Young Hoon Chun

Dual-Mode Microstrip Open-Loop Resonators and Filters

A miniature dual-mode microstrip open-loop resonator is proposed. Distinct characteristics of this new type of dual-mode resonator are investigated using full-wave electromagnetic simulations. It is shown that the two operating modes, i.e., the even and odd modes, within a single dual-mode resonator of this type do not couple. It is also found that there is a finite-frequency transmission zero inherently associated with the even mode. Two two-pole filters using this type of dual-mode resonator are demonstrated with opposite asymmetric responses, which result from different locations of the transmission zero. Higher order filters of this type are also investigated. Both simulated and measured results are presented.

Compact wide-band branch-line hybrids

Wide-band branch-line couplers are designed and tested. The proposed couplers feature compact size on a single circuit layer structure without via-holes. For the broad-band property and cost effectiveness, we have designed a four-branch hybrid with mixed distributed and lumped distributed elements. Analysis on the equivalent circuits was performed carefully in order to obtain a sufficient bandwidth with reduced design area. The fabricated hybrids have the fractional bandwidth larger than 56% at the center frequency of 2 GHz. They also show size reduction up to 55.2% compared with the conventional design method.

Electronically Reconfigurable Dual-ModeMicrostrip Open-Loop Resonator Filter

A new type of reconfigurable asymmetric frequency response bandpass filter using dual-mode open-loop resonator is investigated. It explores the unique characteristic of the dual-mode open-loop resonator whose two operating modes, i.e., the even- and odd-modes do not couple. Thus, tuning the passband frequency is accomplished by merely changing the two modal frequencies proportionally, which makes the electronic tuning simple. Furthermore, for a single filter of this type, its selectivity can be electronically reconfigured to exhibit a higher selectivity with a finite-frequency transmission zero on either side of the passband. For the demonstration, both simulated and measured results are presented.

Switchable Embedded Notch Structure for UWB Bandpass Filter

A reconfigurable ultra-wideband (UWB) bandpass filter (BPF) with switchable notch for UWB system is presented. The UWB BPF is embedded with two identical switchable notch structures, in which PIN diodes are used for electronic switching. A bias circuit for UWB applications was investigated and designed to control the state of PIN diodes in order to activate or deactivate the notch without an affect on the response of the BPF. A demonstrator for this type of switchable notch UWB filter is designed and fabricated. Simulated and measured results are described.

BST-Varactor Tunable Dual-Mode Filter Using Variable

Ferroelectric materials like barium-strontium-titanate (BST) have become attractive for microwave tunable circuit applications. This letter presents an investigation of BST-varactor tunable dual-mode filter using variable characteristic impedance or ZC transmission line. The interdigital BST varactors are fabricated and modeled, which are then deployed to realize a bandpass filter with tunable bandwidth capability. The use of tunable impedance line provides additional flexibilities in the design of microwave tunable circuits. A tunable bandpass filter of this type with a center frequency of 1.8 GHz and a bandwidth tuning ratio of 1.15:1 is demonstrated experimentally.

{Z}_{C}

This paper presents an investigation of tunable bandstop filter using slotted ground structure. A Barium-Strontium-Titanate (BST) varactor chip is used to tune each resonator and its location is determined by electromagnetic simulation for an optimum frequency tuning. 2-pole bandstop filter is measured at the center frequency from 1.2 to 1.4 GHz and its rejection is more than 15 dB at the stop band while the insertion loss at the pass band is less than 1 dB.

Transmission Line

This paper presents the design of a broadband branch-line coupler. The proposed coupler features compact size on a single circuit layer structure. For the high power capability, broadband property and cost effectiveness, we have designed, fabricated and tested a new three-branch hybrid with lumped-distributed-elements. It has the fractional bandwidth of 45% at the center frequency of 2 GHz. Also, it shows the size reduction more than 35 % compared with the conventional design method.

BST varactor tuned bandstop filter with slotted ground structure

A new type of electronically tunable asymmetric frequency response bandpass filter based on dual-mode open-loop resonator is investigated. By employing the unique characteristic of the dual-mode open-loop resonator, that is, whose two operating modes (odd-and even-modes) do not couple to each other, tuning the passband frequency becomes simple with single DC bias circuit. Two designed tunable bandpass filters of this type are demonstrated experimentally, which show more than 10 dB of return loss and less than 3 dB insertion loss over a tuning range of 12% from 0.83 to 0.93 GHz.

Design of a compact broadband branch-line hybrid

This letter describes the design of a novel transmission line, where characteristic impedance can be adjusted electronically, and its application to a phase shifter. A tunable transmission line enables microwave circuit designers to have flexibility and better return loss which can enhance its tuning range. A UHF band distributed analog phase shifter, as well as a tunable transmission line, is presented. The characteristic impedance of a fabricated novel transmission line varies from 10 to 69.5/spl Omega/, which demonstrates its tunability, and the fabricated UHF phase shifter using this novel line shows the possibility of better reflection coefficient and wider tuning range over the conventional capacitively-loaded distributed phase shifter.

Compact Tunable Microstrip Bandpass Filters with Asymmetrical Frequency Response

This paper presents an investigation of a tunable bandstop filter using barium-strontium-titanate (BST) varactors. 3-pole bandstop filter with varactors is fabricated on MgO substrate. It is measured at the center frequency from 8.77 to 9.26 GHz and its maximum rejection is more than 26 dB at the stop band while the insertion loss at the pass band is less than 2 dB.