Nafati Aboserwal

A stripline-based composite right/left-handed (CRLH) leaky-wave antenna (LWA) with a tapered aperture is designed for an increased effective aperture size. Experimental results show that the CRLH LWA is able to scan from −33° to 25.5° by sweeping the frequency from 76.75 GHz to 83 GHz, with a half-nower heamwidth (HPRW) of less than 5°.

This article presents an accurate full analytical model to assess the impedance response of a proximity-coupled microstrip patch antenna (PC-MSPA). An improved formulation of the patch resonant frequency is used to calculate the quality factor, resonant resistance, and feeding circuit parameters of the antenna. The proposed model also assesses the PC-MSPA impedance response while considering the fabrication constraints. For the validation of the proposed model, at first, the antennas are simulated for $S$ -, $C$ -, and $X$ -bands. Then, two prototypes are fabricated and measured. The proposed model predicts the antenna resonant frequency and impedance bandwidth with less than 1% error.

The design of an X-band dual-polarization slotted waveguide antenna (SWGA) array for high polarized performance over 200 MHz bandwidth and wide scan in the azimuth plane, ideal for high-power dual-polarized radar system, is presented. The proposed design uses a compact array unit cell where the overall dimensions is reduced to 50% in comparison with that of the dual-polarization slotted waveguide antenna array using the conventional rectangular waveguides. The new design overcomes with fundamental a limitation of zero electronically scanning, due to large element spacing (1.2λ∘), when conventional waveguides are used. Reducing the element spacing to 0.6λ∘ (in the azimuth plane), based on a partial H-plane waveguides, enables a 1D e-scanning range up to 84°(±42°) in the azimuth plane perpendicular to the waveguide axis. An active sub-array panel of 8×8 elements, excited with 8 high-power transmit and receive modules are proposed. This active sub-array can be scaled to obtain a large array without any constrain in size and power. The proposed design uses the broad wall shunt slots for V-polarization antenna and non-inclined edge wall slots for H-polarization antenna. The proposed design offers stable impedance, gain, cross-polarization isolation and excellent co-polar mismatch over the whole frequency band of interest. Having a cross-polarization isolation better than -60 dB and co-polar mismatch below ± 0.12 dB across the scanning range, make this array unit cell (8×8 elements) a perfect candidate for high power e-scanned dualpolarization phased array radar for weather observations.

This paper presents a new design technique to develop a multi-layer radome for ultra-wide-band, dual-polarized radar and communication systems. In the proposed technique, a multi-layer radome is designed using a combination of A-sandwich structures, which are not used in conventional multi-layer radomes. In contrast with conventional radomes, this technique enables a substantial increase of bandwidth with a negligible change in the overall radome thickness. In addition, it provides excellent RF performance, thermal isolation, and mechanical strength. Three different multi-layer radomes for different bandwidths are designed. Parameters such as co-polarization mismatch and depolarization ratio are used to evaluate the proposed dual-polarized radome as a function of incident angle and frequency. To validate this new technique, a 5A-sandwich radome is designed to operate from 1 GHz to 14 GHz and its RF performance is evaluated by measuring S-parameters. The proposed radome is further investigated by measuring the radiation patterns of horn antennas at different bands (S-, C-, X- and Ku-bands) with and without the radomes. The measured losses recorded are below 0.5 dB with an absolute error less than 0.05 dB between the calculations and measurements. An S-band electronically scanned active phased array antenna is also used to evaluate the radome as a function of incident angles. In this case, the maximum recorded losses are below 0.4 dB and the absolute errors between the calculations and measurements are below 0.1 dB. The proposed technique and radome can be used in different applications such as surveillance systems, earth exploration satellite, aeronautical radio-navigation, and especially in dual-polarized weather radars that require a high polarization performance.

This paper presents the design and synthesis of a low-loss substrate with low effective permittivity ( $\varepsilon _{eff}$ ) for microwave and mm-Wave applications. The proposed design is based on the two-phase Maxwell Garnet mixing theory, where the $\varepsilon _{eff}$ of the RF substrate can be synthesized depending on the geometry and the permittivity of mixing particles and the permittivity of the host material. A comprehensive review and error analysis of the most common mixing techniques are conducted to guarantee an accurate design for high-performance RF substrates. Several analyses based on the geometries of various particles are carried out to identify the most accurate mixing model used in the design of the proposed substrate. The effects of the direction of excitation as well as the polarization of the incident field on the $\varepsilon _{eff}$ of the anisotropic particle are analyzed and discussed. The proposed method enables the use of existing high-performance materials that do not necessarily provide a low dielectric constant and low loss tangent. For mm-Wave antenna applications, materials with a dielectric constant of 2–4, and loss tangent of less than 0.002 are desirable to maximize gain and radiation efficiency. Commercial RF substrates can satisfy those requirements, however limited thermal expansion coefficient and lamination difficulties increase the cost significantly. The proposed method enables the use of inexpensive materials that provide excellent thermal properties and great compatibility with a multi-layer fabrication process with desirable $\varepsilon _{eff}$ and loss tangent. For validation of the analysis, samples are fabricated and tested in the microwave frequency (S-band) at 3.5 GHz as well as in the mm-Wave frequency (W-band) at 77 GHz. Measured results show a reduction of 45% in the $\varepsilon _{eff}$ and 38% in the loss tangent values in the S-band, and 32% and 72% reduction in $\varepsilon _{eff}$ and tan $\delta $ , respectively, in the mm-Wave frequency band. The measured results are in excellent agreement with the simulation and calculated results.

This paper presents a new set of analytical equations to calculate the impedance bandwidth of electrically thin and thick proximity-coupled square microstrip patch antenna (PC-MSPA). The proposed mathematical model uses the relationship among different antenna parameters, material, and antenna dimensions to estimate the percentage impedance bandwidth with high accuracy. The proposed model was validated with rigorous full-wave solutions, and experimental antenna prototypes implemented for different thicknesses, patch dimensions, frequencies, and different substrates. The theoretical bandwidth results of S-, C- and X-band PC-MSPA antennas obtained using the new model are in very good agreement with simulations and the experimental results. Errors between the proposed analytical model and both simulation and measurement are less than 3.1%. These equations are mostly valid for permittivities between 2.2 and 6.15, and with feed substrate thickness less than 0.1λr. The PC-MSPA is a candidate element for integration with MIMIC devices and wireless communication applications.

This paper presents an accurate procedure to design, characterize and test a radome for millimeter-wave applications. In this procedure, an accurate analytical model is presented to design a radome structure that takes into consideration the bandwidth, losses, reflections and depolarization factor as a function of frequency and incident angle. To guarantee a good operational electrical performance, the proposed procedure includes a material characterization and accurate test procedure based on the free-space Gaussian beam method and time gating filtering technique. Four radomes (two-monolithic and two A-sandwich) at 82 GHz and 94 GHz are designed, characterized and tested to validate the proposed technique. Results obtained with this procedure are compared with numerical simulations and experimental results. This method is shown to be accurate and versatile for radomes in mm-Wave applications.

This contribution presents the results of a dual-polarized radiating element designed to achieve low cross-polarization (lower than -40 dB measured for the E-and H-plane, at least -30 dB in the D-plane based on simulations) and large fractional bandwidth (18%) over wide scanning angles (±60°). The proposed design includes multiple features that enable high isolation between ports, reduction of spurious radiation, highly symmetrical radiated fields, and suppression of diffracted fields between contiguous subarray gaps. To verify the polarimetric requirements for a weather radar, simulated and measured results, including electronic scanning of the array and embedded element patterns of the antenna, are shown.

With the growing interest in polarization diversity in communications and radar systems, the use of Ludwig's second and third definitions has become controversial among scientists and antenna engineers. Therefore, this paper is an attempt to clarify some of the ambiguity and confusion caused by these definitions. A detailed comparison of Ludwig's second and thirrd definitions of cross polarization, as applied to linearly polarized antennas, was performed. The results show that, in the diagonal plane, Ludwig's second definition leads to a lower crosspolarization level than the third definition for x- or y-polarized current sources. For a Huygens source, by Ludwig's third definition, the radiation pattern has a lower cross-polarization level than that obtained by Ludwig's second definition. For some applications, the antenna is usually placed in the yz plane. Therefore, new polarization bases are proposed according to which the source is used as a reference, and also on how this source is oriented in the yz plane. To complement the theoretical framework demonstrated in this contribution and to provide readers with a better and simpler understanding of the crosspolarization definition, the analysis of several practical antennas for diverse applications was presented. Numerical and measured radiation patterns of wire and printed dipoles, rectangular patch, pyramidal horn, and open-ended rectangular waveguide (OEWG) antennas were investigated according to the polarization formulations presented in this paper. In addition, a dual-polarized element and a dual-polarized active phased array at broadside were utilized to generalize the application.