Reducing the height of a circular array of monopoles using top hats and dielectric coatings

Using a Radial Guide Field Matching Method, an investigation is performed into reducing the height of an electronically steered circular array of monopole antennas composed of a central active element surrounded by passive elements being either short- or open-circuited. It is shown that a considerable height reduction can be achieved using top hats attached to monopoles ends and by applying dielectric coating underneath the top hats. The trade-off in achieving height reduction is narrower impedance bandwidth.

Investigations into diversity of A 2x2 MIMO system with the use of an indoor testbed

This paper presents investigations into an indoor 2×2 multiple input multiple output (MIMO) system, whose diversity performance is assessed using a high precision test-bed. In this system, transmitter and receiver are equipped with 180° or 90° 3dB hybrids with their two output ports terminated with co-polar monopole antennas. By feeding a signal to one of the two input ports of the hybrid (while the other input port is matched terminated) different communication channels in a rich-scattering environment can be created. The test-bed allows for the signal strength measurements around the receiver/ transmitter sides for a given feeding configuration of hybrids when the receiver is moved over a circular region in an indoor environment. The signal strengths maps obtained for various modes of this 2×2 MIMO system are foundations for investigating transmit/receive diversity schemes. As the signal strength measurement results are obtained with Bluetooth modules operating in the ISM 2.4 GHz, the results are of importance to many other wireless systems that aim at utilizing MIMO diversity schemes to enhance their performance in this frequency band.

Indoor antenna diversity testbed

This paper presents a high precision testbed for evaluating antenna diversity techniques in an indoor environment. Details concerning mechanical, electrical and electronics hardware and associated measurement software are described. Initial measurement results for two Bluetooth modules operating with co-polar and cross-polar monopole antennas in the ISM 2.4 GHz band are given.

New modal feed network for a compact monopole array with isolated ports

An element spacing of less than half a wavelength introduces strong mutual coupling between the ports of compact antenna arrays. The strong coupling causes significant system performance degradation. A decoupling network may compensate for the mutual coupling. Alternatively, port decoupling can be achieved using a modal feed network. In response to an input signal at one of the input ports, this feed network excites the antenna elements in accordance with one of the eigenvectors of the array scattering parameter matrix. In this paper, a novel 4-element monopole array is described. The feed network of the array is implemented as a planar ring-type circuit in stripline with four coupled line sections. The new configuration offers a significant reduction in size, resulting in a very compact array.

Tunable decoupling and matching network for diversity enhancement of closely spaced antennas

A tunable decoupling and matching network (DMN) for a closely spaced two-element antenna array is presented. The DMN achieves perfect matching for the eigenmodes of the array and thus simultaneously isolates and matches the system ports while keeping the circuit small. Arrays of closely spaced wire and microstrip monopole pairs are used to demonstrate the proposed DMN. It is found that monopoles with different lengths can be used for the design frequency by using this DMN, which increases the design flexibility. This property also enables frequency tuning using the DMN only without having to change the length of the antennas. The proposed DMN uses only one varactor to achieve a tuning range of 18.8% with both return loss and isolation better than 10-dB when the spacing between the antenna is 0.05λ. When the spacing increases to 0.1λ, the simulated tuning range is more than 60%.

Integrated decoupling and matching network incorporated in the ground plane of a compact monopole array

Compact arrays enable various applications such as antenna beam-forming and multi-input, multi-output (MIMO) schemes on limited-size platforms. The reduced element spacing in compact arrays introduces high levels of mutual coupling which can affect the performance of the adaptive array. This coupling causes a mismatch at the input ports, which disturbs the performance of the individual elements in the array and affects the implementation of beam steering. In this article, a reactive decoupling network for a 3-element monopole array is used to establish port isolation while simultaneously matching input impedance at each port to the system impendence. The integrated decoupling and matching network is incorporated in the ground plane of the monopole array, providing further development scope for beamforming using phase shifters and power splitters in double-layered circuits.

Simple control of the polarisation in uniform hybrid waveguide-planar leaky-wave antennas

A simple and original mechanism to control the polarisation of uniform hybrid waveguide-planar leaky-wave antennas is proposed. The operation is based on introducing simple modifications of the planar dimensions of the structure cross-section, which is shown to control the horizontal and vertical components of the radiated fields. The proposed antenna dispenses with the need for periodic elements, commonly used in flexible polarised leaky-wave antennas, and therefore significantly reduces the design complexity. Parametric curves have been obtained to assist in the simple and efficient design of the proposed antenna. The novel mechanism is illustrated by means of several antenna prototypes operating at 5.7 GHz, producing linear, elliptical and circular polarisations. Commercial three-dimensional Finite Element Method has been used for the simulations, and the results are validated with experimental testing.[br].

Antennas for over-body-surface communication at 2.45 GHz

In this paper, the on-body performance of a range of wearable antennas was investigated by measuring vertical bar S-21 vertical bar path gain between two devices mounted on tissue-equivalent numerical and experimental phantoms, representative of human muscle tissue at 2.45 GHz. In particular, the study focused on the performance of a compact higher mode microstrip patch antenna (HMMPA) with a profile as low as lambda/20. The 5- and 10-mm-high HMMPA prototypes had an impedance bandwidth of 6.7% and 8.6%, respectively, sufficient for the operating requirements of the 2.45-GHz industrial, scientific, and medical (ISM) band and both antennas offered 11-dB higher path gain compared to a fundamental-mode microstrip patch antenna. It was also dernonstrated that a 7-dB improvement in path gain can be obtained for a fundamental-mode patch through the addition of a shortening wall. Notably, on-body HMMPA performance was comparable to a quarter wave monopole antenna on the same size of ground-plane, mounted normal to the tissue surface, indicating that the low-profile and physically more robust antenna is a promising solution for bodyworn antenna applications.

Compact, frequency reconfigurable, printed monopole antenna

This paper proposes a possible implementation of a compact printed monopole antenna, useful to operate in UMTS and WLAN bands. In order to accomplish that, a miniaturization technique based on the application of chip inductors is used in conjunction with frequency reconfiguration capability. The chip inductors change the impedance response of the monopole, allowing to reduce the resonant frequency. In order to be able to operate the antenna in these two different frequencies, an antenna reconfiguration technique based on PIN diodes is applied. This procedure allows the change of the active form of the antenna leading to a shift in the resonant frequency. The prototype measurements show good agreement with the simulation results.

Investigations on the Radiation Characteristics of Planar Printed UWB Antennas With Modified Ground Planes

A major challenge in the transmission of narrow pulses is the radiation characteristics of the antenna. Designing the front ends for UWB systems pose challenges compared to their narrow and wide band counterparts because in addition to having electrically small size, high efficiency and band width, the antenna has to have excellent transient response. The present work deals with the design of four novel antenna designs- Square Monopole, Semi-Elliptic Slot, Step and Linear Tapered slot - and an assay on their suitability in UWB Systems. Multiple resonances in the geometry are matched to UWB by redesigning the ground-patch interfaces. Techniques to avoid narrow band interference is proposed in the antenna level and their effect on a nano second pulse have also been investigated. The thesis proposes design guidelines to design the antenna on laminates of any permittivity and the analyzes are complete with results in the frequency and time domains.

Investigations on Broadband Plannar Monoplole Antennas with Truncated Ground Plane

The space constraints on wireless gadgets is a challenge to antenna designers as the ground plane dimensions of the printed monopole significantly affect s the antenna characteristics.Investigations on ground plane truncations have led to the development of an extremely broad band printed monopole antenna.Omnidirectional radiation characteristics with moderate gain makes this antenna highly suitable for mobile/wireless applications .This thesis also highlights the development of UWB printed antenna along with design equations .Optimum ground plane dimensions for compact antenna applications,folding technique for miniaturization and double folding for dual band application are the other highlights of this thesis.

Design and Development of Compact Coplanar Waveguide Fed Antennas for Wireless Applications

The need of miniaturization in the present day communication industry is challenging. In the present scenario, printed antenna technology is highly suitable for wireless communication due to its low profile and other desirable radiation characteristics. Small monopole type antennas are overruled by compact small antennas for present day mobile communication applications. Coplanar waveguides (CPW) are printed on one side of a dielectric substrate. CPW have attracted the attention of antenna designers due to their excellent properties like ease of integration with ‘MMIC’, low cost, wide bandwidth, flexibility towards multiband operation, low radiation leakage and less dispersion. The requirement of omnidirectional coverage, light weight and low cost made these CPW fed antennas a good candidate for wireless applications. The main focus of the thesis is the study of coplanar waveguide transmission line. Rigorous investigations were performed on both the ground plane and signal strip of a coplanar waveguide transmission line to create effective radiation characteristics. Good amount of works have been done to transform CPW line to antenna suitable for mobile phone applications

Design and development of compact printed ultra wide band antennas

In recent years, there is a visible trend for products/services which demand seamless integration of cellular networks, WLANs and WPANs. This is a strong indication for the inclusion of high speed short range wireless technology in future applications. In this context UWB radio has a significant role to play as an extension/complement to existing cellular/access technology. In the present work, three major types of ultra wide band planar antennas are investigated: Monopole and Slot. Three novel compact UWB antennas, suitable for poratble applications, are designed and characterized, namely 1) Ground modified monopole 2) Serrated monopole 3) Triangular slot The performance of these designs have been studied using standard simulation tools used in industry/academia and they have been experimentally verified. Antenna design guidelines are also deduced by accounting the resonances in each structure. In addition to having compact sized, high efficiency and broad bandwidth antennas, one of the major criterion in the design of impulse-UWB systems have been the transmission of narrow band pulses with minimum distortion. The key challenge is not only to design a broad band antenna with constant and stable gain but to maintain a flat group delay or linear phase response in the frequency domain or excellent transient response in time domain. One of the major contributions of the thesis lies in the analysis of the frequency and timedomain response of the designed UWB antennas to confirm their suitability for portable pulsed-UWB systems. Techniques to avoid narrowband interference by engraving narrow slot resonators on the antenna is also proposed and their effect on a nano-second pulse have been investigated

Development and Investigations of Mobile Antennas for less Radiation Hazards

Antennas, the key element in wireless communication devices had undergone amazing developments especially in the direction of compactness and safety aspects. In the last two decades, the use of the cellular phones has become the most popular mode of communication across the globe. At the same time, the concerns about the radiation effects have increased in the general public. The main concern of this thesis is to develop a mobile antenna which gives reduced RF interference to the user. The reduction of the power absorbed by the user can tremendously avoid any possible health hazards. The radiation characteristic of a monopole antenna is modified with good radiation characteristics suitable for a mobile handset. The modification is implemented by using different resonating structures which provides reduced radiation along one direction. The direction of less radiation can be changed by modifying the planar antenna structure to a ground folded antenna. This modified structure with excellent radiation characteristic is suitable for modern wireless handheld devices with less user RF interference. Specific Absorption Rate (SAR) is an important parameter for mobile handset. The SAR is estimated for the newly developed antenna for different conditions and discussed in this thesis.

Simple approach to determine resonant frequencies of microstrip antennas

A simple approach for accurate determination of the resonant frequencies of microstrip antennas of regular geometries is developed and presented. In this approach, a generalised empirical formula for the computation of effective dielectric permittivity is given which takes into account the ratio of the fringing area to the area of the patch. A correction to the equivalent side length of an equilateral triangular patch, previously published, is modified and a new formula is given. A correction to the effective dimensions of an elliptical microstrip antenna is also carried out. Numerical results obtained for the resonant frequencies of elliptical, circular, rectangular and equilateral-triangular microstrip antennas are in good agreement with the available theoretical and experimental results reported by others. The present approach is more efficient, simpler and more accurate