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Per-Simon Kildal


Prof. Per-Simon Kildal
Antenna Group
Department of Signals and Systems
41296 Gothenburg, Sweden
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Per-Simon Kildal (M’82-SM’84-F’95) has M.S.E.E., Ph.D., and Doc¬tor Technicae degrees from the Norwegian Institute of Technology (NTH) in Trondheim. He was with SINTEF research institute in Trondheim from 1979 till 1989, and since then he has been a Professor at Chalmers Uni¬versity of Technology, Gothenburg, Sweden, where he has educated 17 persons to a PhD in antennas. Kildal has done several services to the IEEE Antennas and Propagation Society: elected member of the administration committee 1995-97, distinguished lecturer 1991-94, associate editor of the transactions 1995-98, and associate editor of a special issue in the transactions 2005. He has authored or coauthored more than 100 journal articles or letters in IEEE or IET journal, concerning antenna theory, analysis, design and measurement.

He gives short courses and organizes special sessions at conferences, and he has given invited lectures in plenary sessions at several conferences. His textbook Founda¬tions of Antennas - A Unified Approach has been well received. SINTEF awarded his work in 1984. He has received two best paper awards in IEEE Transaction on Antennas and Propagation. He holds several granted patents and patents pending.

Kildal has done the electrical design of two very large antennas, including development of the numerical methods and software: the 40m x 120m cylindrical parabolic reflector antenna of the European Incoherent Scatter Scientific Association (EISCAT), and the Gregorian dual-reflector feed of the 300m diameter radio telescope in Arecibo, the latter on a contract for Cornell University. He has invented several feeds for reflector antennas, such as the dipole-disk feed used for 10 years in the commercial satcom ship terminal of the Norwegian company NERA, the hat feed used for 10 years in commercial radio links, and the decade bandwidth log-periodic Eleven feed developed for use in radio telescopes for VLBI2010 and Square Kilometer Array (SKA).

Kildal and his co-workers have pioneered the reverberation chamber to an accurate tool for Over-The-Air (OTA) testing of small antennas and wireless devices, being commercialized in the company Bluetest AB ( Bluetest was founded in 2000, and experiences now a rapid growth in the market.

Kildal introduced the concept of soft and hard surfaces in 1988, representing a generalization of the corrugated surface, and having similarities with the later electromagnetic bandgap surface. The soft and hard surfaces are today considered as metamaterials. On this background he invented in 2008 a new quasi-TEM so-called gap waveguide that appears in the air gap between two parallel conducting plates. The gap waveguide has been demonstrated to have decade bandwidth, low loss, and application for packaging of electronic high-frequency circuits. It is expected to find application up to THz.

Gap Waveguides and Antennas up to Terahertz

The gap waveguide is a new quasi-TEM transmission line appearing in the air gap between two parallel metal plates, one of which is provided with a texture or a substrate with metal traces and patches. The waves follows strips, ridges or grooves in the texture, and are prohibited from propagating in other directions within a stopband realized by periodicities in the texture, thereby avoiding the need for conducting contact between the two metal plates. Such conducting contact is needed in normal cylindrical waveguides, and is known to be difficult and expensive to realize, in particular above 30 GHz. The waveguide has been demonstrated to have low losses and octave bandwidth. It can be potentially be applied to realize high-frequency circuits up to THz, and has demonstrated that it also can be used for packaging of passive and active circuits realized by other transmission line technologies.

The lecture will explain how the gap waveguides have evolved from research on artificial surfaces, such as the soft and hard surfaces defined in 1988, and the later high-impedance surfaces (artificial magnetic conductors) and electromagnetic bandgap (EBG) surfaces. The ideal counterparts of such surfaces can be called canonical surfaces, and Kildal states the need for the boundary conditions of the canonical surfaces to be built into commercial electromagnetics software to enable fast initial feasibility studies and designs.

The lecture will then give the basic theory of the gap waveguides and explain how they work, describe how to design the stopband of normal parallel-plate modes using different periodic metal elements, such as pins (nails), patches with via holes (mushrooms), and helices (springs), introduce the three different realizations of it referred to as ridge, strip and groove gap waveguides, and show examples of antennas and components such as OMT, couplers and filters realized in this technology. Examples of packaging applications will also be shown, using a lid of springs at low frequencies and a lid of nails at high frequencies, as well as a systematic advantageous approach to packaging referred to as PMC packaging, in which the circuit design is done inside a PEC/PMC package, and thereafter the PMC is realized.

OTA-MIMO Measurements of Wireless Stations in Reverberation Chamber

Antenna measurements are normally done in anechoic chambers emulating free space, because free space is a good reference environment for traditional antenna locations on roof-tops and masts with Line-Of-Sight (LOS) to the opposite side of the communication link or target. However, modern small antennas on wireless stations are not located on mast and rooftops, and they are exposed to multipath often without LOS, and a resulting fading. Therefore, a new reference environment is needed for Over-The-Air (OTA) tests, such as the isotropic multipath environment emulated by a reverberation chamber. Also, modern wireless stations have or will be provided with multi-port small antennas combating the negative effects of fading by antenna diversity and MIMO (Multiple Input Multiple Output) technology, and then it is also needed to emulate a fading-type reference environment to test these functions, such as that emulated by reverberation chambers.

The rich isotropic reference environment has a uniform Angle-of-Arrival (AoA) distribution, for which the average received power is proportional to antenna efficiency and total radiated power and independent of the orientation of the antenna and wireless station. A wireless station will also in average experience a rich isotropic environment when it is moved between different real-life environments, and in particular if it has an arbitrary orientation with respect to the vertical when it is used. Therefore, the rich isotropic multipath is believed to be a good new reference environment for OTA tests of wireless stations for use in multipath.

The reverberation chamber has during the last 10 years been developed into a fast, accurate and cost-effective instrument for emulating rich isotropic multipath and thereby characterizing small antennas and wireless stations. The lecture will explain how the chamber works, and give formulas for the average transfer function as well as the uncertainty by which we can measure efficiency, diversity gain, maximum available MIMO capacity, total radiated power and receiver sensitivity. The latter can be obtained both as total isotropic sensitivity (TIS) and average fading sensitivity (AFS), the latter measured during continuous fading.

The last part of the lecture will be devoted to through-put measurements of complete systems with MIMO capability, such as for WLAN, LTE and WiMAX. The lecture will also explain how the time and frequency domain characteristics of the chamber (Doppler spread, time delay spread, coherence bandwidth) can be determined, and controlled by loading the chamber with absorbing objects.

Low Noise Decade-Bandwidth Eleven feed for Future Radio Telescopes

The Eleven antenna is a log-periodic dual-polarized dual-folded-dipole antenna with constant beamwidth and phase center over a decade bandwidth. The antenna is mainly intended as a feed for Square Kilometer Arrays (SKA) and geodetic VLBI2010 radio telescopes, but several other applications are possible e.g. in anechoic far-field or compact ranges, and for EMC. The Eleven antenna can easily be reconfigured for use with 2-ports, 4-ports or 8-ports which makes it interesting for use in connection with MIMO communication systems or as a multi-port wideband reference antenna for testing/validation of these.

The lecture will first give an introduction to common feeds for reflector antennas and how their radiation fields can be characterized in terms of the feed efficiency and its subefficiencies accounting for spillover, illumination taper, phase errors, and polarization loss. This characterization is sufficient for normal feeds, but it will be argued that for antennas with octave or more bandwidth an additional so-called “BOR1” subefficiency is needed in order to characterize how clean the radiation pattern is with respect to higher order azimuth variations in the far-field function.
The lecture will describe how the Eleven antenna has been numerically optimized and designed to achieve high feed efficiency over a decade bandwidth, without performance notches. The description includes co-design and integration with low-noise amplifiers (LNA), and cryogenic mechanical design allowing for cooling down to 20 K together with the LNAs. A model for the overall achieved system noise temperature will be presented, agreeing well with measured performance.

Finally, the lecture will give results for measured and computed correlation and diversity gain as a function of frequency when the multi-port Eleven antenna is used in a MIMO system.