Filtenna design with selectivity enhancement for modern communication system

This thesis presents filtenna design with selectivity enhancement for modern communication systems. Filtennas are designed to simplify the radio frequency (RF) front-end, reduce cost and eliminate signal losses. Two filters, (Filter A and Filter B) and two filtennas, (Filtenna A and Filtenna B) have been designed to overcome a few drawback such as decrease in the peak gain, poor selectivity, increase in feeding area and structure complexity of the existing filtennas. Filtenna A and Filtenna B are designed based on Filter A and Filter B, respectively, by using filter synthesis technique. All designed structures were simulated using Computer Simulation Technology (CST) Microwave Studio and validated through fabrication and measurement of the prototypes. Firstly, an improved technique for creating sharp selectivity of a T-shaped stub bandpass filter (Filter A) is designed. The T-shaped stub is loaded with vertical resonators to produce good selectivity at both edges of the passband at 3.6 GHz. The advantage of this filter is the potential ability to adjust the center frequency and the bandwidth to suit the system demands. Secondly, a novel and compact second order Chebyshev bandpass filter (Filter B) with sharp selectivity is designed to operate at 5.8 GHz. The sharp selectivity is obtained by using U-shaped resonators and Defected Ground Structure which are responsible for the rejection at the higher and lower band edge, respectively. The advantage of this design is size compactness. About 56% area reduction is achieved over the second order Hairpin bandpass filter. Thirdly, the T-shaped stub bandpass filter is synthesized with a microstrip patch antenna to form a T-shaped stub fed filtenna (Filtenna A) with enhanced selectivity. The advantage of this design is that it maintains the same bandwidth as the conventional patch antenna with enhanced gain and good out-of-band suppression. The fourth design involves the synthesis of the second order Chebyshev designed filter with a U-shaped patch (Filtenna B). The designed filtenna operates at 5.8 GHz and has sharp selectivity as no degradation of the peak gain. The superiority of the proposed design over the conventional patch antenna is verified by a 99 % decrease in the out-of-band suppression and a 11.86 % increase in the gain performance. The designed filtennas address the limitations faced by existing filtennas and can be used in Wireless Local Area Network (WLAN) application

Error bounds for wireless localization in NLOS environments

An efficient and accurate method to evaluate the fundamental error bounds for wireless sen-sor localization is proposed. While there already exist efficient tools like Cram`er-Rao lower bound (CRLB) and position error bound (PEB) to estimate error limits, in their standard formulation they all need an accurate knowledge of the statistic of the ranging error. This requirement, under Non-Line-of-Sight (NLOS) environments, is impossible to be met a priori. Therefore, it is shown that collecting a small number of samples from each link and applying them to a non-parametric estimator, like the Gaussian kernel (GK), could lead to a quite accurate reconstruction of the error distribution. A proposed Edgeworth Expansion method is employed to reconstruct the error statistic in a much more efficient way with respect to the GK. It is shown that with this method, it is possible to get fundamental error bounds almost as accurate as the theoretical case, i.e. when a priori knowledge of the error distribution is available. Therein, a technique to determine fundamental error limits – CRLB and PEB – onsite without knowledge of the statistics of the ranging errors is proposed

Multiband CPW-fed slot antenna for WLAN/WiMAX applications

A square slot antenna fed by a coplanar waveguide (CPW) is presented in this paper. The design consist of two pairs of “F” shaped planar strips placed within a square slotted ground. The strips are used to excite multiple resonant frequencies, the strips are connected to the ground plane by means of ideal switches. The proposed antenna has achieved multiple resonant frequencies of 2.4/5.2/5.8 GHz for WLAN and 3.5/5.5 for WiMAX applications. The measured results shows a good agreement with the simulated results in terms of return loss, radiation pattern and gain. The proposed antenna is designed for the frequency range of 2 GHz to 7 GHz which makes it suitable for Bluetooth, WLAN and WiMAX applications

A review on filter-antennas

A review on the recent advancements made on filtennas are presented in this paper. RF fronts ends continue to generate a lot of research attention in communication systems due to the effect it has on the overall bit error rate and SNR. Issues such as compactness, interference and noise are addressed by embedding the bandpass filter into the antenna to form a filtenna. Designing a filtering antenna has its own challenges also. Various techniques (synthesis approach, T shaped resonator or slots.) are being used to design filtennas in order to achieve “weak coupling between the feed and the radiating structure” hence yielding better selectivity. The filter-antenna gain results compared to that of the conventional antennas show better rejection of the out of band gain. This helps reduce interference with adjacent frequency band. This paper presents a review of the techniques, challenges faced and potential research trend in filtering antennas