A compact decoupling network for enhancing the port isolation between two closely spaced antennas is proposed in this paper. In the network, we first connect two transmission lines (TLs) individually to the input ports of two strongly coupled antennas. The length of the TLs is designed so that the trans-admittance between ports changes from a complex one at the antenna inputs to a pure imaginary one. A shunt reactive component is then attached in between the TL ends to cancel the resultant imaginary trans-admittance. Finally, a simple lumped-element circuit is added to each port for input impedance matching. The even-odd mode analysis is adopted to investigate the currents excited on the antennas for predicting the radiation pattern of the two-element antenna array. Two examples of printed antennas at 2.45 GHz are tackled by using the proposed decoupling structure. The measurement results agree quite well with the simulation ones. High antenna isolation and good input return loss are simultaneously achieved in both cases, which demonstrates the feasibility of the structure. The decoupled antenna array in each example radiates, as prediction, toward different but complementary directions when the input power is fed in turn to the two input ports. The array efficiency is estimated better than 75% in each example. This pattern diversity effect is helpful for reducing the channel correlation in a multiple-input multiple-output (MIMO) communication system.

https://ir.nctu.edu.tw:443/bitstream/11536/8064/1/000263032000006.pdf

A Decoupling Technique for Increasing the Port Isolation Between Two Strongly Coupled Antennas

One or more embodiments are directed to a multimode antenna structure for transmitting and receiving electromagnetic signals in a communications device. The communications device includes circuitry for processing signals communicated to and from the antenna structure. The antenna structure is configured for optimal operation in a given frequency range. The antenna structure includes a plurality of antenna ports operatively coupled to the circuitry, and a plurality of antenna elements, each operatively coupled to a different one of the antenna ports. Each of the plurality of antenna elements is configured to have an electrical length selected to provide optimal operation within the given frequency range. The antenna structure also includes one or more connecting elements electrically connecting the antenna elements such that electrical currents on one antenna element flow to a connected neighboring antenna element and generally bypass the antenna port coupled to the neighboring antenna element. The electrical currents flowing through the one antenna element and the neighboring antenna element are generally equal in magnitude, such that an antenna mode excited by one antenna port is generally electrically isolated from a mode excited by another antenna port at a given desired signal frequency range without the use of a decoupling network connected to the antenna ports, and the antenna structure generates diverse antenna patterns.

Multimode antenna structure

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.

https://publications.lib.chalmers.se/records/fulltext/161662/local_161662.pdf

OTA Testing in Multipath of Antennas and Wireless Devices With MIMO and OFDM

A novel transmitarray element consisting of only two layers of modified Malta crosses printed on a dielectric substrate is proposed, and vias are employed to augment the transmission magnitude and enhance its phase shift range. A prototype transmitarray with a circular aperture of 338 mm in diameter is then designed, fabricated, and tested to validate the proposed design. The simulation and measurement results show good radiation characteristics with measured gain of 33.0 dBi at 20 GHz and aperture efficiency of 40%. The proposed element considerably simplifies the complexity of a transmitarray, reducing its thickness, mass, and cost.

A Double-Layer Transmitarray Antenna Using Malta Crosses With Vias

While 3G has been an outstanding success, the ever-growing demand for higher data rates and higher quality mobile communication services continues to fuel conflict between the rapidly growing number of users and limited bandwidth resources. In the future, a 100-fold increase in mobile data traffic is expected. That will necessitate further improvements to 3GPP LTE (Long-Term Evolution) and create limitless opportunities for engineers who understand the technology and how to apply it to deliver enhanced services.Long Term Evolution: 3GPP LTE Radio and Cellular Technology outlines the best way to position yourself now for future success. With coverage ranging from basic concepts to current research, this comprehensive reference contains technical information about all aspects of 3GPP LTE. It details low chip rate, high-speed downlink/uplink packet access (HSxPA)/TDSCDMA EV 1x, LTE TDD, and 3G TDD. It introduces new technologies and covers methodologies to study the performance of frequency allocation schemes. The authors also discuss the proposed architecture of Mobile IPRR and distributed dynamic architecture in wireless communication, covering performance evaluation of the TD-SCDMA LTE System.With each passing day, more and more users are demanding mobile broadband data access everywhere, to facilitate synchronization of e-mails, Internet access, specific applications, and file downloads to mobile devices such as cell phones, smart phones, PDAs, and notebooks. LTE, successor to the 3G mobile radio network, is essential to creating radio coverage in the rollout phase and high capacity all over the radio cell in the long term. The 3GPP LTE will become increasingly crucial to supporting the high demand of data traffic rates generated by future mobile user terminals. Authored by international experts in the field, this practical book is an extremely valuable guide that addresses emerging current and future technologies associated with LTE and its future direction.

Long Term Evolution: 3GPP LTE Radio and Cellular Technology

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.

https://publications.lib.chalmers.se/records/fulltext/local_164015.pdf

Characterization of Reverberation Chambers for OTA Measurements of Wireless Devices: Physical Formulations of Channel Matrix and New Uncertainty Formula

Traditionally, the reverberation chamber has been used as a low-loss cavity to gain high signal levels. For testing of the radiated properties of wireless terminals and their antennas, this is not an issue, and lossy objects like for instance a head phantom can be introduced in the chamber without problem. However, for testing of active units, the bandwidth of the system itself plays an important role. In order to avoid distortion of the signal transmitted in the chamber, the bandwidth of the chamber must be larger than the bandwidth of the signal. This is one reason for loading the reverberation chamber. Another reason is a potential increase in the measurement accuracy, since an increased bandwidth makes more modes excited at a particular frequency. The purpose of this paper is to investigate the effect of loading on the statistics of the chamber and its bandwidth

Investigation of Heavily Loaded Reverberation Chamber for Testing of Wideband Wireless Units

We present a new compact wideband multiple input multiple output (MIMO) antenna—the double-sided 4-port arm-tapered self-grounded monopole array, briefly referred to as the butterfly antenna, in the communication. The antenna is very compact with low correlation between ports and high diversity gain. The genetic algorithm optimization scheme has been employed in the design. Simulation results have been verified against measurements. The measured reflection coefficients at all ports are below $-$ 7 dB over 0.5–9 GHz and below $-$ 4.5 dB over 0.4–0.5 GHz and 9–15 GHz. The measured correlation coefficients are below 0.4 over 0.4–15 GHz and lower than 0.1 in most of the frequency band. This new MIMO antenna is developed as a transmit antenna in reverberation chambers, and we believe that it will find more applications in other systems, such as micro base station antennas in wireless communication systems.

https://publications.lib.chalmers.se/records/fulltext/199329/local_199329.pdf

A New Compact Wideband MIMO Antenna—The Double-Sided Tapered Self-Grounded Monopole Array

In this paper, we have presented the reverberation chambers (RC) evaluation of the multiple-input-multiple-output (MIMO) system performance of several UMTS four-antenna systems with low and high planar inverted-F antennas (PIFAs) isolation. It has been measured that the neutralization technique is always improving the performances even with the presence of the user's head, due to the high isolation obtained between the antennas and their high total efficiencies.

MIMO performance of enhanced UMTS four-antenna structures for mobile phones in the presence of the user’s head

This paper presents the evaluation of the diversity performance of several two-antenna systems for UMTS terminals. All the measurements are done in a reverberation chamber and in a Wheeler cap setup. First, a two-antenna system having poor isolation between its radiators is measured. Then, the performance of this structure is compared with two optimized structures having high isolation and high total efficiency, thanks to the implementation of a neutralization technique between the radiating elements. The key diversity parameters of all these systems are discussed, that is, the total efficiency of the antenna, the envelope correlation coefficient, the diversity gains, the mean effective gain (MEG), and the MEG ratio. The comparison of all these results is especially showing the benefit brought back by the neutralization technique.

/pdf/diversity-characterization-of-optimized-two-antenna-systems-1ydtttfvof.pdf

Magnus Franzen

Papers

Characterization of Reverberation Chambers for OTA Measurements of Wireless Devices: Physical Formulations of Channel Matrix and New Uncertainty Formula

Investigation of Heavily Loaded Reverberation Chamber for Testing of Wideband Wireless Units

A New Compact Wideband MIMO Antenna—The Double-Sided Tapered Self-Grounded Monopole Array

MIMO performance of enhanced UMTS four-antenna structures for mobile phones in the presence of the user’s head

Diversity characterization of optimized two-antenna systems for UMTS handsets