Jung Woo Baik

Broadband Circularly Polarized Crossed Dipole With Parasitic Loop Resonators and Its Arrays

A novel printed crossed dipole with broad axial ratio (AR) bandwidth is proposed. The proposed dipole consists of two dipoles crossed through a 90°phase delay line, which produces one minimum AR point due to the sequentially rotated configuration and four parasitic loops, which generate one additional minimum AR point. By combining these two minimum AR points, the proposed dipole achieves a broadband circularly polarized (CP) performance. The proposed antenna has not only a broad 3 dB AR bandwidth of 28.6% (0.75 GHz, 2.25-3.0 GHz) with respect to the CP center frequency 2.625 GHz, but also a broad impedance bandwidth for a voltage standing wave ratio (VSWR) ≤2 of 38.2% (0.93 GHz, 1.97-2.9 GHz) centered at 2.435 GHz and a peak CP gain of 8.34 dBic. Its arrays of 1 × 2 and 2 × 2 arrangement yield 3 dB AR bandwidths of 50.7% (1.36 GHz, 2-3.36 GHz) with respect to the CP center frequency, 2.68 GHz, and 56.4% (1.53 GHz, 1.95-3.48 GHz) at the CP center frequency, 2.715 GHz, respectively. This paper deals with the designs and experimental results of the proposed crossed dipole with parasitic loop resonators and its arrays.

A Reconfigurable Circularly Polarized Microstrip Antenna With a Slotted Ground Plane

This letter describes a square patch antenna with a switchable circular polarization (CP) sense. The proposed antenna has four L-shaped slots on the ground plane, and the CP radiation can be generated by current perturbation due to the slotted ground plane. Because the CP sense of the proposed antenna is altered by the current path that is redirected with switched p-i-n diodes on the slots, the CP direction of the proposed antenna can be simply switched between the right-handed and left-handed CPs. As the slot and bias circuits are not placed on the patch side, the proposed antenna has a simple structure and can radiate a CP wave without altering the main beam direction. The experimental results show that antennas have excellent switchable radiation performance at 2.4 GHz.

A Slot-Loaded Composite Right/Left-Handed Transmission Line for a Zeroth-Order Resonant Antenna With Improved Efficiency

In this paper, a new composite right/left-handed transmission line (CRLH-TL) with equilateral slots is proposed for efficiency-improved zeroth-order resonant antennas. A 1-D infinitesimal equivalent transmission line circuit model is derived, and the characteristic impedance and dispersive relation are theoretically computed. Based on the isotropic arranged unit cells of the slot-loaded composite right/left-handed transmission line (SL CRLH-TL), 2-D zeroth-order resonators are designed for planar magnetic monopole antenna applications. The SL CRLH-TL provides the zeroth-order resonance with some degradation of the quality factor. Therefore, a highly efficient radiating resonator can be designed with higher gain at the zeroth-order frequency. The theoretical approach was verified by the experimental results. The radiation efficiency was improved by up to 45.6% for the nine-rectangular zeroth-order resonant antenna and 21.4% for the seven-hexagonal zeroth-order resonant antenna without degrading the radiating performance. Moreover, the antenna gains of these two antennas were enhanced by 7.56 and 6.31 dB, respectively, due to the increase of the radiation efficiency.

Compact Ultra-Wideband Bandpass Filter With EBG Structure

Two bandpass filters (BPFs) for ultra-wideband (UWB) applications are proposed using the uniplanar compact- electromagnetic bandgap (UC-EBG) and the foliated UC-EBG (FUC-EBG) structures for size reduction. The sizes of the proposed UWB BPFs are reduced by 20 ~ 22% compared to the conventional one with the microstrip multiple-mode resonator (MMR). Both EBG structures are shown to cause a slow-wave effect, which is required for compactness and the characteristic impedance Zc close to 50 Omega, which is needed for wideband match.

A polarization switchable microstrip patch antenna with a circular slot

A single probe-fed reconfigurable circularly polarized microstrip patch antenna with a circular slot is proposed. As one right (left) side point of the circular slot is shorted between the inside of the slot and the rectangular patch, the proposed antenna yields right (left) - handed circular polarization. Each of polarization modes is operated at the same frequency. The proposed antenna has been implemented and the experimental results have shown dual polarized radiation characteristics.

A compact microstrip antenna on a cross-shape slotted ground with a switchable circular polarization

A compact circular microstrip patch antenna with a switchable circular polarization (CP) is proposed at 2.4 GHz. An unequal cross-shaped slot on a ground plane is utilized as a perturbation. By switching pin diodes mounted on the slot, the CP sense of each antenna can be simply switched from left-handed (LH) CP to right-handed (RH) CP vice versa. Since the perturbation can be made on the ground plane and no bias circuit is required on the patch side, there is less distortion on the radiation pattern. From the experimental results for both CP senses, the impedance bandwidth and CP bandwidth of the proposed antenna are up to 150 MHz and 35 MHz, respectively.

Novel Circularly Polarized Printed Crossed Dipole Array with Broad Axial Ratio Bandwidth

The novel printed crossed 2times2 dipole array is proposed for broad axial ratio (AR) bandwidth. The broad bandwidth of axial ratio is due to a parasitic dipole crossing over the original dipole that is driven by a semi-rigid coaxial feed with the characteristic impedance of 75 Omega. The crossed dipole, a unit element of the dipole array proposed in this paper, can produce a broad circularly polarized (CP) operation by itself because of the sequentially rotated configuration. The measured 3 dB AR bandwidth is 39.2% and the gain is 13 dBi at the CP center frequency of 2.32 GHz. Details of the proposed dipole array design are described and both the simulation and the experimental results are presented and discussed.

Inductance loaded circular patch antenna for switchable circularly polarization

In this paper, a single-fed microstrip patch antenna with switchable circularly polarization (CP) sense is proposed. The proposed antenna consists of a circular patch with a perturbation segment and an inductor. The antenna without an inductor has a right handed CP, while the antenna with an inductor yields a left-handed CP. Experimented results show good agreements with simulated ones.

Compact cascaded quadruplet bandpass filter (CQ-BPF) using folded loop resonator with via-hole

A compact cascaded quadruplet bandpass filter (CQ-BPF) using short-circuited loop resonators is proposed for size reduction. The short-circuited loop has a resonance at a half wavelength by utilizing a via-hole and is modified to a folded structure to reduce a loop size. Comparing with the conventional loop resonator, the proposed resonator shows a size reduction of about 81%. The frequency responses of the proposed BPF have also been calculated via transmission and reflection rational functions. The measured insertion and return losses at the designed center frequency of 2.12 GHz are about 2 dB and 15 dB, respectively. The group delay is less than 1.55 ns. The full wave simulated results are well agreed with the measured ones.

An offset-fed microstrip antenna with reusable harmonics based on a composite right/left-handed transmission line resonator

In this paper, a new reusable harmonic microstrip antenna with an offset feed is presented. The proposed antenna consists of 9 isotropic arranged square unit-cells with an offset-feed at the centre cell. Based on a composite right/left-handed transmission line (CRLH-TL) resonator and the cavity model of a microstrip antenna, additional resonant frequencies and radiation patterns are analyzed. Moreover, the theoretical approach is discussed for the proposed structure. The multiple resonant frequencies are occurred due to both of CRLH-TL and microstrip patch resonant characteristics. Particularly, the antenna has a gain of about 10 dBi and a patch-like radiation at the harmonic mode.