Jaegeun Ha

Numerical and experimental electro-thermal characterization of log-periodic antennas

Thermal domain characterization of a printed log-periodic (LP) antenna is presented. Novel wide-boom geometry is proposed to reduce coupling loss to dipole elements without compromising turn-on frequency. Electro-thermal multiphysics simulation shows that wide-boom improves thermal performance alongside impedance match and gain. Temperature map of the antenna is also measured and experiments verify the multiphysics analysis.

Ultrawideband TEM Horn Circular Array

An eight-element circular array of miniaturized combined transverse electromagnetic horn and loop elements for joint frequency and time operation is presented. The use of such ultrawideband and compact directional element leads to stable wideband radiation patterns with moderate gain for omnidirectional phase mode 0 of operation. Moreover, a directional mode enabled by simply exciting specific element(s) in the array is also demonstrated. Obtained directional beams can be steered to a desired direction in horizontal plane simply by exciting an appropriate element. Low dispersion of the utilized element permits distortionless pulse radiation for both modes of operation. The performance of the proposed array is characterized computationally and experimentally in frequency and time domains for both modes. The fabricated circular array has VSWR < 2, good omnidirectional (wobble on the wave <5 dB) and directional (front to back ratio >10 dB) radiation characteristics, nominal gain >6 dBi, cross polarization level <−15 dB, and excellent time-domain performance with high-fidelity factor over more than two octaves.

Omnidirectional/directional TEM horn circular array for joint time and frequency operation

A wideband TEM horn circular array with directional and omnidirectional patterns for joint time and frequency operation is presented. The omnidirectional mode of operation is obtained by exciting the circular array phase mode 0 whereas the directional mode at a specific direction is achieved by exciting a specific element(s) in the array. A miniaturized combined TEM horn and loop antenna is used as a unit cell leading to 8:1 operating bandwidth with good time and frequency domain performances.

Wide bandwidth and beamwidth flush-mountable planar and pyramidal log-periodic antennas

The design of planar and pyramidal wide bandwidth and beamwidth flush-mountable log-periodic (LP) antennas is discussed in this paper. Planar LP antenna is backed by a cylindrical cavity having a conical inset utilized to widen its beamwidth. Pyramidal LP antenna is designed first to achieve unidirectional, wide beamwidth performance in free space; then the antenna is integrated with a shaped conical cavity to enable a platform specific integration. Lossy absorber is added at strategic locations such that interaction between antennas and cavity is reduced and loss kept at acceptable levels. Both antennas achieve good impedance match and wide beamwidth over a decade bandwidth (4–40 GHz) and can be used for many emerging applications.

Electrothermal Design of Bidirectional Wide-Boom Log-Periodic Antennas

A wide-boom, microstrip-fed planar bidirectional log-periodic (LP) antenna is proposed and improvements in its impedance match, radiation, and thermal performances are demonstrated. The boom width of each arm is increased by moving its virtual apexes into the other arm while preserving the small flare angle and self-complementarity. This modification widens the ground plane for the microstrip feed line and results in enhanced impedance match and gain. In addition, electrothermal multi physics analysis demonstrates that the wide-boom mitigates hot spots logarithmically developed on LP’s active regions. The impedance and far-field measurements show that the fabricated antenna achieves VSWR ≤ 2 and flat gain around 5 dBi over a decade bandwidth. A non contact thermal imaging system is used to measure temperature response of the antenna under a ~5 W input power over 1.71–1.85 GHz range. The measured temperature images correlate well with the multi physics simulations, therefore validating the conclusions obtained via electrothermal analysis.

Monostatic Co-Polarized Full-Duplex Antenna With Left- or Right-Hand Circular Polarization

A monostatic dual-polarized simultaneous transmit and receive (STAR) antenna system with high isolation is introduced. A beamforming network (BFN) producing 0°, ±90°, ±180°, and ±270° phase progression is used to feed TX and RX ports of four dual-polarized antenna elements arranged in a sequential rotation array (SRA). Due to the phase progression and geometrical symmetry of SRA, the coupling from TX to RX ports is canceled at the RX port of the BFN; therefore, infinite system isolation is theoretically obtained. Full-wave simulations are used to verify the theory and study effects of element spacing and BFN imbalances. An additional cancelation layer is designed and used to compensate for the imbalances by the BFN and nearby scatterers. The proposed STAR antenna system is prototyped and tested in the 2.4–2.5 GHz industrial, scientific, and medical band where the measured isolation and return loss are above 47 and 22 dB, respectively. A dual circularly polarized antenna performance with realized gains above 7 dBic, broadside axial ratio <1.6 dB, and symmetric beams is demonstrated. An ability of the proposed monostatic STAR antenna system to achieve wideband operation is also demonstrated with a quad-ridge horn as an element.

Wideband, loaded, low profile, small diameter monocone antenna

Compact monocone antennas loaded with helical resonators are presented. The proposed loading introduces an anti-resonance nearby the original resonance of the cone reducing the turn-on frequency by ~22%. Moreover, the antenna maintains a decade bandwidth with good impedance match and consistent patterns. By terminating the helical posts with 50Ω loads, an impedance match is maintained to very low frequencies while the high frequency gain remains intact.

High efficiency cavity-backed log-periodic antenna

High efficiency uni-directional log-periodic antenna with low-profile cavity-backing is presented. The proposed concept offers a novel approach for transforming a broadband bi-directional aperture to a uni-directional antenna. To eliminate lossy materials inside the cavity, a parasitic cross bow-tie slot with controlled coupling and dissipation is introduced at the bottom of the cavity. The numerical and experimental results show VSWR <; 3:1, gain > 1.5dBi and average efficiency of 82% from 0.55GHz to 6GHz.

Simple and low-cost wideband omnidirectional antenna on metallic cylinders

Use of an electrically fat pin inserted in a 2.92 mm connector as a monopole at K/Ka-band is reported for the first time. The proposed antenna has wide bandwidth of over 36% and consistent radiation pattern both as a stand-alone unit and when mounted on a cylinder. The effects of the cylinders dimensions on the antenna radiation pattern are also evaluated. It is shown that the beamwidth and the direction of radiation in the E-planes strongly depend on the length and diameter of a cylindrical platform while the omnidirectionality in the H-plane is maintained regardless of platform parameters.