Jafar Shaker

Broadband Design of a Single Layer Large Reflectarray Using Multi Cross Loop Elements

A novel method is proposed to design a single layer large printed reflectarray with multi cross loop elements of variable loop length for broadband operation. Different classes of cross loop elements were used in the design and optimization of this reflectarray. The dimensions of these cross loops are adjusted using an optimization technique to achieve the required phase distribution in a given frequency band. A Ku-band square offset-fed reflectarray of 400 mm times 400 mm dimensions was designed and fabricated using this technique and both simulations and measurement results demonstrated improved gain bandwidth performance. A large Ku-band reflectarray of 800 mm times 800 mm dimensions was designed using the same technique, and the calculation results show a significant improvement in gain-bandwidth performance for the optimized reflectarray.

Novel photonically-controlled reflectarray antenna

A novel method for generating a reconfigurable reflectarray based on the creation of photoinduced plasma inside the semiconductor substrate of a reflectarray is presented in this paper. A reflectarray antenna prototype is fabricated and measured to demonstrate the validity of the design methodology. Measurements were carried out to characterize the bandwidth and the gain of the antenna in both the OFF and ON states of an optical flash lamp that was used to induce photoconductivity inside the silicon substrate.

A broadband reflectarray antenna with double square rings as the cell elements

A reflectarray antenna composed of double square rings of variable lengths that are etched on a conductor backed substrate is proposed for bandwidth enhancement. Using this technique, a single layer reflectarray that has a wider bandwidth compared to conventional single layer reflectarrays is designed, fabricated and tested. Measured results demonstrate radiation efficiency close to 52% and 1-dB gain bandwidth of 9%, centered at 22.0 GHz. Another class of ¿loop¿ cell element namely, double cross loop, is also used as the building block of reflectarray and simulation and measurement results that demonstrate a comparable performance in the order of what was achieved for the reflectarray composed of square rings, are presented.

Investigation of FSS-Backed Reflectarray Using Different Classes of Cell Elements

A variety of cell elements are presented in this paper for the construction of frequency selective surface (FSS) backed reflectarrays. Among the cell elements are the conventional ring elements for FSS and slotted patch for the reflectarray. Different combinations of FSS cell elements and reflectarray cell elements are employed for the realization of FSS-backed reflectarrays and the criteria for the selection of the optimum structure are presented. Prototypes of these reflectarrays were fabricated and tested. The measurements demonstrated that for an optimum design, the gain of an FSS-backed reflectarray is about 1.0 dB lower than its counterpart backed by solid ground plane. Characterization of the out of band performance of these antennas demonstrated close to 1.0 dB insertion loss.

Chebishev Bandpass Spatial Filter Composed of Strip Gratings

A new filter composed of a cascade of strip gratings with a 3rd order Chebishev frequency response that operates within a prescribed frequency band, is presented in this paper. Theoretical development was undertaken to establish equivalence between electromagnetic characteristics of a frequency selective surface (FSS) configuration and equivalent model based on circuit parameters that are used in the realization of Chebishev frequency response. The FSSs replace the impedance inverter elements in circuit implementation of the filter and the spacing between FSSs, which are adjusted to obtain the desired electrical performance, correspond to resonant elements in the circuit implementation. Dielectric slabs similar to the ones that were employed in FSS stages were used as the spacers between the constituent FSS layers to increase the robustness and rigidity of the structure. The fabrication process is described in detail and methods are introduced to account for tolerances in the permittivity and etching process during the design stage. Close agreement between measurement results demonstrates the validity of the design procedure.

Derivation and Validation of the Basic Design Equations for Symmetric Sub-Reflectarrays

The basic design equations for symmetrical sub-reflectarrays are derived. These provide the required phase-distribution on the sub-reflectarray surface. Both ellipsoidal-type and hyperboloidal-type sub-reflectarrays are designed and fabricated using single-layer rectangular patch elements. Measured amplitude and phase patterns are shown for both types of sub-reflectarray, and compared to predictions. The behaviour of the ellipsoidal-type sub-reflectarray is furthermore compared to measured patterns of its solid subreflector counterpart. These experimental results show that the sub-reflectarrays indeed emulate the behaviour of their solid subreflector counterparts, and the validity of the basic design equations is thus established.

Observations on the performance of reflectarrays with reduced inter-element spacings

Several authors have described the use of reduced inter-element spacing as a means of improving the performance of reflectarray antennas. This paper discusses some additional aspects that complement their conclusions, and emphasizes some of the reasons for these improvements.

Orthogonally-polarized dual-band MEMS-tunable double-slotted unit cell for reflectarray applications

This paper presents a single-layer MEMS-reconfigurable reflective unit cell that supports two bands (12 and 14 GHz) at two orthogonal polarizations. A pair of MEMS varactors is used for continuous and independent tuning of each band. The dynamic phase range of 310 degree is obtained with a maximum loss of 0.23 dB. The resultant reflectarray can have a separate scanned beam of given polarization at each of its two operating frequency bands. This unit cell has the requirements of Cognitive Radio and Satellite two-way communication.

Applications of the Talbot Array Illuminator in the Millimeter-Wave Band

We propose and experimentally examine several novel millimeter-wave applications of the Talbot effect. First, several different millimeter-wave Talbot array illuminator (TAIL) configurations are examined. The TAILs are formed by combining a lens and a phase grating with different antenna array layers. Subsequently, a second phase grating is introduced at an appropriate location beyond the array layer to arrive at an architecture that is suitable for use as an active transmit antenna. Finally, with the addition of a second lens to collect the energy beyond the transmit structure, a spatial power amplification architecture is presented.

A novel multi-layer electromagnetic band gap structure (EBG) comprised of 3-D lattice of square rings

A novel electromagnetic band gap structure composed of stacked U-shaped-periodic array of metallic open square rings (OSRs) and its potential application to microwave integrated circuits is presented. Specifically, the dispersion diagrams and field patterns of an infinite array of cells are computed and shown. Different geometrical parameters are shown to produce varying band gap at various frequencies. Using this insight, we introduce a systematic study of two-dimensional (2-D) EBG slab.