Showing papers by "Per-Simon Kildal published in 2009"

Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates

Abstract: This letter presents a new metamaterial-based waveguide technology referred to as ridge gap waveguides. The main advantages of the ridge gap waveguides compared to hollow waveguides are that they are planar and much cheaper to manufacture, in particular at high frequencies such as for millimeter and sub- millimeter waves. The latter is due to the fact that there are no mechanical joints across which electric currents must float. The gap waveguides have lower losses than microstrip lines, and they are completely shielded by metal so no additional packaging is needed, in contrast to the severe packaging problems associated with microstrip circuits. The gap waveguides are realized in a narrow gap between two parallel metal plates by using a texture or multilayer structure on one of the surfaces. The waves follow metal ridges in the textured surface. All wave propagation in other directions is prohibited (in cutoff) by realizing a high surface impedance (ideally a perfect magnetic conductor) in the textured surface at both sides of all ridges. Thereby, cavity resonances do not appear either within the band of operation. The present letter introduces the gap waveguide and presents some initial simulated results.

Three metamaterial-based gap waveguides between parallel metal plates for mm/submm waves

Abstract: This paper presents the basic ideas of how local waveguides and transmission lines can be designed to propagate along desired paths in the air gap between two metal surfaces. The principle of operation is related to the performance of artificial magnetic conductors, EBG surfaces and soft and hard surfaces. Three different major types of gap waveguides are described: ridge gap waveguides, microstrip gap lines and groove gap waveguides. Different realizations of the cut-off structures suppressing normal parallel plate modes are described, as well as expected applications, and possible problem areas preferably seen as research challenges.

Corrections to “Channel Sounding of Loaded Reverberation Chamber for Over-the-Air Testing of Wireless Devices—Coherence Bandwidth Versus Average Mode Bandwidth and Delay Spread”

Abstract: This letter finds the relation between different parameters that characterize the reverberation chamber as a channel emulator for over-the-air (OTA) testing of wireless devices and components. It is shown experimentally for the first time that the coherence bandwidth is proportional to the average mode bandwidth of the chamber. Both coherence bandwidth and average mode bandwidth increase when the chamber is loaded with absorbing objects, and thereby, the reverberation chamber can be controlled to emulate many different real-life environments. The relationship between RMS delay spread and coherence bandwidth are found from the measured channel response and are equal to the theoretical relation for isotropic multipath environments, being within previously published fundamental limits.

Waveguides and transmission lines in gaps between parallel conducting surfaces

Abstract: A new way of realizing microwave devices, such as electromagnetic transmission lines, waveguides and circuits of them, is disclosed, that is advantageous when the frequency is so high that existing transmission lines and waveguides have too large losses or cannot be manufactured cost-effectively with the tolerances required Thus, the new technology is intended to replace coaxial lines, hollow cylindrical waveguides, and microstrip lines and other substrate-bound transmission lines at high frequencies The microwave devices are realized by a narrow gap between two parallel surfaces of conducting material, by using a texture or multilayer structure on one of the surfaces The fields are mainly present inside the gap, and not in the texture or layer structure itself, so the losses are small The microwave device further comprises one or more conducting elements, such as a metal ridge or a groove in one of the two surfaces, or a metal strip located in a multilayer structure between the two surfaces The waves propagate along the conducting elements No metal connections between the two metal surfaces are needed At least one of the surfaces is provided with means to prohibit the waves from propagating in other directions between them than along the ridge, groove or strip At very high frequency the gap waveguides and gap lines may be realized inside an IC package or inside the chip itself

Design and Realization of a Linearly Polarized Eleven Feed for 1-10 GHz

Abstract: A new linearly polarized eleven feed for operation between 1 and 10 GHz is presented. This frequency band is higher than the realized before, and the input reflection coefficient is better than ${-}8$ dB over the frequency range, which also is an improvement over previous models. The log-periodic dipole petals have been designed by using a simple one-by-one parameter optimization scheme with a simulation tool based on moment method. The final analysis has been improved by applying an finite-difference time-domain (FDTD)-based solver for the central part of the feed and then a circuit network program to combine the results of the center part with the result of the dipole panels. The antenna has been manufactured by printed circuit board (PCB) technology on a metalized Kevlar sheet in order to obtain better tolerances and smaller dimensions than in previous models. Measurements show agreement with the analysis.

Decoupling Efficiency of a Wideband Vivaldi Focal Plane Array Feeding a Reflector Antenna

Abstract: A focal plane array (FPA) feeding a reflector can be used to achieve a large field of view (FOV) with overlapping simultaneous beams. In order to provide a continuous FOV over more than an octave bandwidth, the inter-element spacing in the FPA has to be electrically small over large parts of the band. This will inevitably result in strong mutual coupling effects between the array elements. On transmit, the total lost power due to mutual coupling can be quantified by the decoupling efficiency, a term recently introduced for antenna arrays. This paper presents measured decoupling efficiencies of a Vivaldi element FPA operating between 2.3 and 7 GHz. The radiation patterns of the FPA are calculated for two beam excitations by using measured embedded element patterns, and the corresponding decoupling efficiencies are evaluated by using measured S -parameters between all element ports. The FPA is assumed to illuminate a deep reflector with F/D=0.35 , and the overall reflector aperture efficiencies are computed. The decoupling efficiencies are also determined through the measurements of the total radiation efficiencies in a reverberation chamber, which includes material absorption losses.

Experimental Demonstration of Local Quasi-TEM Gap Modes in Single-Hard-Wall Waveguides

Abstract: This letter reports an experimental study of a gap waveguide which is able to support a plurality of degenerate local quasi-TEM modes. No sidewalls are needed to separate these modes, which is a very useful property in the upper microwave and millimeter-wave bands. The waveguiding media is formed in the gap between a conducting plate and a hard surface. The working principle is described first. Next a practical realization is explained and tested experimentally.

Fundamental properties of canonical soft and hard surfaces, perfect magnetic conductors and the newly introduced DB surface and their relation to different practical applications including cloaking

Abstract: There exist different types of artificial surfaces that can be used to control wave propagation. Examples are soft and hard surfaces, high impedance surfaces and electromagnetic bandgap (EBG) surfaces. Ideal canonical representations of such surfaces are desirable for initial analysis and proof of concept in new applications, before starting detailed time-consuming numerical simulations and design. The soft and hard surfaces are well represented by an ideal canonical PEC/PMC strip grid, and the high impedance surface by a PMC. The EBG surface has no ideal canonical form, but in the present paper it is argued that the newly introduced DB surface (with boundary condition D n =B n = 0) can be considered an ideal canonical representation of an EBG surface, or in other words an isotropic soft surface. There exists also a theoretical DB´ surface (with boundary condition dDn /dn = dBn /dn =0), but this has no known realization. It is argued that if the latter could be realized, it will be very suitable for cloaking.

Direct coupling as a residual error contribution during OTA measurements of wireless devices in reverberation chamber

Abstract: We have presented an improved theory for the uncertainty of measurements in reverberation chamber. The theory is obtained by including the error due to the direct coupling between the antenna under test and the wall-mounted antennas. The theory includes the Rician K-factor that can be estimated from simple formulas, and an empirical mechanical stirring bandwidth B mech that is adjusted to get good agreement with the measured STDs. However, B mech is fixed for a given chamber and stirrer configuration. The new theory is able to describe variations of uncertainty with frequency and loading, and it can very well predict the degradation when platform and polarization stirring is not used. The validation of the theory is representative for efficiency measurements, but it will be equivalent for measuring total radiated power and receiver sensitivity.

Design of transition from coaxial line to ridge gap waveguide

Abstract: This paper presents the design of a simple transition from ridge gap waveguide to coaxial line transition. First, a straight ridge gap waveguide with single transition on end is simulated. Then a ridge gap waveguide with two 90° bends is simulated with two transitions on each end. Available commercial FDTD simulation tool was used to design the transitions. A return loss of −10 dB was achieved over the frequency band of 12– 15.75 GHz.

Theoretical derivation and measurements of the relationship between coherence bandwidth and RMS delay spread in reverberation chamber

Abstract: This paper presents the derivation and measurements of the relationship of coherence bandwidths and RMS delay spreads in reverberation chamber. The measured results are in good agreement with the theory. The coherence bandwidths are controlled to be between 2.5 and 10 MHz by loading the chamber.

Numerical analysis of a metamaterial-based ridge gap waveguide with a bed of nails as parallel-plate mode killer

Abstract: This paper presents a numerical analysis of a ridge gap waveguide. Ridge gap waveguides belongs to a new metamaterial-based waveguide technology for millimeter and submillimeter waves which emerged recently. The magnetic boundary condition or high-impedance surface (ideally a PMC) has been realized by means of a bed of nails as parallel-plate mode killer. Field plots of the ideal PEC-over-PMC ridge gap waveguide are presented, as well as when the PMC is realized by the bed of nails. The quasi-TEM mode shows an octave useable bandwidth for the bed of nails case.

Cut-off bandwidth of metamaterial-based parallel plate gap waveguide with one textured metal pin surface

Abstract: This work explores the possibilities of creating stop bands (or bandgaps) for TEM mode in parallel plate waveguides by using artificial surfaces in one of the plates. Particularly, as artificial surface a textured periodic surface made of metal pins has been selected. The present paper reports a parametric study of the “Fakir's bed of nails” structure in terms of the size of the achieved bandgap when the structure is placed within a parallel plate waveguide. Bandwidths larger than 2:1 are seen to be possible. The proposed structure could be used for the design of the new type of waveguides named gap waveguides.

Study of the characteristic impedance of a ridge gap waveguide

Abstract: This paper presents a study of the characteristic impedance of a ridge gap waveguide. Ridge gap waveguides belongs to a new metamaterial-based waveguide technology for millimeter and submillimeter waves which emerged recently. A formula for the characteristic impedance of an ideal PEC-over-PMC ridge gap waveguide has been derived. A preliminary numerical study of the characteristic impedance of a real ridge gap waveguide where the PMC is realized by a bed of nails is also presented.

Modelling of soft and hard surfaces using ideal perfect electric conducting/perfect magnetic conducting strip grids

Abstract: Strip-loaded surfaces and corrugated surfaces can be efficiently analysed using asymptotic boundary conditions that are valid in the limit of vanishing strip and corrugation period, respectively. An even simpler boundary condition is obtained by assuming that the surfaces are ideally soft or hard. This corresponds to a curvilinear grid of quasi-parallel perfect electric conducting (PEC) and perfect magnetic conducting (PMC) strips of incremental width and period, referred to as a PEC/PMC strip grid. Such a simple model for soft/hard surfaces speeds up the design process and provides the proper object parameters under the ideal soft or hard conditions. After reaching the designed characteristics, one can study the bandwidth of realisations of the surface using the asymptotic boundary conditions and finally make a complete and detailed study of all characteristics of the realisations by including even the finite period of the strips and corrugations. The ideal PEC/PMC strip model is used here as an example applied to bodies of revolution (BOR) such as soft horns with transverse corrugations and hard horns with longitudinal corrugations. The longitudinally corrugated horn is not a BOR, but both the asymptotic boundary condition and the ideal PEC/PMC strip model make it possible to analyse it as a BOR with an anisotropic wall and this reduces the computer time enormously compared to a full wave analysis for a finite corrugation period. It is shown that the PEC/PMC strip grid can predict the radiation patterns well at the centre frequency, but the bandwidth cannot be determined.

Wideband, lowloss, low-cost, quasi-TEM metamaterial-based local waveguides in air gaps between parallel metal plates

Abstract: The paper presents a new waveguide appearing in the air gap between two parallel metal plates. One of the plates has a metal texture, and confined local waves follow ridges in the texture whereas they are prohibited from propagating in other directions by metal pins in the texture. The pins (or bed of nails) provide a high impedance surface that creates a stop band when used together with a metal surface, i.e. a parallel plate cut-off. The principle performance of the ridge gap waveguide is explained by numerical simulations of the dispersion diagram, both to show the parallel plate cut-off generated by the pin surface, but also to see the quasi-TEM wave propagating along the ridge. The performance is validated by numerical simulations and experimentally of a ridge gap waveguide with two 90 deg bends, including transitions to coaxial connectors. The ridge gap waveguide has a large potential for use up to THz because it can be realized without conducting joints between metal parts, and it lends itself to co-design and integration with active components.

Alternative ridge gap waveguide design using a mushroom-type EBG surface

Abstract: The new proposed ridge gap waveguide can be implemented with different types of periodic surfaces. In this manuscript we have shown how to use the mushroom-type EBG surface to this aim besides the previously used “Fakir's bed of nails”. The bandgap of the periodic structure inside the parallel plate gives the upper limit of the band of operation of the gap waveguide, being the distance to the upper plane or gap, a key parameter for the bandwidth. In both geometries, a reduction in this gap means a significant increase on the bandgap of the structure. Nevertheless, both structures have a bandwidth which is large enough for most of the applications, even if larger gap size values are considered. Due to its physical realization and volume, the pin surface is more suitable for high frequencies whereas the mushroom-type EBG surface could be used in lower frequency ranges.

Accuracy of antenna input reflection coefficient and mismatch factor measured in reverberation chamber

Abstract: It has previously been shown that radiation efficiency and input reflection coefficient S 11 fs of small antennas in free space can be obtained from measurements in reverberation chamber. The S 11 fs is obtained by so-called complex stirring of the S11 measured when the antenna is in the chamber. In the present paper it is shown that the accuracy of S 11 fs can be very good even for larger directive antennas at high frequency provided additional complex frequency stirring is applied. The corresponding deterioration loss in frequency resolution is small at high frequency, in the relative sense. The presented S 11 fs results match results measured in anechoic chamber down to −40 dB.

Study of excitation on beam ports versus element ports in performance evaluation of diversity and MIMO Arrays

Abstract: The main concern of the current communication is to elicit the influences of beam-forming upon different Multiple-Input Multiple-Output (MIMO) parameters in a rich scattering environment. A detailed study of desired parameters is presented with particular stress on total radiation efficiencies observed on Element ports and Beam ports. Measurements are performed in a Reverberation Chamber (RC). The results illustrate that performance as viewed through Element and Beam ports are, in general, equal. Hence, they confirm that in a rich and isotropic scattering environment, beam-forming technique does not prove beneficial. They also demonstrate that as long as received radiation power is preserved, the shapes of the elements' patterns are irrelevant.

Accuracy in Reverberation Chamber for wireless testing: Simple formulas for the number of independent samples

Abstract: The growing use of the Reverberation Chamber (RC) for wireless applications calls for methods of evaluating RC measurement accuracy. Focus is turning towards improved understanding of the processes that influence accuracy of measurements in a RC when different stirring techniques are employed. Measurement accuracy relies on the number of independent samples in measurement sequences. This paper presents simple formulas for the number of independent samples in RC measurements when different stirring techniques are employed. The theoretical model has been experimentally validated. The proposed formula is very simple and provides an understanding of the physical and electromagnetic processes involved in RC measurements. Moreover, it is general and should be applicable also to other reverberation chambers if similar stirring methods are used.

X-Ka dual band prime focus feed for satellite earth terminals

Abstract: In this paper we propose new technology for combining X and Ka band prime focus feed for use in satellite earth terminals with simultaneous transmit/receive in circular polarization and also with tracking opportunity. The paper discusses the electrical and mechanical design of Ka band choke horn integrated with X band Eleven feed formed by two parallel dipoles over ground plane. The simulated results show input reflection coefficient better than −15dB and feed patterns give aperture efficiency better than −3dB over X as well as Ka band for 50° half subtended angle of reflector.

Optimization of large log-periodic dual-dipole antenna by using Genetic Algorithm on embedded element in small log-periodic array

Abstract: The paper introduces a new method that can predict the reflection coefficient of a complete large log-periodic array (with large number of elements) by calculating the embedded S-parameters between all input and output ports of similar elements that are embedded in a much smaller log-periodic array. By this method we can apply global optimization scheme such as Genetic Algorithm on embedded element in the smaller log-periodic array to improve the reflection coefficient of the larger log-periodic array very efficiently. As an example, an Eleven feed for 2 – 13 GHz has been optimized by using Genetic Algorithm with the present method. The result is a reflection coefficient below −10 dB from 2 GHz to 13 GHz.

Analysis of global eigenmodes in an oversized rectangular waveguide with a hard surface on one broad wall for planar slot array antenna applications

Abstract: The problem of determining the eigenmodes of a rectangular waveguide with one broad hard wall formed by longitudinal corrugations with grooves filled with dielectric is considered. The dispersion equation is derived on the basis of using the asymptotic boundary conditions for corrugated surfaces. It is shown analytically that if the groove depth is equal to the value 0.25λ/(e−1)½ corresponding to the hard wall condition, the TE eigenmode spectrum of the waveguide comprises an infinite set of degenerated quasi-TEM modes with different transverse propagation constants and identical longitudinal propagation constants equal to the wavenumber k. Such solutions are important for understanding the local waves appearing along ridges in such waveguides, that has inspired to the invention of new so-called gap waveguides.

Development of a coolable 2–14 GHz Eleven feed for future radio telescopes for SKA and VLBI 2010

Abstract: The Eleven feed is a log-periodic array of parallel dipoles in Eleven (II) configuration. It exhibits constant beam width and phase center position over a decade bandwidth, and finds therefore application as a wideband feed for reflector antennas. The present paper gives a summary of the present performance of a 2–14 GHz Eleven feed that is under development for use as a feed for VLBI 2010 radio telescopes for geodesy. Previous reported Eleven feeds did not reach that high in frequency. The intention is also to develop a feed that can be integrated with a low noise amplifier inside a cryostat at temperature of 14K, and receive the waves focused by the primary reflector through an RF window in the cryostatic cavity. Thereby the lowest system noise temperature is ensured. The present model has successfully survived cooling to 14 K.

Local wave Green's functions of parallel plate metamaterial-based gap waveguides with one hard wall

Abstract: The purpose of the presented paper is to give the derivation of the Green's functions of oversized waveguides with one hard wall. Two different realizations of the hard wall were considered: idealized PEC/PMC model and the corrugated hard surface. The applied analysis method avoids the complexity of the Floquet mode approach by using appropriate asymptotic boundary conditions for the observed periodic structure. This is possible because the period of the used periodic structures is very small compared to the wavelength. The developed Green's functions have poles corresponding to surface wave modes and waveguide modes, and their properties are determined by considering the pole distribution. We have also developed a program that calculates the electromagnetic field distribution inside the considered waveguides. The computed results are compared with the results obtained with the general electromagnetic solver, and the agreement is very good.