Showing papers by "Per-Simon Kildal published in 2012"

Characterization of Reverberation Chambers for OTA Measurements of Wireless Devices: Physical Formulations of Channel Matrix and New Uncertainty Formula

Abstract: The paper deals with reverberation chambers for over-the-air (OTA) testing of wireless devices for use in multipath. We present a formulation of the S-parameters of a reverberation chamber in terms of the free space S-parameters of the antennas, and the channel matrix in the way this is known from propagation literature. Thereby the physical relations between the chamber and real-life multipath environments are more easily explained. Thereafter we use the formulation to determine the uncertainty by which efficiency-related quantities can be measured in reverberation chamber. The final expression shows that the uncertainty is predominantly determined by the Rician K-factor in the reverberation chamber rather than by the number of excited modes, assumed by previous literature. We introduce an average Rician K-factor that is conveniently expressed in terms of the direct coupling between the transmitting and receiving antennas (corresponding to a line-of-sight contribution) and Hill's transmission formula (corresponding to a multipath or non-line-of-sight contribution). The uncertainty is expressed in terms of this average K-factor and geometrical mode stirring parameters, showing strong reduction by platform and polarization stirring. Finally the formulations are verified by measurements, and the new understanding of uncertainty is used to upgrade an existing reverberation chamber to better uncertainty.

OTA Testing in Multipath of Antennas and Wireless Devices With MIMO and OFDM

Abstract: New over-the-air (OTA) measurement technology is wanted for quantitative testing of modern wireless devices for use in multipath. We show that the reverberation chamber emulates a rich isotropic multipath (RIMP), making it an extreme reference environment for testing of wireless devices. This thereby complements testing in anechoic chambers representing the opposite extreme reference environment: pure line-of-sight (LOS). Antenna diversity gain was defined for RIMP environments based on improved fading performance. This paper finds this RIMP-diversity gain also valid as a metric of the cumulative improvement of the 1% worst users randomly distributed in the RIMP environment. The paper argues that LOS in modern wireless systems is random due to randomness of the orientations of the users and their devices. This leads to the definition of cumulative LOS-diversity gain of the 1% worst users in random LOS. This is generally not equal to the RIMP-diversity gain. The paper overviews the research on reverberation chambers for testing of wireless devices in RIMP environments. Finally, it presents a simple theory that can accurately model measured throughput for a long-term evolution (LTE) system with orthogonal frequency-division multiplexing (OFDM) and multiple-input-multiple-output (MIMO), the effects of which can clearly be seen and depend on the controllable time delay spread in the chamber.

Narrow-Band Microwave Filter Using High-Q Groove Gap Waveguide Resonators With Manufacturing Flexibility and No Sidewalls

Abstract: This paper presents a new type of narrow band filter with good electrical performance and manufacturing flexibility, based on the newly introduced groove gap waveguide technology. The designed third and fifth-order filters work at Ku band with 1% fractional bandwidth. These filter structures are manufactured with an allowable gap between two metal blocks, in such a way that there is no requirement for electrical contact and alignment between the blocks. This is a major manufacturing advantage compared to normal rectangular waveguide filters. The measured results of the manufactured filters show reasonably good agreement with the full-wave simulated results, without any tuning or adjustments.

Improved Microstrip Filters Using PMC Packaging by Lid of Nails

Abstract: This paper shows that microstrip filters perform like textbook examples when packaged with perfect magnetic conductor (PMC). A PMC is made as a pin surface or lid of nails, and this is used to package a microstrip parallel coupled line bandpass filter. Our measurements confirm that parallel plate, cavity modes, and radiation are suppressed. This paper also includes a study of the reasons for a frequency shift between the ideal PMC packaged case and the realized case.

Slot antenna in ridge gap waveguide technology

Abstract: A Slot antenna design based on recently developed gap waveguide technology has been presented in this work. This antenna can be built easily by having the feed network on the bottom metal plate, where the ridge will be distributing the waves for equal excitation of each slot element, and the top metal plate will have the slots. Design and simulation results of the basic T-junction for a corporate-feed network and the single element slot show that — it is possible to have an array antenna with BW of 15 % or more based on ridge gap waveguide technology.

Numerical Prepackaging with PMC Lid - Efficient and Simple Design Procedure for Microstrip Circuits Including the Packaging

Abstract: The paper presents an efficient method for the design of printed microstrip circuit with packaging in mind, referred to as numerical prepackaging with a perfectly magnetic conductive (PMC) lid. The method comprises making the design including the packaging from the start by using a PMC lid, rather than first designing the open-aired circuit; and thereafter, considering the packaging effect and the often required retuning of the circuits themselves. The advantage is that no parallel plate modes can propagate between the perfect electric conductor (PEC) ground plane and the PMC lid plate if the spacing is smaller than an effective quarter of wavelength. This provides a limited computational volume so that the computation time is significantly reduced in the case of the finite element method (FEM) or the finite difference time domain method (FDTD). By using numerical packaging with PMC lid, the ideal PMC lid has to be realized afterwards e.g. by using a lid of nails, which is a minor task as compared to existing approaches.

Micromachined ridge gap waveguide and resonator for millimeter-wave applications

Abstract: The ridge gap waveguide is a fundamentally new high-frequency waveguide. It does not need any electrical contact between the split blocks which gives it an advantage compared to the rectangular waveguide which is the standard today. These waveguides are conventionally fabricated by milling, although above 100 GHz milling is not adequate anymore. MEMS technology on the other hand, can offer high-precision fabrication and thus opens the path for new types of high-frequency components. In this paper both a ridge gap waveguide and a ridge gap resonator have been fabricated for the frequencies 220–325 GHz using MEMS technology. Support packages have been designed to enable device measurements. Simulations show that the reflection coefficient for the ridge gap waveguide is below −15 dB between 240 and 340 GHz. Two resonance peaks were measured at the frequencies 234 GHz and 284 GHz for the ridge gap resonator with unloaded Q-values of 336 and 527 respectively. Both the waveguide and resonator have the potential to obtain similar performances as the rectangular waveguide without strict requirement on electrical contact, allowing simplified fabrication and assembly technique.

Contactless non-leaking waveguide flange realized by bed of nails for millimeter wave applications

Abstract: Waveguide flanges are typically used to connect and measure high frequency circuits. When good conductive contact is not provided between the joining flange surfaces, currents will flow between them, and thereby causing leakage and losses affecting the circuit performance. This work presents a non-leaking contactless waveguide flange made with bed of nails. The flange does not need any contact when connected to another smooth flange, since the pins surface and the smooth surface together form a stopband suppressing any current and wave propagation between the two joining surfaces of the flanges.

Design of Compact Dual-Polarized 1.2–10 GHz Eleven Feed for Decade Bandwidth Radio Telescopes

Abstract: The Eleven antenna is a log-periodic folded-dipole-pair array with two unique radiation characteristics: a constant beamwidth and a fixed phase center location over a decade bandwidth. This paper presents a new compact design of a 1.2-10 GHz Eleven antenna, as a feed for reflector antennas by re-arranging the geometry of the outermost elements of the antenna. Due to the compact size, it is possible to put the whole feed system inside a compact cryostat and cool it down to cryogenic temperatures, in order to reduce the system noise temperature in radio telescope applications. The new compact Eleven feed has only a 40% volume of the original standard Eleven feed with a very similar performance. This reduces the capacity requirement for the cryogenic cooling system significantly and therefore the power consumption for future radio telescopes, such as the square kilometer array (SKA). The concept behind this compact design is analyzed in the paper. Simulations and measurements presented here have verified the design.

Gap waveguide components for millimetre-wave systems: Couplers, filters, antennas, MMIC packaging

Abstract: Gap waveguides were first presented in [1] as an alternative guiding technology especially attractive for frequencies over 30 GHz up to THz. At those frequencies, the current technologies show some deficiencies regarding to the performance, integration ability, or product cost. Planar technologies, such as microstrip and coplanar, are often chosen due to their good integration ability and manufacture simplicity, but they suffer from higher losses with increasing frequency as well as from the presence of cavity resonances when encapsulated. Hence, hollow waveguides are usually resorted for low-loss applications, in spite of their difficulty for integration with active components and a high manufacturing cost. The need of new transmission line technologies for mm- and sub mm-wave systems is leading to the apparition of alternative technologies. Substrate Integrated Waveguide (SIW) technology has been widely used for high-frequency applications [2], but it exhibits significant losses at increasing frequencies due to wave propagation in substrate. Gap waveguides, on the contrary, support waves in the air gap between two metal plates. One of the plates is provided with a texture, in the form of a bed of nails, to create a high impedance condition at the surface, which in turn forces a cut-off for the parallel-plate modes [3]. On the same plate, there are metal ridges in between the nails providing a path to the waves so that fields are confined to the air gap between the ridges and the metal plate on top. This propagation path can alternatively be provided by a microstrip line lying on the bed of nails, or by a groove in between the nails. An interesting application using similar technology can be found in [4] where a multi-layered phased array antenna developed in Japan was presented.

Design of a coplanar waveguide-to-ridge gap waveguide transition via capacitive coupling

Abstract: A transition from Coplanar Waveguide (CPW) via capacitive coupling in order to provide feeding to the so-called Ridge Gap Waveguide (RGW) has been investigated. The main objective of this work is to find a way to facilitate integration of active electronics with the gap waveguide structure and also to do measurements of the components made in gap waveguide technology working around 100 GHz. The transition design and simulation of S parameters for the designed topology is presented.

Investigation of a Microstrip-to-Ridge Gap Waveguide transition by electromagnetic coupling

Abstract: A transition from Microstrip to Ridge Gap Waveguide (RGW) has been studied and numerically analyzed in terms of S parameters. The RGW technology shows potential to be used up to THz frequencies. Therefore, good transitions are needed in order to make possible the measurements of RGW components at frequencies above 100 GHz.

LTE MIMO multiplexing performance measured in reverberation chamber and accurate simple theory

Abstract: We present measurement results of the data-rate throughput inside a reverberation chamber of a commercial USB dongle operating in 2×2 MIMO spatial multiplexing configuration. A simple and accurate theory is provided by which the measured throughput can be accurately explained. The theory is based on a recently published digital threshold receiver model.

Metamatrial based packaging method for improved isolation of circuit elements in microwave modules

Abstract: In this work, periodic structure has been used to design a new type of packaging technique to improve the isolation between microwave components within a module. In contrast to the conventional packaging technique, the new technique relaxes the requirement for using vias in the substrate and using conductive adhesive or gasket material within a typical multiple compartment microwave modules. On the other hand it uses a periodic structure of metal pins to form a lid for the microwave module. The achieved level of isolation in X-band and Ku-band for a two compartment test circuit is better than 65 dB which is better than the existing packaging technique within the band of interest.

Development of the cryogenic 2–14 GHz Eleven feed system for VLBI2010

Abstract: We present an overview of the recent developments of a cryogenic 2–14 GHz feed system for the Very Long Baseline Interferometry 2010 (VLBL2010) project. The developments include a new balun feeding network, a new circular Eleven feed, system noise temperature modeling and testing, integration with different low noise amplifiers (LNAs), and cryostat design and integration.

Diversity gains in random line-of-sight and rich isotropic multipath environment

Abstract: Antenna diversity gain for theoretical as well as measured antennas is studied in two extreme environments, the rich isotropic multipath environment (RIMP) and the random line-of-sight environment. The RIMP diversity gain was previously defined based on improved fading performance, here we equivalently consider it as a metric for the cumulative improvement of the 1% worst users randomly distributed in the RIMP environment. Similarly, we consider the diversity gain in the random line-of-sight environment to be the performance improvement of the 1% of the users which receives the weakest signal relative to a theoretical Rayleigh distribution of the signal levels among the users. The random line-of-sight environment is regarded as being caused by the statistics of an ensemble of users (or terminals) with arbitrary 3D orientations.

Modeling system throughput of single and multi-port wireless LTE devices

Abstract: We have recently introduced a simple theoretical model for estimating the relative throughput of LTE devices. We validated the model through measurements performed in reverberation chamber for 1×2 SIMO with 90ns channel delay spread. In the present paper, we extend our previous study to compare the frequency diversity offered by different channel delay spreads emulated in reverberation chamber for SISO and 1×2 SIMO configurations.

Fast analysis of gap waveguides using the characteristic basis function method and the parallel-plate Green's function

Abstract: The Characteristic Basis Function Method is employed in conjunction with the parallel-plate dyadic Green's function method to obtain the impedance characteristics of electrically large gap-waveguide structures. Numerical results are shown for the groove gap waveguide demonstrating reduced execution times relative to the HFSS software, while the solution accuracy is barely compromised.

Experimental and theoretical study of OTA throughput of 4G LTE wireless terminals for different system bandwidths and coherence bandwidths in Rich Isotropic Multipath

Abstract: The 3rd Generation Partnership Project (3GPP) has provided successful reports and specifications for Long Term Evolution (LTE). The LTE standard is the latest communication technology standard today which is extensively adopted by the industry to satisfy the demands of their customers with high speed internet and low latency. The major differences between LTE and its predecessor telecommunication standards i.e. WCDMA and GSM are Orthogonal Frequency Division Multiplexing (OFDM), Multiple-Input Multiple-Output (MIMO), and scalable bandwidth which provide improved receiver sensitivity, higher throughput data-rates, and flexibility. The purpose of the present paper is to study measured throughput for different system bandwidths and see how well the OFDM model works for all these, and to investigate how the threshold level change with the system bandwidth.

Capacity characterization of Eleven antenna in different configurations for MIMO applications using reverberation chamber

Abstract: In this paper, we characterize the multiple-input multiple-output (MIMO) performance of a multi-port wideband receive antenna with three ideal (i. e. unity embedded radiation efficiency and no correlation) transmit antennas. Different configurations (feeding networks) of the antenna under test (AUT) are examined by measurements in a reverberation chamber. These configurations are studied in terms of embedded radiation efficiencies, correlations, and ergodic MIMO capacities.

MIMO LTE OTA measurements in reverberation chamber: Rich isotropic reference environment makes agreement with theoretical system model

Abstract: The reverberation chamber has during the last 10 years been developed into an accurate instrument for OTA measurements, having a well-defined rich isotropic multipath environment. This has been introduced as a new reference environment for testing of wireless devices, complementing the traditional anechoic reference environment. The rich isotropic multipath environment and the definition of an ideal error-correcting digital receiver have made it possible to develop simple theoretical models that predict the measured throughput data rate in a reverberation chamber versus received power within a few tenth of dBs The present paper overviews the developments of the reverberation chamber that has made it possible to achieve such agreement, as well as the on-going work of determining relevance of the rich isotropic environment compared to real-life environments.

Comparison of parallel-plate Green's function acceleration techniques

Abstract: A comparative study of acceleration methods for computing the infinite series summation arising in parallel-plate Green's functions is performed. The spectral summation, the application of the Shanks-transformed spatial summation, and the Ewald method are examined. Results are presented which show that, although the convergence rates of Ewald's method and the spectral summation are generally largest (i.e. less number of terms), the total series evaluation time for reaching a certain specified accuracy — which is ultimately of more practical importance — is shortest for the Shanks accelerated spatial summation for most of the cases we considered.

A study of uncertainty models in a reverberation chamber at NIST

Abstract: The reverberation chamber has become a good alternative for over-the-air (OTA) testing of small antennas. Here the uncertainty of total radiated power measurements is evaluated for a reverberation chamber at National Institute of Standards and Technology (NIST), Boulder, Colorado. A procedure for measuring the uncertainty based on the standard deviation of nine different antenna orientations in the RC has been used.

Evaluation of losses in microstrip gap waveguide for slot antennas applications

Abstract: The new microstrip gap waveguide supports a quasi-TEM mode in the air by the use of artificial magnetic conductors which force the field to travel in the air rather than in the substrate. This paper presents an evaluation of losses by measuring the Q-factor of a resonator made in this technology, made using a mushroom-type EBG surface. Losses are crucial when using printed circuits to feed slot antennas, thereby motivating this work. Comparisons with standard microstrip lines will be provided, showing promising results.

Analysis of the strut and feed blockage effects in radio telescopes with compact UWB feeds

Abstract: The international radio astronomy community is currently pursuing the development of a giant radio telescope known as the Square Kilometre Array (SKA). The SKA reference design consists of several wideband antenna technologies, including reflector antennas fed with novel multi-beam Phased Array Feeds (PAF) and/or wide band Single Pixel Feeds (SPFs) that can operate at frequencies from 1 to 10 GHz [1], [2]. The baseline of this design represents an array of several hundred to a few thousand reflector antennas of 15-m diameter and that will realize sensitivity of 10,000 m2/K. During the past years, several different reflector and feed concepts have been proposed and examined, but only a small number of these design options (that have a sufficient level of maturity) will be built and tested in a set-up that is closely resembling the final SKA system [3]. These tests are aimed to evaluate the overall system performance as well as construction and operational costs. The final choices for the dish and feed evaluation tests might include: (i) off-set Gregorian and axi-symmetric reflector antennas and; (ii) an optimized octave corrugated horn and the single-pixel wideband feeds such as quad-ridged horn and Eleven antenna [2], [4].

Analytical modeling and experimental verification of coupling between transmission lines in gap-waveguides

Abstract: Modeling of gap-waveguide structures with single and multiple transmission lines is performed using spectral domain Green's functions approach. The approach is extended using even/odd mode analysis in order to also estimate the crosstalk levels between neighboring transmission lines. The results of this analysis are compared with the results of a commercial electromagnetic solver and with the measured results.

Ka-band gap waveguide coupled-resonator filter for radio link diplexers

Abstract: Gap waveguide technology represents an interesting alternative as low-loss, cost-effective and high-performance transmission line and package of microwave and millimeter-wave systems. A Ka-band coupled-resonator filter for a radio link diplexer, which requires high selectivity to isolate transmit and receiving channels, is proposed and realized using gap waveguide technology. The band-pass filter, which has a central frequency of 37.37 GHz and a pass bandwidth of 560 MHz, is fabricated between two metal parallel plates leaving an air gap between them. Measurements show a minimum in-band insertion loss of 1 dB and agree quite well with simulations.

Evaluation of multi element antennas in reverberation chamber

Abstract: This paper focuses on the latest advances in the use of reverberation chambers for active device testing. Contained are description and comparison of different figure-of-merits that are applicable to multi element antennas, with a specific focus on LTE devices with MIMO capability. There are two new parameter concepts introduced: Modified Total Isotropic Sensitivity measurements to include MIMO signaling, and a Throughput Threshold Level for simplified quantification of data bit throughput measurement results.

Packaging of active and passive microwave circuits using a grid of planar conducting elements on a grid of vertically arranged substrates

Abstract: The present invention represents a new, way of packaging passive and active microwave circuits, and in particular circuits involving microstrip transmission lines and similar substrate bound transmission lines. The circuits are located between two conducting surfaces, one of these surface may be the ground plane of the microwave circuit, and at least one of these surfaces are provided with conducting elements formed as angular or curved conducting lines arranged on substrates. The conducting lines may e.g. have a zigzag shape. The two surfaces may form the bottom and lid of a cavity with conducting sidewalls. The conducting elements may with advantage be arrange in a periodic grid, and create together with the ground plane of the microwave circuit board or the smooth metal plane below the microwave circuit board a stop band for waves propagating between the lid with conducting elements and the ground plane. Thereby, cavity resonances are avoided or suppressed that otherwise create a big problem associated with the packaging in metal boxes with smooth metal walls.