Harmen Schippers

Conformal phased array with beam forming for airborne satellite communication

For enhanced communication on board of aircraft novel antenna systems with broadband satellite-based capabilities are required. The installation of such systems on board of aircraft requires the development of a very low-profile aircraft antenna, which can point to satellites anywhere in the upper hemisphere. To this end, phased array antennas which are conformal to the aircraft fuselage are attractive. In this paper two key aspects of conformal phased array antenna arrays are addressed: the development of a broadband Ku-band antenna and the beam synthesis for conformal array antennas. The antenna elements of the conformal array are stacked patch antennas with dual linear polarization which have sufficient bandwidth. For beam forming synthesis a method based on a truncated singular value decomposition is proposed.

Finite Element Model for the Computation of the Transfer Impedance of Cable Shields

The transfer impedance of a cable shield is a parameter that characterizes its shielding effectiveness. To calculate this parameter, we can use analytical or semiempirical approaches but, in this study, the objective is to adapt a general-purpose finite element formulation. The advantage of a numerical method is that it can be applied to a wider variety of situations, where complex geometries and materials may be present. To obtain numerically the transfer impedance, we first express it as a function of the electric field and then we compute the field by means of the finite element method. The only input data required in the process are the geometry and the material properties of the shield. To validate our numerical model, we apply it to a few cable shields and compare the results of the simulations with analytical models and measurements obtained from the literature.

Broadband optical beam forming for airborne phased array antenna

For enhanced communication on board aircraft, novel antenna systems with broadband satellite-based capabilities are required. The technology will enhance airline operations by providing in-flight connectivity for flight crew information and will bring live TV and high-speed Internet connectivity to passengers. The installation of such systems on board aircraft requires for aerodynamic reasons the development a very low-profile aircraft antenna, which can point to satellites anywhere in the upper hemisphere. Major keystones for the success of steerable low-profile antennas are multi-layer printed circuit boards (PCBs) with an array of broadband antenna elements, and compact micro-wave systems with appropriate beam steering capabilities. The present paper describes the development of a prototype 8x1 optical beam forming network using cascades of optical ring resonators as part of a breadboard Ku-band phased array antenna.

Development of dual-frequency airborne Satcom antenna with optical beamforming

For enhanced communication on board aircraft, novel antenna systems with broadband satellite-based capabilities are required. The amount of data agglomerated over a range of passenger services (VoIP, Web, Email, SMS, MMS) and over a range of flights, appears highly asymmetrical. The inbound traffic is about 5 times higher than the outbound. The inbound traffic requires the availability of a broadband Ku-band antenna in receive mode only. The outbound traffic services can be supplied by the Inmarsat SBB link, which requires the installation of an L-band transmit antenna. In order to avoid both the installation of L-band antenna and Ku-band antenna, the concept of a hybrid dual-frequency antenna operating both L-band and Ku-band is being explored in this paper.

Development of the SANDRA antenna for airborne satellite communication

Novel avionics communication systems are required for increasing flight safety and operational integrity, for optimizing economy of operations and for enhancing passenger services. One of the key technologies to be developed is an antenna system that will provide broadband connectivity within aircraft cabins at an affordable price. This paper describes the development of an electronically steered Ku-band phased array antenna with low aerodynamic profile. The antenna front-end consists of at least 1800 antenna elements, of which the beam has to be steered continuously to geostationary satellites. Best performance for the beam steering is expected from a hybrid architecture with small sub-apertures having their local own beamformers (using phase shifters). The beamformer to steer the sub-apertures of the entire antenna uses True Time Delays with an optical ring resonator. 1 2

Generic prediction of crosstalk between shielded wires

A closed-form expression for near-end crosstalk between an unshielded and a double shielded wire is derived. Analysis in the frequency domain of such crosstalk expressions leads to generic crosstalk predictions. These predictions contain regions of different frequency dependencies separated by transition frequencies.

Hole inductance in braided cable shields

The shielding effectiveness of metal braids of cables is governed by the geometry and the materials of the braid. The shielding effectiveness can be characterised by the transfer impedance of the metal braid. Analytical models for the transfer impedance contain in general two components, one representing diffusion of electromagnetic energy through the metal braid, and a second part representing leakage of magnetic fields through the braid. The second part is a local phenomenon, which again has three parts: hole inductance, braid inductance and skin inductance. The hole inductance is governed by the penetration of magnetic fields through the apertures of the braid. Well-known analytical models overestimate the contribution of the hole inductance by a factor two. This can be easily corrected by multiplying the hole inductance terms by a factor (2/π)3/2.

Smart Antennas in aerospace applications

The interest in Smart Antennas for aerospace applications is growing. This paper describes smart antennas which can be used on aircraft. Two aerospace applications are discussed in more detail: a phased array antenna with optical beam forming and a large vibrating phased array antenna with electronic compensation techniques.

On DOA estimation of vibrating antenna arrays

Array antennas which are integrated onto lightweight structures of aircraft and Unmanned Aerial Vehicles (UAVs) are subject to unsteady aerodynamic loads. Mechanical forces and these aerodynamic loads will cause deformation of the antenna supporting structure. As a consequence, the positions and orientations of the elements of the array antenna change. The relative phases of the respective signals of the array antenna elements are affected, and therefore also the processing of the received signals is influenced. In this paper the effects of vibration of the array antenna on estimating Direction of Arrival (DOA) are investigated. To this end the MUSIC algorithm is applied to signals which are received by antenna elements of a demonstrator vibrating array antenna.

A finite element tool for the electromagnetic analysis of braided cable shields

In this work we present a finite element tool for the electromagnetic analysis of braided cable shields. This tool is able to calculate the transfer impedance of a cable shield and it can be applied to a wide variety of situations where complex geometries and materials may be present. Also, it can help in the development, validation and improvement of novel, or existent, analytical models. Analytical models are computationally less expensive than a numerical approach but, they may be not available for some types of cable shields and, when available, they may be hard to compare directly against measurements. On the other hand, we can easily compare the analytical results against the numerical tool because all the parameters involved in the comparative are exactly known. Therefore, our computer tool offers a new extra criterion to assess whether a model is correct or not. Moreover, it allows studying in great detail the behavior of the fields and currents in and around the shield. This feature makes the tool very useful for gaining new insights into the physics behind the shielding process.