A novel design of an electrically small, dual-band quasi-isotropic antenna with a microstrip balun is presented. A quasi-isotropic radiation pattern is realized from the total current flow over the proposed structure at two different frequency bands. The electrical size ka of the antenna is 0.49 with an extremely thin profile of 0.0014g. The antenna measurements reveal good uniformity of the radiation pattern with a maximum gain deviation of 5.83 dB at 942 MHz and 8.24 dB at 1.71 GHz with 57% and 95% radiation efficiency, respectively. The radiation performance of the antenna is also verified through wireless power receiving experiments in an office non-line-of-sight environment.

We propose a novel double-layered insulator configuration for a human-brain-implanted impulse radio ultra-wideband (IR-UWB) antenna. The dimension of the antenna is $10.0\times 11.0\times0.954$ mm ³ , including the dual-layer insulator. The insulator provides a dielectric loading effect of $\varepsilon _{r}~\approx ~50$ (lossless) for obtaining an improved radiating power and the broadband-impedance-matching characteristic in brain tissues. The outer layer is made of biocompatible 3-D printing material, and the inner insulator is filled with deionized water with $\varepsilon _{r}~\approx ~80$ and loss tangent (tan $\delta$ ) $\approx ~0.25$ at 4 GHz. A slotted UWB antenna with the proposed insulator is located between the emulated dura and CSF tissues inside the skull for brain signal detection. The design uses a multilayer phantom, mimicking the seven tissue layers of the brain. The impedance and radiation performance of the proposed antenna configuration are also discussed using the commercial high-precision human phantom model. The designed IR-UWB antenna shows a boresight radiation characteristic toward the top of the head with a proper high gain in the target frequency of 3–5 GHz. The computed expectations are verified experimentally. Furthermore, it is demonstrated that the UWB spectrum generated from a UWB radio-frequency (RF) transmitter can be transmitted stably using the proposed antenna as a transmitting antenna. In addition, the link budget of the system setup is analyzed. The improved gain characteristic of the antenna from the proposed dual-layer insulator can be utilized to retain the link margins while satisfying the UWB communication regulation and average specific absorption rate (SAR) limitation.

A wideband monoconical antenna with a null-filled radiation pattern for airborne applications is presented. A rotating current distribution, which radiates an electric field at the null point ( θ = φ = 0°) of an omnidirectional radiation pattern of a conventional monoconical antenna, is formed using the proposed slotted structure in a monoconical radiator. In the proposed design, the null point is effectively filled over the 1:12 impedance-matched frequencies, while the size of the reference monoconical antenna is maintained. A figure of merit composed of the electric field intensity in the main radiation area (0° ≤ θ ≤ 45° and 0° ≤ φ ≤ 360°) and the profile of the antenna shows that the proposed antenna performs better than a conventional monoconical antenna or a fan-dipole antenna used in airborne applications. The impedance and radiation performances of the proposed antenna are verified experimentally from a 5.85:1 scaled built prototype.

This paper presents a ferrite core-loaded, low-profile antenna for very high frequency (VHF) communication. The proposed antenna takes the form of a magnetic dipole source on a conducting ground for vertical polarization on the integrated mast of a battleship. In practice, a bowtie-loop is grounded, and a ferrite core is internally loaded to decrease operating frequencies. Ferrite core is used for antenna miniaturization, as it stores magnetic energy inside the resonant core of the antenna. The size of the proposed antenna with a housing assembled for stable loading at the mast is 0.12 × 0.053 × 0.0076 [ λ ³ ] with respect to the lowest matched frequency of 36.8 MHz, with a criterion VSWR of less than 3. The measured realized gain at 30 MHz is –16.9 dBi, demonstrating the upward trend across the VHF band and the sufficiently high value given the size of the antenna. The proposed antenna achieves the highest realized gain at the lowest operating frequency among the previously reported ferrite core-loaded VHF antennas.

A new actuation technique is introduced for overcoming the complexity and radiation performance degradation issues of actuators-based reconfigurable antennas. We employ shape memory alloy (SMAlloy) spring actuators to control the positioning of the fluidic channels, in contrast to the manual filling/loading and evacuating/offloading of dielectric fluids employed in conventional fluidically reconfigurable antennas. To demonstrate this new actuation method, a simple low-cost frequency reconfigurable microstrip patch antenna is fabricated, and two SMAlloy spring actuators are incorporated along the microfluidic channels in the axes of the radiating slots. Electrical control of the pitch of the two SMAlloy springs enables mechanical movement/transformation of the microfluidic channels in two directions along the axes of the radiating slots to attain the required frequency-switching characteristics of the antenna. It should be noted that in contrast to the traditional switching techniques where switches are positioned over the radiating aperture, the proposed method does not deteriorate the performance of the antenna because SMAlloy springs are underneath the radiating patch.

An electromagnetic (EM) absorber-embedded Ka-band double-layer tapered slot antenna (DLTSA) is proposed in this work. The EM absorber is placed on both sides of the tapered radiating slots as a means of achieving the reduced monostatic radar cross section (RCS) at the X-band. A conventional tapered slot antenna (TSA) with EM absorbers at the same position suffers from the distorted current distribution from the feedline to the radiating slots and causes a degraded radiation performance with a tilted beam. In contrast, the DLTSA with EM absorbers maintains the impedance and radiation characteristics of the antenna without the EM absorbers, while achieving the reduced monostatic RCS for the cross-polarized incident wave. The functionality of the reduced RCS is verified with the 4-by-4 DLTSA array design. The 4-by-4 array prototype with FGM-125 EM absorbers is matched at the Ka-band with a 14.7 dBi boresight gain at 35 GHz. The monostatic RCS is measured in an indoor environment, showing 6.5 dB monostatic RCS reduction at the X-band on average, verifying the computed expectations. This work validates the possible use of EM absorbers at the front side of a missile seeker composed of end-fire radiating elements.