Tae Hak Lee

Broadband Circularly Polarized Crossed Dipole With Parasitic Loop Resonators and Its Arrays

A novel printed crossed dipole with broad axial ratio (AR) bandwidth is proposed. The proposed dipole consists of two dipoles crossed through a 90°phase delay line, which produces one minimum AR point due to the sequentially rotated configuration and four parasitic loops, which generate one additional minimum AR point. By combining these two minimum AR points, the proposed dipole achieves a broadband circularly polarized (CP) performance. The proposed antenna has not only a broad 3 dB AR bandwidth of 28.6% (0.75 GHz, 2.25-3.0 GHz) with respect to the CP center frequency 2.625 GHz, but also a broad impedance bandwidth for a voltage standing wave ratio (VSWR) ≤2 of 38.2% (0.93 GHz, 1.97-2.9 GHz) centered at 2.435 GHz and a peak CP gain of 8.34 dBic. Its arrays of 1 × 2 and 2 × 2 arrangement yield 3 dB AR bandwidths of 50.7% (1.36 GHz, 2-3.36 GHz) with respect to the CP center frequency, 2.68 GHz, and 56.4% (1.53 GHz, 1.95-3.48 GHz) at the CP center frequency, 2.715 GHz, respectively. This paper deals with the designs and experimental results of the proposed crossed dipole with parasitic loop resonators and its arrays.

Reconfigurable Dual-Stopband Filters With Reduced Number of Couplings Between a Transmission Line and Resonators

This letter proposes a new design method for a bandstop filter with two stopbands. Contrary to a conventional method, the presented method allows for achieving two stopbands without increasing the number of the couplings between resonators and the transmission line connecting the input and output ports. In addition, a filter designed using the presented method can not only have different center frequencies but also have different bandwidths by adjusting the resonant frequencies of the resonators. For verification of the proposed approach a dual-stopband filter using four tunable substrate-integrated waveguide resonators has been designed and measured.

K-Band Substrate-Integrated Waveguide Resonator Filter With Suppressed Higher-Order Mode

In this letter, we present a design method for K-band substrate-integrated waveguide (SIW) resonator filters utilizing TM02 mode. More importantly, a methodology for suppressing an unwanted higher-order mode ( TM11) close to the passband is demonstrated. It is shown that suppressing the unwanted mode give rise to the improved stopband performance. In addition, the resonator used in this filter design has capability of adjusting the resonant frequency, and this allows for compensating the fabrication error. Verification of the presented design method has been carried out by fabricating and measuring the filter.

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.

Bandstop Filter (BSF) Topology With Variable Attenuation

In this paper, we provide a new third-order bandstop filter (BSF) topology with attenuation control capability. The proposed BSF topology contains inter-resonator coupling structures and it can duplicate the frequency responses of the conventional BSF topology, which does not have inter-resonator couplings. In addition, the proposed topology can control the attenuation level by adjusting the resonant frequency of each resonator, and this characteristic cannot be obtained from the conventional one. Two BSFs utilizing the conventional and proposed topologies are designed, fabricated, and measured to support the presented theory. Two filters have been designed and fabricated employing frequency tunable substrate integrated cavity resonators. The measurement verifies that the BSF utilizing the presented topology is capable of adjusting the attenuation level as well as reproducing the conventional bandstop responses.

NEW NEGATIVE COUPLING STRUCTURE FOR SUB- STRATE-INTEGRATED CAVITY RESONATORS AND ITS APPLICATION TO DESIGN OF AN ELLIPTIC RESPONSE FILTER

This paper presents a new type of a negative coupling structure for designing elliptic-response fllters with cross-coupling. The proposed coupling structure consists of short-circuited coupled transmission lines. Using the fact that insertion phase of the coupled line structure is difierent from that of an inductive iris, it is shown that the proposed coupling structure can be used as the negative coupling structure. In order to verify the proposed coupling structure, we designed a 4th-order cross-coupled elliptic-response bandpass fllter with substrate integrated waveguide resonators. A pair of transmission zeros in measurement and simulation results validates that the proposed structure can be used as the negative coupling structure.

Extension of Bandstop Filter Topology With Inter-Resonator Coupling Structures to Higher-Order Filters

This letter presents a rigorous extension of the concept for the bandstop filter (BSF) with inter-resonator couplings to a higher order filter. We show that a BSF topology with inter-resonator couplings can exhibit the frequency response that a conventional BSF topology without inter-resonator couplings generates. Equivalence between the coupling matrices of the two topologies are shown. As an example, this letter shows that fourth-order BSFs with and without inter-resonator couplings can exhibit identical frequency responses.

First-order reflectionless lumped-element lowpass filter (LPF) and bandpass filter (BPF) design

This work presents design methods for first-order reflectionless lumped-element lowpass and bandpass filters. Each of the proposed filter structures contains an impedance matching circuit that can theoretically cancel out the reflected wave. We have derived the analytic design equations so that the reflectionless filters can be designed without using any sophisticated math techniques. In addition, by virtue of the design equations, the reflectionless lowpass and bandpass filters can be designed in a way to produce exactly the same transmitted power ratio as the conventional reflective filters. Both conventional reflective filters and proposed reflectionless filters have been fabricated and measured to verify the newly presented reflectionless filter design theory. The experimental results show that the proposed filter structures have excellent return loss performances in the stopbands as well as in the passbands. In addition, the measured transmitted power ratios of the reflectionless filters are not distinguishable of the reflective filters.

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.

Small GPS antenna with lumped elements and interdigital structure

In this paper, a miniaturized global positioning system (GPS) antenna embedded in a printed circuit board (PCB) is presented. The proposed antenna employs lumped elements and an interdigital structure to reduce an operating frequency and to achieve good input matching. Furthermore, the system ground plane is included to work out a radiator. The size of the proposed antenna is 8 mm × 4.5 mm. The bandwidth under VSWR of 2:1 is 20 MHz from 1561 MHz to 1581 MHz. The measured antenna gain and the efficiency are 1 dBi and 40% at 1575 GHz, respectively.