Tetsuo Anada

Novel Compact Ultra-Wideband Bandpass Filter by Application of Short-Circuited Stubs and Stepped-Impedance-Resonator

To realize the compact ultra-wideband (UWB) bandpass filters, a novel filter prototype with two short-circuited stubs loaded at both sides of a stepped-impedance resonator (SIR) via the parallel coupled lines is proposed based on a distributed filter synthesis theory. The equivalent circuit of this filter is established, while the corresponding 7-pole Chebyshev-type transfer function is derived for filter synthesis. Then, a distributed-circuit-based technique was presented to synthesize the elements values of this filter. As an example, a FCC UWB filter with the fractional bandwidth (FWB) @ -10 dB up to 110% was designed using the proposed prototype and then re-modeled by commercial microwave circuit simulator to verify the correctness and accuracy of the synthesis theory. Furthermore, in terms of EM simulator, the filter was further-optimized and experimentally-realized by using microstrip line. Good agreements between the measurement results and theoretical ones validate the effectiveness of our technique. In addition, compared with the conventional SIR-type UWB filter without short-circuited stubs, the new one significantly improves the selectivity and out-of-band characteristics (especially in lower one -45 dB@1-2 GHz) to satisfy the FCCs spectrum mask. The designed filter also exhibits very compact size, quite low insertion loss, steep skirts, flat group delay and the easily-fabricatable structure (the coupling gap dimension in this filter is 0.15 mm) as well. Moreover, it should be noted that, in terms of the presented design technique, the proposed filter prototype can be also used to easily realize the UWB filters with other FBW even greater than 110%.

Novel wideband bandpass filter using open-ended stub loaded parallel coupled short-circuited three-line unit

Open-ended stub loaded parallel coupled short-circuited three-line structure is proposed to realize a new wideband bandpass filter. The characteristics of the new coupling unit were firstly investigated based on simulation, followed by proposing a two-step design scheme: 1. A Chebyshev filter is synthesized on the desired passband, using symmetric three-line coupling units. 2. The transmission zeros are then introduced to improve the skirt and stopband characteristics by properly designing the stubs. Then, a UWB bandpass filter covering the lower UWB band (BW: 3.1–4.8GHz, FBW: 43%) is designed to explain the proposed design procedure. The filter was then simulated, fabricated and measured to compare with the theoretical predictions. A good agreement validates the effectiveness of the proposed new coupling structure and corresponding filter design technique.

Non-contacting near-field mapping of planar circuits in microwave frequency band

An ultra-wideband near-field mapping system has been setup to scan the electromagnetic (EM) surface field above planar/PCB circuits. A semi-rigid coaxial electric probe is employed to measure the electric field up to 18 GHz and an improved CPW loop-type magnetic probe with self-resonance-suppression characteristics is used to measure the magnetic field up to more than 10 GHz. In order to verify the performance of our new system, EM surface field measurement were conducted for a short-circuited microstrip line, and a UWB (3.1 GHz - 10.6 GHz) filter using broadside-coupled structure, etc. The results demonstrate that the presented new measurement system is a powerful tool to accurately characterize the behavior of planar circuits in very wide frequency bands. The comparison between the measured results and the reference data validate the good performance of our system. In addition, a further study on extracting the effective dielectric constant of the PCB substrate is also demonstrated with the experimental validation by our system.

Design of a Microstrip UWB Bandpass Filter Having Sharp Attenuations and Wide Stopbands

In this paper, a novel ultra-wideband (UWB) bandpass filter having a midband frequency of 4.1 GHz and a fractional bandwidth of 34.1% is designed with a combined use of a microstrip stub-loaded dual-mode ring resonator and parallel-coupled step-impedance two-mode resonators. Advantages of both the stub-loaded ring resonator and the step-impedance two-mode resonator are exploited, and the UWB filter shows sharp attenuations near the passband and very wide stopbands. The frequency response of the filter meets quite well Japans low-band limit for UWB applications.

Synthesis of Ultra-Wideband (UWB) Bandpass Filter with High-Performance

In this paper, a high-performance ultra-wideband bandpass (UWB) filter consisting of two short-circuited stubs combined with two-stage of stepped impedance resonators (SIRs) is proposed to meet FCCs specifications. The filter is first designed by newly-presented synthesis scheme, then optimized by EM simulator, fabricated in microstrip line and finally characterized by network analyzer. The experimental filters responses compare very well with the theoretical ones, which successfully validates our synthesis techniques. In addition, the designed filter exhibits good characteristics of low insertion loss, quite sharp skirts, flat group delay, deep attenuations in stopband (especially in lower one) and well-satisfies even FCC outdoor specifications. It should be note that the proposed filter prototype can be also used to realize a UWB filter with an FBW even greater than 110%.

Recent Progress in Synthesis Techniques of Microwave Ultra-Wideband (UWB) Filters

This paper describes our recent research works on the synthesis theory for designing novel microwave ultra-wideband (UWB) bandpass filters (BPFs). Based on Z-transformation and analytical method of variable separation, we have implemented two different synthesis techniques, in terms of which three types of microstrip UWB BPFs were developed by comparing the newly-derived ideal and real transfer functions to obtain the structural parameters. The filter prototypes include the one using periodically loaded short-/open-ended stubs, the ones consisting symmetrical/quasisymmetrical/asymmetrical multi-mode stepped-impedance resonators (SIRs) and the other ones with two short-/open-circuited stubs positioned at both sides of SIRs. Several design examples of wideband BPFs are provided. All of them are verified well by experiments and exhibit good performances, such as compact sizes, low return loss in passband, flat group delay and good stopband property etc.

Time Domain FD-BPM for Calculating Pulse Propagation Properties of MMI Device with Photonic Crystal Structure

A time domain beam propagation method (TD-BPM) based on the finite-difference alternating direction implicit method is described for the numerical analysis of reflections in multimode interference circuits with photonic crystal structures. It is shown that TD-BPM using the Pade (1, 1) approximation is less sensitive to the choice of spatial step and allows a larger time step size to be used compared to the FD-TD method. Furthermore, the validity and accuracy of the TD-BPM based on the ADI method will be discussed through numerical examples in MMI circuits with photonic crystal structures.

Doublet Modular for Design of Microwave Filters

A novel doublet modular in filter design is introduced in the paper. We can use the doublet modular in bandpass filters. Using the doublet modular, asymmetry transmission zeros are created in the bandpass filter. We can locate the two transmission zeros at one side of the passband or both side of the passband. The doublet modular is demonstrated very flexible by showing a number of coupling matrices of cases. It is earlier to design higher order filters of high performance by cascading such doublet modular. And the response of the filter will be improved. In this paper, zero-shifting properties of the filter with source and load coupling are also proposed, which is different from zero-shifting properties proposed in filters without source and load coupling.