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A new compact Cylindrical Dielectric Resonator Antenna (CDRA) with a defected ground for ultra-wideband applications is presented. The structure is based on two cylindrical dielectric resonators asymmetrically located with respect to the center of an offset rectangular coupling aperture, with consideration of three and four Dielectric Resonators (DR). The resonant modes generated by the defected ground are studied and investigated. A parametric optimization study of the antenna design has been carried out to determine the optimal dimensions of the defected ground plane, resulting in an impedance bandwidth of over 133% that covers the frequency band from 3.6 GHz to 18.0 GHz. A power gain of about 7.9 dBi has been achieved. Design details and measured and simulated results are presented and discussed.

A compact dielectric resonator antenna for ultrawideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower-band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper-band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed. &nbsp

A new low-cost dual-segmented dielectric resonator (DR) antenna design is proposed for wideband applications in the X-band region. Two DRs coupled to an S-shaped slot introduce interesting features. The antenna performance was characterised in terms of the reflection coefficient, gain, and radiation pattern, and detailed simulation studies indicate excellent antenna performance from 7.66 to 11.2 GHz (37.5% fractional bandwidth) with a maximum gain of 6 dBi at 10.6 GHz, whereas the fabricated prototype has a matched bandwidth from 7.8 to 11.85 GHz (41% fractional bandwidth) and maximum gain of 6 dB i . The antenna is compact, size 1 × 0.83 × 0.327 times the wavelength at 10 GHz. The two DR segments may be located on the same side or on opposite sides of the substrate, giving, respectively, improved gain or more uniform field patterns. Experimental testing of the prototype performance showed reasonable agreement with the predicted performance.

This study reports on balanced dual-segment cylindrical dielectric antennas with ultra-wideband (UWB) operation. A T-shaped slot and L-shaped microstrip feeding line was suggested to furnish a balanced coupling mechanism for feeding two DRAs, and then the performance of the proposed antenna was analysed and optimised against the target frequency band. The proposed antenna was then modified by adding a C-shaped strip to increase the gain. The performances of both balanced antennas were characterised and optimised in terms of antenna reflection coefficient, radiation pattern, and gain. The antennas cover the frequency range from 6.4 to 11.736 GHz, which is 58.7% bandwidth. A maximum gain of 2.66 dB was achieved at a frequency of 7 GHz with the first antenna, with a further 2.25 dB increase in maximum gain attained by adding the C-shaped strip. For validation, prototypes of the two antennas were fabricated and tested. The predicted and measured results showed reasonable agreement and the results confirmed good impedance bandwidth characteristics for UWB operation from both proposed balanced antennas.

In radar antennas, asymmetric side lobes are useful, where undesired signals such as noise and ground clutter should be minimized. Also, for practical implementation, the feeding network of such antennas should be efficiently designed. In this paper, a simple analytical method for synthesizing asymmetric side lobe pattern with a wide-angle steered null in the nonuniformly excited linear arrays is presented. In this method, the difference in the side lobe levels on both sides of the main beam is achieved by varying just the phase excitations of the two-edge elements. The major novelty of this paper lies in the fact that the required asymmetric side lobe pattern can be achieved by changing a single phase shifter resulting in a simple feeding network.

A sidelobe cancellation over a wide angular range for the uniformly excited planar array is proposed. The approach is to readjust the amplitude and phase excitations of the boundary elements only, while keeping the rest of elements unchanged. Simple expressions for computing the required amplitude and phase excitations of these boundary elements are given. The technique simplifies the feed network as it requires only one attenuator and two phase shifters. Simulation results show that cancellation of sidelobes across a wide angle can be obtained.

A compact dielectric resonator antenna (DRA) for wideband applications is proposed. Two cylindrical dielectric resonators that are asymmetrically located with respect to the center of a rectangular coupling aperture are fed through this aperture. By optimizing the design parameters, an impedance bandwidth of about 29%, covering the frequency range from 9.62 to 12.9 GHz, and a gain of 8 dBi are obtained. Design details of the proposed antenna and the results of both simulation and experiment are presented and discussed.

In this paper, a new approach to the design of an UWB monopole antenna with dual band-notched characteristics is presented. The antenna has the form of an elliptical monopole over a ground plane having an elliptical slot to achieve the UWB. The dual-band notch function is created by inserting a U-shaped and a C-shaped slots on the radiating patch, thus no extra size is needed. The proposed antenna shows a good omnidirectional radiation pattern across the band from 3.2 to more than 14 GHz. The dual band-rejection is for 4.88-5.79GHz centered at 5.4GHz and 7.21-8.46 GHz centered at 7.8 GHz. The antenna prototype using the FR-4 substrate with εr=4.3 has a compact size of 25mm×25 mm ×1.45mm. The fabricated prototype showed experimental results comparable to those obtained from the simulations.

In most practical applications of the phased array antennas, the generated nulls toward the interfering signals should have enough depth and width to accommodate ∞uctuations in frequency and direction of the interferer. Due to these ∞uctuations, the nulls can be easily deviated from its desired angular locations in the traditional adaptive nulling arrays since the nulls are very sharp and sensitive. An innovative technique for wide nulling arrays has been recently presented. The wide nulls can be introduced by setting properly the excitation coe-cients of the two edge elements of the antenna array. In this paper, the efiect of frequency ∞uctuation on the nulling performance is investigated. By generating wide and deep nulls toward and around the interference directions, the proposed method provides robustness against frequency ∞uctuation. Simulation results in realistic situations with frequency ∞uctuation are presented to illustrate the performance of the proposed technique. Comparisons with the standard fully adaptive nulling array are shown.

In this paper, a balanced dual segment cylindrical dielectric antenna (CDRA) with ultra wide-band operation is reported. First a T-shaped slot and L-shaped microstrip feeding line are suggested to furnish a balanced coupling mechanism for feeding two DRAs. Performance of the proposed antenna was analyzed and optimized against the target frequency band. The antenna cover the frequency range from 6.4 GHz to 11.736 GHz, which is 58.7% bandwidth with a maximum gain of 2.66 dB. The predicted and measured results of the fabricated prototype showed reasonable agreement.

The focusing properties of six array configurations in the form of square, square with interlaced elements, square ring, cross (+) shape, cross (X) shape, and square ring plus diagonals shape arrays are investigated. The performance parameters, such as field distribution in the focal region, size of the focal spot, depth of field, level of field at focal point, and sidelobe structure, are compared. Computer simulations using MTALAB environment are performed in the investigations. The square ring and square ring plus diagonals configurations show favorable focusing properties. The resultant field patterns will help to find the arrays usefulness for hyperthermia and imaging applications.

The design of a microstrip reflectarray formed by 81 variable size double elliptical rings illuminated by a conical feed is presented.Because of double resonance, the double elliptical rings provide an increased phasing range of unit cells that exceeds the required minimum of 360°. Printed on a single substrate and supported by a layer of foam and a conducting ground, they also offer a slow phase slope as a function of their size, and thus provide an increased operational bandwidth and a good manufacturing error tolerance. The performance of the designed reflectarray is investigated via full-wave electromagnetic simulations and measurements on the manufactured prototype. The presented results show a wideband performance of the designed reflectarray.

In this paper, the self-complementary principle has been applied to develop the traditional planar monopole antenna into a dipole antenna whose frequency range exceeds UWB requirements. The proposed design has compact, planar, and simple shape arranged in self-complementary manner connected to the (SMA) connector via rectangular microstrip line. The self-complementary structure ofiers better reduction of the imaginary part of antenna impedance, which allows matching on a wider band of frequencies. The proposed antenna showed i10dB return loss bandwidth extending from 1.86GHz up to 17.7GHz. Moreover, this antenna has a simple shape as compared with complicated and irregular shapes with curves, slots or parasitic elements. The proposed design is validated by experimental measurements. The phase of the return loss is investigated for more insight into antenna matching.

This paper presents a new wideband microstrip circular patch antenna (MCPA) fed by proximity-coupled line with double-stub matching to achieve dual-band operation. Bandwidth extension is achieved by exciting higher-order modes in the circular radiating patch, and using two stubs to achieve adequate matching across the obtained two bands. The characteristics of the antenna such as reflection coefficient, impedance bandwidth, gain and radiation pattern are investigated and optimized through parametric studies using the CST Microwave Studio Suite. The antenna achieved a large relative bandwidth of 45.16% at the upper band, while the lower one has 10.3% relative bandwidth. The maximum achieved gain of the dual-band antenna in the 5.8GHz band is 4.62dBi while it is 4.85dBi in the upper band. The antenna has an overall size of 30×30×3.2mm3 corresponding to 0.58λ × 0.58 λ × 0.062 λ at the lower band of 5.8 GHz. The proposed antenna should be useful for WLAN and X-band communication systems.

The paper reports on investigations into phase characteristic of a unit cell of a single-layer microstrip reflectarray, which includes patch or ring elements of variable size. The aim is to have a smaller gradient (slower slope) of the reflected wave phase as a function of the elements' size to achieve a wider operational bandwidth and smaller susceptibility to manufacturing errors. The results obtained for single resonance elements demonstrate that a slower slope can be achieved using thicker substrates at the expense of an inadequate phase range of less than 300deg. This inadequate phase range leads to the reflectarray elements phase errors, which reduce its directivity. To overcome this problem the use of multiresonance multiring elements is postulated. It is shown that square and circular shaped multiple rings printed on a thick substrate can offer a slower phase slope and the phase range exceeding 360deg. The achieved slopes and ranges of double rings are comparable with those of double stacked patches printed on the equivalent low permittivity dielectric substrate. Choosing suitable dimensions of double-ring elements, the phase characteristic can be made approximately a linear function of their size.

The paper describes a theoretical investigation into a limited bandwidth operation of a microstrip reflectarray. Two main factors limiting the bandwidth are considered. One is related to the requirement of phase compensation to convert a spherical wavefront launched by a feed into a planar wavefront. The other one is linked to the limited phasing range of microstrip antenna elements. The two factors contribute to the reflectarray phasing errors that in turn reduce its gain as a function of frequency. Simple formulas for an upper bound of gain bandwidth are derived, assuming the phase compensation by the elements is independent of frequency changes and verified against the results produced by other researchers. It is shown that the phase errors incurred in the path equalization to obtain conversion from spherical to planar wavefronts have a more profound effect on the reduction of operational bandwidth of the reflectarray than the phase truncation implemented on the required phase from each element.

This paper reports on the investigations into new configurations of unit cells which offer an increased phasing range for a single-layer printed reflectarray. It is shown that the extended phasing range can be obtained by utilizing similar in shape but different in size resonant elements. Using this principle it is shown that two resonant elements forming a unit cell can double while three elements can almost triple the phasing range of a single resonant element unit cell. These investigations also show that the relative sizes and spacing between the elements in the cell can be adjusted to linearize the phasing curves as a function of the elements dimensions. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1028-1032, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23285

Synthesis of wide beam array antennas is investigated using phase-only excitations for uniform amplitude array. In this approach random phase distribution is proposed. Symmetrical and asymmetrical distributions of the random phase are considered. The obtained patterns are assessed by comparing beam width and maximum level of the radiated field with those obtainable from the conventional broadside array. The obtained results showed many fold increase in the −10dB beam width, and a reduction of up to 8.5dB in the maximum level of the pattern as compared to the case of broadside array. The proposed technique offers a simple method to synthesize arrays of wide beam, where only (N/2-1), and (N-1)/2 for even, and odd number of elements N respectively are required for an N-element array.

The performance of six configurations for focused array antennas is investigated. The proposed arrays are in the form of; Ring, Four corners with central elements, Ring with Cross, Four orthogonal arrows rotated by 45 degree, Octal with Cross and Octal with Cross without central elements arrays. The studied parameters are the size of focal spot, the depth of field, the level of field at the focal point, and sidelobes of the focused field. Computer simulations using MATLAB are used to estimate these parameters. The array of Octal firm with a cross shape shows the lowest sidelobe level. These results will be useful in array design for the different near field applications.

This paper presents design and performance analysis of various element shapes for microstrip reflectarray formed of patches of variable size. The comparison focuses on effect of the elements boundaries on the performance represented by the range and slope of the reflection phase response. Variation of the response with frequency is also investigated to assess the frequency response of the proposed elements. Various shapes in the form of patches and double-rings inspired by the Koch fractal are investigated. The analyses were performed using the CST Microwave Studio software Package.

A microstrip reflectarray antenna utilizes a planar array of printed patch elements and a conventional prime or offset feed to form an alternative to the parabolic reflector [1]. It transforms the spherical wave of the feed into the planar wave by employing microstrip patch elements as radiators and phase shifters. Due to the use of planar technology, it offers a good balance between conventional reflector antennas and phased arrays. Because it uses many radiating elements it provides flexibility with respect to radiation pattern formation [2–4]. Its disadvantage is a limited operational bandwidth, which for the case of moderate gain is mainly due to a limited phase range and a high phase slope of the elements. In the wave transformation process, a full phasing range of 360° is desirable for unit cells containing patch elements. However, a variable size patch antenna developed on a single layer substrate offers a phasing range of about 300°. To overcome this problem, multilayer substrates including stacked variable-size patches for phasing the unit cells of a reflectarray have been devised to extend the phase range to multiples of 360°. The multi-layer approach with stacked patches not only extends the phase range but also reduces the slope of the phase curve as a function of patch dimensions [5–6]. However, the use of multi-layer substrates means that in practice layers of the reflectarray have to be manufactured separately and the assembly should leave no air gaps. This results in an elaborate and expensive manufacturing process. To overcome this problem, printed double-ring elements to form a single-layer reflectarray have been proposed. The double rings improve the phasing range of unit cells by utilizing multi-resonance behaviour. The extended range for unit cells containing double-ring elements has been demonstrated for the case of normal (TEM) wave incidence [7]. The assumption of normal incidence is less accurate for peripheral elements. Therefore in [8], TE and TM waves were considered to obtain an oblique incidence to obtain more accurate phasing characteristics of unit cells.

In phased arrays the mainbeam is scanned by either varying the phase excitations of the elements or varying the frequency of operation. In spite of their extensive use, these methods need either variable phase shifters or frequency sweeping. It is shown here that beam scanning is also feasible by varying magnitudes of the array element excitations thus alleviating the need for phase shifters or frequency variation. In this technique, the amplitude excitations of some side elements are reduced while those of the others are increased by proper power division or weighting in the feed network of the array. Theoretical analysis and computer simulations are presented to verify the proposed idea. A 3-element array is studied first, then the idea is extended to a 7-element array. Simulation results show appreciable scan angles with minor variation in the mainbeam level. Some degradation in the array pattern is noticed at large scan angles.

The reflection characteristics of oblique angles of incidence on single-layer double-ring unit cells for reflectarray antennas have been investigated. The presented results have revealed that the normal incidence can present acceptable approximations for the phasing response for angles up to 30deg degrees. The resonance characteristics of the double-ring elements have also been investigated. A simple method to approximate the reflection phase swing regions with respect to element size has been presented followed by parametric studies. By using the design guide lines presented in this paper, single-layer double-ring structures with an extended phasing range of more than 600deg and a considerably slow slope have been demonstrated.

In this paper, we focus our considerations on a single layer microstrip reflectarray because it is easy to manufacture. By selecting suitable phasing elements we aim to overcome the main problem faced in many single-layer microstrip reflectarray designs, which are reduced phase range and a large phase gradient. The reduced phase range and the sharp slope contribute to the phasing errors of the reflectarray that in turn degrade its directivity. We turn our attention to multi-resonant variable size planar antenna elements, for which we have shown in that they can offer an extended phase range when used in a unit cell of a single-layer reflectarray. Here we choose printed double cross elements to form a reflectarray unit cell with an extended phase range and a lower slope. In the presented investigations, we show that a unit cell containing a single resonant cross still faces similar phase range and slope problems as a unit cell with single dipoles or patches. By using a double cross element on the same substrate we demonstrate that the phase range can be doubled. Next, to reduce the slope and still keep the phase range more than 360deg, we use a thick composite material including a thin laminate and a thick layer of foam to support the double cross. Such substrate combination offers phase responses of reduced slopes over an acceptable phase range. We compare the obtained results with those for double stacked patches developed on similar thickness foam.

Position perturbation of the array elements is used for reducing the sidelobe structure in the radiation pattern of phased arrays. Results of computer simulations showed good improvements in the side lobe structure as compared to the equal size linear array. A quantitative measure of the improvement is postulated. Results are compared with those obtainable from the technique of adding 2 auxiliary elements.

In this paper, we investigate planar antenna elements in the form of multi-rings of square and circular shapes, and explain the concept behind their increased phase range in a unit cell of a single layer microstrip printed reflectarray. It has been shown that the extended phase range can be obtained by utilizing similar in shape, but different in size, resonant elements. Using this principle it has been shown that two resonant elements forming a unit cell can double while three elements can almost triple the phasing range of a single resonant element unit cell, while the slope of the phase response remains almost unchanged. The issue of bandwidth improvement has not been considered. However, this can be achieved using thicker substrates similarly, as in the multi-layer approach.

The reflectarray is the type of antenna that includes a feed similar to that used in a conventional curved reflector antenna but its reflector is planar and formed by an array of reflecting elements. These elements use a suitable phasing mechanism to beam an incident wave, as launched by the feed, in a desired direction. Recent years have seen a considerable interest in microstrip reflectarrays. One important issue in the design of microstrip reflectarrays is obtaining a wide phasing range and a slow phase variation (slope) as a function of the phasing element's variable size. The present paper reports on investigations into the phase change with respect to the element's size change (dPhi/dS) for a single layer microstrip reflectarray. The investigations are commenced with comparing phase response parameters (range, slope, and working size) for various element shapes that are adopted in a typical single layer microstrip reflectarray. Next, the effect of the substrate characteristics such as its dielectric constant and thickness is considered. The study is carried out by applying full EM simulations of a single unit cell containing a phasing element.

The focusing properties of an array in the form of semi-circle are investigated. Such array geometry is inherently focused at its center. When the focal point is required at any point other than the center, the focal region distribution deteriorates. It is suggested here that the array elements are oriented to be perpendicular to the line joining the focal point and the element position such that maximum radiation of each element is directed towards the focal point computer simulations for power distributions in two media are shown.

This study reports investigations into phase characteristics of a unit cell of a single-layer microstrip reflectarray exploiting fractal geometries. The aim is to have the phase range larger than 360° accompanied by a smaller slope of the reflected wave phase as a function of the elements' size. These are required to achieve a wide operational bandwidth and a smaller sensitivity to manufacturing errors. To achieve this goal, multi-resonance fractal elements are investigated. It is shown that sliced patches of square and circular shapes as well as multiple rings printed on a thick substrate can offer slower phase slopes while maintaining phase ranges exceeding 360°. The achieved ranges and slopes of these elements are comparable with those of double-stacked patches printed on the equivalent low permittivity dielectric substrate. Choosing suitable dimensions and scaling factors of these elements, the phase characteristic can be made approximately a linear function of their size.

Prony's technique is used to estimate multipath parameters from range-gain patterns produced by ground multipath interference in line-of-sight radio links. The field distribution at the transmitting antenna side is obtained by digital reconstruction from the range-gain pattern that is recorded, at constant height, along ground surface. The technique is presented as a competitive alternative to the Fourier transform, where much shorter data windows are sufficient for the proposed technique. The technique is validated by calculated and measured range-gain patterns, and the predicted values are in good agreement with the actual ones. Prony's technique produced predictions with comparable errors to the Fourier technique from much smaller data windows.

A new technique is presented where the range gain pattern produced by ground multipath interference is considered as a hologram. The technique can be applied to both flat and spherical earth models. Field distribution at the transmitting antenna side is obtained by digital reconstruction from the range gain pattern. Transmitting antenna height and ground reflection coefficient can therefore be predicted. The technique is validated by calculated and measured range gain patterns, and the predicted values are in good agreement with actual ones.

Ducting in LOS radio links is investigated. A technique is proposed to estimate the number of refracted rays that could reach the receiver due to the presence of a duct, their angle of arrival and their relative amplitude in comparison to the direct ray.