Pedram Mousavi

Wideband L-Shaped Circular Polarized Monopole Slot Antenna

A wideband circularly polarized L-shaped monopole slot antenna with a single C-shaped feed is designed and fabricated. The measured results demonstrate that the antenna has an axial ratio (AR)<; 3dB, a reflection coefficient <; -10dB, and 23% circular polarization (CP) bandwidth. The monopole quarter-wavelength slot antenna design occupies half of the area on the corner of circuit board as compared to a half-wavelength slot antenna that requires double the area at the center of the board. This feature is attractive for compact wireless devices that operate at low frequencies in which planning for the smallest circuit board area combined with the shortest length for signal routing are the two major concerns. The antenna is extremely low-cost and does not require any truncation corner, reflector surfaces, or via connections, all of which increase the fabrication cost.

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.

Fast Beamforming for Mobile Satellite Receiver Phased Arrays: Theory and Experiment

The purpose of this paper is to present a robust and fast beamforming algorithm for the low-cost mobile phased array antennas. The proposed beamforming algorithm uses a sequentially perturbation gradient estimation method to update the control voltages of the phase shifters, with the objective of maximizing the received power by the array. This algorithm does not require either the knowledge of phase shifter characteristics or signal direction-of-arrival. Moreover, in this paper, the algorithm parameters are derived for the stationary and mobile platform configurations. For the stationary array, it is shown how the proper selection of the beamforming parameters limits the noise effects and increases the array output power. For the mobile array, a condition for the fast convergence is derived and the advantage of using nonuniform step size to update the control voltages is illustrated. When phase shifters suffer from the imbalanced insertion loss the proposed beamforming technique perturbs the phase-conjugate condition to increase the total received power. This algorithm has been implemented with the low-cost microwave components and applied to a Ku-band phased array antenna with 34 sub-arrays. The experimental results verify the broadband performance, and the fast convergence of the algorithm for different platform maneuvers.

Integrated interconnect networks for RF switch matrix applications

In this paper, two new types of integrated RF interconnect networks are presented. The circuits are printed on double-sided alumina substrates, eliminating the need to use multilayer manufacturing technology. The interconnect networks employ finite ground coplanar lines and vertical transitions and can be easily integrated with semiconductor and microelectromechanical-systems switches. A wide-band 3/spl times/3 interconnect network utilizing single and double three-via vertical transitions is investigated theoretically and experimentally. The measured results show a return loss of -20dB and an isolation of better than -40dB up to 30 GHz. A vialess double-sided interconnect network is also studied and optimized for satellite Ku-band applications. This type of interconnect network uses a process requiring only front and back pattern metallization. The measured results indicate a return loss of better than -17dB and an isolation of better than -45dB.

Low-Profile Integrated Microstrip Antenna for GPS-DSRC Application

This letter describes the concept, design, and measurement of a low-profile integrated microstrip antenna for dual-band applications. The antenna operates at both the GPS L1 frequency of 1.575 GHz with circular polarization and 5.88 GHz with a vertical linear polarization for dedicated short-range communication (DSRC) application. The antenna is low profile and meets stringent requirements on pattern/polarization performance in both bands. The design procedure is discussed, and full measured data are presented.

The Effects of Imbalanced Phase Shifters Loss on Phased Array Gain

In the presence of imbalanced insertion loss of phase-shifters, satisfying phase conjugate condition does not necessarily lead to the maximum phased array gain. This paper introduces noncoherent beamforming and uses lab-measured characteristics of varactor-based phase shifters to prove that by perturbing coherency partially, the array gain can increase significantly, e.g., 1.6 dB for a 12 element array. Moreover, it is shown that reduction in the average insertion loss increases the array efficiency by almost the same amount. These results are extendible to the optical beamforming networks where different lengths of fiber are used to make true time delay lines.

Miniaturized Reflectarray Unit Cell Using Fractal-Shaped Patch-Slot Configuration

This letter introduces a new class of miniaturized reflectarray unit cells with increased phase swing employing Minkowski fractal-shaped patch-slot elements. Square, 1st Minkowski, and 2nd Minkowski fractal patches are designed as a reflectarray unit cell. A slot with variable lengths of 0 <; Ls <; 6 mm is used in the ground plane to perform the phase variation function. The resonant frequency corresponding to the maximum phase swing is reduced from 10.6 GHz for the square patch down to 8.8 and 8.3 GHz for the first- and second-order Minkowski fractal patches, respectively, which is equivalent to 17% and 22% size reduction. Unit cells with different patch type and slot length are fabricated, and close agreement is observed between the measured and simulated results. As it has been proven for conventional phased array antennas, this size reduction can lead to a decrease in mutual coupling in reflectarray antennas. Alternatively, it allows for smaller distance between reflectarray antenna elements, which renders a wider beam-scanning range.

A Dual-Band High-Gain Resonant Cavity Antenna With Orthogonal Polarizations

In this letter, a new study on the theory and the design of a dual-band dual-polarized high-gain resonant cavity antenna (RCA) is presented. The RCA includes two layers of orthogonal dipole arrays each located at a designated height above the ground plane of a microstrip patch antenna. A prototype is fabricated, and the measured results confirm the theory. The measured prototype has a lower-band gain of 19.6 dBi with the vertical polarization (V-pol) at 10 GHz and the upper band gain of 18 dBi with horizontal polarization (H-pol) at 11.6 GHz. The cross polarization (Xpol) is better than -27 dB at each band. It is demonstrated that the separation between the two bands is controlled arbitrarily.

Application of Invasive Weed Optimization to Design a Broadband Patch Antenna With Symmetric Radiation Pattern

In this letter, we present a patch antenna over a high impedance surface (HIS) substrate, using Jerusalem cross-shaped frequency selective surfaces (JC-FSSs). The objective in this design is to obtain the enhancement in bandwidth (BW) while achieving the symmetric radiation pattern over the frequency band of interest. In order to derive optimal dimensions of the patch antenna and JC-FSS parameters, a hybrid optimization algorithm that originates from invasive weed optimization (IWO) empowered with the analytical lumped circuit model has been employed. In general, we utilized the IWO features while proposing additional contributions in terms of efficient design and computational efficiency. The optimization benefits from the use of circuit model as a powerful tool to find specific limits for its variables. Therefore, it provides a reasonable starting point for the optimization procedure. For the most efficient design, the antenna and FSS ground plane are optimized simultaneously. In this case, the optimization time can be noticeably reduced. The simulations compared very well with measured results. This antenna shows relative bandwidth 10.44% with the radiation efficiency of better than 85% over the entire bandwidth.

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.