materials diodes transistors detectors and mixers switches oscillators amplifiers monolithic microwave integrated circuits LEDs and laser diodes. Part 10 Vacuum devices: space-charge waves Klystron amplifiers slow-wave structures travelling wave tubes crossed-field tubes fast-wave devices electron accelerators. Part 11 Microwave measurements: measurement of frequency measurement of power measurement of gain and loss measurement of return loss (part contents).

Radiation of arbitrary shape symmetrical patch antenna coupled with a director

The radiation admittance of arbitrarily shaped symmetrical patch antennas has yet to be expressed.1 A quasi TEM two coupled transmission lines is now used to determine the conduction and polarisation current distributions and the radiation patterns of arbitrary-shape symmetrical patches coupled with a director and acting in a large bandwidth. In the particular case of the circular shape, the theoretical results are in good agreement with the experiments.

Effets de propagation et de brouillage dans les interconnexions de circuits hybrides

The authors present results of modelling and time domain analysis for the interconnecting lines of hybrid circuits. The quasi tem approximation used in our analysis is justified by an electromagnetic study based on spectral domain method. So, we can use the transmission line concept for the time domain analysis. They present the theory of a simulator for the study of resistive coupled lines mounted in cascade. The effects of mismatching, point discontinuities and losses on signal distortions are discussed in the case of one transmission line. For a set of coupled lines, we clarify the parasiting effects between adjacent lines. We show that a screen-line can reduce these effects if some design rules are respected.

Influence of feed-point location on radiation resistance of a short-circuited flat dipole

A quasi TEM lossy transmission line model is used to calculate the effect on the radiation resistance which is produced by moving the feed-point location along a short-circuited flat dipole acting at quarter-wave resonance. Very good agreement is obtained between theoretical and experimental results.

Theoretical radiation admittance of a large bandwidth flat symmetrical folded dipole

A theoretical model, equivalent to several lossy transmission lines acting at quasi TEM mode, is given to explain the bandwidth and the radiation admittance of the flat symmetrical folded dipole. We deduced that the flat dipole is acting at its third resonance with the largest bandwidth. Theoretical results are in good agreement with experiments realised on a model already used in several arrays of high gain or low sidelobe level.

Plasma Diagnostics with Short Electromagnetic Pulses

The propagation of short electromagnetic pulses in an ionized medium and the reflection of transient pulses from bounded ionized regions is discussed. Analytical expressions for transient oscillations in reflected and propagated electromagnetic fields excited by a unidirectional pulse are derived for certain simple cases. The transient oscillations show a periodicity which is directly related to the plasma frequency and are useful for nearly instantaneous plasma diagnostics. An experiment is described in which the reflection and transmission of unidirectional pulses of approximately 1 nanosecond duration is observed in the afterglow of a coaxial discharge tube. In addition to the dispersion of the quasi TEM mode in the coaxial test tube a transient oscillation with much lower periodicity is also observed and interpreted as arising from a surface-wave propagating near the interface between glass walls and the annular ionized region. This surface-wave propagates only at frequencies below the plasma frequency of the ionized region and its application for diagnostics of dense plasma is indicated.