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Relation between diagram correlation factors and S-parameters of multiport antenna with arbitrary feeding network
Electronics Letters
Abstract
Antenna diversity demands a sufficiently low diagram correlation factor p. A universal relation between p and the scatter parameters of a multiport antenna is derived for arbitrary numbers of ports and radiating elements. It is shown that the diagram correlation factor depends significantly on the number of ports. While for a two-port antenna a vanishing correlation factor can be achieved with port matching only, this is not possible for multiport antennas with port numbers greater than two.
... And second, the number of coefficients that needs exami- nation grows with the number of radiators. The popular branch correlation coefficient [3], which may be calculated from the scattering matrix [4]- [6], bears similar problems, since there are multiple coefficients for more than two radiators. Furthermore, the branch efficiencies must be taken into account separately [7], [8]. ...
... These source waves are transformed through to yield a set of waves (6) Above relation has been identified as the decomposition of the incident wave vector into modal weights [9,Eq. (6)], hence the subscript: if an eigenmode of the antenna array is excited with unit power, then , and consequently the th element of will be one and all other elements will be zero. ...
Mutual coupling has negative impact on the radiation properties of compact antenna arrays when the spacing of individual radiators is considerably closer than half a wavelength. We have previously put forward a description of the radiation efficiency of an arbitrary antenna array in terms of orthogonal radiating eigenmodes. The present publication elaborates on this concept and presents a descriptive equivalent circuit model for a coupled antenna array. We show that eigenmodes undergo independent Rayleigh fading under appropriate conditions. Also, we demonstrate how practical closed-form expressions in terms of the array's scattering matrix can be derived, which characterize the diversity performance and therefore are convenient measures for the radiation quality of a compact antenna array.
... The shape of the antenna pattern for patch and ring is different, so that they radiate differently which ensures pattern diversity. In order to evaluate MIMO performance of the antenna, the envelope correlation coefficient of the antenna is computed from S-parameters [31] and is presented in fig. (12). ...
In this paper, a systematic procedure is presented to feed placement in multi-mode MIMO antennas based on characteristic mode theory. Using modal radiated power, a circuit model for multi-mode MIMO antennas is proposed and optimal feed positions are found to excite orthogonal modes of these antennas. Characteristic mode analysis is done to determine orthogonal radiating modes of the antenna and using modal radiated power and reflection coefficient of the antenna, optimal feed locations are determined to excite these modes. The proposed method is verified by simulation and measurement of a four-port MIMO antenna. This method can be used to feed locate in any planar antenna with any number of orthogonal modes.
... 10,11 Another technique used to reduce coupling between radiating elements is orthogonal placement of antenna elements. 12 The latest research is about two elements or four elements, some of which do not possess low envelope correlation coefficient (ECC) or ECC has not been reported. In Reference 18 8-element MIMO antenna, an array presented with high isolation is presented but its size is the constraint. ...
A planar six‐elements, dual‐polarized, high‐gain, multiband antenna for diverse application is proposed in this manuscript. The proposed design consists of six radiating elements and a parasitic element on the top side of the structure. Each radiating element consists of overlapped ellipse with a line feeding technique. Iterations have been carried out on the number of antenna elements as well as on the spacing between the elements to get a minimum coupling between antenna elements. To compensate the coupling effect as well as to increase the impedance bandwidth, a ground plane structure has been modified with “L” shape structures. Fabricated prototype has an isolation less than −2 dB with highest gain of 6.7 dBi. Diversity in polarization is achieved by orienting antenna elements in vertical as well as in horizontal directions. A simple and compact design of antenna with good gain and less correlation coefficient makes an antenna useful for multiple input multiple output (MIMO) applications in the wireless communication systems. Simulation and measurement results validates the use of proposed structure in various applications like ISM, WLAN, Wi‐Fi, short range radar, and satellite applications.
... Multiport antennas have been used in numerous applications for many years including phased array antennas and Multiple-Input-Multiple-Output (MIMO) antennas [1][2][3]. With the development of integrated circuit technologies, multiport antennas are more and more integrated with amplifiers, phase shifters, and other devices to realize a compact, low-loss, and multifunctional antenna system. ...
—Proof-of-concept is presented of a novel slot antenna structure with two excitation ports. Although this antenna provides a wide impedance bandwidth, its peak gain and optimum radiation efficiency are observed at its mid-band operational frequency. The antenna structure is etched on the top side of a dielectric substrate with a ground plane. The antenna essentially consists of a rectangular patch with two dielectric slots in which multiple coupled patch arms embedded with H-shaped slits are loaded. The two dielectric slots are isolated from each other with a large H-shaped slit. The radiation characteristics of the proposed antenna in terms of impedance bandwidth, gain and efficiency can be significantly improved by simply increasing the number of radiation arms and modifying their dimensions. The antenna’s performance was verified by building and testing three prototype antennas. The final optimized antenna exhibits a fractional bandwidth of 171% (0.5–6.4 GHz) with a peak gain and maximum radiation efficiency of 5.3 dBi and 75% at 4.4 GHz, respectively. The antenna has physical dimensions of 27×37×1.6 mm3 corresponding to electrical size of 0.0452λ0 ×0.0627λ0 ×0.0026λ0, where λ0 is freespace wavelength at 0.5 GHz. The antenna is compatible for integration in handsets and other
broadband wireless systems that operate over L-, S-, and C-bands.
... The diagram correlation fa S-parameters of a multiport a ports is as [5] ...
Future generation wireless communication systems demand higher data rates and improved channel capacity. Multiple Input Multiple Output (MIMO) antenna system improves channel capacity with a certain requisite distance between individual antenna elements. Mobile terminals have limited space and demand more compact antenna system. Therefore multiport antennas are designed with small size and sufficient decoupling between the antenna ports. In this paper, a two port orthogonal fed circular microstrip antenna is presented, for 2.6 GHz LTE/WiMAX band (2.5-2.7 GHz), with measured bandwidth of 69 MHz supporting 4G applications. The performance of proposed antenna is evaluated based on simulated S-parameters, decoupling between the ports and diagram correlation coefficient between the radiation patterns of each port. A very good agreement was observed between simulated and measured results.
... A relation between correlation factor ρ ij and scattered parameters for N port antenna is derived in [10] and is given as ...
A multimode collocated microstrip patch antenna with reduced mutual coupling is proposed in this paper. The antenna is designed to achieve polarization and pattern diversity for use in multiple-input-multiple-output (MIMO) terminals. The four-port antenna resonates at 2.45 GHz and have total dimension of 1.03¸ with reduced mutual coupling (< -20 dB) between its ports. It consists of a simple square patch and a square ring antenna, with a novel square ring slot defected ground structure (DGS). Square ring slot on ground improves isolation by 7 dB by reducing surface waves in both E and H planes. With defected ground structure (DGS), coupling between patch and ring antennas is about -25 dB and correlation factor is less than 0.1. Pattern diversity, mutual coupling and correlation coe±cient between signals for a four-port antenna fabricated using FR4 substrate is discussed in this paper.
... This complex procedure can be simplified by using the scattering Matrix S N Â N of the array. According to Ref. (25) and under the assumption of a lossless antenna, S can be used to calculate the correlation factors as ...
Given the absence of a body coil, the radio frequency screen of a whole-body 9.4T magnetic resonance imaging scanner can be used as a circular waveguide. In the unloaded case, the screen allows propagation of the dominant TE(11) - as well as the TM(01) -mode. In the first part of this study, the optimum coupling of a circular polarized TE(11) -mode was determined empirically for excitation and reception with a rectangular patch antenna. Employing full-wave simulations, two simulation models and two phantoms, different patch positions were tested to find the optimum position with respect to coupled power and homogenous excitation field. The best simulation results were validated with measurements. The second part of this study describes the design and measurements of a multimode excitation device. Using the parallel transmit system of the MR scanner, all propagable traveling wave modes could be excited and detected independently. The performance of the multimode device related to field of view, B(1) (+) -efficiency and radio frequency shimming was assessed by phantom measurements. Initial results show that three modes are sufficient to homogeneously excite regions of interest at 9.4 T. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
... Previous designs of compact antenna arrays often aim to eliminate mutual coupling and impedance mismatch altogether and thus always result in an ideal array without need for further analysis [12], [13], [14]. Other papers concentrate on the port correlation coefficient [15], [16] or treat impedance mismatch (or the mean effective gain, MEG) as distinct quantities [1], [17], [18]. By contrast, the above figures of merit include both effects -signal correlation and impedance mismatch -in a single quantity. ...
A quick, reliable, and simple evaluation of mutual coupling effects is essential for the optimization of antenna arrays for small mobile communications devices. In recent papers we have proposed novel figures of merit that quantify the impact on diversity reception in terms of scattering matrix of the array and have confirmed the validity of these formulas by practical diversity measurements. The present paper provides an extended analysis of the measurement data and contrasts the benefits of this method of array characterization with existing approaches.
In this paper, a method is presented for antenna beamforming based on characteristic mode theory. A multi-mode antenna with two elements and four significant orthogonal modes is presented in 5 GHz. Feed positions of the proposed antenna to excite its four characteristic modes are determined; Then with the help of characteristic mode analysis and the reciprocity theorem, amplitude and phase of the excitation coefficients of the proposed antenna are found to change the antenna beam direction in whole azimuth plane. Moreover, changing the weights of the antenna feeds enables elevation beamforming of the proposed antenna.
in this paper a dual polarized antenna array with shaped beam for outdoor WiFi access points, e.g. hotspots operating at the upper WiFi frequency band of 5.8 GHz is described. The aperture is composed of 64 waveguide antenna elements. By controlling the amplitude and the phase of only 24 elements, a shaping of the pattern in the main beam is achieved. Both polarisations are also excited by each antenna element. The presented base station array has therefore a broad half power beamwidth allowing for an easy alignment/installation of the base stations in the field. Last but not least, it shows low correlation factors which mean that it can be also used for MIMO antenna systems.
Die Verwendung von zwei oder mehreren Antennen auf einer oder jeder Seite des Funkkanals im Mobilfunk hat eine Reihe von Vorteilen, die in diesem Kapitel beschrieben werden. Die klassische Antennendiversität verwendet mehrere Antennen auf der Empfangsseite. Die damit erzielbaren Gewinne bzw. Verbesserungen der Empfangswahrscheinlichkeiten werden hergeleitet. Ferner befasst sich das Kapitel mit der räumlichen Entzerrung (MIMO), beschreibt die wichtigsten Verfahren (Zero-Forcing, MMSE, Matched-Filter) und behandelt die Korrelation der Antennencharakteristik sowie die Kalibrierung von MIMO-Systemen. Hinweise auf Video-Demonstrationen der räumlichen Entzerrung schließen das Kapitel ab.
The paper investigates a new application of a previously designed pattern reconfigurable antenna. A single antenna is able to rotate its dipole-like radiation pattern on a single axis. This paper demonstrates how once can efficiently extend this performance by combining two such antennas into a linear array. The proposed array allows continuous steering of the main beam direction between two orthogonal planes. The theoretical predictions are in good agreement with numerical simulations (CST MWS).
Envelope correlation coefficient is a key parameter for MIMO antennas, allowing assessment of the signal correlation between multiple input/outputs of an antenna system. A simplified method allows calculation of this coefficient by using only S-parameters, however the method is less accurate and only applies to lossless antennas.
This paper discusses a possible correction to the above method, for the case where the losses occur in the feed cable and not in the antenna itself. A lossless MIMO antenna system with lossy feeds is discussed, both analytically and using simulation tools. It is shown, that even losses as small as 0.3 dB can lead to substantial underestimation of the coefficient. A new equation is proposed, which compensates for the lossy feeds. It is also demonstrated, that even for a lossless case, some discrepancies exist between the two commonly used methods to calculate envelope correlation coefficient.
Die Verwendung von zwei oder mehreren Antennen auf einer oder jeder Seite des Funkkanals im Mobilfunk hat eine Reihe von Vorteilen, die in diesem Kapitel beschrieben werden. Die klassische Antennendiversität verwendet mehrere Antennen auf der Empfangsseite. Die damit erzielbaren Gewinne bzw. Verbesserungen der Empfangswahrscheinlichkeiten werden hergeleitet. Ferner befasst sich das Kapitel mit der räumlichen Entzerrung (MIMO), beschreibt die wichtigsten Verfahren (Zero-Forcing, MMSE, Matched-Filter) und behandelt die Korrelation der Antennencharakteristik sowie die Kalibrierung von MIMO-Systemen. Hinweise auf Video-Demonstrationen der räumlichen Entzerrung schließen das Kapitel ab.
A compact 4 port MIMO antenna system is proposed in this paper with an area of 60×60 mm2. The antenna operates at 2.45 GHz with an overall area of nearly 1λ. The antenna consists of a cross patch embedded inside a square ring patch antenna. The strong mutual coupling between ports is reduced below -24 dB by etching a square ring defected ground structure on the ground. The isolation structure reduces surface waves and cross polarization levels providing an isolation improvement of 8.5 dB. The antenna can be used for multiple input multiple output systems and have very low envelope correlation less than 0.1 between its waveforms. Measurements and characteristics of antenna system fabricated on an FR4 substrate are provided.
A defected ground structure (DGS) for improving isolation between four ports in a collocated multiple-input-multiple-output (MIMO) antenna is proposed. Isolation improvement by 7 dB is achieved by reducing surface waves within the dielectric substrate. Mutual coupling values as low as -25 dB are obtained along both the E- and H-planes. The MIMO antenna includes a square patch antenna surrounded by a square ring patch antenna with the DGS etched in the form of a square ring. The DGS effectively suppresses the cross-polarisation levels for all radiating modes. The design and effectiveness of the DGS in improving isolation for a fabricated 4-port antenna are discussed.
In this paper we discuss antenna correlation coefficient and its application in a two-element receiving antenna system within a simple multipath rich environment. We conjecture here, that in general, the antenna correlation coefficient does not necessarily provide an accurate estimation of how well or how poorly a multiple antenna receiving system will perform in a multipath rich environment. In general, the reliability of the communication channel is as much if not more a function of the multipath environment and the choice of diversity scheme or MIMO implementation, factors that the antenna correlation coefficient do not characterize. We consider the performance of a two-element antenna system in a simple multipath rich environment as part of this discussion. Finally, we discuss the significance of the antenna correlation coefficient when two receiving antennas are closely spaced and may be highly coupled.
Multiport antennas are widely used and often integrated with active components, such as low noise amplifiers, in antenna systems. It is important to verify and evaluate the radiation efficiency of a multiport antenna before being integrated in the system. When the radiation efficiency of a multiport antenna is measured, a multiport feeding network is always needed in order to provide the same antenna excitation as it is during its operation after being integrated in the system. This letter addresses how to measure the radiation efficiency of a multiport antenna excluding the losses in the feeding network used for the measurement, particularly when the impedance match between the antenna and the feeding network is not perfect. A rigorous feeding network correction approach is introduced by using measurement data of the radiation efficiency of the whole antenna with feeding network and the {\mbi S}-matrices of both the feeding network and the antenna. As an example of this approach, the radiation efficiency of a multiport Eleven antenna has been determined and verified against the simulated results.
An algorithm for MIMO antenna matching based on minimization of the single figure of merit called total multi-port reflectance or equivalently maximization of Total Multi-Port Return Loss (TMRL) is presented. A general approach for matching of an N-port MIMO antenna system is shown and for the special case of a symmetric two-port MIMO antenna a case-specific, simplified and explicit algorithm is described. As an example, a symmetric two-port antenna for the 1710–1880 MHz band is designed. The matching network topology and element values for the structure are given together with S-parameters, TMRL and Power Envelope Correlation Coefficient (PECC), in order to prove the usefulness of the proposed matching concept.
In order to analyze the influence of adaptive match- ing for MIMO applications, the theoretical performance of a Π-matching network with a constant inductance and variable capacitances is explored. An expression for ideal matching is derived and the impact on the correlation factor of a MIMO system is analyzed. Simulations for differents scenarios show that the presented concept will lead always to very small reflection factors. Index Terms—Impedance Matching, switched capacitors, MIMO diagram correlation.
After some basic definitions regarding the ultrawideband radio channel, this paper illustrates the characteristic effects of varying the bandwidth on the channel impulse response ranging from narrowband to ultra-wideband. A coherent description of antenna transfer functions that are suited as building blocks for ultra-wideband channel models is reviewed and a coherent equivalent to Friis' formula based thereon is given. Furthermore, the particular shape of the multipath envelope found in some ultra-wideband channels, which is different from a simple exponential decay, is discussed using the example of measured data.
In this paper, a multiport antenna (Four-port antenna) used for MIMO systems at 5.6GHz will be presented. It is an integration of conventional antennas which provides both decoupling between the ports as well as uncorrelated radiation patterns. The measured and simulated S-parameters, the measured radiation patterns and radiation pattern correlation factors will be presented.
In this paper we present a concept for the selective excitation of different orthogonal modes of a small terminal chassis. The concept can be used to realize an efficient multi port antenna system in order to enable MIMO (Multiple Input Multiple Output) for small terminals. The idea is based on the TCM (Theory of Characteristic Modes). The selective excitation of these modes is achieved by sets of couplers that are located at specific positions on the terminals' PCB (Printed Circuit Board). Passive matching circuits care for a good impedance match to 50 Ω. As a result it is demonstrated that nearly perfect de- correlation of the ports of the multi antenna system can be achieved. I. INTRODUCTION
This paper aims at investigating some significant integration aspects involved in daily practical mobile terminal design and their impact on the correlation coefficient of multiple antenna elements. While the antenna elements itself are kept as simple as possible the influence of its location on the terminal platform is investigated systematically. The investigations show, that the influence of the integration is significant on the one hand. On the other hand the general physical behaviour can be easily estimated and can also be used to find simple design rules for closely spaced de-correlated antennas on small terminals.
This paper provides a brief introductions into the challenges involved when designing antenna for MIMO (Multiple Input Multiple Output) systems on small terminals. The investigation is based on the fundamental parameter of cross-correlation of the antenna transfer functions. Some considerations on the correlation of antennas implemented on small terminals are undertaken. It is shown that the correlation of the elements of a multiple antenna system which is implemented on a small terminal is significantly affected by the integration impairments and the platform itself.
A very promising method to enlarge the radio channels capacity is the use of MIMO (multiple input multiple output) systems. The need to deploy more than one antenna leads to the problem of the restricted available area surface reserved for the antennas, especially on the terminals. In this paper, a concept for a compact multiport antenna is presented, which provides a sufficient decoupling between the ports. It is based on the combination of elementary antenna types such as a microstrip resonator as well as a monopole and a magnetic dipole. Return loss coefficient of each port, decoupling between the ports and the radiation pattern of each antenna are presented. Finally the system performance of this antenna is investigated based on the analysis of the diagram correlation factor of the elements.
The aim of this paper is to analyze the different Wireless Sensor Network (WSN) transport protocols by identifying various experimental parameters in order to undertake a comparative evaluation. To build the groundwork, we first discuss the generic design for a transport protocol based on three key concepts, congestion control, reliability support and priority support. The basis of this design was developed by assessing several aspects of numerous transport protocols. However they all using different set of parameters and settings and hence it is difficult to benchmark one against the other. In this paper, we discuss the simulation settings like packet size, number of exploited sensors and their distribution in the field, buffer size, coverage area and power levels.
A simple formulation to compute the envelope correlation of an antenna diversity system is derived. It is shown how to compute the envelope correlation from the S-parameter description of the antenna system. This approach has the advantage that it does not require the computation nor the measurement of the radiation pattern of the antenna system. It also offers the advantage of providing a clear understanding of the effects of mutual coupling and input match on the diversity performance of the antenna system.
As well known, the capacity of a radio frequency channel can be enlarged by multiple input multiple output (MIMO) antenna system. By using identical antennas with the same orientation, a certain antenna distance must be respected for achieving the full MIMO gain. On mobile terminals, usually only a limited surface area for antennas is available. Therefore multiport antennas with small dimensions are requested, which offer sufficient decoupling between the ports. The present paper describes a 3-port antenna, operating at 5.6 GHz, which can be used e.g. for MIMO-WLAN applications. The design is outlined and simulated and measured results are given.
The conditions for antenna diversity action are investigated. In terms of the fields, a condition is shown to be that the incident field and the far field of the diversity antenna should obey (or nearly obey) an orthogonality relationship. The role of mutual coupling is central, and it is different from that in a conventional array antenna. In terms of antenna parameters, a sufficient condition for diversity action for a certain class of high gain antennas at the mobile, which approximates most practical mobile antennas, is shown to be zero (or low) mutual resistance between elements. This is not the case at the base station, where the condition is necessary only. The mutual resistance condition offers a powerful design tool, and examples of new mobile diversity antennas are discussed along with some existing designs.