Gholamreza Rafi

A Low-Cost Ultra Low Profile Phased Array System for Mobile Satellite Reception Using Zero-Knowledge Beamforming Algorithm

In this paper, a stair-planar phased array antenna system for mobile broadcast satellite reception in Ku-band will be introduced. The height of the antenna is only 6 cm and the system has two-dimensional electronic scanning capability. The design procedures of low profile high gain microstrip sub-array antennas, low noise amplifiers, hybrid analog phase shifters, along with a novel fast electronic beamforming algorithm will be discussed in this paper. The mobile phased array antenna receives LHCP and RHCP signals simultaneously. For each polarization 496 microstrip elements have been used to provide a radiation gain of 31.5 dBi. This phased array system scans plusmn2.8deg in azimuth and plusmn20deg in elevation with less than 3 dB scanning loss. The main objective of this design is to develop a Ku-band phased array system with very low cost components and a minimum number of tracking sensors. A novel beamforming algorithm compensates for the fabrication inaccuracies of the microwave components and variations in their characteristics due to ambient changes. Neither a priori knowledge of the satellites direction, nor the phase-voltage characteristic of the phase shifters are required in this algorithm which results in eliminating an expensive laborious calibration procedure. The real time field tests verify that the developed mobile antenna system can nullify the base vehicle yaw disturbances up to 60 deg/s and 85 deg/s 2.

Active Stabilization of Vehicle-Mounted Phased-Array Antennas

In this paper, a novel hybrid tracking method for mobile active phased-array antenna systems is developed. The proposed technique consists of a mechanical stabilization loop and a direction-of-arrival (DOA) estimation algorithm, which is based on electronic beamforming. Compared with other tracking methods, the proposed method requires only one low-cost yaw rate sensor. The method utilizes electronic feedback from the phased-array antenna to compensate for the low-cost sensor irregularities. The effectiveness of the proposed tracking method is demonstrated by measured performance of a fast-moving ultra-low-profile phased-array satellite terminal, which uses the proposed approach. The field test results confirm that the hybrid tracking mechanism can nullify the base vehicle yaw disturbances up to 60deg/s and 85deg/s2 and keep the azimuth angle error at less than the permissible bound of [-1deg, +1deg]. Although performance of the proposed tracking system is verified in the context of a mobile satellite television reception system, the basic principles can be applied to any tracking system that employs phased-array antennas. The mobile satellite Internet terminal is an important example.

Electrically switching transverse modes in high power THz quantum cascade lasers

The design and fabrication of a high power THz quantum cascade laser (QCL), with electrically controllable transverse mode is presented. The switching of the beam pattern results in dynamic beam switching using a symmetric side current injection scheme. The angular-resolved L-I curves measurements, near-field and far-field patterns and angular-resolved lasing spectra are presented. The measurement results confirm that the quasi-TM(01) transverse mode lases first and dominates the lasing operation at lower current injection, while the quasi-TM(00) mode lases at a higher threshold current density and becomes dominant at high current injection. The near-field and far-field measurements confirm that the lasing THz beam is maneuvered by 25 degrees in emission angle, when the current density changes from 1.9 kA/cm(2) to 2.3 kA/cm(2). A two-dimension (2D) current and mode calculation provides a simple model to explain the behavior of each mode under different bias conditions.

MIMO antenna design and optimization for mobile applications

A novel design strategy has been proposed for multiple antenna elements in MIMO systems to maximize the system capacity. Firstly, one single antenna has been effectively designed by HFSS software. Since it is very difficult to optimize the MIMO antenna parameters using HFSS, the single antenna has been modeled by a magnetic current to be used in optimization procedure. The magnetic current distribution can be employed in reciprocity approach along with MoM analysis to calculate the field radiation pattern of antenna element in presence of practical ground plane. This approach provides a calculation method, which is very suitable for optimization purposes. The optimization has been performed on correlation coefficient between antenna elements to obtain the optimum physical parameters. Ultimately, the optimal design has been validated by HFSS simulation.

A synthesis technique for reducing mutual coupling between closely separated patch antennas

The paper presented a general synthesis method that can be applied to guide the design procedure of many modern antenna/array problems. The technique is also useful in interpreting lots of measurement findings, and should facilitate the optimization process for enhanced solutions. A diversity antenna was designed and measured to demonstrate the capabilities of the proposed design methodology.

Switch loss and antenna directivity effects on MIMO antenna selection

In this paper, we study the effect of antenna directivity on multi-input-multi-output (MIMO) antenna selection. A 4 orthogonal pattern antenna array platform at the receiver side associated with an antenna selection mechanism is used in this study. The performance of the proposed method is evaluated for two cases where the antenna selection switches are located either after or before Low Noise Amplifiers (LNA), on a MIMO system under the diversity transmission. The results show how the antenna directivity and switch loss can affect the overall MIMO system performance.

An Efficient Integrated Antenna Structure on Low-Resistivity Silicon Substrate

This paper presents an efficient integrated antenna structure compatible with silicon IC process. The antenna consists of a slot antenna on top metal layer of the technology and a rectangular cubic dielectric resonator on top of the slot. The slot configuration of the design isolates the antenna from substrate and thus blocks the antenna interference through the substrate to other RF circuits on substrate

Gain Measurement of Embedded On-Chip Antennas in mmW/THz Range

A method for gain measurement of embedded on-chip antennas in mmW/THz range is presented. In this method, the radiation pattern is first measured in a quasi-optical configuration using a power detector. Subsequently, the radiated power is estimated from the integration over the radiation pattern. Finally, the antenna gain is obtained from measurement of a two-antenna system. The experimental results of applying this method on an on-chip planar dipole with substrate lens are demonstrated, and verified against simulation. A radiated power of around 40 μW and measured gain of 17 dB are reported at 180 GHz for this antenna structure.

On the fundamental Q-bandwidth relations for antennas

A procedure for extracting the unloaded Q of antennas was presented. The technique accurately predicts the asymmetric response in the reflection coefficient of canonical antenna problems. Portions of the verifications using different commercial solvers were listed in this short paper. The proposed technique is extremely useful when designing different classes of antennas. Its extension to multi-pole models provides a promising systematic method for the design of multiband/wideband antennas. It should be emphasized that the analysis is not limited to naturally resonant structures, and can be extended to study Q and BW of electrically small antennas.

A 4×4 circularly polarized aperture coupled antenna array for Ka-band satellite communication

A 4×4 circular polarized planar antenna array design is presented. It can be used as a building block for a large-scale Ka-band satellite communication phased array antenna. The array is easy to be fabricated and integrated with electronic devices (e.g. phase shifters). It shows high circular polarization purity (axial ratio less that 1dB at the range of 650MHz/29GHz) and the reflection coefficient of better than -19dB over a wide bandwidth of 17 %.