Amir I. Zaghloul

Radiation from a rectangular waveguide with infinite flange--Exact solution by the correlation matrix method

A rectangular waveguide is terminated by an infinite conducting flange and radiates into half-space. Modal expansions of the TE and TM waveguide fields lead to Hermitian forms for the incident and reflected waveguide power ( P_{wg} = P_{wg}^{+} - P_{wg}^{-} ) in terms of the corresponding electric field mode amplitude vectors and a diagonal field admittance matrix [ Y ]. The power radiated from the aperture is expressed in terms of correlation functions of the aperture electric fields, and yields a Hermitian form for the radiated power P_{r} in terms of the electric mode amplitude vectors and a matrix derived from the field correlation functions-the correlation matrix. Applying the principle of conservation of complex power ( P_{wg} = P_{r} ) leads directly to a nonvariational expression for the scattering matrix [S] for the flanged termination. From [S] the effective TE_{10} load admittance Y_{L, 10} can be deduced. Numerical results for the latter are compared graphically with previous variational results. Also given are the farfield power patterns for two aperture sizes which are then compared with the traditional patterns due to the TE_{10} mode only.

How to enhance the immunity of LTE systems against RF spoofing

Long Term Evolution (LTE) networks offer high-speed wireless access to meet the increasing demand in user traffic. LTE technology is also considered for mission-critical networks. Hence, it is critical to ensure that the LTE system performs effectively even in harsh signaling environments. This paper analyzes the effect of different levels of radio frequency (RF) spoofing applied to LTE. The simplest form of spoofing is LTE synchronization signal spoofing, where standard-compliant primary and secondary synchronization sequences are transmitted by a fake cell. More sophisticated RF spoofing attacks include transmitting some of the LTE control messages, without the ability to exchange the authentication keys. The experimental results show that LTE control channel spoofing can cause permanent denial of service for user equipment during the cell selection process. We provide the technical explanation for this using the LTE specifications. Mitigation techniques are proposed to effectively enhance the immunity of LTE systems against targeted interference and ensure that it is secure and available when and where needed.

Enhancing the Robustness of LTE Systems: Analysis and Evolution of the Cell Selection Process

The commercial success of LTE makes it the primary standard for 4G cellular technology, and its evolution paves the path for 5G technology. Furthermore, LTE Unlicensed has been proposed recently to allow cellular network operators to offload some of their data traffic to LTE component carriers operating in the unlicensed band. Hence, it is critical to ensure that the LTE system performs effectively even in harsh signaling environments in both licensed and unlicensed spectrum. This article analyzes the effect of different levels of RF spoofing applied to LTE. RF spoofing affects LTE devices during the initial cell selection process, where a strong nearby cell can impede access to a serving LTE network. This is a serious threat and can be caused unintentionally, in the case of dense and uncoordinated LTE deployment in unlicensed spectrum, or intentionally, where an adversary sets up a fake LTE cell in either licensed or unlicensed LTE spectrum. This article analyzes and experimentally demonstrates the severity of these threats for the evolution of LTE and proposes effective mitigation techniques to prevent denial of service. These mitigation techniques improve the cell selection process at the LTE user equipment, and are backward-compatible with existing LTE networks. We recommend that these modifications be enforced in future releases for increasing the availability and scalability of LTE.

Auxiliary vector selection algorithms for adaptive beamforming

The auxiliary vector (AV) algorithm iteratively generates a sequence of filters that converge to the minimum variance distortionless response filter. The early, nonasymptotic elements generated by this algorithm offer favorable bias/variance characteristics and outperform in mean-square filter estimation error, filters generated by other iterative methods. This paper develops two new algorithms for selecting the best AV filter: a MMSE method that can either utilize a training sequence or can operate in a blind decision-directed mode, and a cyclostationary method that exploits the property that cyclostationary signals generate spectral lines when certain nonlinear transformations are applied to them. These new methods are simulated along with previously derived methods in an adaptive beamforming application, and compared with other common beamforming algorithms.

System aspects and transmission impairments of active phased arrays for satellite communications

The communications link and system aspects of active phased arrays that are used in multiple-beam satellite systems are assessed through measurements and analysis. Three link parameters are investigated and their effects on the overall carrier-to-interference ratio (CIR) are quantified. The first parameter is the intermodulation components that are generated at the nonlinear amplifier outputs and contribute to well-formed interference in the far-field radiation of the array. The second is the bit-error ratio (BER) degradation due to the multi-carrier operation of the active array. Measurement results are shown to demonstrate this effect. The third link parameter is the cochannel interference caused by frequency reuse in multiple-beam systems. The paper starts by reviewing early developments of phased arrays for multiple-beam satellite communications applications. A key component in these developments is the modular monolithic microwave integrated circuit (MMIC) beam-forming matrices that generate a number of simultaneous and independently digitally controlled beams

Evolutionary development of a dual-band, dual-polarization, low-profile printed circuit antenna

This paper follows the evolutionary development of a low-profile dual-band, dual-polarization printed circuit antenna element. In an early development, a single-feed single-band circular- polarization printed-circuit perturbed slot element fed with a low-loss stripline was used for a low-cost array. In a second development, a shorted annular ring element operating at a low frequency is modified by filling the inner ring with a conducting cylinder in the form of a waveguide that operates at a higher frequency, thus creating a dual-band element. The two concepts are combined in the third development. The outside perimeter of a square annular ring is notched (perturbed) to produce a single-fed circular polarization at a low frequency band. The ring can be fed separately at two orthogonal points to produce two orthogonal circular polarizations. The area inside the shorting cylinder is used to house a notched square slot element fed with two independent orthogonal striplines and produces two orthogonal circular polarizations at a higher frequency band.

Dual-polarized dual-band antenna element for ISM bands

A dual-band element that operates in two separate industrial, scientific, and medical (ISM) bands is presented that provides dual-linear or dual-circular polarization in each band. The element is ideal for wireless communication applications utilizing multiple protocol and/or Bluetooth technology. This design is realizable in cost effective printed circuit board technology making it an attractive design for low cost personal communications devices.

A new root‐based direction‐finding algorithm

[1] Polynomial rooting direction-finding (DF) algorithms are a computationally efficient alternative to search-based DF algorithms and are particularly suitable for uniform linear arrays of physically identical elements provided that mutual interaction among the array elements can be either neglected or compensated for. A popular algorithm in such situations is Root Multiple Signal Classification (Root MUSIC (RM)), wherein the estimation of the directions of arrivals (DOA) requires the computation of the roots of a( 2N � 2) -order polynomial, where N represents number of array elements. The DOA are estimated from the L pairs of roots closest to the unit circle, where L represents number of sources. In this paper we derive a modified root polynomial (MRP) algorithm requiring the calculation of only L roots in order to estimate the L DOA. We evaluate the performance of the MRP algorithm numerically and show that it is as accurate as the RM algorithm but with a significantly simpler algebraic structure. In order to demonstrate that the theoretically predicted performance can be achieved in an experimental setting, a decoupled array is emulated in hardware using phase shifters. The results are in excellent agreement with theory.

Intermodulation and bit-error ratio performance of a Ku-band multibeam high-power phased array

The overall transmission quality of a communications satellite utilizing a multibeam phased array antenna system is dependent upon the uniformity of the components within the communications payload. This system dependency is no greater in any component than in the solid-state power amplifier (SSPA) modules. Significant variations in the individual characteristics of the SSPAs have an impact on all the signals transmitted by the satellite. Moreover, as the amount of traffic being handled by the satellite increases, the available power per channel is reduced. The result is a degradation in the overall quality of the communications channels. A common measure of the quality of a digital communications link is the bit error ratio (BER) with respect to the carrier-to-noise ratio. Therefore, it is beneficial to perform an in-depth analysis for multiple, individually steerable beams vis-a-vis the intermodulation and BER characteristics in multiple signal scenarios. The paper includes results from both software simulation and laboratory measurements of a 24-element Ku-band active phased array under a variety of operational scenarios. The resulting data achieves a mutual validation of COMSATs software simulation tools as well as the multibeam phased array concept as applied to communications satellite systems.

An optimized lossy back cavity loaded four arm sinuous antenna

Sinuous antennas have wideband characteristics (constant beam width and low axial ratio over a broad range of frequencies), and thus they are suitable for communicating (transmitting and receiving) over bands of frequencies (multiple channels) in airborne and communication systems [1, 2]. In the presence of the back cavity, the performance of the sinuous antenna is affected. This paper presents an optimized loaded lossy back cavity that does not degrade the performance of the antenna. The simulated performance of a four arm sinuous antenna with unloaded back cavity is compared with the antenna loaded with the optimized back cavity. Sinuous antennas, first conceived by DuHamel[3], is formed by rotating the curve formed by using the equation[5]: