Conformal antennas are practicable candidates to the aerodynamic platforms. A wide-angle scanning conformal phased array antenna for an unmanned aerial vehicle (UAV) platform is designed and presented in this article. An eight-element linear phased array loaded with frequency selective surface (FSS) operating in S-band is investigated. The horizontally polarized antenna element is designed based on a tapered slot feeding dipole. The antenna aperture can be easily conformed to the front wing airframe of the UAV due to the flexibility of the employed polyimide film. To fulfill the requirement of the airborne communication system, two kinds of FSSs are loaded on the dipole antenna to enhance the gain and reduce the 3 dB beamwidth of the main lobe in the elevation plane. To improve the active impedance matching when the beam scans to the large angles, a novel parasitic structure is proposed. Finally, a 1 ×8 linear conformal array prototype is simulated, fabricated, and measured. The experimental results indicate that the antenna array achieves a fractional bandwidth of 22.1% with ±70° scanning along the E-plane. The measured results validate the performance of the proposed conformal array and the design.

Polyimide film is a practicable alternative to the conventional substrates utilized in conformal antennas. Due to its flexibility, the antennas based on polyimide film can be easily conformed to the platform surface. An 8-element linear phased array operating at P band with wide scan angle is investigated in this letter, which is constructed by the dipoles printed on polyimide film. The antenna surface is mounted on the front wing of an unmanned aerial vehicle (UAV). Strong coupling is observed between array elements when the beam scans. Therefore, decoupling structures are loaded in the array elements to broaden the scan angle. To satisfy the requirement of the radar system, directors and reflectors are also employed on the surface of the front wing to narrow main lobe beamwidth in the elevation plane. The proposed phased array achieves a fractional bandwidth of 16.7% when scanning up to 60 in the E-plane. The validity of this design is verified by simulation and measurements of a 18 array prototype.

Indium tin oxide (ITO) material is a practicable alternative to metal utilized in transparent antennas. However, the conductor loss of ITO material is the major obstacle to antenna design. In this work, an optically transparent reflectarray based on glass substrate with ITO film operating at 28 GHz is presented. A novel sub-wavelength element operating in hybrid modes with 0.167λ0 (λ0 is the free-space wavelength at 28GHz) spacing is proposed for transparent reflectarray design. The peak loss of the proposed element is below 3.4 dB and a phase variation of 420° is achieved at 28 GHz. A 54×54-element reflectarray with a focus to diameter ratio (F/D) of 0.7 is designed and simulated for demonstration. It achieves radiation efficiency higher than 73% at the center operating frequency. The proposed reflectarray is verified by the measurements, which is reasonably consistent with the full-wave simulated results.

In this paper, we present a rigorous numerical approach for the electromagnetic (EM) analyses of a hypersonic object with plasma sheath. First, the effective EM parameters of the plasma flow are constructed by solving the Navier-Stokes fluid dynamics equation combined with proper thermochemical models. Then, the EM characteristics of the hypersonic complex are examined by the method of moments based on the volume-surface integral equations. Both the fluid field properties and the associated EM effects are analyzed for a real sphere-cone object that flies at a hypervelocity of 7650 m/s and at an altitude of 61 or 71 km. The impacts of the plasma sheath on the propagation, scattering, and radiation properties are discussed. The plasma sheath may block the transmission and radiation of radio waves for a wide range of frequencies, as the attenuation may exceed 20 dB. Also, the plasma sheath may influence the backscattering radar cross section to an extent of 20 dB. As the frequency increases, the effects tend to weaken and eventually may be ignored beyond 50 GHz. The simulation results are found in good agreement with available experimental data, which indicates that the proposed approach is reliable for predicting the level of radio blackout.

Entire-structure-oriented work-energy theorem (WET) framework is used to establish the characteristic mode theory (CMT) for material scatterers. Diagonalizing driving power operator (DPO) method is proposed to calculate characteristic modes (CMs). Solution domain compression (SDC) scheme is introduced to suppress spurious modes. An electromagnetic energy characteristic equation similar to the energy eigen-equation in quantum mechanics is derived for unifying the modal analysis theories of classical electrodynamics and quantum mechanics. Using the concept of driving power in the WET framework, the physical meaning of characteristic values is revealed; the reason leading to the nonorthogonal characteristic far fields of lossy scatterers is provided; it is explained why the conventional CMT fails to analyze some classical transmitting antennas; the physical interpretation for normalizing modal real power to 1 is given; the Parseval’s identity in CMT is derived; the classical concept of quality factor ( $Q$ -factor) is generalized to a novel concept of field-current phase-mismatching factor ( $\Theta $ -factor). Using the diagonalizing DPO method with the SDC scheme, the spurious modes outputted from the conventional diagonalizing impedance matrix operator method are suppressed. Both the novel SDC and conventional dependent variable elimination schemes confirm the same conclusion that the spurious modes originate from overlooking the dependence relationships among the currents in CM-generating operator.

Aeromagnetic compensation, elimination of magnetic interferences produced by the aircraft platform, plays a vital role in aeromagnetic applications. Conventional compensation methods are based on the Tolles–Lawson (T–L) model, which accounts for only the manoeuvring interferences. However, magnetic interferences due to other factors, such as currents from electrical systems and movable parts, are found significant in practice. In this study, the authors take these interference factors into consideration, including the strobe light and beacon light, the rudder and elevator. The magnetic interference from constant current is equivalent to the ‘permanent magnetisation’ and has been contained in the T–L model. The interferences due to the strobe and beacon lights are modelled to be proportional to the currents and their temporal variations. The model coefficients can be estimated in advance in a ground experiment. The interferences by the pivoting rudder and elevator are still characterised by the T–L model but in the local rudder or elevator coordinate systems, and the compensated coefficients can be obtained on the ground or in the sky. Onsite experiments both on the ground and in the sky are conducted to illustrate the proposed modelling, and improved compensation results are obtained.