Unbalanced Antenna Research Articles

Algorithm for determining the design of an unbalanced wave channel antenna with a given direction of maximum radiation in the vertical plane

An integral part of the communication system with unmanned aerial vehicles is the airborne antenna-feeder system. As a rule, a circular pattern is required in the horizontal plane. However, since omnidirectional antennas have a small gain, they switch to schemes of several directional switchable antennas. It is proposed to use an unbalanced antenna for such systems. Unbalanced antennas have limited substrate dimensions. The maximum gain is achieved not towards the horizon, but at some elevation angle. Proposes a design definition algorithm an unbalanced antenna wave channel with a given direction of maximum radiation. For example, a similar antenna is constructed using the algorithm. An antenna for operation in the frequency range of 2,3…2,7 GHz is taken as the initial data. The dimensions of the antenna elements are obtained from numerical experiments using an optimization module in CAD. A study of the directivity characteristics of an unbalanced wave channel of an antenna with a limited substrate and the dependence of the elevation angle of the maximum of the directivity pattern is carried out. The minimum size of the substrate at which the gain in the direction to the horizon stops growing is revealed. The range of values of the elevation angle of the maximum of the amplitude radiation pattern in the vertical plane is determined.

Iterative Compensation for Clipping Noise in Spatial Modulation OFDM Systems

Clipping is an effective technique to adjust the peak-to-average power ratio (PAPR) of spatial modulation (SM) orthogonal frequency-division multiplexing (OFDM) systems. In this paper, an iterative soft compensation method is proposed for mitigating the effect of the clipping noise. In the proposed method, the sparsity and relativity of all transmit antennas are exploited, and the mean and power of the clipping noise are estimated based on the a priori information. Furthermore, the attenuation factor in each iteration is updated to yield a more accurate system model. Simulation results show that the proposed method is capable of providing considerable bit error rate (BER) performance gains over conventional compensation methods for both balanced and unbalanced antenna configurations.

Coupled-Resonator Theory of Isolation in Multi-Mode Antennas

The literature currently maintains the assumption that mutual coupling is the mechanism that leads to the degradation of isolation between the active ports of antenna arrays. However, this paper shows that a coupled-resonator model with series-coupled mutual coupling breaks down when applied to multi-mode/multi-port antenna arrays and limits the achievable isolation. An improved model based on parallel-coupled modes is presented. This model suggests that poor isolation is more accurately caused by unbalanced antenna modes. Using this model, several novel examples of simple and compact dual- and triple-mode antennas show how to maximize isolation in multi-mode antennas by balancing the modes’ resonant frequencies and radiation bandwidths. For comparison, the mutually coupled assumption limits isolation to around 20 dB in the proposed novel structures, whereas 40–70 dB is possible when parallel-coupled modes are considered. Based on the developed concept, a compact triple-mode two-pole-filtering antenna is fabricated at 3500 MHz with 160 MHz of bandwidth and more than 40 dB of isolation between the antenna ports.

Time-Domain Turbo Equalization for Single-Carrier Generalized Spatial Modulation

In this paper, low-complexity time-domain turbo equalization (TDTE) detectors based upon soft-interference-cancellation (SIC)-aided minimum mean-square error (MMSE) criterion are proposed for single carrier generalized spatial modulation (SC-GSM) systems. First, a symbol-by-symbol-aided TDTE detector for application to the small-scale GSM systems is proposed, where the zero symbols are considered as constellation points when performing SIC. Then, vector-by-vector-aided TDTE (VV-TDTE) detectors for application to larger-scale antenna systems are introduced, where the GSM symbol is treated as an entire vector when performing SIC. As for the proposed VV-TDTE detectors, in addition, different time-varying filter coefficients are designed, in order to strike a flexible tradeoff between complexity and performance. By relying upon extrinsic information transfer chart analysis, we show that the proposed TDTE detectors are capable of providing considerable bit error rate performance gains over existing TDTE detectors and over the classic frequency-domain equalization-based MMSE detector, especially for the unbalanced antenna configurations.

A dual-feed microstrip grid array antenna for balanced or unbalanced operation

The development of a dual-feed microstrip grid array antenna for either balanced or unbalanced operation to radiate pencil-beam patterns has been described. As an example, the dual-feed microstrip grid array antenna on RT/duroid 5880 substrate with a size of 60 × 60 × 0.787 mm3 or 4.8λ × 4.8λ × 0.063λ at 24 GHz were designed and fabricated. The measured results show that the dual-feed microstrip grid array antenna has achieved excellent performances: 4.85% impedance bandwidth, 9.03% gain bandwidth, and 20.6-dBi gain at 24.15 GHz as a balanced antenna and 6.05% impedance bandwidth, 7.74% gain bandwidth, and 17.8-dBi gain at 24.15 GHz as an unbalanced antenna. The dual-feed microstrip grid array antenna is a suitable antenna candidate for radar and sensor applications.

Design and Evaluation of Full-Duplex Terminal Antennas in Realistic User Scenarios

In this letter, a two-port antenna system based on orthogonal excitation of the ground plane modes is presented for full-duplex (FD) mobile device applications. An antenna isolation method based on employing a balanced and unbalanced antenna is used to achieve a high level of antenna decoupling. Moreover, the theory of characteristic modes is used as a systematic tool to analyze the orthogonal modal behavior of the antenna system. A prototype consisting of a balanced dipole antenna and a monopole antenna on a 120 $\times$ 55-mm $^2$ chassis is fabricated and measured. The measurement results verify the simulation results and show a high isolation value of 40 dB between the ports in free space. Furthermore, to evaluate the antenna system performance in realistic scenarios, the prototype was measured in three different user scenarios. The isolation level between the ports in user scenarios varies from 42 to 33 dB in the worst scenario. The proposed design can be applied in an FD system to suppress the self-interference as the first stage of interference cancelation.

Carbon Nanotube Thin-Film Antennas.

Multiwalled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT) dipole antennas have been successfully designed, fabricated, and tested. Antennas of varying lengths were fabricated using flexible bulk MWCNT sheet material and evaluated to confirm the validity of a full-wave antenna design equation. The ∼20× improvement in electrical conductivity provided by chemically doped SWCNT thin films over MWCNT sheets presents an opportunity for the fabrication of thin-film antennas, leading to potentially simplified system integration and optical transparency. The resonance characteristics of a fabricated chlorosulfonic acid-doped SWCNT thin-film antenna demonstrate the feasibility of the technology and indicate that when the sheet resistance of the thin film is >40 ohm/sq no power is absorbed by the antenna and that a sheet resistance of <10 ohm/sq is needed to achieve a 10 dB return loss in the unbalanced antenna. The dependence of the return loss performance on the SWCNT sheet resistance is consistent with unbalanced metal, metal oxide, and other CNT-based thin-film antennas, and it provides a framework for which other thin-film antennas can be designed.

MIMO Multiband Balanced Antenna Design for Wireless Communication

In this paper the wide band antenna with broad bandwidth that can be utilized in different frequency band. Band covers from 750 to 5000 MHZ and GSM, UMTS, Bluetooth, GPS, & Wifi applications is examined The antenna has been design on HFSS. It is a low Profile Balanced antenna. Linear phase and constant radiation pattern with proper return loss and resonant on multiple frequencies General Terms Wide band balance antennas, low profile balanced antenna, unbalanced antenna, VSWR, radiation pattern, Return losses,

Achievable Degrees of Freedom of Cellular Multiuser Two-Way Relay Networks

In this paper, we study a network information flow problem for cellular multiuser two-way relay networks (MU-TWRNs) where uplink and downlink messages are exchanged through a multiantenna relay node using two-way relaying. Both single- and two-cell scenarios are investigated. In particular, for the two-cell scenario, we consider two schemes with and without base station (BS) cooperation, respectively. By comparing the degrees-of-freedom (DOF) upper bounds obtained via cut-set theory, we derive the feasibility conditions to achieve the optimal DOF for all the schemes. These DOF bounds are shown to be achieved by suitably applying some physical-layer signaling techniques, such as physical-layer network coding, signal alignment, block diagonalization, and the newly proposed successive interference nulling. By comparing one-way relaying in terms of the normalized DOF, we observe that the proposed two-way-relaying-based scheme can double the performance with symmetric antenna configurations; however, the gain is reduced under unbalanced antenna configurations.

S-Parameter Method and Its Application for Antenna Measurements

SUMMARY This paper focuses on the S-parameter method that is a basic method for measuring the input impedance of balanced-fed antennas. The basic concept of the method is summarized using the two-port network, and it is shown that the method can be enhanced to the unbalanced antennas using a formulation based on incident and reflected waves. The compensation method that eliminates the influence of a measurement jig and the application of the S-parameter method for the measurement of a radiation pattern with reduced unbalanced currents are explained. Further, application of the method for measuring the reflection and coupling coefficients of multiple antennas is introduced. The measured results of the input impedance of a dipole antenna, radiation patterns of a helical antenna on a small housing, and S-parameters of multiple antennas on a small housing are examined, and the measured results obtained with the S-parameter method are verified.

A Low Cost 8 × 8 W-Band Substrate Integrated Waveguide Antenna Array Detector on LCP

The design and fabrication of a W-band 64 element slot antenna array based on the substrate integrated waveguide structure is presented in this communication. The prototype antenna array is fabricated on a liquid crystal polymer substrate using standard printed circuit board (PCB) manufacturing processes. Characterization of the unbalanced antenna is accomplished through the use of a millimeter-wave diode detector circuit, which is integrated onto the antenna array. Measurements show a beamwidth of approximately 13.2°. The maximum sensitivity of the antenna array with the diode detector is 121 mV/mW at 96 GHz. The total size of the antenna array with detector circuit is 4 × 3 cm2. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1825–1830, 2013

A Novel Internal Dual-Polarized EBG Antenna for Indoor Reception of UHF Terrestrial Digital TV Broadcasting

A novel internal antenna has been developed for indoor reception of UHF terrestrial digital TV broadcasting. The overall size of some configurations of the new antenna is less than 2 cm3, and its weight is less than 1 gm. It is made of a flexible material that can be bent or folded and shaped in any form. It is an unbalanced resonant antenna that does not need a matching circuit. The new antenna can be fully embedded inside TV sets or portable computers. It has a bandwidth of about 68%. Thus, it can also cover the bands of GSM and CDMA, which is advantageous in case of portable computers. The new antenna is linearly polarized. It can be easily modified to be dual polarized by combining two orthogonal antennas with one or two feed points. The overall efficiency of some configurations of the new indoor digital TV receiving antenna is more than 80%, and its peak gain is about 2 dBi over the whole UHF band. The peak gain can be increased to more than 5 dBi by adding EBG (electromagnetic bandgap) structures. The EBG structure also increases the efficiency to around 90%.

A LOW-PROFILE UNIDIRECTIONAL CAVITY-BACKED LOG-PERIODIC SLOT ANTENNA

A low-proflle unidirectional cavity-backed coplanar waveguide-fed uniplanar log-periodic slot antenna suitable for the ultra-wideband applications (3{18GHz) is presented. Due to the in- herent balanced structure compared with the unbalanced antennas, such as dipole or loop antenna, the impedance matching and radiation performances of the proposed antenna are quite stable and satisfac- tory. There is a potential advantage for low proflle ultra-wideband unidirectional antennas, and this paper demonstrates a technique for transforming the bidirectional beam into a unidirectional beam by us- ing a special cavity in this ultra-wideband antenna. Meanwhile, the multi-resolution time domain (MRTD) method is applied to analyze this antenna. Experimental results reveal that the cavity has a small afiect on the S-parameter of the origin antenna, and remains the per- fect re∞ection property within the desired operation band.

T-matched dipole antenna integrated in electrically small body-worn wireless sensor node

A 2.4 GHz antenna for an electrically small body-worn sensor node is presented. Usually, unbalanced antennas are used in such applications. Implementing a balanced antenna in a small node deployed on the body is problematic from the points of view of both design and characterisation. A solution using a T-matched dipole integrated in the node housing is presented. Techniques for characterisation both in free space and on the body are described. Besides antenna port impedance and radiation efficiency, radiated power and radiation patterns of the active antenna fed by a transceiver in a fully functional sensor node are measured. The benefits and drawbacks of the chosen antenna design and characterisation techniques are discussed.

Modelling and Simulation of the Conversion of Correlated and Unbalanced Antenna Diversity Systems

Due to the increasing interest in mobile/wireless communication, there has been a continuous research in antenna diversity to combat fading. And the model of correlated and unbalanced diversity branches reflects the real-world scenario. The diagonalizer is introduced here before the diversity branches are combined, which can transform the correlated and balanced branches to the uncorrelated and unbalanced ones, and vice versa. This paper assumes a generic model, in which noise and interference components are correlated with a correlation equal to or smaller than the correlation of signal components. Discussions on how to maximize diversity gains are made in various signal and noise conditions, and with different combining methods. Modelling and simulation of a real world example and the performance are shown in the paper for various dual diversity scenarios.

A balanced T-shaped antenna for 3G IMT2000 mobile handsets for WLAN

In this paper, a novel balanced T-shaped printed antenna is proposed for 3G IMT2000 mobile handsets for the WLAN (IEEE802.11b) module. This balanced T-shaped antenna is designed for microstrip-feeding with balanced signals. The antenna was designed by merging an unbalanced T-shaped antenna and a planar balun. A prototype of the antenna for operation at the IMT2000/IEEE802.11b bands is constructed and described. The measured and simulated return loss (in terms of the mixed-mode S-parameters) and measured radiation patterns are obtained. The experimental results demonstrate the broad bandwidth and omnidirectional radiation performance of the newly developed antenna. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 131–133, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21285

Adaptive MIMO-OFDM with Low Signalling Overhead for Unbalanced Antenna Systems

The knowledge of channel state information (CSI) at the transmitter (TX), which in case of time division duplex (TDD) systems can be easily obtained due to radio channel reciprocity, can dramatically increase the spectral efficiency of a multiple-input multiple-output (MIMO) system. This paper presents a robust link adaptation method for TDD systems employing MIMO-OFDM channel eigenmode based signalling. We propose a rather simple logarithm-free, bit and power loading algorithm which requires low signalling overhead. Proposed method maintains constant frame error rate (FER) by controlling the instantaneous transmitted power in such a way that the average SNR at the equalizer output is kept constant. The scheme takes into account channel estimation errors at TX side by partial compensation of the SNR estimation errors. By using a simple scalar channel encoder, for an unbalanced MIMO system with larger number of transmit than receive antennas, the achieved spectral efficiency at low and medium SNR is significantly higher than the outage MIMO capacity with unknown CSI at the TX. The simulation results show that for a constant FER, the throughput degradation compared to the universally accepted Hughes-Hartogs algorithm is negligible.

SAR and radiation performance of balanced and unbalanced mobile antennas using a hybrid computational electromagnetics formulation

A procedure to reduce the effect of the mobile antenna on the handset by using balanced antennas has been investigated. Use of this type of antenna may degrade the antenna performance, such as bandwidth and gain, although it can cause less effect on the body to which they are adjacent. If the antennas are well designed, the maximum specific absorption rate (SAR) values are likely to be reduced when placed next to the head, since the coupling of such antennas to the body of the handset is very weak. A study on balanced and unbalanced antennas for mobile handsets next to the human head is presented, using a hybrid electromagnetics method for the analysis. The method uses the hybridisation technique between the frequency-domain method of moments (MoM) and the finite-difference time-domain method (FDTD). The antenna was modelled using MoM whereas the head tissues were modelled using FDTD. Two antennas were designed and investigated with respect to the SAR and radiation performance for two different antenna positions on the top edge of a mobile handset. Radiation patterns are presented and compared, with and without the head, and the maximum SAR values and field distributions inside the head are discussed. The balanced antenna shows good improvements with respect to the unbalanced antenna in terms of the SAR values and variations of the input impedances.

Electrically Small Unbalanced Four-Arm Wire Antenna

An electrically small antenna element is presented. It is an unbalanced antenna, consisting of four wire arms arching over a groundplane. One of the wire ends is the feed, and the other three are connected to the groundplane, via a capacitance, short, and load, respectively. The resonance frequency is tuned by varying the capacitance, which can be set fixed or used to accomplish electronic tunability with a tuning range of several octaves. The momentary bandwidth of the antenna is approximately 3%. Applications are typically antennas for very small terminals in narrowband systems, or alternatively broadband systems where electronical tuning can be implemented in the antenna. The exact shape of the wires is not critical and can be chosen to conform to mechanical design requirements.

Broadband semiloop antenna

AbstractAn unbalanced loop antenna of simple construction is proposed for broadband linearly polarized applications. By introducing a gap in a half loop mounted vertically over a ground plane, the bandwidth of the antenna can be substantially increased relative to its classical balanced version. The antenna presented here has a bandwidth of 30% for a maximum −10‐dB return loss, and is fed directly from a coaxial cable without the need for a balun. Numerical and experimental results show that the antenna can cover the entire PCN, UMTS, and IMT2000 frequency allocations and also offer the prospect for reduced SAR. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 233–234, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10425