Kwi-Soo Kim

Design of Dual-Band Bandpass Filters with Controllable Bandwidths Using New Mapping Function

In this paper, a novel design method for a dual-band bandpass fllter (BPF) with arbitrary controllable bandwidths based on a simple frequency mapping function is proposed and its analytical design equations are also derived. The circuit conversion techniques are employed for implementation with distributed transmission line. To validate the proposed dual-band BPF with controllable bandwidths, a low temperature co-flred ceramic (LTCC) transmission line as well as microstrip lines are used, respectively. The two types of design for the dual-band BPF have the same and signiflcantly difierent fractional bandwidths (FBWs), respectively. The flrst type of dual- band BPF with same FBWs are implemented at 2.11{2.17 and 3.45{ 3.55GHz. The second type of dual-band BPF with difierent FBWs are implemented at 3.40{3.60 and 5.15{5.25GHz. The measured and theoretical results show good agreement, signiflcantly validating the proposed frequency mapping function methodology.

A New Branch-Line Hybrid Coupler with Arbitrary Power Division Ratio

This paper proposes a new branch-line hybrid coupler with controllable power ratio at the output ports. It is structured as two 90deg branch-line hybrid couplers connected by a variable impedance transmission line. The power division ratio is adjusted by controlling the impedance of the transmission line. Modeling the transmission line as series and parallel resonators shows that its impedance can be changed by changing the inductance and capacitance. In practice, using a varactor diode facilitates ease in dealing with the impedance of the transmission line and thus the power division ratio of the coupler.

A new open stubs structure of Kuroda low-pass filter using DGS

This paper presents a new open stub structure of Kuroda low-pass filter using DGS(Defected Ground Structure). Low-pass filter based on Richards transformation and Kurodas identity has sharp slope in transition band and very good characteristic in stop band. But it is hard to fabricate the microstrip line because of high impedance of the open stub. So, this paper proposes a new structure that can realize high open stub impedance line through using DGS that inserts into the ground plane of the open stub. 5-orders low-pass filter with proposed design method has been fabricated, measured and compared with the existing structure. The experimental results show excellent agreements with designed and simulated ones.

A Novel Balun with Vertically Periodic Defected Ground Structure

In this paper, a novel balun which can be applied for a microstrip-to-slotline transition is presented. This proposed balun has a DGS (defected ground structure) pattern on the ground plane. This balun has an advantage that does not require any addional electrical length. The proposed microstrip-to-slotline transition can be made to have power division and 180 degree out-of-phase characteristics. The DGS pattern on the ground plane decides the operating frequency of the proposed balun. In addition, the balun with a VPDGS (vertically periodic defected ground structure) pattern on the ground plane is presented, designed, fabricated and measured

An equivalent circuit model for multi-port networks

This paper suggests an equivalent circuit model and extraction method for the equivalent circuit elements using Y-parameter of multi-port networks. A coupled line directional coupler is selected as the example for verification of the suggested technique. The accuracy of the extracted equivalent circuit is evaluated by comparing the S-parameters obtained from EM simulation data to circuit simulation results.

A New Wide Bandpass Filter Design with Symmetric Attenuation Characteristics

This paper proposes a new frequency transformation method for improving the asymmetrical attenuation characteristics of a conventional lumped element band-pass filter (BPF). This new method results in formulas for filter components. The performance of a BPF designed using this method is tested using simulation and measurement. Since the new BPF design method is shown to be very useful for designing BPFs with wide passbands, it is applicable to broadband wireless communication filters, such as those used in ultra-wide band (UWB) wireless communication technology.

A new defected ground structure with islands and equivalent circuit model

A novel defected ground structure with islands (DGSI) and its equivalent circuit model is proposed. Two islands are placed at both sides of microstrip line on the upper plane where DGS is realized on the bottom plane. The equivalent circuit is composed of one pair of open stub and short stub, which are connected to each other. The equivalent circuit elements are extracted from a simple circuit analysis method. In order to show the validity of the proposed DGSI and its equivalent circuit model, several EM simulation results on DGSI are compared to the corresponding S-parameters obtained from the circuit simulation using the equivalent model.

A new extraction method for the characteristic impedance and effective dielectric constant of transmission line with DGS

In this paper, we propose a new extraction method for the characteristic impedance and effective dielectric constant of a microstrip line. It extracts the characteristic impedance and effective dielectric constant of a microstrip line that uses the results of S-Parameters through the EM - Simulation. And it also extracts the characteristic impedance and effective dielectric constant of microstrip line with DGS and compare the variation of frequency response. We simulate a microstrip line which has a dumbbell type DGS, and extract the electrical length, characteristic impedance and effective dielectric constant according to the DGSs size and the number of DGS. From these results, we analyze how DGS influence the variation of the transmission line characteristics such as the characteristic impedance and effective dielectric constant of a microstrip line.

A new design method for a dual-band power divider

This paper presents a dual-band 2 section Wilkinson power divider. The proposed method is used that transmission lines of the divider are transformed to π-type equivalent circuits, which can be same impedance and electrical length. To validate the proposed method, we design a dual-band divider which is used for 0.9GHz cellular and 1.8GHz 3rd generation system. The specified dual-band divider which has 1:1 power division ratio at two bands is designed, fabricated and measured. The measured results show excellent performance with an insertion loss of less than 0.25dB, a return loss of less than 118.74dB, and good isolation characteristics.

A new extraction method of characteristic parameters of a coupled transmission line

This paper suggests a new extraction method of the characteristic parameters of a coupled transmission line, which is structured like a microstrip line. A coupled line coupler that has −20dB coupling at the center frequency 1.5GHz is used for the extraction of the characteristic parameters. First, it extracts the characteristic parameters using the simulation results of the coupler. The paper shows the accuracy of this extraction method by comparing the results of EM simulation with the results of circuit simulation using the extracted characteristic parameters.