Showing papers by "Per-Simon Kildal published in 2011"

Design and experimental verification of ridge gap waveguide in bed of nails for parallel-plate mode suppression

Abstract: This study describes the design and experimental verification of the ridge gap waveguide, appearing in the gap between parallel metal plates. One of the plates has a texture in the form of a wave-guiding metal ridge surrounded by metal posts. The latter posts, referred to as a pin surface or bed of nails, are designed to give a stopband for the normal parallel-plate modes between 10 and 23 GHz. The hardware demonstrator includes two 90 bends and two capacitive coupled coaxial transitions enabling measurements with a vector network analyser (VNA). The measured results verify the large bandwidth and low losses of the quasi-transverse electromagnetic (TEM) mode propagating along the guiding ridge, and that 90 bends can be designed in the same way as for microstrip lines. The demonstrator is designed for use around 15 GHz. Still, the ridge gap waveguide is more advantageous for frequencies above 30 GHz, because it can be realised entirely from metal using milling or moulding, and there are no requirements for conducting joints between the two plates that otherwise is a problem when realising conventional hollow waveguides.

Numerical studies of bandwidth of parallel-plate cut-off realised by a bed of nails, corrugations and mushroom-type electromagnetic bandgap for use in gap waveguides

Abstract: Recently it has been shown that so-called gap waveguides can be generated in the gap between parallel metal plates The gap waveguides are formed by metal ridges or strips along which local waves propagate, and parallel plate modes are prohibited from propagating by providing one of the surfaces with a texture that generates an artificial magnetic conductor (AMC) or an electromagnetic bandgap (EBG) surface on both sides of the ridges or strips The bandwidth of the gap waveguide is determined by the cut-off bandwidth of a parallel-plate waveguide where one surface has such a texture (and no ridges or strips) This paper studies the bandwidths (or stop bands) of such parallel-plate cut-offs when the AMC or EBG is realised by a metal pin surface, corrugations or a mushroom surface It is shown that cut-off bandwidths of up to 4:1 are potentially available, and thereby similar bandwidths should be achievable also for gap waveguides

Cryogenic 2–13 GHz Eleven Feed for Reflector Antennas in Future Wideband Radio Telescopes

Abstract: The system design of a cryogenic 2-13 GHz feed is considered with emphasis on its application in future wideband radio telescope systems. The feed is based on the so-called Eleven antenna and the design requires careful integration of various sub-designs in order to realize cryogenic operation. The various sub-designs include the electrical design of the Eleven antenna, design of the critical center puck, alternative solutions for integrating the Eleven antenna with low-noise amplifiers (LNAs), mechanical and cryogenic design and tests, and system noise temperature estimation and measurements. A great deal of simulated and measured results are presented throughout this paper, including the electrical, mechanical and cryogenic performance, and an assessment of the system noise temperature. The objective of this work is to present a good feed candidate that is well-suited for VLBI2010 and SKA radio telescopes. Further developments needed to completely fulfill the requirements for these future wideband radio telescopes are also discussed.

Dispersion Characteristics of a Metamaterial-Based Parallel-Plate Ridge Gap Waveguide Realized by Bed of Nails

Abstract: The newly introduced parallel-plate ridge gap waveguide consists of a metal ridge in a metamaterial surface, covered by a metallic plate at a small height above it. The gap waveguide is simple to manufacture, especially at millimeter and sub-millimeter wave frequencies. The metamaterial surface is designed to provide a frequency band where normal global parallel-plate modes are in cutoff, thereby allowing a confined gap wave to propagate along the ridge. This paper presents an approximate analytical solution for this confined quasi-TEM dominant mode of the ridge gap waveguide, when the metamaterial surface is an artificial magnetic conductor in the form of a bed of nails. The modal solution is found by dividing the field problem in three regions, the central region above the ridge and the two surrounding side regions above the nails. The fields within the side regions are expressed in terms of two evanescent TE and TM modes obtained by treating the bed of nails as an isotropic impedance surface, and the field in the central ridge region is expanded as a fundamental TEM parallel-plate mode with unknown longitudinal propagation constant. The field solutions are linked together by equalizing longitudinal propagation constants and imposing point-continuity of fields across the region interfaces, resulting in a transcendental dispersion equation. This is solved and presented in a dispersion diagram, showing good agreement with a numerical solution using a general electromagnetic solver. Both the lower and upper cutoff frequencies of the normal global parallel-plate modes are predicted, as well as the quasi-TEM nature of the gap mode between these frequencies, and the evanescent fields in the two side regions decay very rapidly away from the ridge.

Threshold Receiver Model for Throughput of Wireless Devices With MIMO and Frequency Diversity Measured in Reverberation Chamber

Abstract: We present a simple theoretical model for the throughput data rate of a wireless LTE device including the improvements of data rate due to diversity in frequency (OFDM) and spatial domains (MIMO) under frequency selective fading. The model is based on defining an ideal threshold receiver for the line-of-sight (LOS) case, corresponding to reception with advanced error-correcting codes. The theoretical throughput model is in agreement with measurements in a reverberation chamber of a commercial LTE device for the 1 × 2 SIMO case, both regarding diversity and MIMO array gains, and it can therefore be used to complement measured results in evaluation of performance of LTE devices.

Estimation of Average Rician K-Factor and Average Mode Bandwidth in Loaded Reverberation Chamber

Abstract: A well-stirred reverberation chamber without noticeable direct coupling between the transmitting and receiving antennas emulates an isotropic Rayleigh fading environment and can therefore be used for qualitative over-the-air (OTA) measurements of wireless devices with small nondirective antennas. By loading such a chamber, it is possible to generate a Rician environment. This letter introduces an average Rician K-factor that describes the reverberation chamber better than the normal K-factor, in particular when the chamber is provided with platform and polarization stirring. This letter shows how to estimate this average K-factor. The average mode bandwidth also changes by loading the chamber. While the average K-factor determines uncertainty, the average mode bandwidth determines the channel coherence bandwidth. They are therefore the two most important parameters for the characterizations of a reverberation chamber.

Comparison of Ergodic Capacities From Wideband MIMO Antenna Measurements in Reverberation Chamber and Anechoic Chamber

Abstract: It has previously been shown that ergodic multiple-input-multiple-output (MIMO) capacity of a multiport antenna system can be conveniently determined from channel measurements in a reverberation chamber. In this letter, we compare such MIMO capacity results to results based on measurements in an anechoic chamber of the embedded far-field functions and efficiencies at all antenna ports. The comparison is performed over two-octaves bandwidth by using the decade bandwidth eleven antenna, a log-periodic dual-dipole array. The agreement between the reverberation chamber results and the anechoic chamber results is good over the entire frequency band 2-8 GHz.

Increasing parallel plate stop-band in gap waveguides using inverted pyramid-shaped nails for slot array application above 60GHz

Abstract: This paper presents a proposal for a slot array antenna for frequencies above 60 GHz. Also, The array is using the new air gap waveguide as a feeding structure. Here we present a new structure for the parallel plate stop-band based on replacing the uniform cross sectional nails with inverted pyramidal shaped pins. This new type of pin is more suitable for micromachining and manufacturing of gap waveguides above 60 GHz. The wider parallel-plate bandwidth achieved with this new type of pins makes it suitable for integration of very wideband active MMIC circuit with gap waveguide without package resonance problem. Once the RF circuitry is integrated with gap waveguide, the slot arrays can be easily built by having slots on the top metal wall of the gap waveguide thus enabling low cost integrated antenna solution at frequencies above 60GHz.

New low loss inverted microstrip line using gap waveguide technology for slot antenna applications

Abstract: Recently, a new transmission line concept, called gap-waveguide, has been introduced. This technology generates a quasi-TEM mode in the gap between parallel metal plates and prohibits all other modes to propagate by making use of artificial magnetic conductors (AMCs) in the forms of e.g. lid of nails or mushrooms-type EBG surfaces. It has been shown how such geometry can replace standard microstrip lines and waveguides since it needs neither dielectric nor metal joints, being then an advantageous alternative that can be used for several applications at high frequency. This paper shows how the gap waveguide can also be realized in printed technology creating a new type of inverted microstrip line, called microstrip gap waveguide, which has low loss and large bandwidths can be achieved.

Optimization of Reflection Coefficient of Large Log-Periodic Array by Computing Only a Small Part of It

Abstract: A new method is described in the paper to predict the reflection coefficient of a complete large log-periodic array (with large number of elements) from the computed performance of a small part of the array. The small part is referred to as the partial array. The method involves computing the embedded S-parameters between all the elements of this partial array and then using these S-parameters to predict the performance of the full array. As an example, the method has been applied to optimize the Eleven antenna for 2-13 GHz. The result of the optimization is that the reflection coefficient is improved significantly to be below -10 dB over the whole frequency band. The results have been verified by measurements.

Measurements of RFID Tag Sensitivity in Reverberation Chamber

Abstract: The reverberation chamber is now commonly accepted and used for fast and accurate performance evaluation of mobile phones and other wireless devices for in particular new systems such as LTE 4G and IEEE 802.11n Wi-Fi. In this letter, we describe a new methodology of measuring sensitivity of RFID tags in a reverberation chamber, and we show how the measurements time can be shortened by using the fact that the RFID tag behaves like an ideal threshold receiver. We then extend to tag population measurements that can be used to select the best tag among the many during the same measurement sequence.

Determination of maximum Doppler shift in reverberation chamber using level crossing rate

Abstract: Doppler spread has been observed in reverberation chambers (RC) with moving mode-stirrers. In this paper, we propose a simple method to determine the maximum Doppler frequency shift in the RC by using level crossing rate (LCR). The Doppler spread bandwidth is twice of the maximum Doppler frequency. RC loading effect on Doppler spread is also studied in this paper. Using the method, it is found that maximum Doppler spread bandwidth tends to reduce when lossy objects are located into the RC, and the larger reduction the more larger lossy objects.

Fast Converging Measurement of MRC Diversity Gain in Reverberation Chamber Using Covariance-Eigenvalue Approach

Abstract: In this paper, we show that the covariance-eigenvalue approach converges much faster than using cumulative distribution function (CDF) for determining diversity gain from channel measurements in reverberation chamber. The covariance-eigenvalue approach can be used for arbitrary multi-port antennas, but it is limited to Maximum Ratio Combining (MRC).

Comparisons of different methods to determine correlation applied to multi-port UWB eleven antenna

Abstract: In this paper, we compare different methods to determine correlation. First, we did analytical study on correlation of two parallel dipoles. We present two methods for analytical correlation calculation. In addition, the effect of source impedances is also studied. It is found that these two analytical methods result in the same correlation, and that source impedance matched to embedded element impedance gives the smallest correlation. Then, we compared different methods of determining correlations of multi-port antennas from measurements. Wideband eleven antenna was used for measurements. It is shown that correlation can be determined correctly either using embedded radiation far field functions based on anechoic chamber (AC) measurement (i.e., embedded far field method), or using cross-correlation definition based on reverberation chamber (RC) measurement (i.e., RC method). Scattering parameters (S-parameter) can only be used to determine correlation of lossless multi-port antenna (i.e., S-parameter method). It is also shown that for general lossy antenna, RC method is most convenient to use.

Improving microstrip filters with gap waveguide packaging

Abstract: A study is presented of the performance of microstrip filters packaged with Perfect Magnetic Conductor (PMC) and realization of the PMC using a lid of nails. A 3rd order parallel coupled-line bandpass filter is designed and packaged with a lid of nails at the Ku-band. The study shows the PMC packaging technique is very efficient in improving the filter characteristics including the insertion loss in the bandpass region.

The PMC-Amended DB Boundary - A Canonical EBG Surface

Abstract: Replacing realistic materials and structures by their ideal counterparts, canonical surfaces, is of great interest for initial and conceptual electromagnetic (EM) studies. The recently introduced DB boundary is defined by a set of simple boundary conditions forcing the normal components of the D- and B- fields to be zero at the boundary. We show that this DB boundary produces many 2-D scattering results that are similar to how practical so-called electromagnetic bandgap (EBG) surfaces behave within the bandgap. Still, it is not directly useable as a canonical EBG surface, because, as we demonstrate in this paper, it is incomplete, creating an anomaly for normal incidence which causes unphysical field solution for 3-D field problems. We have removed this anomaly by introducing the PMC-amended DB boundary. This works in the same way as a practically realized EBG surface for both 2-D and 3-D problems within the bandgap, and is therefore a canonical EBG surface.

Simple calculation of ergodic capacity of lossless two-port antenna system using only S-parameters - Comparison with common Z-parameter approach

Abstract: In this paper, we show how to correctly include overall antenna effects in a numerically generated Rayleigh channel matrix when calculating ergodic MIMO capacity of lossless multi-port antenna system located in rich isotropic multipath. The overall antenna effects can be included correctly using either impedance parameters (Z-parameter method) or scattering parameters (S-parameter method). These two methods are compared and validated by measurements in anechoic and reverberation chambers. A narrowband handset antenna with negligible ohmic loss is used for the measurements. There are very good agreements between the capacities obtained using both methods from anechoic chamber measurement and that from direct channel measurement in reverberation chamber.

Measurement uncertainties of capacities of multi-antenna system in anechoic chamber and reverberation chamber

Abstract: It has been shown that multiple-input multiple-output (MIMO) capacity of multi-antenna system can be determined either from direct channel measurements in reverberation chamber or indirectly from antenna far field radiation function measurements in anechoic chamber (combined with numerically generated channel). In this paper, we try to investigate uncertainty of MIMO capacity obtained in these two ways from antenna viewpoint. It is found that the measurement uncertainty of capacity depends on measurement uncertainties of both efficiency and correlation, and that the former tends to dominate, given moderate correlation.

Wearable textile antennas' efficiency characterization using a reverberation chamber

Abstract: Characterization of efficiency is an important consideration to ensure the proper operation of an all-textile wearable antenna. In this work, a small, novel textile antenna is designed based on a planar inverted-F structure (PIFA). The structure incorporates an edge-feeding plate, symmetrical design, and well-placed slot, in order to ease fabrication. A thin conductive textile, Pure Copper Polyester Taffeta Fabric (PCPTF), and fleece is used to fabricate the structure. The efficiency is then verified and measured using a commercial reverberation chamber. Observed results indicate excellent agreements between simulations and measurements.

The method of equivalent dipole moments (MEDM) combined with CBFM for the fast and accurate solution of dielectric scattering problems

Abstract: High-resolution basis functions are employed for accurate modelling of electromagnetic scattering from dielectric objects. It is shown that the field radiated by each of these micro basis functions resembles the dipole field, even in the immediate vicinity of its cubic support. This, in turn, significantly eases the computational burden of generating the off-diagonal elements of the moment matrix. Furthermore, the on-diagonal self-term is known analytically and only governed by the electrostatic field (electrodynamic part is negligible). This method has been hybridised with the Characteristic Basis Function Method (CBFM) and the Adaptive Cross Approximation (ACA) algorithm to reduce both the size and generation time of the moment matrix equation. It is demonstrated that the proposed method, herein referred to as MEDM, is not only fast and memory efficient but it also generates an accurate solution of scattering problems associated with complex-shaped, thin and electrically large objects.

State-of-the-art measurements of LTE terminal antenna performance using reverberation chamber

Abstract: This paper presents a proposed measurement method utilizing the reverberation chamber to measure MAC layer throughput for LTE enabled wireless devices By using the reverberation chamber a statistically isotropic environment is produced, which is a suitable reference environment for terminal antenna testing

Performance of Directive Multi-element Antennas versus Multi-beam Arrays in MIMO Communication Systems

Abstract: Performance of Directive Multi-element Antennas versus Multi-beam Arrays in MIMO Communication Systems

About Random LOS in Rician Fading Channels for MIMO OTA Tests

Abstract: It is often claimed that Rician fading must also be included for Over-The-Air (OTA) testing of mobile devices with Multiple-input Multiple-output (MIMO) capabilities. However, the Line-Of-Sight (LOS) component varies with orientation and location of the mobile device. Therefore, we study Rician channels with random LOS to determine its significance

Micromachined ridge gap waveguide for sub millimeter and millimeter wave applications

Abstract: High-frequency waveguide technology has become a field of great interest lately. In this paper we present a ridge gap waveguide with two 90 degree bends and a ridge gap waveguide resonator, both fabricated with MEMS technology. It is the first time the ridge gap waveguides have been fabricated for millimeter waves. The ridge gap waveguides is realized of two conducting plates, one of them with a texture, and can provide low transmission losses without any requirements to alignment between the two plates, and with neither conductive joints nor sidewalls. The Ridge gap waveguide makes use of a ”bed of nails” structure which acts as a magnetic conductor and creates a cut-off for parallel plate modes between the two plates. Thereby, wave propagation is confined to the electric conducting ridge, without making use of electrically conducting sidewalls. MEMS technology can provide precision machining which makes it possible to go up in higher frequency bands than with conventional machining. The purpose of this paper is to describe the the fabrication process of the surface textured with pins and ridge.

The gap waveguide as a metamaterial-based electromagnetic packaging technology enabling integration of MMICs and antennas up to THz

Abstract: This paper presents new topics that will be lectured in the short course Metamaterials for Antennas within the European School of Antennas in Spring 2012. These relates to new so-called gap waveguides that are advantageous for use above 30 GHz, because they are quasi-TEM over wide bandwidth, and do neither require dielectric material nor conductive joints between metal parts. The gap waveguides originate from research on soft and hard surfaces that also are forerunners for EBG surfaces (acting as isotropic soft surfaces) and metamaterial cloaks (realized first by hard surfaces). The course will contain material related to all these topics, and in addition an overview of the last years research on the gap waveguides including experimental demonstration of principles as well as working hardware components. In this presentation special emphasis will be given to electromagnetic (EM) packaging, the principle of PMC packaging and integration of MMICs.

An Improved MM-PO Method with UV Technique for Scattering from an Electrically Large Ship on a Rough Sea Surface at Low Grazing Angle

Abstract: ─ An improved MM-PO-UV hybrid method is developed to calculate the bistatic scattering from the two-dimensional (2-D) composite model of an electrically large ship (ELS) on a one-dimensional (1-D) rough sea surface at a low grazing angle (LGA). The subdivision of the MM and PO region is performed flexibly according to the physical considerations. The MM region contains not only the ship but also a small portion of the neighboring sea region where the surface currents need to be modeled accurately. An iterative solution BiCGSTAB is adopted to solve the final matrix equation of a large dimension caused by the ELS. Then, a UV matrix decomposition technique is applied as the fast algorithm to accelerate the matrix-vector productions and the matrix elements filling in. The improved method makes it possible for the Monte-Carlo simulation of large-scale complex target/rough surface problems under an LGA. The accuracy is validated in comparison with the traditional MOM method. Index Terms ─ LGA, MM-PO hybrid method, target/rough surface scattering, UV.

Uncertainties in estimating ergodic MIMO capacity and diversity gain of multiport antenna systems with different port weights

Abstract: The performance of multiport antenna systems located in multipath environment is characterized by their ergodic capacity and diversity gain. The impact on convergence and statistical uncertainties involved in the estimation and evaluation of these performance metrics is studied for different port weights (i.e. different embedded element efficiencies) and correlations. The study is performed by using an upgraded version of the multipath simulation tool Rayleigh Lab which emphasizes the presentation of the statistical characteristics on the ports rather than the electromagnetic modelling. Therefore, the Rayleigh fading channels are generated in a very simple way by using arrays of randomly distributed complex numbers, and the user can input efficiencies and correlations rather than farfield functions and mutual couplings.

Design of cryogenic 2-14 GHz eleven feed for reflector antennas for future radio telescopes

Abstract: The design of the cryogenic 2-14 GHz Eleven feed for reflector antennas in future wideband radio telescope involves electrical design of the Eleven antenna, design of center puck, different alternative solutions for integrating with low noise amplifiers (LNAs), mechanical and cryogenic design and tests, system noise temperature estimation and so on. All these design aspects will be described in the paper. A large quantity of simulated and measured data has been obtained in order to verify the electrical, mechanical and cryogenic performance, and the system noise temperature. The objective of this work is to provide a good feed candidate for reflector antennas in VILB 2010 and US SKA projects. The system configuration of the Eleven feed can be represented by the block diagram shown in Fig. 1, which consists of three parts: the Eleven antenna, center puck and the LNA-integration circuit board. Fig. 2 shows a photo of the Eleven feed. The reflection coefficient measured at Caltech (California Institute of Technology) is shown in Fig. 3, and the aperture efficiency and other subefficiencies measured at DTU (Denmark University of Technology) are shown in Fig. 4. Fig. 5 shows Steady state analysis of the thermal distribution along the feed with head load of 20W/m2. More simulated and measured data will be shown in the paper. In conclusion, the Eleven feed has good performance in the frequency range of 2 – 14 GHz, and has gone through several cryogenic tests.

New BOR1 and decoupling efficiencies for characterizing ultra-wideband reflectors and feeds for future radio telescopes

Abstract: This paper presents some new topics that will be lectured in the December 2011 course within European School of Antennas course on Reflector and Lens Antennas. The new material is mainly related to characterization of wideband feeds for reflector antennas for future radio telescopes, such as for SKA and VLBI 2010. The lectures will contain details of how to design decade bandwidth log-periodic antenna feeds and in particular the so-called eleven feed, as well as focal plane arrays (FPA) for producing multiple beams shaped for optimum system performance. The designs has taken advantages of two newly defined efficiencies that are essential for optimum system performance: i) The socalled BOR1 efficiency characterizing the power loss due to higher order azimuthal variations in the far field function being very important in characterizing decade bandwidth feeds. And, ii) the decoupling efficiency being of importance for characterizing non-uniformly excited arrays such as FPAs, and being related to the classical embedded element efficiencies of normal phased arrays as well as their active (scanned) impedance.