Seunggoo Nam

K-Band Frequency Tunable Substrate-Integrated- Waveguide Resonator Filter With Enhanced Stopband Attenuation

In this paper, we present a K-band substrate-integrated waveguide resonator bandpass filter structure. The filter uses an antisymmetric mode of the resonator for the first time. A design method for the external coupling structure of the resonator utilizing the antisymmetric mode is described. In addition, a methodology for suppressing neighboring resonances close to the passband is demonstrated. This method can enhance stopband attenuation performance without additional loss. The proposed filter can tune the center frequency by adjusting tuning components. In order to verify the proposed filter structure and design method, we have fabricated and measured a K-band filter and demonstrated higher order filter design.

Single-Filter Structure With Tunable Operating Frequency in Noncontiguous Bands

In this paper, we present a frequency-tunable substrate-integrated waveguide bandpass filter of which the operating frequency band can be switched between S-band and X-band. One of unique features of the presented filter is that a single-filter structure can replace a filter bank composed of an S-band filter, an X-band filter, and two switches at input and output ports for selecting one of two filters. In addition, the filter can tune the center frequency in each band. This paper provides the design method, fabrication, and measurement of the presented filter structure.

Positive-to-zero continuously tunable inter-resonator coupling structure for applications in filter array systems

This paper presents a novel positive-to-zero continuously tunable inter-resonator coupling structure for high Q substrate-integrated waveguide resonators. Two nearly nonmutually coupled distinct inter-resonator structures were integrated. One structure provides positive static inter-resonator coupling while the other composes a continuously tunable negative coupling. The negative coupling can be tuned to be large enough to cancel out the static positive coupling and create a near-zero inter-resonator coupling state. Using the proposed tunable structure, a second-order continuously tunable Butterworth filter has been designed and fabricated. The bandwidth of the fabricated filter can be tuned from 3% to 0% at 1.3 GHz. Similar tuning is possible for all frequencies within the frequency range 0.95 GHz ~ 1.6 GHz. The fabricated filter has been measured to have frequency tuning ratio of 1.7:1.

Integration of Interresonator Coupling Structures With Applications to Filter Systems With Signal Route Selectivity

This paper presents a positive-to-zero continuously tunable interresonator coupling structure for postloaded substrate-integrated cavity resonators. Two interresonator coupling structures with the opposite coupling signs were integrated. The continuously tunable negative microstrip line coupling structure can generate large enough coupling to cancel out the positive coupling by the inductive iris and accomplish near-zero coupling. The proposed structure was implemented on designing a tunable Butterworth-response filter of which the center frequency and bandwidth can be continuously adjusted. It was further applied to a six-resonator-array filter structure that essentially requires the zero coupling capability in order to acquire signal route selectivity. The two-, three-, and four-pole responses with different signal paths were measured within a frequency range, and for the two-pole case, two signals were simultaneously measured, while one signal is frequency tuned.

Reconfigurable bandpass filter topology using cul-de-sac resonators with adjustable notches

In this paper, we present a fully reconfigurable bandpass filter structure capable of controlling the center frequency, bandwidth, and notches in the stopband. For the design purpose, we also present a filter topology containing frequency-tunable dangling resonators. The filter has a multi-layer structure having both microstrip-line resonators and substrate-integrated waveguide (SIW) resonators. For achieving high-rejection notches, the filter has been designed in such a way that the notches and passband are produced by SIW resonators and microstrip-line resonators, respectively. Measurement shows that the center frequency can be tuned from 1 GHz to 1.4 GHz and the bandwidth has the tuning range from 100 MHz to 150 MHz. In addition, two notches can be controlled independently with maximum 87 dB attenuation.

A New Class of K-Band High-Q Frequency-Tunable Circular Cavity Filter

A new type of K-band high-Q frequency-tunable waveguide filters is proposed in this paper. The presented filter structure adopts a new technique for tuning the resonant frequency of each resonator. A dielectric plate is inserted in each resonator and rotating it leads to the frequency tuning. Unlike the conventional frequency tuning methodologies for tunable waveguide cavity filters, the new frequency tuning technique alleviates the electrical grounding issue for tuning devices. In addition, we demonstrate a new design method that allows the filter to have an absolute constant bandwidth in the frequency tuning range without using tunable coupling structures.

Constant-absolute-bandwidth frequency-tunable half-mode SIW filter containing no tunable coupling structures

A new half-mode frequency-tunable SIW (substrate-integrated waveguide) bandpass filter with a constant absolute bandwidth is presented in this paper. For achieving the constant bandwidth, we have developed new external and internal coupling structures capable of exhibiting specified coupling values over the frequency tuning range of the presented filter. Hence, the presented filter employs no tuning components in the coupling structures and this avoids the insertion loss increase due to tuning components. For verification, a second-order filter has been designed, fabricated, and measured. The filter has the insertion loss smaller than 2.0 dB over the frequency tuning range from 1.85 GHz to 2.3 GHz. The bandwidth slightly varies from 136 MHz to 142 MHz.

Theory for Pseudo-Butterworth Filter Response and Its Application to Bandwidth Tuning

This paper presents a new class of filter responses called pseudo-Butterworth filter response. A detailed mathematical analysis on the pseudo-Butterworth response has been carried out. In addition, the comparison between the typical complete Butterworth response and the new pseudo-Butterworth response is provided. The theory for the pseudo-Butterworth filter response indicates that bandwidth tuning maintaining excellent return loss performance can be executed adjusting not all coupling structures of a filter. As an example, a bandwidth tuning method for a second-order filter is presented. For verifying the presented bandwidth tuning theory, a second-order substrate-integrated waveguide (SIW) resonator filter has been designed, fabricated, and measured. As an example of applications to higher order filters, a theory for the fourth-order pseudo-Butterworth responses and a bandwidth tuning method for the fourth-order filters have been developed. A fourth-order filter has also been fabricated and measured for verifying the presented bandwidth tuning technique.

Frequency-Tunable Tri-Function Filter

In this paper, we present a reconfigurable filter capable of having three different responses, such as bandstop, bandpass, and all-pass responses. For designing the tri-function filter, we have developed a new topology containing coupled resonators and a switch-embedded transmission line running from the input to output ports. A bandpass response can be obtained by opening the switches embedded in the transmission line. On the other hand, closing the switches produces bandstop and all-pass responses. The details of the coupling structure design satisfying three sets of the coupling coefficients for the three responses are presented. In addition, we also discuss in detail an approach for incorporating the measured parameters of the nonideal switch in our filter design. For demonstration, a frequency-tunable tri-function filter has been designed using substrate-integrated waveguide resonators. It is shown that the designed filter is able to exhibit three responses over a 1.2:1 frequency tuning range.

Reconfigurable Bandpass Filter With Resonators in Cul-De-Sacs for Producing Notches

We present a new design method for bandpass filters capable of adjusting center frequencies, bandwidths, and notches. For designing such filters, filter topologies employing frequency-tunable resonators in cul-de-sacs are developed. The cul-de-sac resonators are mainly responsible for constructing notches, while the resonators in main paths form passbands. For verifying the presented design method, we have designed two bandpass filters. Each filter consists of two different resonator types: microstrip-line resonators for forming passbands and substrate-integrated waveguide resonators for producing notches. The measured results of the two designed filters show that frequency-tunable notches can be placed next to the passbands without producing unwanted resonant peaks that are usually observed in bandpass-bandstop filter cascades. This indicates that the filters designed using the presented topologies can replace bandpass-bandstop filter cascades.