Showing papers by "Per-Simon Kildal published in 2015"

Design and Validation of Microstrip Gap Waveguides and Their Transitions to Rectangular Waveguide, for Millimeter-Wave Applications

Abstract: The paper describes the design methodology, experimental validation, and practical considerations of two millimeter-wave wideband vertical transitions from two gap waveguide versions (inverted microstrip gap waveguide, and microstrip packaged by using gap waveguide) to standard WR-15 rectangular waveguide. The experimental results show $S_{11}$ smaller than $-{\hbox{10 dB}}$ over relative bandwidths larger than 25% and 26.6% when Rogers RO3003 and RO4003 materials are used, respectively. The vertical transition from standard microstrip line packaged by a lid of pins to WR-15 shows measured return loss better than 15 dB over 13.8% relative bandwidth. The new transitions can be used as interfaces between gap waveguide feed networks for 60-GHz antenna systems, testing equipment (like vector network analyzers), and components with WR-15 ports, such as transmitting–receiving amplifiers. Moreover, the paper documents the losses of different gap waveguide prototypes compared with unpackaged microstrip line and substrate integrated waveguide (SIW). This investigation shows that in $V$ -band, the lowest losses are achieved with inverted microstrip gap waveguide.

Interpreting the Total Isotropic Sensitivity and Diversity Gain of LTE-Enabled Wireless Devices From Over-the-Air Throughput Measurements in Reverberation Chambers

Abstract: The characterization of the performance of wireless devices is key to developing new RF products conforming to the latest communications protocols. Traditionally, communication performance tests have focused on the RF performance of the tested devices, e.g., smart phones, pads, laptops, and so on. In particular, the focus has shifted from conducted (i.e., cabled) measurements to more realistic over-the-air (OTA) characterization of the RF performance of these devices in transmit or receive mode. For example, the receiver performance of 2G and 3G wireless devices can be measured in terms of the total isotropic sensitivity (TIS) that depends on the antenna and the receiver parts of a wireless device. These measurements can be performed in a reverberation chamber setup. However, standard TIS measurements can be time-consuming and do not reflect the actual performance gains of multiple-input multiple-output antenna systems operating over orthogonal frequency division multiplexing channels, such as those encountered in 4G long-term evolution (LTE) systems. Therefore, in order to meet both time and cost efficiency requirements, we propose here a new method to determine the TIS, as well as the diversity performance, of an LTE device based on throughput measurements. The proposed method shows that the TIS of an LTE device is characterized much faster directly from OTA throughput measurements than from standard TIS measurements and with excellent accuracy.

V-band groove gap waveguide diplexer

Abstract: In this paper a novel V-band diplexer, based on the newly introduced groove gap waveguide technology is presented. The diplexer structure consists of an H-plane T-junction and two RX and TX filters having 1.5% relative bandwidth at 59.5GHz and 62.5GHz center frequencies, respectively. Also, two groove gap waveguide to WR-15 transitions are designed. The main advantages of the groove gap waveguide diplexer compared to the classical rectangular waveguide diplexer are that there is no need for electrical contact between the top and bottom metal plates, and it adds an opportunity of packaging the active transceiver circuits together with the diplexer. The design procedure and the simulated results are presented.

A groove gap waveguide iris filter for V-band application

Abstract: This work presents a V-band iris filter, based on recently introduced groove gap waveguide technology. In this technology, it doesn't need to have electrical contact between two constituting metallic surfaces, as it is needed in conventional hollow waveguides. Therefore, it is cheaper to manufacture gap waveguide components, in particular in millimeter wave frequency range. In this work, square shape groove gap waveguide cavities are used as filter resonators. To realize the input/output coupling and also inter cavity coupling, two larger pins are used to act as an iris. A fifth order bandpass Chebyshev filter is designed with 1 GHz bandwidth at 59.5 GHz center frequency and a prototype is manufactured to validate the simulation results. Design process, simulated results, and measured results are presented here.

Initial measured OTA throughput of 4G LTE communication to cars with roof-mounted antennas in 2D random-LOS

Abstract: We present initial Over-The-Air (OTA) throughput measurements of an LTE device in a Volvo XC90 car with roof-mounted antennas. The measurements were performed in a semi-anechoic chamber and only in the horizontal plane. The throughput results are presented as a probability of detection (PoD) in 2D Random Line-Of-Sight (Random-LOS) with fixed polarization of the antenna at the base station side. Two car-mounted antennas were measured: a wideband two-port shark-fin type antenna in SISO and SIMO receive diversity-mode, and a narrowband monopole antenna. The PoD curves clearly show the expected performance improvements due to the antenna diversity. In addition, the Random-LOS measurements made it possible to discover potential for improvements of the tested antennas.

Measuring user-induced randomness to evaluate smart phone performance in real environments

Abstract: The radiated performance of a wireless device depends on its orientation and position relative to the user. In addition, the antenna performance is different on different devices and it depends on the device model. Hence, to understand the impact of the users behaviour on the device antenna and the resulting network performance an investigation of the device usage and signal quality is of high importance. This paper presents a first analysis of the orientation usage of wireless devices based on data gathered from 5 smart phones over a period of more than two months. The data was obtained from the built-in sensors in the phone, and includes angles of orientation, information about signal quality and the connected network. Some interesting trends regarding typical orientations of the phone are presented for both voice and data services. We believe that data of this type has the potential to be used for optimizing the device and the network performance, e.g., when the data is correlated with the experienced channel quality.

A self-grounded surface mountable bowtie antenna arrangement, an antenna petal and a fabrication method

Abstract: The present invention relates to a self-grounded bowtie antenna arrangement (10) comprising an antenna structure (11) comprising a number of antenna petals (1, 1) comprising arm sections tapering towards a respective end tip portion (6,6) and being made o fan electrically, conducting material, the end tip portions (6,6) being arranged to approach a base portion (9) on a first side thereof and to be connected to feeding ports, a specific port being provided for each antenna petal(1,1). The base portion (9) comprises a conducting ground plane or a Printed Circuit Board (PCB), and each antenna petal(1,1)is made in one piece from a metal sheet or similar, and it is adapted to be fabricated as separate units (9), and to be mountable onto a front or back side of the base portion or ground plane(9) by means of surface mounting. The ground plane may be a Printed Circuit Board (PCB), meaning that the bowties can be mounted by automatic placement and soldering machines. Placement machines are more commonly known as pick-and-place machines.

A microwave or millimeter wave rf part realized by die-forming

Abstract: A method and apparatus for producing an RF part of an antenna system, eg for use in communication, radar or sensor applications, is disclosed, as well as thereby producible RF parts The RF part has at least one surface provided with a plurality of protruding elements In particular, the RF part may be a gap waveguide The protruding elements are monolithically formed and fixed on a conducting layer, and all protruding elements are connected electrically to each other at their bases via the conductive layer The RF part is produced by providing a die having a plurality of recessions forming the negative of the protruding elements of the RF part Particularly, the die may be a multilayer die, having several layers, at least some having through-holes to form the recessions A formable piece of material is arranged on the die, and pressure is applied, thereby compressing the formable piece of material to conform with the recessions of the die

Comparison of 2-bitstream polarization-MIMO performance of 2 and 4-port bowtie antennas for LTE in random-LOS

Abstract: We evaluate the performance of a dual-polarized wideband antenna in terms of polarization-MIMO in Random-LOS for two different modes of operation: 2 and 4-port excited mode. The 2-port mode was obtained by differential excitation of two opposite ports of the 4-port design by using two baluns. The Zero-Forcing receiver throughput is evaluated based on the Probability of Detection of two bitstreams when orthogonal polarizations provide the MIMO subchannels. Assuming a uniform distribution for the Angle of Arrivals and orthogonally polarized waves incident on the antennas, the overall PoD over coverage cones of 30°, 60° and 90° are presented. The 2-bitstream multiplexing MIMO efficiency defined at the 95% Probability of Detection is evaluated for the two modes of operation at different frequencies and for different coverage cones. The 2-bitstream coverage pattern of the antenna for the two modes are plotted over the range of Angles-of-Arrival (AoA), by choosing fixed polarization (horizontal and vertical) for the incoming waves. The coverage pattern is significantly degraded for the 2-port mode, in particular in the middle of the band.

Effects of Mutual Coupling on LTE MIMO Capacity for Monopole Array: Comparing Reverberation Chamber Tests and Drive Tests

Abstract: The roof of an automobile would appear to be an ideal platform to place multiple-input–multiple-output (MIMO) antennas, having a large ground plane with plenty of space to separate antennas for optimum embedded element radiation efficiency. However, styling concerns often require that the antennas are to be placed close together. Thus, mutual coupling plays an important role in the performance of an MIMO antenna system as it affects the embedded element efficiency and the channel correlation. In this letter, we present a comparison between the measured mutual coupling effect on the ergodic channel capacity of a $2 \times 2$ MIMO system in a reverberation chamber (i.e., Rayleigh channel) and in a suburban outdoor environment (i.e., Rician channel) at Long Term Evolution (LTE) radio band 13. The outdoor MIMO capacity was obtained during a vehicle drive test using commercial over-the-air (OTA) LTE test equipment. All measurements were conducted with two-element monopole antennas on a 24-in-diameter circular ground plane. The impact that mutual coupling has in the degradation of the embedded element radiation efficiency and increased correlation between the antennas, and ultimately the decrease in ergodic MIMO channel capacity, is highlighted by these measurements. In addition, the results provide insight into the differences of channel capacity obtained in the rich isotropic multipath environment of a reverberation chamber and the channel capacity obtained in a real-world suburban environment.

High efficiency 2×2 cavity-backed slot sub-array for 60 GHz planar array antenna based on gap technology

Abstract: This paper presents a two layer 2×2-slot element as a sub-array for 60 GHz planar array antenna based on gap waveguide technology. The proposed element consists of 2×2 slots in a gap waveguide cavity where the cavity is fed through a coupling slot from a ridge gap waveguide corporate-feed network in a lower layer. The 2×2-slot sub-array is numerically optimized in an infinite array environment. The designed sub-array shows the relative bandwidth of 11% with reflection coefficient better than ™13 dB over 58.2–65 GHz frequency band. A prototype of a 8×8-element slot array antenna is designed and fabricated in order to verify the simulations.

A new 2×2 microstrip patch sub-array for 60GHz wideband planar antenna with ridge gap waveguide distribution layer

Abstract: We propose a two layer planar antenna where a ridge gap waveguide corporate distribution network feeds a subarray of 2×2 radiating microstrip patch elements. There exists a coupling slot in the ground plane of the substrate layer which allows the excitation of the microstrip patch elements from the ridge gap waveguide layer. The ground plane of the substrate also serves the purpose of top metal layer for the ridge gap waveguide section. The proposed antenna is operating over 15% relative bandwidth covering 56–66 GHz frequency range with −12 dB reflection coefficient. The simulated directivity of the 2×2 element array is 11.5dbi at the center of the band. The simulated directivity for the 16×16 element array using the infinite array approach is found to be 28.7dBi.

Devising a horizontal chamber array for automotive OTA tests in Random Line-Of-Sight

Abstract: In this paper we propose an approach to design a horizontal array antenna to reduce the uncertainty of reference measurements in Random Line-Of-Sight Over-The-Air testing in anechoic chambers. The main focus is on wireless communications testing to and from automotive vehicles. The proposed procedure allows to determine the size, the spacing and the number of elements of a horizontal array antenna resulting in an absolute error less than 1 dB. The analysis is based on presenting the output of the ideal digital threshold receiver model of the device under test as a Probability of Detection curve.

Preparing for GBit/s coverage in 5G: Massive MIMO, PMC packaging by gap waveguides, OTA testing in random-LOS

Abstract: In this invited presentation I describe how we prepare for 5G in my research division. The background is that we have contributed to 3G and 4G developments with two commercial successes: the hat-fed reflector antenna for backhaul radio links, and Bluetest reverberation chambers for OTA (Oer-The-Air) characterization of devices with MIMO and OFDM. 5G means Gbit/s data rates, for which higher frequencies are needed towards the user terminal, may be up to 30 or 60 GHz. This means that the multipath will be weaker as it gradually diminishes when frequency increases. Therefore, we prepare by introducing a Random-LOS (RLOS) complement to the OTA testing in Rich Isotropic Multipath (RIMP) being provided by Bluetest's reverberation chambers. Further, high gain steerable beams will be needed, requiring new planar packaging solutions for closer integration of antennas and RF chipsets. Therefore, we prepare by research on gap waveguides. Massive MIMO have many technological uncertainties, so others also consider old-fashioned phased arrays, but they will not work in RIMP. The best hardware can only be chosen if we know how to characterize the system performance. The radiation pattern and realized gain cannot be used directly for this purpose due to all the statistical variations caused by the arbitrariness of the user. Therefore, we introduce instead the Probability of Detection (PoD) as a quality metric. This will be different for each desired number of bitstreams. Further, we quantify the difference between different PoD curves in dBiid in RIMP, i.e. in dB relative to the i.i.d. (idependent identically distributed) case, and in dBt in RLOS, i.e. in dB relative to an ideal polarization- and coverage- matched threshold receiver. The presentation will give an overview of this research.

MIMO OTA Testing of a Communication System Using SDRs in a Reverberation Chamber

Abstract: This paper presents a study of measuring complete over-the-air (OTA) system performance of software-defined radios (SDRs) such as the Universal Software Radio Peripheral (USRP) developed by Ettus Research and National Instruments. We use the reverberation chamber (RC) for measuring the OTA system throughput (TPUT) when the USRP is configured in single-input single-output, 1 x 2 single-input multiple-output, 2 x 1 multiple-input single-output, and 2 x 2 multiple-input multiple-output. The measured and simulated results are compared. The theoretical model of an ideal threshold receiver is used to simulate the OTA TPUT of the USRP. The total radiated power and total isotropic sensitivity of the USRP is also measured inside the RC. According to the authors' knowledge, complete active system performance measurements of USRPs in an RC are being published for the first time.

Investigation of polarization deficiencies in SIMO systems in Random-LOS propagation channels

Abstract: We study the probability of detecting the bitstream of a 2 × 1 SIMO polarization-diversity system with co-located orthogonally polarized antenna ports on the receiving side of a free-space propagation environment with arbitrary angle-of-arrival, i.e., in so-called Random-Line-Of-Sight (Random-LOS) propagation environments. We show how the diversity gain degrades in directions where the two orthogonal ports have non-orthogonal far-field functions or an amplitude imbalance. We also show that the system performance is better when one side of the link is circularly polarized and the other side is linearly polarized.

Verification of the Rician K-factor-based uncertainty model for measurements in reverberation chambers

Abstract: Measurements in reverberation chamber (RC) produce data that are random, and therefore they need to be processed from the statistical point-of-view for obtaining the desired characteristics and the accuracy. The complex channel transfer function in the RC follows complex Gaussian distribution provided that the RC is well stirred. The authors have recently presented a new uncertainty model based on the presence of an unstirred component of the transfer function, which was modelled by introducing an average Rician K-factor. The model was validated in two RCs with translating mode-stirring plates, being able to correctly describe the improvement in accuracy by rotating the antenna under test, and by blocking the line-of-sight between this and the fixed RC antenna(s). In the present study, they apply this uncertainty model to four RCs with different settings (e.g. RC volumes, number of plates or fixed RC antennas, translating and rotating mode-stirrers etc.). For each RC, they examine the measurement uncertainty under different loading conditions. To repeat (during the different measurements) the actual mode-stirrer positions at which the transfer function is sampled, they conduct all the measurements with stepwise (instead of continuous) mode-stirring. The model is shown to work well for all the cases.

Design of a cavity-backed slot array unit cell on inverted microstrip gap waveguide

Abstract: Inverted microstrip gap waveguide is advantageous for millimeter wave application because of its low-loss, self-packaging characteristics and cost-effectiveness. In this work a planar gap waveguide slot array is presented. It is fed by a corporate distribution network realized in inverted microstrip gap waveguide. The structure consists of three layers. The top layer contains subarrays of 2 × 2 radiating slots. This is backed by an air-filled groove gap waveguide cavity. This cavity layer is fed by the inverted microstrip gap waveguide distribution network formed in the air-gap between the middle and bottom layer. The paper presents a design of the 2 × 2 subarray, i.e. the unit cell using simulations in an infinite array environment. The simulation results show that the S11 is below ™11 dB over 57–66 GHz frequency band covering 14% bandwidth, and the simulated directivity is about 39 dBi when evaluated for a 32 × 32 element slot array antenna.

Impact of the spatial user distribution on the coverage antenna pattern of Maximum Ratio Combining in Random Line-Of-Sight

Abstract: In this paper we investigate the impact of the spatial user distribution on the Maximum Ratio Combining (MRC) of the output signals from an ideal 4-port antenna. The antenna consists of four elementary Huygens sources operating in Random Line-Of-Sight (RLOS). The antenna is assumed to be wall-mounted. Two specific scenarios for the user distribution are considered, i.e., the 3D hemisphere and a rectangular prism emulating a corridor or a rectangular room. We present simulation results in terms of the cumulative distribution functions corresponding to the resulting polarisation and pattern diversity of 1-bitstream and the corresponding coverage radiation pattern of the 4-port antenna system. We also show that there is an antenna arrangement that maximizes the diversity gain that will be different for different spatial distributions of users.

A planar multilayer antenna

Abstract: A planar antenna (170) is presented, which includes a radiation Printed Circuit Board (PCB) layer (310) including at least one array of at least two radiating elements, said radiation PCB layer being arranged for radiation of signals to be transmitted by said antenna. The antenna further includes a power distribution PCB layer (330) in parallel with said radiation PCB layer, arranged for providing each one of said at least two radiating elements with power needed for said radiation of said signals. The antenna further includes a spacing layer (320) arranged between said radiation PCB layer and said power distribution PCB layer, and including at least one spacer (321). Hereby, an air gap adjoining said power distribution PCB layer and having an equal thickness Tspacer over said air gap is created, whereby at least one gap waveguide is provided in said air gap.

Design of millimeter-wave wideband gap waveguide transitions considering integration into the antenna system

Abstract: Two wideband vertical transitions from inverted microstrip gap waveguide to rectangular waveguide (WR-15) for 60 GHz antenna array applications are proposed. These transitions are aimed to interconnect the WR-15 with the gap waveguide feed-network employed to provide feeding to the radiating elements of slot/horn antenna arrays. The wideband field transformation is achieved without the need of adding a quarter-wavelength cavity backshort on a metal block placed over the transition. First, we replace this backshort by creating a cavity in the radiating layer when this is made in Substrate Integrated Waveguide (SIW) technology, and thereafter we use an air-filled pin cavity in the radiating layer. The simulated Sparameters show that the presented transitions cover the unlicensed 60 GHz band (57–64 GHz) with good margins.

On S-parameter based complex correlation of multi-port antenna

Abstract: In this paper, we present a S-parameter based expression for the complex correlations of multi-port antennas. The formula is tested against the correlation formula based on embedded antenna patterns and the measurement in a reverberation chamber (RC). A 4-port wideband antenna is used as an example.

Double Broadband Balun Structure Using CRLH TL for Differential Excitation of Dual-Polarized Self-Grounded Bow-Tie Antenna

Abstract: A broadband compact balun comprising two composite right-left handed transmission lines (CRLH TL) is designed to excite a self-grounded bow-tie antenna. The design is based on a fractal shaped CRLH TL balun modified to the frequency band of interest. This balun consists of one +90° branch and three-90° branches to produce the desired 180° phase difference at the output. The simulated results show an amplitude imbalance of less than 1dB and a phase imbalance of less than 10°over most of the target bandwidth, i.e., 1.6-3 GHz. Two of the designed baluns were integrated with the bow-tie antenna in such a way that the feeding network could totally fit at the back of the antenna. The performance of the whole structure was also evaluated showing a return loss below-10 dB. The radiation pattern and the gain of the antenna with baluns are in good agreement with the ideal differential excitation, with gain degradation of only about 0.5 dB in the worst case.

Investigation of mode stirring with plate on platform in a reverberation chamber

Abstract: The accuracy of the reverberation chamber has been investigated when mode stirring is performed with a plate placed on a rotatable platform, i.e., plate-on-platform stirring. The accuracy and scanning volume of the platform plate are then compared to the original mode stirring plates that are moving alongside two walls. The results are also compared to physical theoretical models. The mode stirring with a plate on the platform provides STD of the measurements that are a factor 2 worse than with the original plate and platform stirring of the chamber. Still, this is good enough for accurate measurements above 2 GHz, provided the AUT is also located on the platform.

An air-filled cavity-backed 2×2 slot sub-array fed by inverted microstrip gap waveguide

Abstract: A wideband 2×2-slot element for a 60 GHz antenna array is designed by making use of air filled cavity fed by inverted microstrip gap waveguide The designed element is a triple layer structure in which the upper layer contains four radiating slots backed by an air-filled cavity The cavity is excited by a coupling slot fed by an inverted microstrip gap waveguide formed in the air-gap between the middle and lower layers The designed 2×2-slot element is considered in an infinite array environment A sample 32×32 slot array aperture is simulated using infinite array approach The results show that the mismatch is better than −15 dB and the directivity larger than 38 dBi over 563–679GHz frequency range, ie 207 % bandwidth

Correction to “MIMO Characterization on System Level of 5G Micro Base Stations Subject to Randomness in LOS”

Abstract: Unfortunately, we had mixed up some results when we plotted the graphs in Figure 7 of the above paper. This affected only the two blue curves in each of the three graphs, for $2\times 2$ MIMO in Random-LOS with LP and CP incidences, and had no influence on the discussion and conclusions in the paper. The correct graphs of Figure 7 are given here, in addition to an explanation of how the best level of the curves are related to the directivity of the antenna under test.

The simple truth about effects of mutual coupling in MIMO arrays for single and multiple bit streams in rich isotropic multipath

Abstract: In this paper, we demonstrate the effects of mutual coupling on embedded radiation efficiency, correlation, diversity gain, and MIMO efficiency for single and multiple bit streams in rich isotropic multipath (RIMP) environment by using parallel dipoles and a compact wideband four-port antenna as examples.

Optimizing small wideband antenna performance for both RIMP and random-LOS

Abstract: Rich Isotropic Multipath (RIMP) environment like reverberation chamber (RC) has proven to be useful for characterizing mobile LTE devices. The user statistics have larger effect in environments with stronger Line-Of-Sight (LOS), because the angle of arrival (AoA) and the polarization of the LOS contribution become randomized due to the user. Thus, we introduce the term Random-LOS. The present paper elaborates on characterization of an example antenna in both RIMP and random-LOS. We show how to characterize the micro BTS by the probability of detection (PoD) of one and more bitstreams in both RIMP and random-LOS, by considering the user randomly located and oriented within the angular coverage sector. We limit the treatment to a wall-mounted BTS antenna, and assume a desired hemi-spherical coverage.

Study of grating efficiency of planar arrays

Abstract: This paper studies the aperture efficiency reduction due to grating lobes of a uniformly excited planar array. The grating lobes will not cause major interference problems in the millimeter wave region, because of the attenuation in the atmosphere, but they cause a reduction of the directivity and thereby aperture efficiency of the antenna. Therefore, we present a simple formula for calculating the aperture efficiency in the presence of grating lobes, from knowledge of the element pattern. The accuracy of the formula is verified by comparing with simulated results for a full array with slot elements.

Design of sector antenna with wideband 2D hat-fed reflector for wireless communications

Abstract: We present the design of a new sector reflector antenna with 2-dimensional hat feed in order to avoid the radio link disconnection in point-to-point link communication systems due to the swinging of link antennas when there is a strong wind or vibration. The antenna has a 32% bandwidth for both the reflection coefficient below ™17.8dB and the sidelobes of the radiation pattern in vertical plane below ETSI Class 3 envelope, based on the simulated results.