Multiport Antenna Research Articles

MRC Diversity and MIMO Capacity Evaluations of Multi-Port Antennas Using Reverberation Chamber and Anechoic Chamber

It has been shown that diversity gains and MIMO capacity of multi-port antennas can be conveniently determined from reverberation chamber measurements. In this paper, we first present the covariance eigenvalue approach and the embedded far field function method to determine diversity gain and MIMO capacity, respectively, for arbitrary multi-port antennas. Then, we discuss the convergence of the covariance eigenvalue approach. In the end, we apply both methods to compare MRC diversity gains and MIMO capacity measured in a reverberation chamber (based on direct channel measurements) and an anechoic chamber (based on measurements of the embedded far field functions and efficiencies at all antenna ports). The comparison is performed over 2-8 GHz using a wideband multi-port antenna in two configurations. There are in general good agreements between the reverberation and anechoic chamber measurement results.

Fast measurement of antenna pattern overlap matrix in reverberation chamber

Presented is a fast way for the measurement of the pattern overlap matrix in an arbitrary multi-port antenna system by a reverberation chamber. This parameter is central for calculation of the spatial correlation between different elements with arbitrary terminations. To the authors' knowledge, this is the fastest method for the measurement of the pattern overlap matrix in a lossy structure.

Experimental Multiport Bicone Antenna

AbstractA practical, easily manufactured multiport bicone antenna suitable for many receiving tasks such as direction finding systems can be made by using sharp-edged metal fins on the feeding coax center conductor to provide a tapered transition and connection path to coaxial probes. This construction resembles an arrow's tail. Already four mutually orthogonal fins can give full 360 degree azimuth coverage with suitable −3 dB port pattern overlap. Five experimental constructions working at Ku and Ka bands, each with fractional bandwidths of 23 to 31 per cent, are shown with full dimensional details. Suitable fin tapering is close to the full air gap in the coax and fin thickness should be less than 1/16th of the outer conductor diameter.

DESIGN AND MEASUREMENT-BASED EVALUATION OF MULTI-ANTENNA MOBILE TERMINALS FOR LTE 3500 MHZ BAND

Design of multi-element antennas for small mobile terminals operating at higher frequencies remains challenging despite smaller antenna dimension and possibility of achieving electrically large separation between them. In this paper, the importance of the type of radiating elements operating at 3400-3600 MHz and their locations on the terminal chassis are highlighted. An isotropic radiation pattern that receives incoming signals from arbitrary directions is obtained by combining the radiation patterns of multiple antennas with localized chassis current distribution. Four multiport antennas configurations with two- and eight-element antennas are designed and evaluated experimentally in indoor propagation environments. Our proposed designs of multi-element antennas provide the highest MIMO channel capacity compared to their counterparts using antennas with less localized chassis current distribution, even in the presence of user's hand.

Characterizing Optimal Multiport Matching Transformers

Multiport transformers offer enhanced matching capabilities for multiport loads. These transformers are analyzed to characterize wideband matching designs. An eigenvalue decomposition of the multiport load produces a geometric description of the sublevel sets of the matching transformers and identifies those frequency bands where multiport transformers are effective. A multiport antenna provides a concrete design example.

Complementary two-port antennas with low mutual coupling

In this study the authors provide designs for two-port antennas with low mutual coupling by using complementary structures. The designs make use of the multi-port extension of Booker's relation which shows that the complement of a multi-port antenna with low mutual coupling will also exhibit low mutual coupling. The use of Bookers relation for array design has been used previously but its use in multiport antennas for communications also opens up new design possibilities. In particular in this study, the authors take the complement of two existing two-port antenna designs to form two new two-port antennas with low mutual coupling. It is then shown that the new antennas can be extended to other compact slot configurations constructed on finite substrates and ground planes. Single- and dual-frequency band operations are demonstrated to have isolation nulls at resonant frequencies.

Measurement of Radiation Efficiency of Multiport Antennas With Feeding Network Corrections

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.

A Method to De-Embed External Power Dividers in Efficiency Measurements of All-Excited Antenna Arrays in Reverberation Chamber

This letter derives a simple and direct way of de-embedding external power dividers used in a passive all-excited measurement of multiport antenna arrays in a reverberation chamber. A new equation is developed that allows for the de-embedding of the power dividers and the deduction of the arrays' radiation efficiency in one. It is shown that the technique could be very useful for the measurement of large arrays (many ports) in the reverberation chamber as large arrays can be characterized in a timely and efficient manner and also in a way that begins to realize a realistic operational scenario. A five-element array is used to practically demonstrate the procedure.

Efficiency characterisation of multi-port antennas

A simple radiation efficiency metric is introduced to include the effects of non-ideal source/receiver impedances. The features of this parameter are highlighted and its compact formula is derived. The notion of mean matching efficiency is established. Simulations prove that this matching efficiency is quite useful in a quick estimation of diversity performance of multi-port antennas in rich isotropic multipath environments.

A Revisit to Spatial Correlation in Terms of Input Network Parameters

An alternative compact formula in terms of input network parameters for calculation of envelope correlations is provided. The main advantage of this formula is that it can be simply modified to include cases of lossy structures and general cases of correlated nonuniform multipath environments. This formula is based on the open-circuit covariance matrix of the multiport antennas. The latter can be either estimated or quickly measured in a reverberation chamber, which removes the need for costly measurements of the embedded far field patterns.

Investigation of the Effect of Noise Correlations on Diversity Gains and Capacities of Multiport Antennas Using Reverberation Chamber

Most of previous studies on diversity gains and capacities of multiantenna systems assumed independent and identically distributed (i.i.d.) Gaussian noises. There are a few studies about the noise correlation effects on diversity gains or MIMO capacities, however, by simulations only. In this paper, the maximum ratio combining (MRC) diversity gain and multiple-input multiple-output (MIMO) capacity including correlated noises are presented. Based on the derived formulas, measurements in a reverberation chamber are performed for the first time to observe the effect of noise correlations on diversity gains and MIMO capacities.

Integration of non-linear, radiation, and propagation CAD techniques for MIMO link design

The paper outlines an exhaustive computer-aided design (CAD) procedure for the circuit-level simulation of entire multi-input multi-output (MIMO) links. The multiple transmitting and receiving antennas are treated as multiport radiating systems characterized by electromagnetic (EM) analysis. The effects of mutual couplings in terms of the frequency-dependent near-field and far-field performance of each element are accounted for in a straightforward and rigorous way. The set of transmitters is treated as a unique non-linear system loaded by the multiport antenna, and is analyzed by non-linear circuit techniques. The same is done for the set of receivers. In order to establish the connection between transmitters and receivers, the radiated far-field is evaluated by EM analysis, and the field incident on each receiver antenna is computed by extending to the MIMO case an available ray tracing technique. EM theory is then used to describe the receiving array as a linear active multiport network. This technique allows analysis of several MIMO systems, exploiting different array element spatial locations and frequencies of operation in a straightforward and automatic way. Bit error rate (BER) computation and minimization are demonstrated at the circuit level.

Comparison of Ergodic Capacities From Wideband MIMO Antenna Measurements in Reverberation Chamber and Anechoic Chamber

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.

A Modal Description of Multiport Antennas

This paper presents a modal description of multiport antennas that leads directly to a rigorous network representation and simple quadratic expressions for gain, efficiency, and effective area. The analysis shows that the transmitting and receiving properties of an element antenna array are exactly described by a element scattering matrix together with a set of orthonormal mode functions and accounts for effects such as mutual coupling, scattering, reflection, and losses. The approach is quite general, only requiring that the antenna be finite and reciprocal. The scattering network description simplifies accounting of power flow while retaining a close connection to the physical antenna characteristics. The orthonormal mode functions provide a complete basis for radiated and received fields, facilitating beamforming. The theory provides rigorous definitions of input-output signals and links them to the underlying electromagnetics in a straightforward manner.

Fast Converging Measurement of MRC Diversity Gain in Reverberation Chamber Using Covariance-Eigenvalue Approach

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).

Diversity performance of multiport dielectric resonator antennas

Single-structure dual and triple linearly polarised cylindrical dielectric resonator antennas (CDRAs) with respective excitation sets of two orthogonal modes and three degenerate modes at 120° to each other are investigated for operation as compact multiport antennas. The diversity performance of these multiport CDRAs is evaluated using theoretical expressions of envelope correlation coefficient, mean effective gain (MEG) and MEG ratio in conjunction with simulation and experimental S-parameter results. The multiport CDRAs portray low mutual coupling (<−6.5 dB), different feed radiation pattern and polarisation directions, low envelope correlation coefficients (<0.27) between feed points and near-equal branch MEG ratios (within±1.8 dB). Thus, they satisfy the diversity performance benchmarks for application as compact multi-polarised diversity or multiple-input multiple-output antennas.

The Pulsed-Field Multiport Antenna System Reciprocity Relation and Its Applications—A Time-Domain Approach

A novel time-domain approach to the derivation of the pulsed electromagnetic field multiport antenna system reciprocity theorem is presented. The theorem interrelates the field and system properties in two states: the transmitting state and the receiving state. General time-domain Thevenin (voltage-source, impedance-based) and Norton (electric-current source, admittance-based) type equivalent circuits are constructed for antenna systems whose local properties are described in terms of multiport Kirchhoff circuits. Applications to an indoor wireless communication performance analysis and the analysis of cosmic microwave background radiation measurement are briefly indicated. Numerical results are provided for the pulsed-field transfer between two wire loops, a configuration that is representative for the operation of wireless telecommunication systems and for the pulsed-field EM interference analysis in nano-electronic integrated circuit devices.

Multiport Sensor RFIDs for Wireless Passive Sensing of Objects—Basic Theory and Early Results

A new family of passive sensor radio-frequency identification devices is here proposed for applications in the context of wireless sensor networks. The new tags, working in the ultra-high frequency band, are able to detect the value or the change of some features of the tagged body without using any specific sensor. Such tags are provided with multiple chips embedded either within a cluster of cooperating antennas or in a single multiport antenna, and exploit the natural mismatch of the antenna input impedance caused by the change of the tagged object. A basic theory of multiport sensor tags is formulated with the purpose to describe the possible classification and detection performances in a unitary context. Some numerical examples and a first experiment corroborate the feasibility of the idea.

Impedance and quality factor of mutually coupled multiport antennas

AbstractIn this study, expressions for the radiation quality factor Q and the input impedance seen at any terminal of a multiport antenna are derived. It is shown computationally that because of the possibility to adjust the antenna current distribution through suitable feeding/loading a multiport antenna can perform lower Qs than a similar single‐port antenna. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2034–2039, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23564

Relation between diagram correlation factors and S -parameters of multiport antenna with arbitrary feeding network

Antenna diversity demands a sufficiently low diagram correlation factor ρ. A universal relation between ρ 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.