Muhammad Farhan Shafique

A Miniaturized Flexible Frequency Selective Surface for X-Band Applications

In this paper, a novel and miniaturized band-stop frequency selective surface (FSS) is presented. This FSS provides effective shielding in X-band, with attenuation of at least 56 dB. The proposed FSS provides 3-dB fractional bandwidth of 48% which is necessary to cover X-band. Moreover, the proposed design is polarization independent as it provides a stable frequency response at normal and oblique angles of incidences for both perpendicular TE and parallel TM wave modes. The copolarized and cross-polarized scattering parameter S21 is analyzed at the selected band-stop/notch frequencies. More importantly, the proposed FSS is suitable for conformal applications and hence finds wider employability. A prototype of the proposed FSS is fabricated and tested. The measured results are in good agreement with the simulated results.

A Miniaturized Dual-Band MIMO Antenna for WLAN Applications

This letter reports on a compact planar dual-band Multiple-Input and Multiple-Output (MIMO) antenna for Wireless Local Area Network (WLAN) applications. The proposed antenna primarily consists of two meandered monopole radiators that are decoupled by introducing a folded Y-shape isolator element and it is shown that the edge coupling between the radiators and isolator introduces the resonance at the lower band. The miniaturization is achieved by passing the signal on to the bottom layer where a meandered line conductor introduces a broadside coupling with the radiator, originating the higher band resonance. The antenna operates between 2.4 GHz to 2.5 GHz and 5.45 GHz to 5.65 GHz with an isolation of more than 25 dB and 15 dB, respectively. The antenna measures only 19 ×23 mm2.

Miniaturization of SIW Cavity Filters Through Stub Loading

This article reports on a simple yet efficient miniaturization technique of substrate integrated waveguide cavity resonators through stub loading. The stubs are attached to the cavity side edges and they are coupled with the magnetic fields of the cavity. This setup allows the stub loaded cavity to operate below its fundamental resonant frequency. This miniaturization technique is demonstrated by developing a two pole filter in horizontally and vertically coupled configurations. The potential to incorporate electronic tuning and various possible applications of these miniaturized cavities in low frequency system-in-package designs make them an excellent choice as compared to their conventional counterparts.

Exact synthesis design theory of analogue broadband bandpass filter

In this article, an exact synthesis design procedure of broadband bandpass filter using step impedance resonator (SIR) and optimum distributed high frequency (ODHF) is presented. SIR provides a large degree-of-freedom owing to its uncomplicated implementation and broad frequency operations. It offers enormous possibilities for its practical applications as well. The filtering function in this work is extracted using the equivalent circuit model. Filtering parameters can be mapped onto Chebyshev type-I polynomials for a narrowband response. However, for broadband filter response this mapping of polynomials will not produce equiripple frequency response. Therefore, the filter polynomials are adjusted such that a required bandwidth with an equiripple response is achieved. The proposed filter structure provides compactness as well as suppression of spurious resonances at high frequencies. Moreover, for the verification purpose, the proposed filter synthesis is also applied to ODHF filter topology. To validate the proposed design procedures, a microstrip-based prototypes are realized. The simulated and measured results are found in good correlation.

An FSS-Based Nonplanar Quad-Element UWB-MIMO Antenna System

In this letter, a low-profile, miniaturized four-element ultrawideband (UWB) antenna for four-port multiple-input–multiple-output (MIMO) configuration is proposed. The MIMO antenna elements are organized in a cuboidal geometry around a polystyrene block. An inverted L-shaped structure provides decoupling among the antenna elements. This structure is frequency-selective-surface-based and has slotted Y-shapes etched in it. In addition to that, a square spiral parasitic structure improves input impedance matching over the desired frequency band. Antenna elements are realized on low-profile FR-4 substrate having compact dimensions of 32 × 36 × 1.5 mm

Development of a cost effective antenna radiation pattern measurement setup

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Radome-covered substrate-integrated cavity-backed patch antenna surrounded by dielectric material

. The proposed three-dimensional (3-D) UWB-MIMO system achieves good impedance matching and an effective isolation of 20 dB among antenna elements in most of the band. The reported configuration is suitable for nonplanar/3-D system-in-package applications where a planar arrangement of four elements is not possible due to size limitations.

UWB-MIMO doublet with split decoupling structure and defected grounds

This paper presents an insight on the recently developed antenna pattern measurement system at COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan. Microwave Components and Devices (MCAD) research group at CIIT has been involved in antenna focused research activities but unavailability of anechoic chamber to measure radiation patterns has remained a huge handicap. In this regard efforts have been made to indigenously develop a radiation pattern measurement system. The system can measure radiation patterns from 600 MHz up to 26 GHz. The reflections from surroundings are suppressed by filtering the delayed signals in time domain. The system is automated through a Labview program which also provides users with the control and flexibility on various parameters. The system can provide gain at four frequency points simultaneously along with phase information.

Efficient Design Methodology for a Complex DRA-SIW Filter-Antenna Subsystem

The substrate-integrated cavity-backed patch antenna embedded in dielectric-coated structure is presented. The aperture of antenna is covered with composite radome. The close proximity of radome to antenna severely degrades input impedance matching. The dielectric coating, a thick dielectric material, significantly deteriorates radiation pattern of antenna due to propagation of surface waves in the surrounding dielectric coating. The proposed planar electromagnetic bandgap structure reduces the propagation of surface waves in the dielectric coating recovering deterioration in the radiation pattern of the antenna. The problem of input impedance mismatching of antenna is resolved by placing a metallic strip on the top of the radome. The simulated results are in good agreement with measured results.

A single layer delay-lines based reflectarray for X-band applications

In this paper, a dual port Ultra wide-band Multiple-Input Multiple-Output (UWB-MIMO) system is presented. The MIMO system has an elliptical UWB antenna elements along with split ground plane decoupling structure. A low cost FR-4 substrate is employed with compact size of 34 mm × 48 mm. The antenna elements are decoupled by employing defected ground structures and frequency selective surface based split decoupling structure. The MIMO system provides an isolation of more than 20 dB over entire Ultra Wideband.