Jen-Tsai Kuo

Dual-Mode Ring Resonator Bandpass Filter With Asymmetric Inductive Coupling and Its Miniaturization

Dual-mode ring resonator filters are implemented with asymmetric inductive perturbation for creating transmission zeros on both sides of the passband. In analysis, dependence of the resonance modes and the zeros on positions and sizes of both the inductive and capacitive perturbations is investigated. Under certain conditions, the even- and odd-mode frequencies for a capacitively perturbed ring are the same as the odd and even ones, respectively, for a ring with inductive perturbation. Theoretical background is clearly explained how the two transmission zeros are split up from the center frequency. Two dual-mode ring resonator filters are fabricated and measured for demonstration. To obtain a miniaturized circuit area, the 1-λ ring trace is folded into a double-ring or spiral configuration. The inductive perturbation is chosen as the crossover and implemented by a short high-impedance coplanar waveguide interconnection in the ground plane of the microstrip. Measurement results show good agreement with the simulation responses.

Compact branch-line coupler filter with transmission zeros

A compact filtering branch-line coupler is developed with short-ended half-wave resonators. For input/ output matching, tapped-line feeds incorporate a skew-symmetric configuration with magnetic inter-resonator coupling, so that transmission zeros can be created on high side of the passbands in the coupled and through outputs, as well as the isolated port. Circuit analysis is conducted based on the transmission line theory for prediction of these zeros. Measured responses of an experimental circuit show good agreement with simulated results.

New miniaturized ring resonator bandpass filter with wide upper stopband

A new configuration for ring resonator is proposed for bandpass filter design with size reduction and stopband extension. The planar self-coupled ring is twisted at its middle and a short CPW section is implemented in the ground plane for the three-dimensional interconnection. The resonator has two resonance modes and the filter possesses one transmission zero on the high side of the passband. With a pair of open low-impedance stubs attached to the ring, the circuit has an area of only 9.65% of that of the conventional ring resonator filter, and the upper stopband is extended up to higher than five times the center frequency. Measured results of a fabricated prototype circuit show good agreement with the simulation.

Bandpass filter with generalized multiple-mode ring resonator configuration

A new generalized multiple-mode ring resonator configuration is proposed for bandpass filter design. The building block is a shorted half-wavelength ring. A quintuple-mode ring resonator bandpass filter is implemented for demonstration. Its entire circuit area is only 72% of that of a conventional dual-mode ring resonator. Coupling matrix method is employed for determining the inter-resonator coupling and synthesis of the passband response. In addition to a transmission zero created at the higher passband due to inductive cross coupling, two zeros near the passband are generated by source-load coupling. The measured results show good agreement with the simulation.

Bandwidth and transmission zero control for compact dual-mode resonator filter by extraction of EM coupling

The electric coupling and magnetic coupling are extracted for a dual-mode resonator filter. The resonator is a half-wave section with its center being shorted to ground. The extraction relies on an equivalent circuit model. With properly tuning of the coupled-line sections, the electric and magnetic coupling coefficients of the two quarter-wave resonators can be adjusted, and hence both the filter bandwidth and zero frequency can be controlled. Two experimental filters are fabricated and measured for validation. Good agreement between measurement and simulation is obtained.

New triple-mode ring resonator bandpass filter with source-load coupling

New triple-mode resonator bandpass filters are implemented by three coupled rings. The three rings are connected to a ground via through three short high-impedance sections. These short sections are equivalent to inductors for providing inductive coupling among the resonant modes. The closed-loop rings can also be implemented by stepped-impedance equivalence for achieving size reduction and wide upper stopband. In addition, with the aid of source-load coupling, two extra transmission zeros can be created on both sides of the passband to improve the frequency selectivity of the filter. Two filters are fabricated and measured to validate the proposed idea. The measured results show good agreement with the simulation.

Diplexer with trisections synthesized by frequency-dependent coupling

Microstrip diplexer is realized with trisection bandpass filters synthesized by frequency-dependent coupling between nonadjacent stepped-impedance resonators. The trisection has a passband response of generalized Chebyshev form with two transmission zeros. The coupling is implemented by sliding both the high- and low-impedance sections to achieve the desired frequency-dependence characteristic at the design frequency. A trisection bandpass Alter at 3.5 GHz and a diplexer with passbands at 3.15 and 3.5 GHz are fabricated and measured. Measured data show good agreement with the simulated responses.

Miniaturized dual-mode spiral-ring resonator bandpass filter

A dual-mode ring resonator filter is devised to have a miniaturized size and its performance investigated. By placing an inductive perturbation at an asymmetric position, with respect to the input and output ports, two transmission zeros are created on the both sides of the passband. The miniaturization is achieved by folding the microstrip ring trace into a spiral configuration, incorporating with metallic via-holes and coplanar waveguide sections as the interconnection. The circuit size is only 20.5% of that of a conventional ring resonator. Measured results show good agreement with the simulation.

Filtering rat-race coupler with transmission zeros using compact miniaturized hairpin resonators

A new compact filtering rat-race coupler is implemented by a 2×2 cross coupled configuration based on compact miniaturized hairpin resonators. Passband responses with transmission zeros are synthesized by an (n+4)×(n+4) coupling matrix. The zeros are created in the output ports by adding source-load coupling and their analytical expressions are derived. An experimental circuit is fabricated and measured. The circuit area is only 23.2% of that of a conventional rat-race coupler. Measured magnitude and phase responses of the four-port S-parameters show good agreement with simulation data.

Miniaturized dual-mode ring resonator bandpass filter with a wide passband

Dual-mode ring resonator filter is designed to have a relatively wide passband with a miniaturized circuit area. The miniaturization is achieved by folding the ring trace to a spiral configuration. The two degenerate modes are split up by an asymmetric inductive perturbation. As a result, the circuit area is only 29% of that of a conventional ring. The strong I/O coupling required by the wide passband property is implemented by adding an impedance transformer for matching the external quality factor (Qext) with the circuit bandwidth. Measured results show good agreement with the simulation.