Muhammad M. Tahseen

Ka-Band Circularly Polarized High Efficiency Wide Band Reflectarray Using Cross Bow-Tie Elements

A Circularly Polarized (CP) high efficiency wide band Reflectarray (RA) antenna is designed for Ka-band using cross bow-tie elements. The reflected wave phase curve is obtained by anti-clockwise bow-tie rotation. The linear phase curve with complete 360 ◦ degree is obtained when left-hand circularly polarized (LHCP) is incident normally in unit cell environment. The proposed method provides high gain, high aperture efficiency, wideband axial ratio (AR), in circularly polarized bow-tie RA using multiple copies of unit cell to form 25 ∗ 25 antenna array. Before designing RA, the unitcell is analyzed, for oblique incidence to predict its bandwidth. The proposed antenna provided good performance in terms of Half Power Beam width (HPBW), Side Love Level (SLL), cross polarization, gain bandwidth and AR bandwidth. A 25 ∗ 25 bow-tie RA antenna provides the highest aperture efficiency of 57%, HPBW of 9.0 degrees, SLL −19 dB, cross polarization −27 dB. A 1-dB gain bandwidth of 32.5%, 3- dB gain bandwidth of 51.4% and 1.5-dB AR bandwidth of 32.9% while 3-dB AR bandwidth of 48.7% is achieved in simulation. These results are validated through fabricated cross bow-tie RA, and the measurements make good agreement with simulation results.

Practical Investigation of Different Possible Textile Unit Cell for a C-Band Portable Textile Reflectarray Using Conductive Thread

Investigation of a unit cell in terms of reflected wave amplitude and phase, for designing linearly polarized single layer Textile-Reflectarray (TRA) at C-band, is presented. The relative dielectric constant of the material is extracted using resonance method, and a WLAN antenna is designed to verify the accuracy of extracted material parameter. An error of 5% is observed in the extracted dielectric constant, when performance of WLAN antenna is measured at WI-FI Band (2.4 GHz). The extracted dielectric constant is used in the unit cell designing for TRA at the C-band (5.8 GHz). The radiating element is made using laying technique with conductive thread. A square patch with a ring is selected after analyzing multiple geometries of the patch providing the required reflected phase range and low losses. By varying size of patch and ring of single layer unit cell in CST periodic environment, reflected phase range of 360 degrees is achieved, which is required for reflectarray (RA) designing. The solid copper ground plane at the bottom of unit cell is replaced with conductive shielded fabric with high level signal attenuation. Four different sizes of textile unit cells are fabricated using conductive thread, and the reflected phase and amplitude are measured using waveguide method. The simulated and measured results are compared when solid copper ground plane at the bottom of unit cell has been replaced with shielded fabric. The proposed method provides the first step towards designing flexible high gain textile reflectarrays.

High efficiency Ka-Band single layer air vias Reflectarray: Design and analysis

Design and analysis of a linearly polarized Ka-Band single layer Reflectarray (RA) based on the principle of dielectric perforation, are presented. The phase characteristics of a single layer unit cell is obtained by varying single air via diameter, located at the cell center. A 340 degrees reflected phase is realized. The resulted 29*29 air vias array design shows good performance in lowering Side Lobe Levels (SLL) and cross polarization while providing wider bandwidth and higher aperture efficiency. The proposed RA provides a 3-dB gain bandwidth of 17.3%, SLL of -23 dB, Half Power Beam width (HPBW) of 6.2 degrees, gain of 28.3 dBi (at 30 GHz), and a maximum aperture efficiency of 59 %. For comprehensive understanding, incident, total and scattered fields are analyzed in terms of amplitude and phase.

Relative permittivity extraction of Textile materials based on ridge gap waveguide technology

The Textile materials are widely used recently in microwave applications. The wearable antennas and the medical applications generate high potential to explore the electrical characteristics of the Textile materials. The mechanical properties of such materials are well known but the challenge is to determine the electric characteristics in an accurate way specially the relative permittivity. There are many traditional methods to identify the relative permittivity of an unknown material e.g. Coaxial probe method, the waveguide method, the free space method, and the cavity method. On the other hand, the Textile materials have relatively small standard thickness. This put some limitations on the used measurement technique. The objective is to select a suitable measurement technique for wide band operation and a small thickness for the sample under test.

Textile-based wideband flexible wearable dielectric resonator antennas for WLAN-band

Flexible wideband dielectric resonator antennas (DRA) are designed using textile materials for wearable application at the wireless local area network (WLAN) band. The antennas are designed with different possible feeding technique e.g. coaxial probe feeding, and the aperture coupled method when feed transmission line is embroidered using conductive thread. Before using textile materials in antenna design, the material parameters are extracted using resonance technique, which are validated with measurements. A solid ground (GND) plane is replaced with shielded fabric GND plane, for more flexibility. To counter the fabrication problems, a fabric (with dielectric constant close to air) covering the DRA and holding it to its accurate position, will be stitched around at the upper layer, that will resolve the possible DRA movement. The proposed DRA antennas provide more than 25 % matching bandwidth, 1-dB gain bandwidth of more than 20 % and the maximum radiation efficiency of 97 % (at 5.8 GHz).

Phase correction techniques for reducing errors due to edge diffraction in reflectarray

Phase correction due to finite reflectarray (RA) antenna size and edge diffraction (ED) is proposed. The process is based on the numerical full wave analysis. The edge diffraction is mainly caused because of amplitude and phase ripples at sharp knife-edges of the outer perimeter of the RA antenna. The diffracted fields at the edges is diffracted in all directions resulting in disturbing the original phase and amplitude distribution, which further affect the pre-expected performance of the antenna. This could cause increasing of sidelobe level (SLL) and reducing aperture efficiency. The degradation in the antenna performance can be reduced by using serrated-edge ground, slotted GND and rolled-over edges with corner blended ground plane in the bottom of RA. The proposed methods provide RA performance when compared with RA antenna using sharp knife-edge (KED) ground plane. The proposed methods are analyzed by designing 19*19 RA antenna in fullwave analysis in the Ka-Band using size varying multi-bowtie radiating elements. The antenna performance is evaluated based on the achieved gain, aperture efficiency, SLL, and cross polarization. The proposed techniques result are compared with original RA using knife-edge ground plane. The best antenna performance is obtained using rolled-over edges GND plane. The antenna provides maximum gain of 26.36 dB, aperture efficiency of 59.5 %, SLL of -17.1 dB and 1-dB gain bandwidth of 11.2%, evaluated at center frequency 30 GHz. Near field analysis is also done for phase correction authentication.

Paneled center-fed reflectarray for bandwidth enhancement

Regardless of the bandwidth of reflectarray (RA) elements, the RA bandwidth is narrower for many possible reasons. For a RA with small f/D, the ray path length varies as we move away from the center, which is compensated by the elements that are designed at the center frequency. However, as the frequency changes, the path length phase errors grows, as we move away from the center, at a more rapid rate than the element frequency phase variation. Therefore, the phase errors introduced as the frequency changes are so significant deteriorating the aperture phase distribution that causes very low aperture efficiency and in return limiting the gain bandwidth. In order to reduce the path length as we move away from the center, the RA is divided into annular planar panels centered with a small square sub-RA. The annular panels are displaced towards the feed position reducing the path length within each panel. A circularly polarized refectarray designed at 30 GHz with wideband cross Bowtie elements is used as an example. The RA size is 25.25λ × 25.25λ, which is corresponding to 101 × 101 elements. The performance of the antenna is compared with the original RA of the same diameter. The proposed method exhibits the maximum simulated aperture efficiency of 48 %, a 1-dB gain bandwidth of 16.9 %, and the 0.5-dB axial ratio bandwidth of 25.6 %.

Artistic textile antennas

A novel concept of transforming complex artistic geometries into antennas in the WLAN band is presented. These artitic antennas are designed to be part of the artistic geometry without any distortion of the original artistic look. Several antennas are designed in the WiFi band for several applications. Some antennas are embedded on the wearable dresses. To make the antennas flexible for the wearable application, the antennas are embroidered on the textile material using conductive thread. Several textile samples under test (SUT) are analyzed for this purpose, and some of them are selected based on their material composition, and the elasticity. The dielectric constant of the fabric is extracted using resonance technique. All the antennas are based on the microstrip antenna concept. The copper ground (GND) plane is replaced with shielded fabric. Among many of our designed antennas, the performances of four of them are presented. A low power Wi-Fi band communication system is designed where the fourth antennas are embedded in many dresses for testing the transmission and reception authentication. The performance of the antennas is evaluated at 2.45 GHz. These antennas exhibit good performance in terms of directivity, radiation efficiency, radiation pattern, and with adequate matching bandwidth.

C-Band flexible and portable circularly polarized textile-reflectarray (TRA)

A novel C-Band flexible, and portable circularly polarized (CP) textile-reflectarray (TRA) design using conductive thread, is presented. Among several textile samples under test (SUT), three of them are selected based on their suitable material characteristics. The material parameters of SUT are extracted using resonance technique which is further are in the design of the TRA elements. A conductive cross-bowtie shape is used as a TRA element. To achieve flexibility, and the roll-ability in the proposed TRA, the solid ground (GND) is replaced with a frequency selective surface (FSS). A slotted circular patch is used as an element for the FSS. The upper radiating layer and the lower FSS layer are to be embroidered using conductive thread. The phase characteristics of the proposed TRA element are obtained using the rotation technique where the cross-bowtie elements rotate counter clockwise (CCW) for the spatial delay phase compensation. An FSS-based 15 × 15 TRA is designed in the C-Band using the CST microwave studio for the full wave analysis. A left hand circular polarized (LHCP) helical feed is used to excite TRA. The TRA performance is evaluated at 5.8 GHz. The proposed TRA provides, a maximum gain of 24.2 dB, a 1.5 dB axial ratio (AR) bandwidth of 12.8 %, and highest aperture efficiency of 30.3 %.

FEED MATCHING IMPROVEMENT FOR CENTER FED REFLECTARRAY

Standing wave between the feed and the reflectarray (RA) deteriorates the matching and antenna gain. A phase perturbation method is investigated to improve the matching of the antenna. The proposed method requires a change or deformation of the RA area facing the feed. A small circularly polarized reflectarray (CPRA) is used as an example. The reflectarray size is 6.25λ × 6.25λ, which is corresponding to 25×25 elements. The feed is circularly polarized (CP) with aperture diameter 1.2×λ. The proposed method provides an acceptable compromise between achieving the matching and gain reduction. The field distribution on the symmetric line between the RA center and the feed is observed to show the behavior of the standing wave before and after implementing the proposed technique. The measured return loss becomes better than 10 dB, and a gain reduction is 0.2 dB. A measured maximum aperture efficiency of 55.4%, a 1-dB gain bandwidth of better than 33%, and the 1.5-dB axial ratio bandwidth of 33.2% are achieved.