OMNIDIRECTIONAL MILLIMETER-WAVELENGTH ANTENNAS BASED ON SEGMENTAL DIELECTRIC RESONATORS WHICH SUPPORT WHISPERING GALLERY MODES

A novel multi-band cylindrical dielectric resonator antenna (CDRA) using microwave laminates with permittivity variation in azimuth direction fed by coaxial probe is proposed in this paper. The proposed structures are constructed using different materials having different permittivities in azimuth direction in cylindrical dielectric resonator (DR). In order to determine the performance of various design parameters on resonance frequency and bandwidth, parametric studies have been performed. The operating band can be scaled up or down by adjusting the design parameters. Dual- band and triple-band CDRAs have been fabricated using commercially available microwave laminates to validate the simulation results. For each case, the input reflection coefficient, radiation pattern and antenna gain are simulated and measured. Good agreement between simulated and measured results has been observed. The proposed antennas may be suitable for WLAN applications.

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A broadband artificial material based on meander-line (ML) structures is proposed for enhancing the gain of printed end-fire antennas. The ML based material with an effective index of refraction greater than 1 behaves as a dielectric lens in improving the directivity of an end-fire antenna. The electric field intensity distribution can be changed by the material, resulting in a more directional emission. Simulated results indicate extending the length or width of the material can lead to more significant gain enhancement without destroying the impedance bandwidth of the antenna. Three printed end-fire antennas with and without material loading are fabricated and measured. The measurements show that end-fire antennas loaded with two and four rows of ML structures can obtain gain increments of 0.6-3.6 dB and 1.2-5.7 dB, respectively, and that the radiation patterns are narrowed in both E -a ndH-planes over the whole operating band (6-11.5 GHz).

The transmitting aerials for terrestrial digital audio broadcasting (DAB) systems should have a low directivity in the horizontal plane. So, for example, the aerial of the central transmitter of a terrestrial single frequency network usually has a circular radiation pattern. The present report discusses the design features and advantages of using cylindrical strip radiators as elements of aerials in single frequency networks.

The calculation and analysis of the far-field radiation of the antenna on the shared tower and the coupling characteristics of the multi antenna system are the key links to study the electromagnetic compatibility and engineering construction of the shared tower. However, there is no relevant research on this issue. In this paper, the full-scale electromagnetic simulation model of the shared tower is established in FEKO software. Then, based on the multi-layer fast multipole theory and the generalized S-parameter theory, the far-field radiation pattern of the antenna and the expression of the coupling degree of the multiple antennas are given. Based on the above research, the change rules of the far-field radiation pattern and the coupling characteristics of the multiple antennas on the shared tower are calculated respectively. The results show that the radiation pattern and coupling degree of multiple antennas are related to harmonics, antenna spacing, antenna frequency and surrounding scatterers. Based on the calculation results, the suggestion of 1.5m protection spacing is given. The research results of this paper can provide reference for EMC analysis and multi antenna layout optimization of the shared tower.

This paper presents an introduction to a deformable plasma antenna excited by an alternating current power supply at a frequency of 12 kHz. The deformable discharge tube could be transformed into many types of shapes, such as a monopole, U-shape, loop, helix, or plane, by means of a simple mounting and rotating system. The characteristics of the antenna were studied for various discharge parameters and antenna shapes. Experimental results demonstrate that the antenna characteristics, such as impedance, radiation pattern, gain, and polarization, can be simply controlled by varying the discharge parameters and antenna shapes. Compared with a conventional plasma antenna made of hard materials, the reconfiguration scope of the deformable plasma antenna is considerably broader. Moreover, the antenna shape can be modified in a manner that is both flexible and easily implemented.

In this article, a high-permittivity rectangular dielectric resonator antenna is proposed. In this configuration, wideband operation is achieved by loading a rectangular dielectric resonator on the center of the rectangular ring slot. Dielectric resonators of three different thicknesses have been studied. In this configuration, slot acts as an effective radiator and the feeding structure of the dielectric resonator. The dual-band resonances of the two radiators, i.e., slot and dielectric resonator are combined to extend the antenna bandwidth. The measured impedance bandwidth obtained is about 81.7%. The return loss, radiation pattern, and half power beam widths are measured and presented. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1077–1079, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25927

This paper presents an electromagnetic (EM) near-field interpolation for spherical near-field (NF) to farfield (FF) transformations. The two-dimensional (2D) NF interpolation techniques are studied in this work including the 2D linear technique namely the bilinear and low-degree polynomials technique, called bicubic Spline, in order to reduce an effect of NF under-sampling data to FF antenna radiation pattern error. The NF-FF transformation algorithm is implemented by using the spherical wave expansion with trapezoidal rule numerical integration. In the investigation, an under-sampling NF data of the seven-patch array antenna is simulated from the CST Microwave Studio simulation program, where the sampling angles are larger than the maximum sampling angles criteria of the NF spherical sampling theorem. It is found that the FF radiation patterns of AUT from the proposed technique using Spline interpolation and simulated FF radiation pattern are in good agreement. The FF antenna radiation pattern error is reduced. The undersampling NF angles of 25.65 % are studied with FF radiation pattern magnitude error lower than 3 dB. The under-sampling NF data provides less time-consuming of NF data collection. The FF antenna radiation pattern error will be reduced by using appropriate NF interpolation techniques.

A wideband circularly polarized (CP) rectangular dielectric resonator (DR) parasitically coupled to a printed rectangular loops is presented. The DR is housed in a thin dielectric substrate with a microstrip line and narrow strip printed from one side and a ground plane and conducting loops and lines connected to the ground plane. The DR is linearly polarized, and for CP, we introduced printed conducting loops in the other side of the DR, which produce the orthogonal polarization with the required quadratic phase. Several loops are used to achieve the wide CP band. The final design achieves CP with 51% bandwidth. The reflection coefficient, axial ratio (AR), radiation patterns, gain, and efficiency of the antenna are studied, and reasonable agreement between the measured and simulated results is observed.

Dielectric resonators (DR) find application in the design of microwave antennas. The radiation patterns of DR antennas are related to their excited resonant model(s). Dielectric resonators of low dielectric constant are usually employed to give a reasonable impedance bandwidth. We demonstrate that the bandwidth of a center probe-fed cylindrical dielectric ring resonator antenna can be increased by stacking another DR of the same dimensions on the top of the fed DR. The return loss and the radiation patterns of the stacked DR antenna are computed using the finite difference time-domain (FD-TD) method. The numerical results so obtained are compared to experimental measurements. >

A truncation error study in the cylindrical near-field (NF) measurement technique is proposed. The maximum angle span of the far-field (FF) radiation pattern from the bore-sight of the antenna under test (AUT) is studied. The truncated NF scan length will be varied. The cylindrical wave expansion is employed to transform the near-field to far-field (NF-FF), where the two-dimensional (2D) numerical integration is employed to calculate associated double integration in the cylindrical wave expansion. The referenced far-field radiation pattern of AUT is simulated by three-dimensional (3D) electromagnetic (EM) software. It is found that the maximum angle span of the FF radiation pattern is dependent on truncated NF scan length and AUT to probe distance. The simulated radiation patterns and the radiation patterns from numerical NF-FF transformation in the valid angle span are in good agreement. Therefore, the greater the truncated NF scans length, the higher the valid angle span of the FF radiation pattern. The actual valid angle span is a bit wider than the estimated maximum angle span, under the condition of the truncated NF scan length is two times larger than the antenna size.

The measurement of far-field radiation patterns is time consuming and expensive. Therefore, a novel technique that reduces the samples required to measure radiation patterns is proposed where random far-field samples are measured to reconstruct two-dimensional (2D) or three-dimensional (3D) far-field radiation patterns. The proposed technique uses a compressive sensing algorithm to reconstruct radiation patterns. The discrete Fourier transform (DFT) or the discrete cosine transform (DCT) are used as the sparsity transforms. The algorithm was evaluated by using 3 antennas modeled with the High-Frequency Structural Simulator (HFSS) — a half-wave dipole, a Vivaldi, and a pyramidal horn. The root mean square error (RMSE) and the number of measurements required to reconstruct the antenna pattern were used to evaluate the performance of the algorithm. An empirical test case was performed that validates the use of compressive sensing in 2D and 3D radiation pattern reconstruction. Numerical simulations and empirical tests verify that the compressive sensing algorithm can be used to reconstruct radiation patterns, reducing the time and number of measurements required for good antenna pattern measurements.

High gain and omnidirectional coverage are the challenging requirement for launch vehicle antenna design. Generally cylindrical array configuration is considered for omnidirectional coverage. This can give 3600 coverage in the azimuth direction. The Number of elements and their position has to be optimized based on cylinder radius for ripple free radiation pattern in the azimuth plane. This paper presents the optimization of cylindrical array using Particle Swarm Optimization (PSO) technique. Analysis of patch array resonating at 2.26GHz mounted on cylinders of 300mm and 2m diameter for omnidirectional radiation pattern is carried out using in-house developed matlab program and the results are compared with the simulation results of HFSS software.

An eigensolution expansion of dyadic Green's function for cylindrical sector structures is presented. The cylindrical structure is limited in azimuthal direction by electric or magnetic walls. Due to orthogonality of the eigensolution functions between the walls, the derivation of the dyadic Green's function can be done in spectral domain. The Green's dyad is used to set up an electric field integral equation for the microstrip structure. The solution is carried out with the method of moments. Numerical results for input impedance and radiation pattern are shown.

This paper postulates a novel omnidirectional low-profile ultra-wideband (UWB) antenna, which is structured by discrete embedded dielectric resonator antenna with features of both low-profile dielectric resonator (DR) and thin planar monopole antenna, where the laminated equilateral triangular DR and the rectangular metal patch monopole are stacked up. This new design can lower the profile of the antenna. Furthermore, the symmetric DR and the monopole structure are able to make the surface currents in some operating modes opposite in phase, together with the characteristics of the coplanar waveguide (CPW) feed structure and the DR, the cross-polarization is reduced effectively. The mode analysis has been done to show how the antenna achieves the UWB. The CPW which can integrate with integrated circuits easily is used to provide the excitation source. The antenna provides consistent omnidirectivity, consistent gain, low cross-polarization, and high-radiation efficiency within the entire operation band. A prototype (dimensions are 17.6 mm $\times33.6$ mm and 1.524 mm thickness) is fabricated and measured. The measurements are well correlated with the simulations.