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This work presents and investigates a novel high-performance antenna design for remote sensing and satellite communications applications that is compact and lightweight. The performance requirements include dual-polarization, wide impedance bandwidth, low cross-polarization, high gain, and high aperture efficiency. To simultaneously achieve all these qualities is challenging and a combination of compatible performance enhancement techniques was selected and derived. A new antenna design, namely an octagonal cavity-backed radiating open prism (OCROP) antenna, was first introduced. The antenna is orthogonally and differentially fed to provide dual-polarization and low cross-polarization. The impedance bandwidth is increased by combining the resonances from the radiating feedlines and the open prism. The corner truncated octagonal ground cavity, instead of a more commonly seen square ground plane or square ground cavity, is used to further suppress the cross-polarization and enhance the gain and aperture efficiency. To show the superiority of the octagonal design, it was compared with a square ground cavity backed antenna. To further improve the gain of this novel antenna, its array and flared configurations are considered, investigated, and compared. The array design offers higher gain and aperture efficiency, while the flared design can provide lower cross-polarization. To achieve higher gain with the flared design, a larger flare angle was chosen which increased cross-polarization. To remedy the problem of the increased cross-polarization, a new iris design concept is proposed and investigated. It shows that this method can successfully suppress the cross-polarization of the flared design. This concept is general and has the potential to be applied to other types of aperture antennas. The design concepts and the simulation results are verified by fabricating and testing two prototypes, i.e., with and without a flare.

This work reports experimental investigation and numerical validation of millimeter-sized Spherical Bragg Resonators (SBRs) fabricated using 3D printing technology. The frequency dependencies of the reflection and transmission coefficients were analyzed, and eigenfrequency values were calculated to examine the density of photonic states in air/PLA-polylactide SBRs, showing the appearance of an eigenmode and an increase in the local density of states in the core of a defect cavity. A decay rate enhancement of ∼10² was obtained for a dipole placed in the core of the defect SBR. The study also investigated the influence of the source position on the resonator's electromagnetic wave energy. Scattering efficiencies up to order twelve of the multipole electric and magnetic contribution in a 10-layer SBR were calculated to validate the presence of the resonant modes observed in the scattering measurements performed for parallel and perpendicular polarizations. The results demonstrate that SBRs can act as omnidirectional cavities to enhance or inhibit spontaneous emission processes by modifying the density of electromagnetic states compared to free space. This finding highlights the potential of SBRs engineering spontaneous electromagnetic emission processes in various applications, including dielectric nanoantennas, optoelectronics devices, and quantum information across the entire electromagnetic spectrum.

RÉSUMÉ: The design and implementation of a dual wide-band mushroom-shaped antenna are presented in this paper. The antenna consists of a cylindrical dielectric resonator (cDRA), a cylindrical dielectric rod as a waveguide (cDR), and a dielectric lens (DL). The cDRA in conjunction with the DL acts as a sub-6-GHz antenna. At the mm-wave band, the small cDR acts as a waveguide, which transfers the wave from the feed toward the larger cDRA and the DL in order to produce a high gain. A dual wide-band antenna is designed and fabricated with different dielectric constants for the cDRA/cDR and the DL. 3D printing is utilized to precisely control the dielectric constant of printed component. Measurement results show a maximum gain of 6.4 dB at 5.3 GHz with a 21% 3-dB gain bandwidth and 12.7 dB at 31.5 GHz with a 26.2% 3-dB gain bandwidth. The sub-6-GHz band exhibits a measured 10-dB return loss bandwidth of 21% (centered at 5.15 GHz), and the mm-wave frequency band demonstrates a measured 10-dB return loss bandwidth of 26.2% (centered at 30.5 GHz).

RÉSUMÉ: This chapter discusses recent development of reconfigurable filters. The technical terminology reconfigurable means that a circuit is designed in a way to have various electrical characteristics comparing with one which has a static feature. For the filter design, the various electrical characteristics can be considered as the filter can tune its operating frequency, bandwidth, and/or have multiple operational modes, that is, bandstop or bandpass modes. Also, recently, the filters that can exhibit an improved impedance matching performance over its stopband have been reported. It provides more options for the filter designers to realize the reconfigurable filters having reflective and/or absorptive frequency response types to satisfy a prior given requirement. In this chapter, recently devised filter designs will be covered and essential frequency tuning elements to realize the reconfigurable characteristic will be introduced as well.

This paper proposes a varactor-based circuit technique intended for amplitude and phase control, with improved linearity in the presence of parasitic capacitances and parasitic inductances. The mechanism causing linearity degradation in an anti-series varactor network that includes significant parasitic elements - a key aspect that, to our knowledge, has never been reported - is first studied using an analytical approach based on multi-tone excitation. It is demonstrated that simply optimizing the ratio of diode sizes is insufficient to circumvent this linearity degradation. The underlying linearity degradation concept serves as the basis for the introduction of a modified anti-series controllable capacitance, followed by a design and practical implementation. Experimental validations with multi-tone and modulated signals demonstrate improved linearity performances with respect to the state-of-the-art when parasitic capacitances and inductances are significant. Moreover, it is shown that the complete varactor-based circuit topology proposed here, which uses the proposed modified anti-series controllable capacitance in conjunction with a second-harmonic trap filter, constitutes a very attractive alternative to the state-of-the-art anti-series/anti-parallel topology, since it reduces the required number of diodes by a factor of 2. Measurements on discrete-component designs operating at 3.6GHz, hence with significant parasitic effects, demonstrate that the proposed circuit topology improves the 3 rd order intermodulation distortion levels by 10.6dB and 6.6dB at output powers of 10dBm and 18dBm respectively, in comparison with the state-of-the-art topology. Measurements with a 16QAM modulated signal also show 3.9dB improvement in ACPR at 18dBm. These performances constitute improved state-of-the-art results in anti-series hyper-abrupt varactor-based electronic control.

The formulations for three-dimensional (3D) scattering from uniaxial objects with a smooth boundary using a multiple infinitesimal dipole method (MIDM) are introduced. The proposed technique uses two sets of infinitesimal dipole triplets (IDTs), including three co-located orthogonally polarized electric infinitesimal dipoles, distributed inside and outside of a scatterer to construct simulated fields. The dyadic Green's functions of uniaxial materials are deployed in the MIDM so as to obtain the simulated fields. The singularity issues in using the uniaxial dyadic Green's functions, which cannot be solved analytically so far for a general uniaxial medium, can be easily eliminated by using the proposed MIDM. In comparison to the traditional single-layered distribution scheme of IDTs, the proposed multiple-layered distribution scheme can handle the scattering from uniaxial objects accurately and efficiently. Several numerical examples are presented to study bistatic radar cross section (RCS) responses under different scenarios. Excellent agreement is achieved by comparing numerical results with those obtained from commercial software packages, while the simulation performance including CPU time and required memory is drastically improved by using the MIDM when computing a general uniaxial material or a relatively larger object. The proposed technique has its merits on simplicity, conciseness and fast computation in comparison to existing numerical methods.