Taek K. Lee

Design of SIW Cavity-Backed Circular-Polarized Antennas Using Two Different Feeding Transitions

Two circular-polarized circular patch antennas which have novel feeding structures such as a substrate integrated waveguide (SIW), a cavity-backed resonator and two different feeding transitions, are proposed and experimentally investigated in terms of electrical performances, including reflection coefficients, optimized parameter values, circular polarized antenna gain, axial ratios and radiation patterns. By inserting asymmetrical inductive via arrays into the interface region between the circular patch and SIW feeding structure, it is found that an enhancement of input impedance bandwidth has been achieved. In addition, in order to check the effects of feeding transition types on the electrical performances of the main radiator, two different feeding transitions, namely microstrip-to-SIW and coax-to-SIW, have been studied by considering reflection coefficients, gain, axial ratios and radiation patterns. As a result, it is experimentally proved that a broadband impedance bandwidth of 17.32% and 14.42% under the criteria of less than VSWR 2:1 and 1.5:1, respectively, have been obtained and an RHCP axial ratio of 2.34% with a maximum gain of 7.79 dBic has been accomplished by using the proposed antenna with coax-to-SIW transition operating at the X-band of 10 GHz center frequency.

Design of a Compact Tri-Band PIFA Based on Independent Control of the Resonant Frequencies

The application of multiple folded radiator to independent frequency control of a compact tri-band planar inverted-F antenna (PIFA) composed of three resonant frequencies, global system for mobile communication (GSM900, 880-960 MHz)/digital communication system (DCS1800, 1710-1880 MHz)/Satellite Digital Mobile Broadcasting (Satellite DMB, 2605-2655 MHz) are treated with the optimized parameter values. The proposed antenna has been designed and analyzed by using commercially available softwares, CST MWS based on the finite-difference time-domain algorithm, High Frequency Structure Simulator (HFSS) based on the finite element method algorithm and a simple resonant equation, respectively. It is also seen that good isolation characteristics and independent frequency control can be accomplished by using the separation of folded parts operating at each different frequency. In addition, the return loss has been measured and compared between measured and simulated data under the criterion of VSWR less than 3. The radiation patterns in each service are the same as the omnidirectional characteristics and the maximum gains are 1.19, 2.93, and 1.48 dBi at 0.92, 1.8, and 2.63 GHz, center frequencies of each service, respectively.

SIW-Based Array Antennas With Sequential Feeding for X-Band Satellite Communication

Novel phased array antennas suitable for X-band satellite communication are introduced and investigated for right-handed circular polarization (RHCP) in a multi-layered fabrication. The primary function of the proposed antennas is to transmit high quality data obtained from satellites and the ground station systems with the lowest amount of loss. For accurate data transmission, the important parameters regarding antenna specifications and electrical performance are the antenna gain and the high-purity polarization. Hence, this paper describes novel procedures for gain enhancements of the array antennas working at X-band (from 8.0 to 8.5 GHz) with an RHCP characteristic, including a single element, 2×2 array, and 2×4 array with four-way and eight-way power dividers, respectively. Taking into consideration the long-distance communication between a satellite and ground station, a substrate-integrated waveguide structure has been proposed, in particular because it is known to have low radiation loss and a low weight comparable to that of a microstrip, as well as low material loss similar to that of a metal-surrounded waveguide.

A Dual-Band Unequal Wilkinson Power Divider With Arbitrary Frequency Ratios

This letter presents a theoretically rigorous investigation and experimental verification for an asymmetrical, unequal power divider working at dual frequency bands. Through the even- and odd-mode analysis that can be applied to dual-band, unequal power divider by assuming virtual open and short points, analytically exact solutions have been derived for the design parameters values. For verification of this analysis, commercially available software including ADS and CST MWS based on circuit theory and full-EM theory, respectively, and already-established equations have been adopted.

Radial guided 4-way unequal power divider using substrate integrated waveguide with center-fed structure

Radially-guided low-profile equal and unequal power division functions are accomplished by using Substrate Integrated Waveguide (SIW) technology with center feeding structures and additional power/phase-control vias. The controlled positions of guiding posts provides the unequal division ratios and phase variations at each port. At this time, the width of the SIW has been kept the same in spite of the shifted position of guiding posts. The electrical performances including return loss, transmission characteristics and phase variations are discussed through simulation and measured data.

A Wilkinson Power Divider with Different Power Ratios at Different Frequencies

The power divider/combiner is very important component for power amplifier design in low power MMIC design and high power system using hybrid scheme. In addition to that, the power divider/combiner is applied for impedance matching, antenna polarization, and phase control in phased array antenna. In this paper, we will consider the power divider/combiner working at two arbitrary frequencies with different power ratios at two output ports including a rigorous analysis and simulation. In order to determine the optimized design parameters, the even-odd mode analysis is carried out rigorously using impedance matching condition and lumped components such as R, L, and C. The validation of analysis and design parameters can be verified using two commercially available softwares based on circuit theory and FIT algorithm, respectively.

Parameter Selection Procedure of Parabolic Reflector Antenna for the Optimum Synthetic Aperture Radar Performances

A procedure for antenna parameter selections is proposed that considers the relationships between synthetic aperture radar performance and the antenna parameters of a parabola-type reflector antenna with a central flat dish. The effects of a central dish designed for weight reduction on the antenna beam pattern are also quantitatively analyzed using commercially available software based on the physical optics algorithm. The results of the theoretical analysis and simulation predict that a larger size of the central dish results in an increase in the sidelobe level, which is the reason for the increase in two important ambiguities, such as range ambiguity ratio (RAR) and azimuth ambiguity ratio (AAR). The dependence of RAR and AAR on Pulse repetition frequency is also analyzed and discussed.

Conductivity Evaluation of a Newly Proposed Material for a SAR Reflector Antenna

Large spaceborne antennas should be lightweight, a factor related to the development costs of launch vehicles. In order to overcome this drawback, a feasibility study of a new carbon fiber reinforced polymer (CFRP) named M55J/RS3 is carried out for a synthetic aperture radar (SAR) reflector antenna. In particular, the high resolution of detected images is taken into consideration. To validate the electrical performance, a test of the CFRP specimen is fabricated, and the transmission/reflection coefficients are measured using a standard Xband waveguide. Finally, the effective complex permittivity and effective electrical conductivity are derived from the obtained measured data. By applying the derived conductivity to the simulation of the radiation pattern, antenna gain, and beamwidth-instead of relying on the assumption of a perfect electric conductor-variations in electrical performance are also investigated and discussed.

Triangular-shaped stepped septum polarizer for satellite communication

In this paper, modified triangular-shaped waveguide-typed septum polarizer has been suggested and verified by using commercially available software and carrying out the comparison with the conventional rectangular waveguide-typed polarizer. It is expected that the proposed structure shows the better electrical performances than the conventional one in terms of the smooth energy-transfer of TE10 and TE01-modes. The simulated result shows that the proposed structure accomplished axial ratio of less than 0.32dB, return losses of lower than −32dB, and isolation characteristics between −24dB and −35dB at the target frequency ranging from 8 to 8.4GHz.

A study on measurement system for electrical characteristics of anisotropic composite material

We present the measurement system for electrical characteristics of inhomogeneous and anisotropic carbon fiber reinforced polymer(CFRP) material by employing waveguide and 2-port measuring method. The effective permittivity and conductivity of CFRP have been estimated according to the fiber direction for radar application in the frequency range from 8GHz to 12GHz.