Bilal Ijaz

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.

A Compact Dual-Band EMI Metasurface Shield With an Actively Tunable Polarized Lower Band

In this letter, a compact tunable metasurface for dual-band electromagnetic interference (EMI) shielding is being proposed. In particular, Jerusalem crosses intersecting diagonally are used to design and synthesize a prototype metasurface shield. It has been shown that a finite 4 × 3 array of the Jerusalem crosses can be used for EMI shielding in the 900 MHz and 1.8-GHz GSM bands. Then, to develop an active shield that is tunable, varactor diodes were attached to the dual-band metasurface. Measurements have shown that the lower band of the metasurface can be changed (tuned) with various control voltages. Finally, simulation, equivalent circuit computations, and measurements are shown to agree.

A Frequency-Reconfigurable Series-Fed Microstrip Patch Array With Interconnecting CRLH Transmission Lines

This letter presents the design of a frequency-reconfigurable series-fed microstrip patch array in which the elements are interconnected with composite right/left-handed transmission lines (CRLH-TLs). Reconfigurable CRLH-TLs are used instead of meandered microstrip lines to reduce the overall size of the array and provide two different zero-phase frequencies of operation for broadside radiation in both instances. p-i-n diodes were used to reconfigure the array by changing the electrical lengths of the patches and microstrip sections of the CRLH-TLs. The measurements were taken in an anechoic chamber to verify the simulation results. The array can be reconfigured to operate at 1.97 and 2.37 GHz.

Analysis of the Noise Voltage Coupling (Crosstalk) Between Right-Handed and Composite Right/Left-Handed (CRLH) Transmission Lines on Printed Circuit Boards

One aspect of the electromagnetic compatibility (EMC) analysis of RF circuitry is the accurate modeling of the coupling between printed transmission lines. Correct modeling of this coupling is essential because unwanted noise voltages can be substantial and create adverse effects on sensitive components. Recently, the development of composite right-/left-handed transmission lines (CRLHTLs) has received considerable attention due to the unique propagation characteristics. Because of this increase in applications, CRLHTLs are being implemented in RF systems with other printed circuitry, such as microstrip transmission lines, in very close proximity. In many of these instances, the coupling may not be intentional. To study this interaction between CRLHTLs and other printed circuitry from an EMC point of view, this paper presents derived analytical expressions for computing the nearand far-end voltage coupling between right-handed (printed microstrip transmission lines) and CRLHTLs. More specifically, these expressions are used to determine the nearand far-end voltages weakly coupled to the CRLHTL when the conventional microstrip right-handed transmission line is driven with a source and terminated with a load. These expressions are then used to illustrate how the induced voltages on the CRLHTL can be reduced by the capacitance and inductance values that support left-handed propagation. This can be a useful alternative to conventional shielding. Furthermore, design guidelines and tradeoffs are presented on the layout of CRLHTL near other printed transmission lines. The expressions derived in this paper are validated with simulations and measurements.

Design and Construction of an Autonomous Fire Fighting Robot

The use of robots in situations that can be too dangerous for human intervention is growing. One such use is the deployment of robots for fire fighting. This paper is based on the construction of a robot for a contest aimed at simulating this real-world scenario. The paper will discuss the design of a fully autonomous fire fighting robot which is able to navigate through a maze of white fluorescent lines on a blue arena designed specifically for line-tracking based maze navigation. The arena has few obstacles which must be avoided by the robot while navigating, and are meant to encompass obstacle avoidance in robot design. The robot will track white lines to detect and reach fire lit at different locations on the arena in the form of candles, and will blow it off using a fan. The concepts implemented in this robot are differential drive control, obstacle avoidance, environmental sensing, electronic circuit design and maze navigation (line tracking). The sensors used in the robot are light dependent resistors (LDRs) and robot is being controlled by ATM EGA 16 microcontroller. The robot is designed according to the rules laid down by, and to compete in the National Engineering Robotics Competition, (NERC), 2005, Pakistan.

A reconfigurable dual-band metasurface for EMI shielding of specific electromagnetic wave components

Metasurfaces are becoming more of an interest to the research community because of the unusual electromagnetic properties that can be achieved. This paper presents a reconfigurable metasurface for EMI shielding purposes. In particular, a dual-band Jersualem cross is developed and pin diodes are use to interconnect elements to control the specific polarization properties of the shield. It is shown that the response of the shield to specific field components can be controlled with simple control voltages. Simulations are validated with measurements throughout this work.

A note on the fundamental maximum gain limit of the projection method for conformal phased array antennas

New expressions for comparing the maximum gain of a phase-compensated conformal antenna have been analytically derived and validated to measurements. In particular, the newly derived analytical expressions were validated with a conformal phased-array antenna prototype attached to a wedgeand inverted-wedged shaped surface. Phase-compensation techniques based on the projection method were used to correct the radiation pattern. These expressions can be used by a designer to predict the maximum theoretical gain of a phase-compensated conformal antenna on a surface that changes shape with time.

Development of a cost effective antenna radiation pattern measurement setup

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.

An electrically small CPW fed frequency reconfigurable antenna

In this paper, an electrically small reconfigurable antenna fed by a co-planar waveguide(CPW) is proposed. The resonance is achieved by providing an extra path for current through additional meander lines which are attached with the main feed line. Two PIN diodes are used to reconfigure the antenna from 4.27 GHz to 3.56 GHz. The proposed antenna measures only 14.5 × 12.8 mm2 and is printed on a low loss 1.524 mm thick Rogers TMM4 laminate with a dielectric constant of 4.5 and a loss tangent of 0.002. The antenna has an omnidirectional radiation pattern at both switching frequencies with a peak gain of 1.3 dBi at 4.27 GHz and 0.2 dBi at 3.56 GHz. The proposed antenna is suitable for WIMAX and indoor wireless applications.

A dual band balanced planar inverted F antenna (PIFA) for mobile applications

A new low profile dual-band balanced planar inverted F antenna with meandered lines resonating in the 1800 MHz and 2100 MHz bands is proposed. The antenna size is 50 × 12 × 10mm3 allowing it to be easily housed in mobile handsets. The return loss, radiation pattern, gain and current distribution of the proposed antenna is presented. Furthermore, agreement between simulations and measurements is shown for a balanced feed with zero phase difference. Then, the design with differential feeding is simulated for various feeding phase angles and the benefits of minimized current flow on the ground plane are highlighted.