Prabhat Khanal

This paper presents a rigorous new analytical derivation of the theorem on the embedded element radiation function of ideally infinite planar array antennas, along with a formula for accurately calculating the main beam direction of finite-sized array antennas based on the theorem. It validates the previously established formula of the embedded element radiation function, where the amplitude is proportional to √cosθ, based on the intuitive reasoning that the effective area of an element should be proportional to its projected area in the direction of interest angle θ, provided that the array antenna has no grating lobes for the full scan, no surface waves, no losses, and active impedance matched. More importantly, the new analytical derivation can accurately predict the embedded element radiation function in cases where there are grating lobes for the array antenna with the full scan, which the intuitive area projection reasoning cannot provide. The theorem concludes that the array’s active element reflection coefficient and inter-element spacing fully determine the embedded element radiation function in all cases. Utilizing this theorem, a new formula for the element phase progression is derived to accurately steer the main beam in the desired direction of the array with a finite number of elements. Several verification cases of wide-scanning array antennas are presented, and the comparisons between numerical simulations, measurements, theoretical results, and some interesting conclusions are discussed in the paper.

A low-profile, wide-scanning phased-array antenna of vertical bowtie elements fully integrated with a structurally efficient radome and ribs of an aircraft fuselage is proposed in this paper. The array is designed to simultaneously fulfil the electrical requirements of an airborne antenna sensor and the mechanical requirements of a load-carrying aircraft fuselage. The array antenna is capable of steering the beam up to ±80° in the azimuth plane over a 20% bandwidth (2.4 GHz to 3 GHz) with the active reflection coefficient (Γ _act ) below –10 dB in an infinite array environment. Experimental results of a 16×16 element array demonstrator agree well with the simulation results. The 16×16 array antenna is capable of steering the beam up to ±60° and ±75° with the bandwidth of 20% and 10%, respectively at Γ _act ≤ –10 dB. The array antenna also achieved good stiffness and performed well in the vibration loads of commercial transport aircraft.

A low-profile and wide-scan phased-array antenna of connected cross-bowtie elements is proposed. The design goals and considerations are based on the applications requiring the integration of a large array antenna with composite sandwich structures, such as antennas on aircraft. In a very large array environment (modelled approximately as an infinite array), the main beam of the proposed antenna can be steered up to ±75° at azimuth and ±15° at elevation over bandwidths of 10% and 25% with active reflection coefficients below −10 dB and −5 dB, respectively. A Monte Carlo analysis of critical manufacturing and alignment tolerances shows the desired performance is achieved with the cumulative distribution probability over 80% under the uniformly distributed random combinations of the tolerances. Experimental results of a $7\times 7$ element array prototype agree well with the simulations of this small-scale array case. The experiments show that this small-scale prototype is capable of steering the beam within the range of [−60°, 60°] at azimuth and [−15°, 15°] at elevation with the predicted performance satisfying the targeted application requirements and mechanical constraints. The achieved combination of the wide beam steering performance, relatively low antenna profile, and suitability of its feeding structure for sandwiched electro-mechanical integration makes this design unique with respect to the previously published results.

This letter presents a new concept of broadband transponder based on frequency-reconfigurable cluster antenna and phase-variable modulators. The transponder in this concept has multiport antenna, whose elements have strong mutual coupling between them. The technique presented in this concept takes advantage of the coupling between the antenna elements instead of avoiding it. By properly weighting the phases of the modulated signals in each port, the backscattered received power can be maximized. The weighting is done differently for different sets of frequencies to achieve instantaneous bandwidth over the frequency band of interest.