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The world's largest single-reflector radio telescope is located in Arecibo. Its Gregorian dual-reflector feed was inaugurated in 1997, representing an enormous improvement in terms of bandwidth (limited by that of a wide-angle corrugated horn) and aperture efficiency compared to using the previous line feeds of about 1% bandwidth. The inauguration was preceded by an upgrading project of more than 10 years duration, during which author of this paper was stimulated to get ideas of several other technologies that were further developed the decades thereafter. The present paper gives an overview of these technologies, and how they are related to the upgrade project: the Comhat antenna (a hat-fed reflector) originating from an initial theoretical model of the line feeds, semi-analytical reflector synthesis by ray tracing, wideband constant wide-beamwidth feed for paraboloids, canonical soft and hard surfaces, and gap waveguides.

The hat antenna is a self-supported rear-radiating waveguide feed used in the Comhat reflector that has been manufactured in more than 1M pieces for use in radio links. The design of hat feeds is done by numerical simulations taking advantage of its rotational symmetry. There exists an early analytical model for the far-field of the hat feed including the axial waveguide, and treating the hat brim as a PEC/PMC strip grid. The purpose of the present paper is to validate the theoretical model by simulations using COMSOL Multiphysics.

Measurements with waveguide flanges at frequencies above 100GHz have a considerable issue with leakage due to problems with achieving good electrical contact between the opposite flanges. The higher the frequency, the higher is the requirement for full contact. However, by using an artificial magnetic conducting (AMC) flange on one side of the interface, full electric contact is not needed between the two joining flanges. The AMC is realized as a pin-surface, and the leakage is stopped by a parallel-plate stopband like in gap waveguides. This paper describes how these AMC pin waveguide flanges can be used for screw redundant measurements.

A new configuration is introduced to integrate diplexers and power dividers. The proposed configuration is based on coupling matrix. The design of the lumped element network is based on addition of an extra term to the conventional error function of the coupling matrix to decouple the two ports of the power divider. An optimized lumped element network is implemented successfully on an EBG based guiding technology known as ridge gap waveguide. The optimization of the physical structure is done efficiently by dividing the diplexer-power divider into many sub-circuits and analyzing the corrected delay response of them.

In this work, we present several gap waveguide planar array antennas for millimeter wave point to point communication systems. The antennas are designed using groove gap waveguide, ridge gap waveguide and inverted microstrip gap waveguide technology. All these three antenna designs are based on the cavity-backed slots as the core radiating elements. There exists a coupling slot in the cavity layer which allows the excitation of the radiating slot elements using three different types of feeding waveguide section. The designed three antennas have 16×16 radiating slot elements and these antennas operate over 15% relative bandwidth from 57–66GHz frequency range with −13 dB reflection coefficient. The simulated directivity for these slot arrays are about 33.3 dBi at the center of the band.

In this paper, a multilayer wideband slot array antenna is presented for high gain applications at V-band. The proposed antenna consists of three unconnected metal layers based on the recently introduced gap waveguide technology. A 2×2 cavity-backed slot subarray is fed by a ridge gap waveguide corporate distribution network. The subarray is optimized to have wide bandwidth and low grating lobes in an infinite array environment. A simple slot-tilting method is used to fulfill the radiation pattern requirement of the ETSI 302 standard for fixed radio links. A prototype consisting of 16×16 slots is manufactured by die-sink Electric Discharge Machining (EDM), a fast modern planar-3D spark machining method. The measured antenna has a relative bandwidth of 18% with input reflection coefficient better than −10 dB, and the radiation patterns satisfy the ETSI 302 standard co-polar sidelobe envelope over 56–67 GHz frequency band. The measured total aperture efficiency is over most of the frequency band better than 80%.

In this paper, we propose a linear array configuration for Random Line-of-Sight Over-The-Air testing set-up in anechoic chamber. For this aim, we use the self-grounded dual-polarized bowtie antenna as the element in the array. We present a new design of the bowtie to improve the array performance in terms of reflection coefficient and directivity. The new design has a simpler profile to manufacture. A good reflection coefficient performance has been achieved over the entire band of interest, i.e., 1.6–3GHz. The directivity of the array is almost constant for both polarizations over the entire frequency band.

This paper deals with the design of low loss wideband power dividers based on groove gap waveguide (GGW) technology. The advantages of GGW power dividers are low insertion loss, high power handling capacities, ease of fabrication and compatibility with integrated microwave networks. A 64-way power divider is designed and used as the feeding network of a 16×16-element slot antenna array at 60-GHz band. The results show that the gain and total radiation efficiency of the antenna are more than 32.5 dBi and 90% over the desired frequency range from 56 to 66.4 GHz.

In this paper we look into a near-field measurement setup consisting of a cylindrical reflector and a linear array feed. The main application is Random Line-Of-Sight Over-The- Air measurements in anechoic or semi-anechoic chambers (i.e., anechoic chamber with reflecting floor). More specifically, the aim is testing the wireless communication systems on automotive vehicles. The aim is to generate the uniform field distribution of a plane wave over a pre-defined test zone containing the car or at least the part of the car containing the antenna(s). The field intensity variations over the testing zone have been investigated for reference measurements over the testing frequency bandwidth, i.e., 1.6–2.8 GHz.

We present simulations of near-field plane wave synthesis by a planar array. The focus is on minimization of reference signal errors within the test zone for Random Line-Of-Sight Over-The-Air characterization of wireless devices on cars. The analysis considers the output of the ideal digital threshold receiver model of the device under test as a Probability of Detection curve. The dimensions, the interelement spacings and the number of elements in a planar array comprising Huygens sources are investigated to produce an absolute error less than 0.5 dB.

Gap waveguide is a promising transmission structure, especially for millimeter wave and THz applications. It does not require conductive connection between the top and bottom plates, and therefore this technology gain advantages over conventional rectangular waveguides and SIWs (Substrate Integrated Waveguides) above 100 GHz. In this paper, a new pin form, the half-height pin, is proposed for the gap waveguide. This new half-height pin form has similar stop-band performance as the previous quarter-wavelength long pin form. However, there must be such half-height pins on both the upper and lower plates, in contrast to one of the two having pins in the original gap waveguide. The shorter length of the pins makes the fabrication of the pin surface much easier, such as by e.g. die-forming, molding or MEMS technology. The current work paves the way for mass production of gap waveguide devices and systems at millimeter wave and THz.

A new low-profile planar eleven antenna is designed as a wideband MIMO antenna for micro-base stations in future wireless communication systems. The design criterion is to minimize both the reflection coefficient and the ratio of the required average received power over the threshold for 95% of the total probability of detection (PoD) in the Rich Isotropic Multipath (RIMP) and random Line-of-Sight (RLOS) scenarios of both one-bit stream and two-bit stream. The design is performed via optimization with a genetic algorithm.

Autonomous cars will in a near future drive around in cities and on highways. Antennas will then be needed to secure the wireless connection to these cars. To be able to test the antennas we have defined two edge environments: the Random Line-of-Sight (LOS) and the Rich Isotropic Multipath (RIMP). This paper shows a throughput performance comparison between measurements and simulations of a car-roof (shark-fin) antenna mounted on a ground plane in both of these environments. The comparison is done for both one and two bitstreams in a 2×2 MIMO system. The analysis is based on probability of detection (PoD) curves representing the throughput performance with digital threshold receivers.

In this paper, a high gain high efficiency 16×16-element slot antenna array is presented for 60 GHz applications. The antenna is designed based on gap waveguide technology. A corporate feed network is realized by a texture of pins and a guiding ridge in a bottom plate. The simulated results show about 16% of reflection coefficient bandwidth (|S11| < −10 dB) covering 57–67 GHz frequency range. Also, the gain of the antenna is more than 32.5 dBi with an efficiency higher than 85% over the desired frequency band.

Currently the inverted microstrip gap waveguide has been considered as a promising technology for millimeter wave wireless applications. Theoretically, the new structure may be considered as a two layer shielded structure where the bottom layer consists of an array of periodic metallic pins which works as an artificial magnetic conductor (AMC). However, it is difficult to evaluate electromagnetic properties and performance of the new waveguide by using traditional waveguide ports or discrete ports in available full-wave simulator. In order to solve the problem, this paper proposes an effective method to determine dimensions of traditional waveguide ports in existing commercial full wave simulator to be used while simulating the inverted microstrip gap waveguide structures. The procedure includes the analysis of quasi-TEM mode of the inverted microstrip gap waveguide and the corresponding size of the waveguide port, as well as the location and boundary conditions used in the simulation software. The numerical port proposed in this work is much better than the ports used previously.

Smart phone sensors provide new possibilities to understand how devices are actually used and handled in real-life situations. Such information can possibly be used to design better handsets, but also to improve network performance. For example, the radiated performance of a wireless device depends on its orientation and position relative to the user. Hence, knowing realistic handset usage plays a major role in the Over-The-Air characterization of antennas and wireless devices in general. This paper presents an analysis of usage positions for voice service. A simplified statistical model based on data collected from devices acceleration sensors is presented. The analysis shows interesting results from which we can identify some typical ways the user is handling the phone when in a voice conversation. Our analysis shows clear differences of the orientation of the handset when used with a handsfree set and when not.

The eleven antenna has been greatly used in many applications to achieve low reflection coefficient and stable-pattern over ultra-wide-bands. However, arraying in the eleven configuration forces the antenna designer to tilt the antenna over an electric conducting ground plane, and this makes it mechanically complicated and increases the profile of the antenna. Seeking new capabilities, the theory of putting log-periodic dipoles in the eleven configuration over magnetic ground is developed. The eleven antenna is formed by two printed folded-dipoles, and we evaluate the performance for a single-pair of dipoles and five-pairs of dipoles. The results are extracted for the cases of PEC ground, PMC ground and without ground. The results are in a good agreement with theory. Also, some discussions are provided for the realization of the artificial-magnetic-ground.

Hannan introduced in 1964 an embedded element efficiency concept that explains the so-called element-gain paradox in antenna arrays, i.e., that the array gain always is smaller than the sum of the element gains. In the present letter, we show for the first time the usefulness of his approach by evaluating directivities and aperture efficiencies of an array of open-ended waveguides by commercial full-wave electromagnetic (EM) solvers for a large range of element spacing. The results show also that by using embedded element analysis, the realized gain of regular arrays actually becomes equal to the sum of the realized gains of the embedded elements. Thus, the embedded element efficiency is more practical to use in design and numerical analysis than the more commonly used active element pattern approach. We also show that the embedded element efficiency can be approximated by a simple formula when the element spacing is smaller than half-wavelength.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The ridge gap waveguide is a new transmission line for millimeter-wave applications. Traditionally, rectangular waveguides are used for those applications due to their low loss. However their fabrication requires precision machining and very good electrical contact and alignment between two joining mechanical parts. Ridge gap waveguides can obtain similar performance without requiring conductive sidewalls and this provides more freedom during the fabrication and assembly process as the structure is no longer sensitive to small gaps between the side walls and the upper lid. The ridge gap waveguide has already been proven been validated for 10-20 GHz using conventional fabrication methods. The ridge gap waveguide prototypes presented in this paper are designed to work in the frequency region between 210 and 340 GHz, and fabricated using MEMS technology. MEMS provides fabrication precision of the structures and thus opens the path for high-frequency components.

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).

In this letter, we study the spatial multiplexing throughputs of multiple-input-multiple-output (MIMO) systems with fixed modulation and coding scheme (i.e., fixed peak rate) based on measurement of the universal software radio peripheral (USRP) in a reverberation chamber. In particular, we propose a simple inverse power allocation scheme for the singular value decomposition (SVD)-based MIMO system. Using the proposed power allocation, the power saving (for achieving the same throughput), compared to the SVD-MIMO without power allocation, is about 2.5 dB. Good agreement is observed between the USRP measurement and the simulation.

This paper emphasizes the importance of recognizing the major role played by mutual coupling effects in array antennas, especially for dense arrays with element spacing within half a wavelength. For array operation in transmit mode, backward waves emanate both from element ports that are excited by forward waves, and from non-excited ports. This overall and excitation-dependent mismatch is herein characterized in terms of a decoupling efficiency. It is shown how this decoupling efficiency reduces to the well-known impedance mismatch factor for a conventional phase-steered array (all elements excited), and to the embedded element efficiency (only one element excited) used to characterize multiple input and multiple output (MIMO) arrays. Generally, this decoupling efficiency can be used to characterize the combined effect of mismatch and coupling for any excitation of an array, for instance, the Airy pattern excitation of focal plane array (FPA) feeds for reflectors, as showcased here. The abovementioned forms of decoupling efficiencies are evaluated and discussed for an example array of idealized rectangular apertures with special emphasis on the Airy excitation.

We propose a simple method to accurately predict Doppler spread in a reverberation chamber (RC) by using frequency domain S-parameters measured with a vector network analyzer (VNA) at many fixed stirrer positions (step-wise stationary mode). Thus, the measurements are done under repeatable stationary conditions, so no Doppler shift is present during the actual measurements. Still, this letter shows that the measured S-parameters in step-wise stationary mode can be used to determine Doppler spread appearing during continuous movement of the stirrers. This can be done by computation for any stirrer speed by assuming that the fixed stirrer position steps are the time steps of a continuous movement of the stirrers, and by adding a virtual stirrer speed between the positions corresponding to the desired continuous movement of the stirrers. The computed Doppler spreads are validated over a large frequency band by measuring the time-varying S-parameters for a given stirrer speed.

Accuracy limitation in evaluation of diversity gains based on cumulative distribution function curves is highlighted. New devised closed-form formulas are provided for Selection Combining and Maximum Ratio Combining diversity schemes rendering diversity gain as a function of correlation and radiation efficiencies. Accuracy of these formulas is studied and verified by numerical simulations. These formulas take a central role for the cases when engineers are limited to a finite number of measured voltage samples at different ports to provide them with accurate calculation of ergodic diversity gain. This letter also reveals dependency of different diversity gains upon total embedded efficiencies of branches and underscores the significance of identical efficiencies of two-element terminals for their optimum performance in multipath environments.

The problem of determining the eigenmodes of a rectangular waveguide with one hard wall formed by longitudinal corrugations with grooves filled with dielectric is considered. The characteristic equation is derived by using the asymptotic boundary conditions for corrugated surfaces. It is shown analytically that if the groove depth is equal to the value 0.25 lambda/(epsilon - 1)(1/2) corresponding to the hard wall condition, the TE eigenmode spectrum of the waveguide contains an infinite set of new non-uniform quasi-TEM modes with different transverse propagation constants in the empty part and identical longitudinal propagation constants equal to the wavenumber k. Analytical solution for the case of excitation of the waveguide by a specified source is given, and an example of forming local quasi-TEM waves is considered and discussed.

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.

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.

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.

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.

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.

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.

We investigate the properties of the dipole frequency selective surfaces-loaded rectangular waveguide. The analysis is carried out by using the method of moments together with an algorithm that solves for a multilayer structure in the spectral domain. The eigenmodes are determined by searching for resonant solutions. Dispersion diagrams obtained from this approach are compared with those generated by commercial software simulations. Experimental validation is also performed

We introduce a partly corrugated hard horn, consisting of a smooth-walled horn with an attached longitudinally corrugated outer section. This alleviates the problems with the manufacturing when the longitudinal corrugations extend into the throat of the horn. The transition between the inner smooth walled part and the outer corrugated part is abrupt. This is used and controlled to design better and shorter single-band horns than otherwise possible. Furthermore, it enables the design of dual-band horns with low cross-polarization and high gain, for multifunction use at Ka-band with transmit and receive frequencies in the same antenna. Measurements on a model of such a dual-band horn are presented and discussed.

The embedded element patterns of two parallel half-wavelength dipoles are calculated for various source impedances and dipole spacings by using classical formulas for self and mutual impedances. These are used to calculate the effective diversity gain, which is shown to vary with source impedances and dipole spacing. The results are verified using a method of moments (MoM) code for wire antennas and via measurements in a reverberation chamber. The numerical model is used to find the source impedances that maximize the effective diversity gain, which has a maximum for the computed cases when the source impedances are conjugate-matched to the input impedances of each of the embedded dipole elements. Then the two antenna ports are uncorrelated. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 532–535, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21400

The dyadic reflection coefficient of a planar surface consisting of parallel PEC and PMC strips is derived and used to study radiation patterns of dipoles located over the surface. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 583–587 2006; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21414

The gap waveguide technology is an advantageous way of packaging passive microstrip components. This work presents a wideband transition from a standard microstrip line packaged by using a bed of nails, to a rectangular waveguide operating in V band. The transition is designed by means of a T-shaped patch that couples the fields into a rectangular waveguide extending vertically from the microstrip circuit. The simulated results show more than 28.5% bandwidth with S 11 lower than −10 dB. This transition is intended to be used as a WR-15 port of a planar array antenna for 60 GHz applications, where the array elements are fed by microstrip distribution networks packaged by gap waveguide technology. Thereby, radiation is avoided from the distribution network itself.

When a spectrum of two-dimensional (2-D) solutions (S2DS) is applied to calculate the far-field functions or impedances of three-dimensional (3-D) elements in the vicinity of two-dimensional (2-D) structures, in general, the calculations have to be performed for both positive and negative values of k/sub z/. This letter analyzes the odd-even property of functions for boundary currents over k/sub z/. Therefore, by using this odd-even property, the calculations of the far-field functions and impedances are only needed to be performed for positive values of k/sub z/, which reduces the computation cost by a factor of 2. A verification case is also presented.

A conical horn with hard wall used for supporting the quasi-TEM-mode having a uniform field distribution over the cross section is modeled. The hard wall is realized as an electromagnetic bandgap (EBG) structure using a dielectric layer loaded with narrow longitudinal strips connected to the basic metallic wall by radial vias to prevent excitation of the strip-line mode. The modeling is based on a stepwise approximation of the horn surfaces by a set of cylindrical sections. Each section consists of a strip-loaded part and a longitudinally corrugated part representing the vias. The stepped horn characteristics are calculated by using the mode-matching method combined with the Winer-Hopf-Weinstein method for accurate account of the wave scattering at the aperture. The strip-line mode resonance effects are studied and demonstrated. It is shown that if the length of the strip part of each section sufficiently differs from the resonance value, the performance of the hard strip-loaded horn with vias is similar to high performance of the appropriate hard corrugated horn. Recommendations are given on appropriate choice of the maximum spacing between the vias providing the absence of resonance effects in the specified frequency band.