Antennas operating at the high-frequency (HF) band (3-30 MHz) are frequently electrically small due to the large wavelength of electromagnetic waves (10-100 m). However, the bandwidth-efficiency products of passively matched electrically small antennas (ESAs) are fundamentally limited. Wideband HF waveforms using bandwidths of 24 kHz or more have recently received significant attention in military communications applications. Efficiently radiating such signals from conventional passive ESAs is very challenging due to fundamental physical limits on bandwidth-efficiency products of ESAs. However, active antennas are not subject to the same constraints. In this work, we present the design and experimental characterization of a high-power, active ESA with enhanced bandwidth-efficiency product compared to {that of} passively matched ESAs. Specifically, the proposed active ESA can radiate wideband HF signals with banwidths of 24 kHz or more, with total efficiencies up to 80$\%$, and radiated power levels approaching 100 W. Our approach uses a highly-efficient, integrated class-E switching circuit specifically designed to drive an electrically small, high-Q HF antenna over a bandwidth exceeding 24 kHz. Using a high-Q RLC antenna model, we have successfully demonstrated wideband binary ASK, PSK, and FSK modulations with the proposed class-E switching architecture. Experimental results indicate that the bandwidth-efficiency product of this class-E active antenna is 5.4-9.8 dB higher than that of an equivalent passive design with the same data rate, and bit-error-rate (BER).
Conventional mechanical antennas provide a strategy in long-wave communication with a surprisingly compact size below 1/1,000 of the wavelength. However, the narrow bandwidth and weak field intensity seriously hamper its practical applications. Here, we present a mechanical antenna based on the electrostrictive effect of PMN-PT-based relaxor ferroelectric ceramic to improve radiation capacity and achieve ultra-wideband characteristics (10 kHz - 1 MHz, the relative bandwidth is beyond 196%). Determined by the different underlying mechanism, the mechanical antenna based on the electrostrictive e…
This paper presents a self-contained factorization for the Vandermonde matrices associated with true-time delay based wideband analog multi-beam beamforming using antenna arrays. The proposed factorization contains sparse and orthogonal matrices. Novel self-recursive radix-2 algorithms for Vandermonde matrices associated with true time delay based delay-sum filterbanks are presented to reduce the circuit complexity of multi-beam analog beamforming systems. The proposed algorithms for Vandermonde matrices by a vector attain $\mathcal{O}(N \log N)$ delay-amplifier circuit counts. Error bounds fo…
This letter presents the design, manufacturing and operational performance of a graphene-flakes based screenprinted wideband elliptical dipole antenna operating from 2 GHz up to 5 GHz for low cost wireless communications applications. To investigate radio frequency (RF) conductivity of the printed graphene, a coplanar waveguide (CPW) test structure was designed, fabricated and tested in the frequency range from 1 GHz to 20 GHz. Antenna and CPW were screen-printed on Kapton substrates using a graphene paste formulated with a graphene to binder ratio of 1:2. A combination of thermal treatment an…
This paper proposes a functionally reconfigurable integrated structure of a Fabry-Perot (FP) antenna and wideband liquid absorber. The partial reflecting surface (PRS) is elaborately tailored to serve as both a component of the FP antenna and the metal ground of the broadband liquid absorber. Then the integrated structure is realized by combining the FP antenna with the liquid absorber. The PRS is composed of patches on the top layer of the substrate and the square loop on the bottom and the microstrip patch antenna is used as a source. The liquid absorber is composed of a 3-D printed containe…
An eight element, compact Ultra Wideband-Multiple Input Multiple Output (UWB-MIMO) antenna capable of providing high data rates for future Fifth Generation (5G) terminal equipments along with the provision of necessary bandwidth for Third Generation (3G) and Fourth Generation (4G) communications that accomplishes band rejection from 4.85 to 6.35 GHz by deploying a Inductor Capacitor (LC) stub on the ground plane is presented. The incorporated stub also provides flexibility to reject any selected band as well as bandwidth control. The orthogonal placement of the printed monopoles permits polari…
In this work, a planar phased array antenna was engineered with ultra-wideband (UWB) performance that covers portions of the L-, S-, and C-bands. The unit cell design contains a driven layer that is directly connected to a single coaxial feed and a parasitic layer located above the driven layer separated by free space. This design does not require a balun or any vias between the antenna ground plane and the driven layer, resulting in a simple antenna stack-up consisting of only planar layers, aside from the feed structure. As a consequence, the complexity, and potentially sensitivity to mechan…
We propose a general method for designing wideband matching tapers in inhomogeneous media where phase velocity is coupled to the taper impedance profile. Such tapers are used to match wideband gradient index (GRIN) lens antennas. To simplify fabrication tapers are often constrained to physically uniform layers wherein commensurate line theory cannot predict the frequency response. Therefore, we present a new design algorithm which derives an effective permittivity $ε_{eff}$ to equalize the electrical length of commensurate and non-commensurate line tapers. The algorithm provides a systematic d…
Sinuous antennas are capable of producing ultra-wideband radiation with polarization diversity. Such a capability makes the sinuous antenna an attractive candidate for wideband polarimetric radar applications. Additionally, the ability of the sinuous antenna to be implemented as a planar structure makes it a good fit for close in sensing applications such as ground penetrating radar. However, recent literature has shown the sinuous antenna to suffer from resonances which degrade performance. Such resonances produce late time ringing which is particularly troubling for pulsed close in sensing a…
Two novel decoupling and matching networks (DMNs) in microstrip technology for three-element uniform circular arrays (UCAs) are investigated and compared to a more conventional DMN approach with simple neutralization lines. The array elements are coaxially-fed quarter-wavelength monopole antennas over a finite groundplane. Three-element arrays are considered since UCAs with an odd number of elements are able to provide an almost constant maximum array factor over the whole azimuthal angular range. The new designs are explained from a theoretical point of view and their implementations are comp…
We present an automated design procedure for the rapid realization of wideband millimeter-wave lens antennas. The design method is based upon the creation of a library of matched unit-cells which comprise wideband impedance matching sections on either side of a phase-delaying core section. The phase accumulation and impedance match of each unit-cell is characterized over frequency and incident angle. The lens is divided into rings, each of which is assigned an optimal unit-cell based on incident angle and required local phase correction given that the lens must collimate the incident wavefront…
A conceptual method to realize an impedance-matched electrically small antenna is discussed, using a transmission line modulated only in time. The time-periodic space-uniform modulation of a distributed shunt array of varcapacitors excites a mode with very small frequency but still a small (microwave) wavelength: the matching line then retains a practical size. The modulated transmission line brings the problem of impedance matching to a frequency $f_0$ much higher than the signal, where the large antenna reactance can be easily compensated with a much higher bandwidth for the same $Q$ factor:…
The unique gate-voltage dependent optical properties of graphene make it a promising electrically-tunable plasmonic material. In this work, we proposed in-situ control of the polarization of nanoantennas by combining plasmonic structures with an electrostatically tunable graphene monolayer. The tunable polarizer is designed based on an asymmetric cross nanoantenna comprising two orthogonal metallic dipoles sharing the same feed gap. Graphene monolayer is deposited on a Si/SiO2 substrate, and inserted beneath the nanoantenna. Our modelling demonstrates that as the chemical potential is incremen…
Achieving an electrically tunable phased array optical antenna surface has been a principal challenge in the field of metasurfaces. In this letter, we demonstrate a device platform for achieving reconfigurable control over the resonant wavelength of a subwavelength optical antenna through free-carrier injection. We engineer and grow, using molecular beam epitaxy, a heterostructure of In1-xAlxAs/InAs/AlyGa1-ySb layers designed to achieve large amplitude and phase modulation of light by maximizing the refractive index change in regions of resonant field enhancement The p-i-n layers are grown on …
Impedance matching is one of the most important practice in wave engineering as it enables to maximize the power transfer from the signal source to the load in the wave system. Unfortunately, it is bounded by the Bode-Fano criterion that states, for any passive, linear and time-invariant matching network, a stringent tradeoff between the matching-bandwidth and efficiency; implying severe constraints on various electromagnetic and acoustic wave systems. Here, we propose a matching paradigm that overcome this issue by using a temporal switching of the parameters of a metamaterial-based transmiss…
Small form-factor, narrowband, and highly directive antennas are of critical importance in a variety of applications spanning wireless communications, remote sensing, Raman spectroscopy, and single photon emission enhancement. Surprisingly, we show that the classical directivity limit can be appreciably surpassed for electrically small multilayer spherical antennas excited by a point electric dipole even if limiting ourselves to purely dielectric materials. Experimentally feasible designs of superdirective antennas are established by using a stochastic optimization algorithm combined with a ri…
Electrically small dielectric antennas are of great interest for modern technologies, since they can significantly reduce the physical size of electronic devices for processing and transmitting information. We investigate the influence of the resonance conditions of an electrically small dielectric spherical antenna with a high refractive index on its directivity and analyze the dependence of these resonances on the effectively excited modes of the dielectric sphere.
