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The Lebedev grid is an alternative to Yee grid where, because the discretized fields lie at the same location in space, there is no need for further field interpolations when modeling anisotropic materials. In this letter, we focus on accurately implementing perfect electric conductors with planar interfaces, as well as 90° and 270° corners. Simulations are provided to demonstrate the overall improvements and also the second-order accuracy of the proposed methods.

Noise correlation matrices and noise parameters are useful for low-noise amplifier designers seeking to achieve the best noise performance out of their circuits. In some applications, such as radio astronomy, antennas and antenna arrays are part of receivers and, thus, modeling of the antenna noise is useful. Currently, antenna noise is modeled through antenna efficiency. A more accurate information on the highest-possible antenna efficiency is obtained from its $S$ -parameters or noise parameters. In this letter, we show how the two-port $S$ -parameters of an antenna can be determined by measuring its reflection coefficients inside two specifically sized Wheeler caps, in addition to a free-space measurement. We use the measurement to determine the noise correlation matrices and noise parameters of an antenna. The challenges of constructing appropriately sized Wheeler caps are discussed, and a new way of constructing a Wheeler cap is shown.

A broadside-scanning half-mode substrate integrated waveguide periodic leaky-wave antenna architecture with antipodal tapered slots is presented. The antenna builds upon a previously proposed architecture by introducing a periodic phase-reversal of radiating elements. This enables the antenna to operate with a comparatively low substrate permittivity while maintaining grating-lobe-free scanning from reverse to forward endfire.

The dielectric resonator antenna (DRA) has several advantages over metallic antennas, which may include low loss and compact design. However, few frequency reconfiguration methods exist for the DRA. This letter proposes, designs, and validates a new frequency-reconfigurable DRA that exploits the air gap effect. Here, air-filled channels are inserted between the DRA and the ground plane, and resonant frequency can be lowered by sliding metallized dielectric slugs under the resonator. The proof-of-concept prototype had a measured switching range of 24.7% and operating frequencies of 21.4 and 16.7 GHz.

A detailed study of a half-mode substrate integrated waveguide (SIW)-fed periodic leaky-wave antenna (LWA) with broadside scanning enabled is presented. Design techniques are outlined. Previously presented simulations have been improved with an enhanced structure model that incorporates substrate anisotropy. Additional theory has been applied to the analysis of the antenna to further validate its leaky-wave operation, and extra prototypes have been characterized for comparison to original measurements and simulations. The prototype antenna displayed a 32% impedance bandwidth within which a 10-dB gain over an 86 ° scan range (including broadside) was observed such that its radiation performance appears to be comparable to some of the newly popular SIW-based composite right/left-handed leaky-wave antennas.

A series-fed “herringbone” microstrip traveling wave circularly polarized antenna array is designed to achieve broadside radiation. It is shown that such an antenna can be modeled as a periodic leaky-wave (LW) structure, providing insight into radiation characteristics of interest, such as the directivity and beam angle of the structure, particularly at broadside. Full-wave simulations as well as a prototype of the design verified the approach. The extracted leaky-wave number properly predicts the behavior seen in radiation measurements, and no degradation in antenna gain is seen at or near broadside.

For a digitally controlled reflectarray consisting of many elements, the cost and complexity increase considerably with every additional control line in each element. A ternary design for controlling microelectromechanical systems (MEMS) capacitive switches is proposed to reduce the number of lines required without decreasing the number of states realized. Three distinct capacitance states are realized with custom-fabricated shunt switches having different pull-in voltages. To increase the versatility of the concept, the capability of designing the pull-in voltage and the capacitance of a switch independently of each other is also demonstrated. This design can be applied to any digital tuning circuit involving MEMS switches for the reduction of biasing layout complexity.

Transverse perturbations in the form of periodic slots in the narrow-wall are employed to suppress the slot-mode radiation in a slitted waveguide. The presence of the perturbations alters the fast wave supported in an unperturbed slot to a slow wave. Slitted waveguides with and without perturbations were compared in full-wave simulations and in measurements. It will be shown that significant and consistent reduction of the slot-mode radiation is achieved with the perturbations.

In this letter, the influence of the truncation effects on the beam-splitting property of a broadside symmetric leaky-wave antenna (LWA) is presented. It will be shown that for finite length LWAs, the maximum broadside beam exists at higher phase constant values than suggested by infinite LWA analysis. The accurate beam-splitting conditions are obtained using a computer search algorithm and are reported for a range of practical LWA lengths. The behavior of the aperture distributions at the split conditions is then discussed. To illustrate the application of the result, the theoretical beam-splitting condition plot is used to identify the beam-splitting point of a microstrip based LWA design. Finally, other design implications of the findings are discussed.

The benefit of low loss exhibited in utilizing MEMS variable capacitors in a reconfigurable reflectarray is undermined by the inconsistency of the fabricated devices. A digitally controlled reflectarray with MEMS capacitive switches is proposed. This paper aims to determine an appropriate number of phase shifting bits for such implementation. Using array theory, the influence of the number of bits on the beam pointing performance is evaluated. A common feed horn is used to illuminate the reflectarrays. In addition, broadside plane wave illumination is also considered for comparison with existing works in phased arrays. Though at certain scan angles the results are different from those for traditional phased arrays, in general the results are found to be similar. This information lays the groundwork for designing a cost-effective digital MEMS reflectarray cell.

The effects of measuring a symmetric broadside leaky wave antenna (LWA) at finite distances are examined. In particular, the broadside beam behavior near the beam splitting condition is studied since the directivity error can be significant. The patterns at various distances, including the rule of thumb distance of 2L2 / lambdao, are calculated and compared to the far-field (FF) pattern. In addition, variations in measurement error at the finite distances due to the sign of the leaky wave phase constant are identified.

It was recently demonstrated that a horizontal dipole radiates with a vertical monopole-like radiation pattern when placed near a two-dimensional periodic patch-loaded grounded slab (PLGS). Such a structure has been proposed as a low-profile surface-wave antenna. In this letter, we examine the radiation mechanism of such an antenna. It is indicated in this letter that the vertical monopole-like pattern is generated by the vertical common-mode current flowing on the outside of the coaxial cable feeding the short dipole, and not from the dipole itself. In this manner, the unbalanced horizontal dipole closely resembles a classic T antenna. Furthermore, we examine the propagation characteristics of the surface wave on the PLGS and discuss its contribution to the overall radiation of this antenna. We find that, in the lower frequency range, the PLGS appears insignificant to the antenna radiation. The investigation is carried out by the use of a full wave method-of-moments simulation.

In this letter, we introduce a new parasitic antenna array with a 360deg switchable coverage in the azimuthal plane. Unlike most switched parasitic arrays which are narrowband or at most dual band, this array covers an octave bandwidth. The frequency band of interest in this letter is the UHF band, particularly the 225-450 MHz tactical communication band. The array consists of a driven element surrounded by two layers of parasitic elements. The driven element is a wire frame biconical antenna and the parasitic elements are V-shaped bent wires. The proof-of-concept was simulated using FEKO method of moments (MoM) package and further verified using Ansoft HFSS. Simulation results show that the antenna gain is 6-10 dBi over an octave bandwidth

This letter presents a new code-division multiple-access (CDMA) system architecture that combines space-time block code (STBC) transmission and adaptive sectorization using electronically tunable reflectarrays. The result is a single base station architecture that can use a combination of diversity and spatial division transmission in order to achieve good performance in a wide range of environments. The reflectarray method has the further advantage of implementing both STBC and adaptive sectorization using a single transmit chain and power amplifier. This significantly reduces the cost of deploying a multiple antenna scheme and makes it possible to retrofit combined STBC/adaptive sectorization transmission to existing single antenna base stations already in the field.

We introduce a new technique for performing space-time coding by using a phase shifting antenna feed network to manipulate the transmitted signal at RF frequencies. The advantage of this scheme is that it allows space-time coding to be implemented with only one transmit chain and amplifier. A code-division multiple-access (CDMA) system that can use this method of space-time coding is described. The antenna feed network is presented along with a modified version of the Alamouti code that is suitable for this application. Imperfections in the antenna phase shifting are quantified using an error vector magnitude (EVM) measure. System level CDMA simulations are also used to evaluate the overall performance of this "RF space-time coding" technique. The results indicate a performance improvement equivalent to conventional space-time codes.

Resistive loading has been proposed as a method for improving the bandwidth of planar antennas. The paper assesses the impact of resistive loading on the performance of a microstrip patch antenna. While resistively loaded antennas offer the benefit of large improvements in antenna bandwidth, it is illustrated through the use of theoretical developments, numerical simulations, and experiment, that the efficiency of some of the antennas reported in the literature is unacceptably low.

The standard Yee grid, though simple and robust, is not well suited to modeling anisotropic media. In contrast, the Lebedev grid is well suited, but is computationally more expensive. A methodology is presented to use the classical Yee grid in isotropic regions and take advantage of the Lebedev method as a subgridded region for anisotropic materials only. Two methods to couple the two regions are proposed and described in detail. The proposed methods show low reflection in a scenario where a normally incident plane wave hits a Yee–Lebedev interface. Also, the two techniques are shown to be both accurate and stable.

In the above named letter, a correction is to be noted in the last line of the right column on p. 550. The correction is presented here.