On the nonexistence of rate-one generalized complex orthogonal designs

Orthogonal space-time block coding proposed recently by Alamouti (1998) and Tarokh et al. (1999) is a promising scheme for information transmission over Rayleigh-fading channels using multiple transmit antennas due to its favorable characteristics of having full transmit diversity and a decoupled maximum-likelihood (ML) decoding algorithm. Tarokh et al. extended the theory of classical orthogonal designs to the theory of generalized, real, or complex, linear processing orthogonal designs and then applied the theory of generalized orthogonal designs to construct space-time block codes (STBC) with the maximum possible diversity order while having a simple decoding algorithm for any given number of transmit and receive antennas. It has been known that the STBC constructed in this way can achieve the maximum possible rate of one for every number of transmit antennas using any arbitrary real constellation and for two transmit antennas using any arbitrary complex constellation. Contrary to this, in this correspondence we prove that there does not exist rate-one STBC from generalized complex linear processing orthogonal designs for more than two transmit antennas using any arbitrary complex constellation.     

Frequency-independent antennas and broad-band derivatives thereof

The principles used in the development of frequency-independent antennas are reviewed. Examples of log-periodic (LP) geometry and the additional requirements that must be met for practical success are given. The evolution of unidirectional, wire-outline, and dipole arrays is presented. Analytical results for LP dipole arrays led to the concept of an active region that remains almost fixed in size relative to the wavelength. Periodic structure theory serves as an aid to understanding LP structures. The analysis of periodically loaded lines shows the problems that may arise from the existence of stop regions on LP antennas and provides procedures for eliminating them. This has led to successful LP monopole and cavity-backed slot arrays. Planar and conical log-spiral antennas are discussed. Frequency-independent, circularly polarized patterns-bidirectional, unidirectional, omnidirectional, and conical-can be provided from log-spiral antennas with two or more arms. Recently, the LP design principles have been applied to low-profile antennas: patches, thin cavities, and spirals over ground. They have also produced flush-mounted aircraft antennas that can respond simultaneously to two different linear of circular polarizations     

利用线极化天线快速测量圆极化天线轴比的方法

针对轴比测试需要连续旋转线极化天线极化轴,在高频段旋转关节难以消除高速旋转带来的电缆抖动所引起的幅度和相位不一致性,提出了一种快速、精确测量圆极化天线轴比的测试方法。基于椭圆极化波的正交分解理论,该方法利用线极化天线对待测圆极化天线进行两组正交的线极化幅度测量,通过计算得到圆极化天线的轴比等极化椭圆参数的信息。在此基础上又提出了只用三个线极化分量测量圆极化天线轴比的方法。通过在微波暗室中对圆极化天线进行多次测试,验证了该方法的有效性。该方法提高了圆极化天线的测试效率,降低了测试难度,对于工程应用有重要的应用价值。     

On Space-Time Block Codes from Complex Orthogonal Designs

Space-time block codes from orthogonal designs recently proposed by Alamouti, and Tarokh-Jafarkhani-Calderbank have attracted considerable attention due to the fast maximum-likelihood (ML) decoding and the full diversity. There are two classes of space-time block codes from orthogonal designs. One class consists of those from real orthogonal designs for real signal constellations which have been well developed in the mathematics literature. The other class consists of those from complex orthogonal designs for complex constellations for high data rates, which are not well developed as the real orthogonal designs. Since orthogonal designs can be traced back to decades, if not centuries, ago and have recently invoked considerable interests in multi-antenna wireless communications, one of the goals of this paper is toprovide a tutorial on both historical and most recent resultson complex orthogonal designs. For space-time block codes from both real and (generalized) complex orthogonal designs (GCODs) with or without linear processing, Tarokh, Jafarkhani and Calderbank showed that their rates cannot be greater than 1. While the maximum rate 1 can be reachedfor real orthogonal designs for any number of transmit antennas from the Hurwitz–Radon constructive theory, Liang and Xia recentlyshowed that rate 1 for the GCODs (square or non-square size) with linear processing is not reachable for more than two transmit antennas.For GCODs of square size, the designs with the maximum rates have been known, which are related to the Hurwitz theorem.In this paper, We briefly review these results and give a simple and intuitive interpretation of the realization. For GCODs without linear processing (square or non-square size), we prove that the rates cannot be greater than 3/4 for more than two transmit antennas.     

An iterative method of solving a system of linear equations and its physical interpretation from the point of view of scattering theory

The iterative method is useful to find the approximate solution of large systems of linear equations when the exact method becomes too expensive to be implemented. One well-known iterative method is the Gauss-Seidel method. The author presents an alternative algorithm which has certain simplicity in its formulation. He uses the system of linear equations encountered in the theory of coupled antennas to illustrate this method and give a physical interpretation of the successive approximations from the point of view of scattering theory. A simple numerical example is given to compare the products resulting from this method and those obtained by the Gauss-Seidel method     

Measured properties of bare and insulated antennas in sand

An experimental system for measuring the electrical properties of antennas embedded in moist sand is described. Measured antenna input admittances for bare linear and circular-loop antennas in sand are compared with theory. Insulated linear and circular-loop antennas with the dielectric constant of the insulation comparable to that of the surrounding medium are considered. Measured input admittances of linear antennas with different insulation sizes and dielectric constants are used to illustrate the effect of the insulation on the admittance. Measured input admittances for the spherically insulated circular-loop antenna are compared with theory and are found to be in good agreement.     

一种简单的高速率线性弥散码

多输入多输出系统要求尽可能得到简单而有效的高速率空时传输方案,以实时处理大的数据流量.V-BLAST码有好的性能,简单的编码和解码,但是要求接收天线数不少于发射天线数,这在实际应用中受到了限制.我们提出的此种高速率编码方案可以适用任意的发射天线数和任意的接收天线数,发射信号是原数据子流在空间和时间上的线性组合,通过最大化发射信号与接收信号间的互信息准则来设计.由于这种线性结构,解码仍可用V-BLAST的译码方式.     

Narrow multibeam satellite ground station antenna employing a linear array with a geosynchronous arc coverage of 60° -- Part I: Theory

The feasibility of using an appropriately squinted linear scan in narrow multibeam satellite ground station antennas employing phased arrays is demonstrated. This linear scan has the potential of reducing the complexity of a narrow-beam planar array to that of a linear array. Calculations for such antennas placed at cities throughout the U.S. show tht the peak beam pointing error in covering the70degW to130degW geosynchronous equatorial arc (GEA) is under 5/ 1000th of a degree. Communication at a 300 MBd rate in the 12/14 GHz band can be made feasible, for a grating lobe-free scan and0.5degbeamwidth antenna, by using a relatively simple time equalization.     

Performance analysis of concatenated space-time coding with two transmit antennas

In this paper, we show how Alamouti's simple but useful transmit diversity scheme for two antennas can be combined with a standard outer error-correcting code to achieve a stronger concatenated space-time coding scheme. By introducing a matrix formalism that allows us to interpret the transmission channel as a rotation in an Euclidean space, it can be easily shown that this scheme with two transmit (TX) and L/sub r/ receive (RX) antennas is equivalent to a simple RX antenna setup with 2L/sub r/ RX antennas. Analytical formulas for pair error probabilities will be derived for the time and/or frequency flat fading and for the ideally interleaved Rayleigh fading channel as well as for the correlated fading channel. As a practical example, we study how the performance of a Walsh-Hadamard coded multicarrier code-division multiple-access system depends on the correlation bandwidth of the channel and the number of RX and TX antennas.     

基于超表面的天线多波束偏转技术研究北大核心CSCD

5G移动通信对天线提出了多极化、多频段、多波束等更高的技术需求。超表面具有很强的电磁调控能力,利用这一特性可以实现天线多波束偏转。本文首先提出新型的基于行波激励网络的双波束偏转方法,利用超表面实现定向波束可控,设计了单频低副瓣高增益的双波束超表面天线。其次,提出基于多相位自由度理论的双频行波激励网络,结合双频超表面,设计了双频双波束偏转角可独立控制的超表面天线。在此基础上,提出基于正相位响应理论的稳定波束偏转角的方法,设计了具有稳定波束的±45°双极化超表面天线。与传统多波束方法相比,本方法省略了复杂的波束形成网络,设计简单、结构紧凑,而且能够实现双频、双极化等特性,可为新一代移动通信天线的研制提供技术思路。     

Trace-Orthonormal Full-Diversity Cyclotomic Space–Time Codes

In this paper, we consider the design of full-diversity space-time codes for a coherent multiple-input multiple-output (MIMO) communication system. Starting from both the information theoretic and detection error viewpoints, we first establish that a desirable property for general linear dispersion (LD) codes is to have an interunitary as well as an intraunitary structure-a structure we call trace-orthonormality. By imposing the trace-orthonormal structure on an LD code and applying cyclotomic number theory, we establish, for an arbitrary number of transmitter and receiver antennas, a systematic and simple method to jointly design a unitary cyclotomic matrix, the Diophantine number, and the corresponding constellation for an LD code. As a result, this enables us to construct full-diversity rectangular cyclotomic LD codes with any symbol transmission rate less than or equal to the number of transmitter antennas. In addition, for the case when the number of transmitter antennas is greater than the number of receiver antennas, by taking advantage of the delay, we also arrive at the design of a special trace-orthonormal full-diversity cyclotomic space-time block code which, for the number of transmitter antenna being equal to 2^m, can be proved to minimize the worst case pairwise error probability of a maximum-likelihood (ML) detector for a q-ary quadrature amplitude modulation (QAM) signal constellation and, therefore, achieves optimal coding gain. Computer simulations show that these codes have bit-error performance advantages over currently available codes     

A mutual coupling study of linear and circular polarized microstrip antennas for diversity wireless systems

In this paper, an analysis of mutual coupling is presented to examine the benefits of orthogonal polarizations and patterns for adjacent microstrip antennas. The mutual coupling between two linear polarized antennas orientated in parallel polarizations (E and H plane) is reduced using low dielectric constant materials. The mutual coupling can be reduced an additional 20-35dB at the same inter-element spacing when adjacent elements are orientated in orthogonal polarizations, O plane. Similarly, the mutual coupling between two circular polarized antennas orientated in the parallel polarization is reduced using low dielectric constant materials. However, the reduction in mutual coupling between two circular polarized antenna elements orientated in the O plane is only an additional 1-6 dB. The mutual coupling between a linear polarized sum beam (1/2/spl lambda/) and difference beam (1/spl lambda/) antenna is reduced 20-35 dB below the case when using identical antennas only in the H- and O-planes. Compact two- and four-element multielement antennas with inter-element spacings less than 0.15/spl lambda/ are fabricated and the S parameters and radiation patterns are measured.     

Self- and mutual impedances of traveling-wave linear antennas

A traveling-wave distribution of current can be produced on a conventional linear antenna, such as a dipole, through resistive loading. The self- and mutual impedances of parallel traveling-wave linear antennas are measured and compared with those of the corresponding conventional linear antennas. The effects of coupling on the input impedance of an array element is discussed, and it is shown that these effects are much less pronounced for traveling-wave antennas, which may be advantageous for some array applications     

Improvements to nonnumerical methods for calculating the transient behaviour of linear and aperture antennas

The time-domain response of linear and aperture antennas is analyzed. The results are based on models which have proven to be satisfactory for sinusoidal steady-state analysis. The calculated results correlate the physical parameters of both transmitting and receiving structures with the time-domain characterization of their response. The methods presented herein are useful to provide simple yet powerful alternatives to numerical techniques for the solution of transient radiation problems. The time-domain impulse response is calculated for thin cylindrical dipoles and the aperture formed by two semi-infinite parallel planes. Comparison between experiment and theory is provided. Analytical expressions are derived which characterize the response to excitations that are bandlimited in a manner dictated by the models, e.g., thin wire approximation and TEM mode excitation limitations.     

MIMO系统中简单的扩展空时块编码分集技术研究

本文提出一种多输入多输出（MIMO）天线系统中简单的扩展空时块编码（SSTBC）分集技术，采用沃尔什码来区分各天线发送数据子流。采用这种方法，在系统带宽一定时，不降低发送信息速率，同时接收机简单。不同天线的发送信息经过了所有收一发天线对之间的空间子信道，获得了所有路径的部分空间分集增益，仿真结果表明，这种增益的获得不受限于接收分集阶数，并且随发射天线的增加以一定的线性关系增加。     

Application of the minimum scattering antenna theory to mismatched antennas

The mutual impedance between canonical minimum scattering (CMS) antennas can be calculated directly from their far-field radiation patterns. While having the potential to greatly simplify array analysis and design, the theory has limited practical applicability because, by definition, CMS antennas are matched to their terminations. It is shown here that the theoretical basis of the mutual coupling calculation does not require the antennas to be matched and that the theory is simply extended to mismatched antennas. The only requirement is that the antennas are invisible, i.e., do not scatter, when open-circuited. This does not impose a greater restriction on the practical applicability of the method, since characteristic mode theory indicates that dipoles and loops, and perhaps other antennas, can be made very nearly invisible by a suitable reactive termination if the frequency is near or below first resonance. A new antenna, consisting of the original antenna plus a particular length of transmission line, will then be almost invisible on open circuit. The theory is applied to calculating the active impedance in an array of small monopole-like elements in a parallel plate waveguide and the results compared with experiment.     

Measurement of the circuit properties of insulated linear antennas in a dissipative medium

The experimental system for measuring the electrical properties of antennas embedded in a dissipative medium is discussed. Measured input admittances of linear antennas with insulations of different sizes and dielectric constants are compared with the theoretical results. Measured current distributions of insulated antennas with the dielectric constant of the insulation comparable to that of the surrounding medium are compared with theory and are found to be in good agreement. The uncertainties in the measurement are discussed.     

Active Integrated Antenna Design Using a Contact-Less, Proximity Coupled, Differentially Fed Technique

A novel contact-less, differential feeding technique suitable for integrated active antenna design is demonstrated. This technique utilizes an odd mode signal to generate fringing fields on either side of a microstrip gap under the antenna. This allows electromagnetic energy to be efficiently coupled from the transmission lines to the radiating antenna. In a balanced integrated antenna amplifier configuration, the proposed non-contact feeding method removes the need for any balun or power combining network. Hence in theory, a compact RF front-end design with lower losses can be realized. This feeding method has been successfully applied to the design of simple passive microstrip patch antennas and active integrated antennas (AIA). Simulated and measured results are also included to validate the proposed feeding concept and antenna designs. The performance of the proposed differential feeding technique on a simple microstrip patch antenna has been systematically studied. The study suggests that the proposed proximity method is broadband in nature, allowing antennas operating at different resonant frequencies to be swapped without the need to change the feed dimensions and without degrading the matching performance     

Design of aperture coupled microstrip antenna array fed bydielectric image line

A novel design for a linear array of microstrip antennas, aperture coupled to a dielectric image line has been developed. The design is based on a simplified theory to determine the impedances of the antennas at their apertures, and in turn, the coupling to each antenna from the image line. The theory developed is verified using an eight-element linear array and the experiment results are very good     

An improved theory for microstrip antennas and applications

An improvement to a recently reported theory for the analysis of the pattern and impedance loci of microstrip antennas is developed. It yields a theory which is simple and inexpensive to apply. The fields in the interior of the antennas are characterized in terms of a discrete set of modes. The poles corresponding to these modes are complex and depend on the losses in the antenna. The representation of the fields in terms of these modes is rigorous only for a bona fide cavity with no copper loss. The proper shift in the complex poles due to the addition of copper and radiative losses is approximated by lumping the latter two together with the dielectric loss to form an effective loss tangent. By so doing, it is found that the resulting expressions for impedance of the microstrip antenna are in good agreement with measured results for all modes and feed locations. The theory is applied to the evaluation of impedance variation with feed location, to multiport analysis, and to the design of circularly polarized microstrip antennas.