Search

Septum polarizers have been used in waveguide systems for over 50 years and are very popular in communication satellites operating in circular polarization. With the progress of computational electromagnetics and computer hardware, combined with advances in manufacturing techniques, there has been a growing interest in septum polarizers with smooth profiles. In particular, a design using Legendre polynomials was recently introduced by the authors. This paper reports on the first experimental validation of this component and introduces also alternative profiles based on cubic splines. The new designs account for considerations on the overhang angle, which is an important parameter in additive layer manufacturing. The axial ratio of these designs is evaluated using a simple and accurate technique based on a back-to-back configuration, which can be implemented outside an anechoic chamber. The proposed characterization technique relies on the custom flanges implemented on the circular common port of septum polarizers to interface with horn antennas. These flanges typically have an 8-fold rotational symmetry, which enables to perform multiple measurements of a back-to-back configuration without requiring further equipment. The measured data is then processed to obtain the axial ratio of the two septum polarizers. This characterization technique is particularly advantageous when a large number of feeds needs to be tested, which is relevant in current and future broadband communication satellites. The technique is validated by comparing with measured data acquired in an anechoic chamber using a standard technique. Various prototypes, designed for operation in C-band communication satellite downlink, are characterized and promising results are obtained, showing very good agreement between simulated and measured data.

In this article, a differentially fed dual-polarized dielectric resonator antenna (DRA) subarray excited by a substrate integrated waveguide (SIW) cavity is proposed. A #-shaped slot etched on the top wall of the SIW cavity is used to achieve the differential excitation due to the intrinsic field distribution of TE120 mode in the SIW. Based on the proposed antenna subarray, a $2\times $ 2 dual-polarized 2-D multibeam DRA antenna array with simple structure is designed, fabricated, and measured, which can achieve high cross-polarization discrimination (XPD) in the direction of maximum radiation. To reduce substrate loss, the printed ridge gap waveguide (PRGW) technology is used to feed the SIW cavity. Two orthogonal PRGW Butler matrices are placed at different layers so as to realize 2-D beamforming scanning with dual-polarization. The SIW cavity is placed in the air gap of PRWG, which can increase the stability of the antenna structure. By cleverly combining the SIW cavity and PRGW structure, the proposed multibeam antenna array has the advantages of high XPD and high radiation efficiency. Measured results show that an impedance bandwidth of 10% (28.5–31.5 GHz) and a peak gain of 11.8 dBi are obtained. Also, the measured XPDs are 28.3 dB at the center frequency and larger than 19.2 dB over the band of operation. Besides, the measured radiation efficiency of 67% is achieved for both the polarizations at 30 GHz. [ABSTRACT FROM AUTHOR]

Based on a planar and compact antenna, extensive measurements are conducted to investigate the behavior of the colocated tri-polarized multiple-input multiple-output (MIMO) system working at 3.5 GHz. Several scenarios with different multipath distributions have been considered, including a reverberation chamber (RC) and also some line-of-sight (LOS) and obstructed LOS (OLOS) real-world indoor environments. Many channel parameters of the MIMO system are analyzed based on the measured data, including cross-polarization discrimination (XPD), Ricean K-factor, correlation coefficient (CC), MIMO channel capacity gain (CG), channel eigenvalues, and ellipticity statistic (ES). The results show that for a multi-polarized MIMO system, the effects of polarization coupling and transition depend strongly on the polarimetric scattering characteristic of the environments. Furthermore, in all the scenarios tested, three non-zero eigenvalues of the MIMO channel matrix are obtained, which indicates that three independent subchannels can be supported by the tri-polarized MIMO system.

This letter presents port-to-port isolation and cross-polarization discrimination (XPD) enhancement techniques for dual-polarized (DP) antenna topologies. Both port-to-port isolation and XPD of DP-antenna degrade due to unwanted cross-coupling signals from one port to another port. Since high port-to-port isolation and XPD are imperative for realization of DP multiple-input–multiple-output (DP-MIMO), the proposed antiphase excitation scheme enabling undesired cross-coupling cancellation for DP-antenna element and array presents significant promise for the implementation. The fabricated differential DP-antenna designed for 57–71 GHz frequency bands exhibits more than 30 dB of port-to-port isolation over 8 GHz of bandwidth and also demonstrates up to 36 dB of XPD with >25 dB over the whole bandwidth. The modulated transmitter (TX) signal measurements on the proposed differential DP-antenna integrated TX exhibits on average less than 1 dB of error-vector-magnitude degradation in comparison with the single-polarized case, which proves the benefits of the proposed isolation enhancement technique for DP-MIMO. [ABSTRACT FROM AUTHOR]

Abstract During the movement of various types of transport (auto, rail) in forest, radio communications in the VHF / UHF bands are sharply disturbed, which is associated with attenuation and a change in the polarization plane (cross polarization effect) of radio waves in the forest. Therefore, this paper reviews the problem of the appearance of the cross-polarization effect appearance in the through propagation of VHF/UHF radio waves in forests. The parameters of cross-polarization are analyzed and the functional dependences XPD {f, ζF, rF}, XPR {f, ζF, rF} are evaluated on the operating frequency, forest vegetation properties and the distance traveled within the forest from the transmitting antenna to the receiving antenna. Rerouted by forward and backward vegetation elements, radio signals contain many cross-polarization components that can have levels comparable to the main (useful) component. An increase in cross-polarization components can be observed in the "forward" region, which can be formed by successively decreasing the useful component, ultimately causing a significant decrease in the XPD value. As a result, the relatively high cross-polarization component can consecutively reduce the level of the useful component, while the cross-polarization effect is random, and the XPD value with fluctuating distance between the transmitting and receiving stations begins to fluctuate relative to XPD = 0. Thus, the influence of forest vegetation on the propagation conditions in VHF/UHF ranges is not only manifested in a random variation of the attenuation coefficient, but also leads to a cross-polarization effect, which ultimately causes deep fading of the radio signal at the receiving point. This work can be used in assessing the fluctuations of received signals due to the occurrence of cross-polarization during transport traffic in the forest. [ABSTRACT FROM AUTHOR]

This paper presents a novel dual-loop array antenna targeted at current and future base station applications. The antenna has four rectangular loops and four trapezoidal loops printed on the front and back sides, respectively, of a substrate placed above a flat square reflector. All eight loop radiators are excited simultaneously with properly designed feed networks to achieve its ±45° polarization states. The trapezoidal loops act like folded (electric) dipoles; the rectangular loops act primarily as magnetic dipoles. The combination of these two loop arrays leads to a type of magnetoelectric loop antenna that has stable directivity patterns with high cross-polarization discrimination (XPD) values across a 45.5% operational fractional bandwidth from 1.7 to 2.7 GHz. A fabricated and measured prototype confirms the simulation results and demonstrates that the half-power beamwidths in the horizontal plane vary between 63° and 70°, the XPD values are >20 dB in the boresight direction, and are >10 dB within the entire cellular coverage angular range: $-60^\circ \leq \theta \leq 60^\circ $. [ABSTRACT FROM AUTHOR]

The satellite communication systems employing either frequency-reuse schemes and/or polarization diversity to improve spectral efficiency are compromised by depolarization-induced interference due to both rain droplets and aloft ice particles. Any development toward an integrated physical model for depolarization will necessarily require the separation of its different contributions. This task was done in the past using dual-polarized satellite beacon signals that have not been available recently. On the other hand, single-polarized satellite beacon signals are worldwide accessible; therefore, the use of alternative techniques to assess the propagation channel properties is mandatory to unlock the advance of the depolarization studies. Two physical methods able to retrieve ice and rain contributions to total depolarization from single-polarized satellite beacon signals are here described, applied and validated on one full year of measurements carried out at Ka-band. [ABSTRACT FROM AUTHOR]

Multipolarized antenna systems are able to reduce equipment size while maintaining low interantenna correlation and are thus attractive for mobile-to-mobile (M2M) wireless communications. In this paper, a polarized multiple-input multiple-output (MIMO) channel model is proposed by using a geometrical theory based on a two-cylinder M2M reference model. A geometrical approach is used to model channel depolarization, where the MIMO signal contributions of the scatterers are determined from a greatly simplified ray-tracing method. The modeling method provides a mechanism for computing MIMO-polarized channel impulse responses analytically, and the cross-polarization discrimination (XPD) and MIMO time–frequency function are further derived. The proposed model shows good agreement with measurements and simulation results from the literature and provides insights on the MIMO channel depolarization behavior. In addition, numerical simulations with appropriate modeling parameters are conducted. The XPD is shown to depend on the distribution of scatterers and MIMO subchannel index. Moreover, the co-polar channel is shown to have a higher time–frequency correlation than the cross-polar channel. This should be carefully considered in a multipolarized antenna system design. [ABSTRACT FROM AUTHOR]

A novel method of enhancing cross-polarization discrimination (XPD) of a \pm 45^\circ dual-polarized base-station antenna, by addition of four parasitic elements placed in a square contour, is presented. First, it was established that high XPD at the broadside can be obtained by addition of four parasitic elements around a simple \pm 45^\circ dual-polarized base-station antenna. Second, we investigated the principle of wide beamwidth high XPD after studying magnitude currents on parasitic element, spacing between parasitic elements and length of parasitic elements. Finally, a \pm 45^\circ dual-polarized base-station antenna was designed, fabricated and measured. Measurement results are in good agreement with the results of simulation in terms of radiation pattern, gain, and Voltage Standing Wave Ratio (VSWR). In particular, the enhanced XPD is more than 20 dB at the boresight and more than 10 dB within \pm 60^\circ of the main lobe at the horizontal plane. [ABSTRACT FROM AUTHOR]

A new geometry-based channel model is proposed for wide-band polarized body-area-network channels consisting of four propagation modes, i.e., cylindrical surface scattering (CSS) for above-ground off-body scattering (BS), BS for body diffracted and on-BS, ground scattering (GS), and line-of-sight. A conservation-of-polarization plane methodology is used for the CSS and GS propagation modes. For the BS propagation mode, a geometrical theory of diffraction is used and related to CSS. The channel cross-polarization discrimination (XPD) and time–frequency correlation function (TF-CF) are derived from the model. Comparisons of the XPD and the TF-CF that are obtained from the model (with appropriate physical parameters) and those obtained from wide-band measurements at 13-GHz are in good agreement. We observed the GS propagation mode to be the dominant mode in our experiments. The azimuth angle of arrival (AAoA) of a ground reflected wave is shown in theory to have a significant effect on the XPD. [ABSTRACT FROM PUBLISHER]

The ultrawideband (UWB) propagation channel is analyzed by means of measurements carried out in the 2–5 GHz frequency band in an office environment for different scenarios. Measurements were performed for different polarizations on the transmitting and receiving arrays so the effect of the signal polarization can be also taken into account in the analysis. The main contribution of this paper is not only the analysis of path loss and RMS delay spread in a bandwidth of 3 GHz, but also the influence of frequency on such parameters. The relationship between the path loss for copolar configurations and the cross-polarization discrimination (XPD), both in space and frequency domain, is also addressed. [ABSTRACT FROM PUBLISHER]

A geometrical theory is proposed for depolarization in narrow-band fixed-to-mobile (F2M) and mobile-to-mobile (M2M) wireless channels. This novel theory is used to reveal the origin of channel depolarization and to provide a mechanism for computing cross-polarization discrimination (XPD). Based on the superposition of polarization components on conservation-of-polarization planes, a new 3-D geometry-based reference model is proposed for XPD in narrow-band F2M and M2M wireless channels. This purely theoretical approach is used to derive the XPD without the aid of measurement data or its approximation. The geometrical theory and reference model provide a relationship between channel depolarization or XPD and channel modeling factors such as the distance between the transmitter (Tx) and the receiver (Rx), the azimuth/elevation angles of arrival and departure, and the distribution of scatterers around the Tx and/or the Rx. Our geometry-based XPD model shows good agreement with previously reported empirical results from other authors and provides insight on the detailed behavior observed in their XPD measurements. [ABSTRACT FROM PUBLISHER]