Jongsik Lim

Design of low-pass filters using defected ground structure

A method to design low-pass filters (LPF) having a defected ground structure (DGS) and broadened transmission-line elements is proposed. The previously presented technique for obtaining a three-stage LPF using DGS by Lim et al. is generalized to propose a method that can be applied in design N-pole LPFs for N/spl les/5. As an example, a five-pole LPF having a DGS is designed and measured. Accurate curve-fitting results and the successive design process to determine the required size of the DGS corresponding to the LPF prototype elements are described. The proposed LPF having a DGS, called a DGS-LPF, includes transmission-line elements with very low impedance instead of open stubs in realizing the required shunt capacitance. Therefore, open stubs, teeor cross-junction elements, and high-impedance line sections are not required for the proposed LPF, while they all have been essential in conventional LPFs. Due to the widely broadened transmission-line elements, the size of the DGS-LPF is compact.

Dual-Band Bandpass Filter With Independently Tunable Center Frequencies and Bandwidths

This paper presents a novel approach to the design of tunable dual-band bandpass filter (BPF) with independently tunable passband center frequencies and bandwidths. The newly proposed dual-band filter principally comprises two dual-mode single band filters using common input/output lines. Each single BPF is realized using a varactor-loaded transmission-line dual-mode resonator. The proposed filter also offers switchable characteristics to select either of the passbands (either the first or the second passband only). To suppress the harmonics over a broad bandwidth, defected ground structures are used at input/output feeding lines without degrading the passbands characteristics. From the experimental results, it was found that the proposed filter exhibited the first passband center frequency tunable range from 1.48 to 1.8 GHz with a 3-dB fractional bandwidth (FBW) variation from 5.76% to 8.55% and the second passband center frequency tunable range from 2.40 to 2.88 GHz with the 3-dB FBW variation from 8.28% to 12.42%. The measured harmonic results of the proposed filters showed a rejection level of 19 dB, which is up to more than ten times of the highest center frequency of the first passband without degradation of the passbands.

A 1: 6 Unequal Wilkinson Power Divider

A 1:6 unequal Wilkinson power divider is proposed. The proposed 1:6 divider has the microstrip line with 207Omega characteristic impedance by adopting a simple rectangular-shaped defected ground structure (DGS). Instead of the previous meander-shaped DGS, the proposed rectangular-shaped DGS produces the transmission line having much higher characteristic impedance because of the decreased equivalent capacitance as well as the increased inductance. The analytic verification procedure for 207Omega is also illustrated. The measured performances show that the proposed 1:6 Wilkinson divider has excellent performances with a good agreement with the predicted ones

Harmonic Suppressed Dual-Band Bandpass Filters With Tunable Passbands

This paper presents a novel approach to the design of tunable dual-band bandpass filter with broadband harmonic suppression characteristics. The proposed filter structure offers the possibility of two tunable passbands, as well as a fixed first passband and controllable second passband. The tunable passband frequency usually causes a shift of the harmonics, which need to be suppressed to improve out-of the passband characteristics. In order to suppress the harmonics over a broad bandwidth, defected ground structures are used at input and output feeding lines without degrading the passbands characteristics. Both theory and experiment are provided to validate the proposed filter. From the experimental results, it is found that the proposed filter exhibits a first passband center frequency tunable range of 34.14% from 0.85 to 1.2 GHz with the almost constant 3-dB fractional bandwidth (FBW) of 13% and second passband center frequency tunable range of 41.81% from 1.40 to 2.14 GHz with the 3-dB FBW of 11%. The measured results of the proposed filters show a rejection level of 20 dB up to more than ten times of second passband frequency can be obtained, thereby ensuring broad harmonics rejection characteristics without degradation of passbands. The measurement data have good agreement with the simulation.

Design of Dual-Band Bandpass Filter Using DGS With Controllable Second Passband

In this letter, the application of a variable characteristic impedance transmission line that can be used to design a dual-band bandpass filter (BPF) is presented. The proposed filter offers a fixed first passband and a controllable second passband. The tuning of the second passband is achieved by varying the characteristic impedance of the shunt open stub of stub loaded resonator (SLR) with the help of a defected ground structure (DGS) transmission line and varactor diodes. In order to validate the theoretical predictions and simulated results, a two stage dual-band BPF with three transmission zeros was implemented and experimentally verified.

Microstrip Line Negative Group Delay Filters for Microwave Circuits

This paper presents a novel approach to the design and implementation of a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delay (NGD) time. The newly proposed filter is based on a simple frequency transformation from a low-pass filter to a bandstop filter. The NGD time can be purely controlled by the resistors inserted into the resonators. The performance degradation of the NGD time and signal attenuation (SA) of the proposed NGDF according to the temperature dependent resistance variation is also analyzed. From this analysis, it is shown that the NGD time and SA variations are less sensitive to the resistance variation compared to those of the conventional NGD circuit. For an experimental validation of the proposed NGDF, a two-stage distributed microstrip line NGDF is designed, simulated, and measured at an operating center frequency of 1.962 GHz. These results show a group delay time of -7.3 ns with an SA of 22.65 dB at the center frequency and have good agreement with the simulations. The cascaded response of two NGDFs operating at different center frequencies is also presented in order to obtain broader NGD bandwidth. NGDFs with good reflection characteristics at the operating frequencies are also designed and experimentally verified.

A New Design of Doherty Amplifiers Using Defected Ground Structure

In this letter, a new Doherty power amplifier having the ideal harmonic termination condition that has been usually ignored is proposed. A defected ground structure (DGS) is adopted on the ground pattern of the output lambda/4 impedance inverter of the carrier amplifier and output offset transmission line of the peaking amplifier that are essential for proper load modulation operation of a conventional Doherty amplifier. As a result of the second and third harmonic termination, excellent improvement in power added efficiency (PAE), gain, maximum output power as well as linearity is obtained. The acquired improvements in gain, maximum output power (P1 dB), PAE, and adjacent channel leakage ratio to wideband code division multiple access 2FA signal are 0.33 dB, 0.42 dB, 12.7%, and 5.1 dB, respectively. Moreover, physical length of microstrip line is shortened fairly by DGS, therefore the whole amplifier circuit size is considerably reduced

A new DGS unequal power divider

An unequal Wilkinson power divider having rectangular-shaped defected ground structure (DGS) is proposed. DGS microstrip line adopted for the divider is composed of double-layer substrate which removes the ground problem of the previous DGS structures in packaging. The first layer includes DGS on the bottom ground plane. The second substrate of which top metal plane has been removed is attached to the bottom plane of the first layer. At first, a conventional DGS unequal Wilkinson power divider is designed according to the previous method on the first layer, and the second substrate is attached. The proposed DGS with double-layer substrate is described in detail and applied to 1:4 unequal dividers as an application example. The measured unequal Wilkinson power divider has an excellent agreement between prediction and measurement.

A 800- to 3200-MHz Wideband CPW Balun Using Multistage Wilkinson Structure

A novel ultra-wide band CPW (coplanar waveguide) balun having the structure of multistage Wilkinson power divider is proposed. It has an 180deg phase inverting structure between signal line and ground planes of CPW transmission line. The 3-stage Wilkinson power divider is transformed directly into the ultra-wide band balun without any cost of the size and performances. The measurement shows the right S-parameters as a power divider and the proper out of phase as a balun. The measured amplitude and phase unbalances at output ports are plusmn 0.5dB and plusmn 6deg, respectively over 800~3200MHz, while the maximum insertion loss is 0.8dB

An Unequal Wilkinson Power Divider with Variable Dividing Ratio

In this paper, an unequal 1:N Wilkinson power divider with variable power dividing ratio is proposed. The proposed unequal power divider is composed of the conventional Wilkinson divider structure, rectangular-shaped defected ground structure (DGS), island in DGS, and varactor diodes of which capacitance is adjustable according to bias voltage. The high impedance value of microstrip line having DGS is going up and down by adjusting the bias voltage for varactor diodes. Output power dividing ratio (N) is adjusted from 2.59 to 10.4 for the unequal power divider with 2 diodes.