Nor Muzlifah Mahyuddin

Antenna in LTCC Technologies: A Review and the Current State of the Art

This paper presents a chronological review of the research carried out on antennas in low-temperature cofired ceramics (LTCC) technology over the last ten years or so. Major breakthroughs in LTCC technologies and its shortcomings are highlighted. The current state of the art of LTCC-technology-based antennas is then evaluated. All realizable features of the LTCC-based antennas, which are compact and of light weight and offer high-speed functionality for portable electronic devices, are illustrated. Different techniques used by researchers for broadbanding, multiband designs, and fabrication of LTCC-based antennas are also presented. This paper ends with some recommendations and concluding remarks.

A 10GHz PHEMT Dielectric Resonator Oscillator

In all microwave systems, oscillators represent the basic microwave energy source. The main problem in oscillator design is the phase noise. This paper will discuss the design and fabrication of a 10GHz parallel feedback type GaAs PHEMT dielectric resonator oscillator. It incorporated an E2000 series dielectric resonator from Tekelec Temex with a quality factor of 5000 at 10GHz. The coupling gap between the resonator and the microstrip lines can be adjusted to optimize the ratio of the loaded to the unloaded quality factor to give a better phase noise, where it can be achieved when an insertion loss of 9.5dB is obtained. Phase noise measurement and analysis on the effect of frequency pushing and pulling towards the oscillator has been done using a spectrum analyzer. The dielectric resonator oscillator was measured and exhibited an oscillation at 9.845 GHz with a phase noise of -115.5 dBc/Hz at 100 kHz

Modeling of a 10GHz Dielectric Resonator Oscillator in ADS

Oscillators are basic microwave energy sources for all microwave communication systems. This paper will discuss the theory and the design of a low phase noise 10GHz parallel feedback GaAs PHEMT dielectric resonator oscillator. The coupling coefficient between the dielectric resonator and the parallel microstrip lines are represented in the form of double coil transformer, while the dielectric resonator is modeled as a parallel RLC component. The coupling gap can be adjusted to optimize the ratio of the loaded to the unloaded quality factor to give a better phase noise. An optimum low phase noise can be achieved when an insertion loss of 9.5dB is obtained. The dielectric resonator oscillator model design was simulated using Agilent ADS software, where at 10GHz exhibited an insertion loss of 8.562 dB with a phase noise of -105.283 dBc/Hz at 100 kHz frequency offset. The output power was exhibited at +15.551 dBm

A Review on Sparse Channel Estimation in OFDM System Using Compressed Sensing

ABSTRACT The ever-increasing demand for high-data-rate communication over a wireless multipath fading channel usually necessitates that at the receiver, prior knowledge about the channel is known. This is often achieved using known pilot signals that track the channel and produce at the receiver channel impulse response reconstruction obtained from the received signals. In a rich multipath channel assumption, classical pilot-based techniques for channel estimation lead to a better signal reconstruction performance. Recently, empirical studies have demonstrated that the rich multipath assumption taken is violated in most physical systems and that the channel instead exhibits a sparse multipath behaviour that is characterized by only a few dominant paths in propagation. In this paper, multipath sparsity is exploited through compressed sensing. It shows that proper pilot pattern designing of the measurement matrix is desirable for a good sensing matrix as well as the use of a suitable nonlinear reconstruction algorithm for an enhanced channel estimation performance.

An implementation of caesar cipher and XOR encryption technique in a secure wireless communication

Due to the openness of the wireless communication, security aspect of data transmission plays important role in respect to the effective measure of the transmission, where cryptography method is often implemented to sustain the security of the communication. A secure communication program is proposed in this paper which involves three design stages, i.e. the encryption technique, serial-transmission and encoding technique. The encryption technique adopts a combination of Caesar Cipher and XOR encryptions, and programmed using C++. Subsequently, few possible cases have been tested to verify the strength of the security program, which indicates an improvement in security of data transmission in wireless medium without affecting the processing time.

Radio frequency energy harvesting using circular spiral inductor antenna

The design of radio frequency (RF) energy harvesting using planar circular spiral inductor antenna is proposed. The purpose is to determine the feasibility to harvest power density produced by the proposed antenna. A single element circular spiral antenna was designed, and subsequently, a 2 × 1 array to enhance the gain. Being a circular spiral inductor, it has a good Q-factor, higher inductance per unit area, and compact capability. The entire structure was investigated using numerical solver such as finite integration technique (FIT) method and Agilent advance design system (ADS) software. Results show that 3.22 dBi gain for single antenna and 5.14 dBi gain for antenna array was achieved at a centre frequency of 520 MHz. The gain of the 2 × 1 antenna array increased to about 37.3% over the single element. There are noticed reasonable agreements between the simulated and measured result.

Improved Time-Domain Threshold Determination for Sparse Channel Estimation in OFDM System

Channel estimation is one of the most essential requirements in Orthogonal Frequency Division Multiplexing (OFDM) system and its exactness severely impacts the performance of the entire system. The most significant tap (MST) selection approach requires prior knowledge of channel statistics which increases complexity and a reduced spectral efficiency. Therefore, in order to tackle the approach of sparse channel estimation in OFDM systems, an improved time domain threshold (ITDT) for sparse channel estimation is thus proposed. The proposed ITDT aims at achieving an improved channel estimation performance with no prior knowledge of channel state information and noise standard deviation. At the start, an initial channel impulse response is obtained by Least Square (LS) approach. Next, a novel ITDT is proposed to obtain the estimated coefficient of noise by extracting the non-zero channel taps. Simulation results indicate a better normalized mean square error (NMSE) of 20-dB gain for a same NMSE for the proposed ITDT compare to the non-sparse LS time domain estimator.

Turn Ratio, Substrates’ Permittivity Characterization, and Analysis of Split Ring Resonator Based Antenna

The turn ratio, coupling space between sections, and substrate permittivity effects on spilt ring resonator (SRR) are investigated. The analysis of the presented SRR with respect to the effects of substrate and number of gaps per ring to further characterize its peculiarities is experimented with miniaturized capability as our intent. Six different SRRs were designed with different turn ratios, and the sixth is rectangular microstrip patch centre-inserted. Different numbers and gap sizes are cut on the SRRs while the gap spacing between the conductors of the SRR was varied to determine their effects taking cognizance of the effects of different substrates. The designs were investigated numerically using 3D finite integration technique commercial EM solver, and the resulting designs were prototyped and subsequently measured. Findings indicate that the reflection coefficient of the MSRR with centre-inserted patch antenna is better compared to MSRR without the patch antenna irrespective of the laminate substrate board, and so is its gain.

Design of a 5.8 GHz Bandstop Filter Using Split Ring Resonator Array

Nowadays, ISM band has been widely used by communication, military, medical and scientific department. The frequencies for this band are 2.4 GHz and 5.8 GHz. Heavy traffic has occurred in this frequency range due to high usage which makes noise easily to occur. Thus, in this work a 5.8 GHz bandstop filter has been designed to filter the noise that present at this frequency band using SRR array. It is designed using CST Microwave Studio software. Designing this filter also requires optimization process i.e. varying the different length of split gap and number of array used. Subsequently, the design is fabricated using Rogers 4003 as the substrate and is measured using Agilent PNA-X network analyzer. The result obtained satisfies a bandstop filter parameters such as insertion loss, return loss, and bandwidth. A 5.8 GHz SRR bandstop filter is successfully designed with 390 MHz bandwidth, insertion loss and return loss of −26.68 and −2.91 dB respectively.

Joint Pilot Placement and Symbol Design Scheme for Sparse Channel Estimation in OFDM systems

Most existing works on the deterministic pilot design for sparse Channel Estimation (CE) in Orthogonal Frequency Division Multiplexing (OFDM) system are based on the assumption that the pilot symbols are equally-powered. This assumption may not necessarily exhibit low coherence compressed CE. This, therefore, calls for the optimization of pilot symbols and their placement which in the literature is considered as a disjoint optimization problem. In this paper, the joint pilot placement and symbol design optimization problem for sparse CE in OFDM systems is considered based on minimizing the mutual coherence of the Fourier submatrix associated with the pilot subcarriers. In order to avoid the disjoint optimization of the pilot symbol values and their placements, a joint pilot placement and pilot symbol design scheme is proposed that optimizes over both the pilot symbol values and their placements as a single design optimization problem. Simulation results demonstrate that the proposed scheme is effective and offer a better CE performance — in terms of Mean Square Error (MSE) and Bit Error Rate (BER), when compared to former pilot placement schemes that assume the equally powered pilot symbols and other schemes that jointly design the pilot symbols and their placement. It was also observed that the proposed scheme can realize 18.75% improvement in bandwidth efficiency with the same CE performance compared with the least squares (LS) CE.