In this paper, a planar balun having simple and compact features with slit ground was proposed. The operating frequency can be designed by the length and position of the defected ground slits. The 20 dB bandwidth of the common mode rejection ratio of the measuring balun was over 90%.

We have proposed a waveguide to microstrip line transition, which perpendicularly connects one waveguide into two microstrip lines. It consists of only a waveguide and a dielectric substrate with copper foils. A backshort waveguide for typical transitions is not needed. Additionally, the transition does not require via holes on the substrate. These innovations simplify the structure and the manufacturing process. We assume that our transition and antennas are co-located on the substrate. We reduced the undesirable radiation from the transition so as not to contaminate the desirable radiation pattern. In this paper, we address output phase of our transition. Since the transition has two MSL output ports connecting to different radiation elements, the phase error between two dividing signals leads to beam shift in the radiation pattern. Unfortunately, misalignment of etching pattern between copper layers of the substrate is unavoidable. The structural asymmetry causes the phase error. In order to tolerate the misalignment, we propose to add a pair of open stubs to the transition. We show that the structure drastically stabilizes the output phase. Though the stubs create some extra radiation, we confirm that the impact is not significant. Moreover, we fabricate and measure a prototype antenna that uses the transition. In the case of with stubs, the radiation pattern is unchanged even if the misalignment is severe.

An f0/2f0 (frequency ratio of two) microstrip diplexer with simple circuit configuration as well as low and wideband insertion-loss characteristics is proposed. It is a parallel combination of a coupled line for f0 port and a wave-trap circuit composed of a transmission line and an open stub for 2f0 port. All the lines and stub have a quarter-wave length for f0. Matching circuits are not needed. Circuit and electro-magnetic simulation results prove that the proposed f0/2f0 diplexer exhibits well-balanced properties of insertion loss (IL), IL bandwidth, and isolation, as compared to conventional simple f0/2f0 diplexers composed of two wave-trap circuits or two coupled lines. The proposed diplexer is fabricated on a resin substrate in a microstrip configuration at frequencies of f0/2f0=2.5/5 GHz. Measured results are in good agreement with simulations and support the above conclusion. The proposed diplexer exhibits ILs of 0.46/0.56 dB with 47/47% relative bandwidth (for f0/2f0), which are lower and wider than f0/2f0 diplexers in literatures at the same frequency bands.

This paper presents a theoretical analysis of a tunable resonator using a coupled line and switches for the first time. The tunable resonator has the capability to tune its resonant frequency and bandwidth. The resonator has two suitable features on its tunable capability. The first feature is that the resonator retains its resonant frequency during bandwidth tuning. The second feature is that the on-state switch for tuning the bandwidth does not affect the insertion loss at the resonant frequency. These features are theoretically confirmed by its mathematically derived input impedance. The results from electromagnetic simulation and measurement of the fabricated tunable resonator also confirm these features. The fabricated tunable resonator changes the resonant frequency from 2.6 GHz to 6.4 GHz and bandwidth between 9% and 55%.

This paper presents a theoretical analysis and experimental confirmation of a tunable ring resonator that can independently change its resonant frequency and bandwidth. The tunable ring resonator comprises a ring resonator, three tunable capacitors, and switches. The resonant frequency changes according to the capacitance of tunable capacitors, and the bandwidth varies by changing the state of the switches. The unique feature of the resonator is that the resonant frequency remains steady when the bandwidth is changed. The fundamental characteristics are shown based on linear circuit simulation and electromagnetic simulation results. The resonator is fabricated using GaAs FET single-pole single-throw switches. The fabricated resonator changes the resonant frequency from 1.5 GHz to 2.0 GHz and the fractional bandwidth from 5% to 30%.

We propose waveguide to microstrip line transitions for automotive millimeter wave radar modules. The transitions perpendicularly connect one waveguide and one or two microstrip lines. The configuration is simple because it consists of a waveguide and a dielectric substrate with copper foils. Additionally the transitions do not need via holes on the substrate. It leads to lower costs and improved reliability. We have already proposed a via-less transition by using multi-stage impedance transformers. The impedance transformers are used for suppressing undesirable radiation from the transition as well as impedance matching. In this paper, we propose a new transition with the microstrip lines on the long axis of the waveguide while most transitions place the microstrip lines on the minor axis (electric field direction) of the waveguide. Though our transition uses bend structures of microstrip lines, which basically cause radiation, our optimized configuration can keep small radiation. We also design a transition with a single microstrip line. The proposed transition with 2 microstrip lines can be modified to the 1 microstrip line version with minimum radiation loss. Electromagnetic simulations confirm the small radiation levels expected. Additionally we fabricate the transitions with back to back structure and determine the transmission and radiation performance. We also fabricates the transition for a patch array antenna. We confirm that the undesirable radiation from the proposed transition is small and the radiation pattern of the array antenna is not worsen by the transition.

The authors have proposed a new type of flexible and printable 12GHz-band phase shifter using polymer actuator for the first time. Polymer bending actuator was used as a termination device of a reflection-type 3-dB, 90° hybrid coupler as the phase-shift control unit which controls the electrical length of the waveguide for microwave signals by the applied bias voltage. The microstrip line circuit of the device has been fabricated using low-cost screen printing method. Polymer bending actuator having three-layer stacking structure, in which an ionic liquid electrolyte layer is sandwiched with two conductive network composite layers, was formed by wet processes. The authors have confirmed that the phase shift could be controlled in analog by low driving voltages of 2-7 V for the actuator with a insertion loss of 2.73 dB. This phase shifter can be integrated with flexible patch antenna and the current flexible polymer electronics devices such as transistors.

We present a design method for miniaturizing double stub resonators that are potentially very useful for wide range of applications but have limited usage for MMICs due to their large footprint. The analytical design model, which we introduce in this paper, allows for determining the capacitances needed to achieve the targeted shrinking ratio while maintaining the original loaded-Q before miniaturization. To verify the model, 18-GHz stub resonators that are around 40% of the original sizes were designed and fabricated in GaAs MMIC technology. The effectiveness of the proposed technique is also demonstrated by a 9-GHz low phase-noise oscillator using the miniaturized resonator.

This paper presents a simple-structured tunable resonator employing semiconductor switches that can change its resonant frequency discretely but precisely. The tunable resonator comprises a transmission line with a comb-shaped pattern and multiple single-pole single-throw (SPST) switches placed between the teeth of the comb-shaped pattern. The resonator changes its resonant frequency according to the switch states, by controlling the path length carrying a high frequency current. The characteristics of the proposed resonator are evaluated through both method of moment electromagnetic simulation and fabrication, using GaAs FET SPST switches. The fabricated resonator changes its resonant frequency from 1.63,GHz to 1.85,GHz. This paper also introduces two circuit designs based on the proposed resonator that expands the tuning range of the resonant frequency or the number of resonant frequencies to be obtained.

In this letter, we propose a partial impedance-matching method using a two-strip resonator for noncontact Passive Intermodulation (PIM) measurements using a coaxial tube. It is shown that the strip closer to the inner tube of the coaxial tube is dominant in the observed PIM characteristics while both strips are excited equally. The ideal efficiency of power to each strip is 50%, which is a significant improvement in comparison with conventional methods.

An equivalent network analysis for an arrangement that combines a microstrip line and coaxial conductor for the purpose of measuring permeability is discussed in this paper. The measurement circuit used consists of a coaxial conductor with a sample housed inside and a short microstrip line connected to both sides. The coaxial conductor is composed of an electrically grounded coaxial metal pipe with open ends and a center conductor. Equivalent networks for this arrangement are investigated to determine the complex permeability from the impedance of the measurement circuit. We have employed a π network composed of a resistor and an inductor connected in series, and shunt capacitors as the equivalent circuit for the measurement portion. It has been found that the measurement error ratio of less than a few percent can be obtained for most frequency ranges of 10 MHz to 500 MHz.

This paper proposes a new three-mode resonator, which consists of a parallel-coupled microstrip line resonator embedded with a slotline resonator, and develops a compact low-loss bandpass filter (BPF) with a sharp roll-off response because of four transmission zeros (TZ) located very near the passband. Resonance mechanism and properties of the three modes are first analyzed by using an eigen-mode analysis, and then an equivalent circuit model is established for expressing a novel coupling scheme of the developed BPF. It is made clear from the results of circuit analysis that the four TZs are produced because of multiple paths between the input/output stub lines formed by the three resonant modes and the direct source/load coupling. The validity of the proposed resonator and filter is supported by the comparison between simulated and measured results.

Mirrored serpentine microstrip lines are proposed for a parallel high speed digital signaling to reduce the peak far-end crosstalk (FEXT) voltage. Mirrored serpentine microstrip lines consist of two serpentine microstrip lines, each one equal to a conventional normal serpentine microstrip line. However, one serpentine microstrip line of the mirrored serpentine microstrip lines is flipped in the length direction, and thus, two serpentine microstrip lines face each other. Time domain reflectometry measurements show that the peak FEXT voltage of the mirrored serpentine microstrip lines is reduced by 56.4% of that of conventional microstrip lines and 30.0% of that of conventional normal serpentine microstrip lines.

This paper presents an ultra-wideband (UWB) bandpass filter (BPF) with sharp attenuation slope characteristics. The circuit structure consists of an inter-digital finger resonator, parallel-coupled lines and phase matching line. The design of the bandwidth was described by using the even and odd mode characteristic impedances in the resonator structure. The parallel-coupled lines were also designed in the same manner. The parameters of the resonator and two parallel-coupled lines in combination as the BPF were then optimized by the simulation with HFSS. The designed BPF was experimentally fabricated and its measured performances showed the bandwidth from 3.6 to 10 GHz with the 20 dB outband rejection. For the U.S. UWB band design, the matching line was inserted between the two parallel-coupled lines. The matching at both band edges was then qualitatively analyzed on the smithchart. The HFSS simulation results of the structure realized the bandwidth from 3.1 to 10.6 GHz with sharp attenuation slope characteristics for SWR < 2.0. The measurement results agree well with the simulation results.

In this paper we present eigenmode analysis of the propagation constant for a microstrip line with dummy fills on a Si CMOS substrate. The effect of dummy fills is not negligible, particularly in the millimeter-wave band, although it has been ignored below frequencies of a few GHz. The propagation constant of a microstrip line with a periodic structure on a Si CMOS substrate is analyzed by eigenmode analysis for one period of the line. The calculated propagation constant and characteristic impedance were compared with measured values for a chip fabricated by the 0.18 µm CMOS process. The agreement between the analysis and measurement was very good. The dependence of loss on the arrangement of dummy fills was also investigated by eigenmode analysis. It was found that the transmission loss becomes large when dummy fills are arranged at places where the electromagnetic field is strong.

In this paper, accuracy or error in permeability measurement using a combined microstrip line-coaxial conductor method was investigated. The measurement circuit used in this study is composed of a microstrip line (MSL) circuit and a grounded metal pipe with a center conductor passing through it coaxially. A sample is placed between the metal pipe and the center conductor. We evaluated the measurement accuracy for this measurement arrangement with electromagnetic simulation for the case where there are gaps between the sample and the holder. As a result, it has been shown that the normalized errors for this method have similar gap size dependence to the conventional coaxial method, but are about 10 to 20 percent greater than the coaxial method. With a view to improving the measurement accuracy, a correction method for the error is also discussed.

A new type of the wide-band BPF made up of an inter-digital resonator and parallel-coupled lines was proposed. The bandwidth of the inter-digital resonator becomes wider by increasing the number of fingers. The design of the parallel-coupled line was performed by optimazing the structural parameters so that the bandwidth is the same as that of the inter-digital resonator. The measured results of the combination of above elements for the BPF agreed well with the simulated ones such that the insertion loss is less than 0.67 dB and that the sharp skirt characteristics are realized by attenuation poles near the edges of the passband.

We have developed a high-temperature superconducting (HTS) filter with narrow bandwidth characteristic for receiver of weather radar in order to reduce interference between adjacent radar channels. To realize a filter with which a narrow bandwidth and low insertion loss are compatible, resonators with high unloaded Q (Qu) value are required. Hairpin microstrip resonators with 1.5 times wavelength were adopted to suppress the radiation loss and achieve a high Qu value. The developed HTS filter has 8-pole quasi-elliptic function response for sharp skirt characteristic. The measured frequency response of the developed filter shows center frequency of 5370 MHz, insertion loss of 2.04 dB and maximum return loss of 15 dB, which agrees with the designed responses.

In this paper, a new formulation of equal-length three-section open stubs having two zeros located on the unit circle and one zero at z=-1 (θ=π) in the Z-plane is presented. In particular, new filter configurations consisting of equal-length two-section open stubs, cascade lines, open stubs, and three-section open stubs are employed to emulate the discrete-time filters. To examine the validity of our formulation, we realized two discrete-time Chebyshev type II low-pass filters in the form of microstrip lines. The frequency responses of these two filters are measured to validate this new formulation.

Transmission characteristics of a left-handed (LH) ferrite microstrip line are significantly affected by the nonuniform DC bias magnetic field in the ferrite substrate (internal magnetic field Hin) caused by the inhomogeneous demagnetizing effect because the strip conductors of these devices must be mounted at the edge of the ferrite substrate. Three dimensional analyses on the LH ferrite microstrip line are performed taking into account the nonuniform internal magnetic field Hin. The analytical results show that the nonuniform internal magnetic field under the strip conductor near the edge of the ferrite substrate is useful for spreading the frequency band of negative permeability and nonreciprocal operation, and for improvement of both the insertion and return losses of the LH ferrite microstrip line. Measured results of more than 20 dB isolation with 2.2 dB insertion loss and 1.33 GHz bandwidth are corresponding well to the analytical results.