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.

This paper presents a new simple method for reducing mutual coupling between dual-element microstrip antennas (MSAs) for bistatic radar using a wave absorber. The two elements are closely placed on a substrate by the distance of λ0/4 through the wall-shaped absorber. The height and width of the absorber were optimized for minimum mutual coupling with the electromagnetic simulator. It was found that less than -60 dB minimum mutual coupling can be achieved by the impedance matching of the absorber in a near field. The influence for the reflection characteristics from the absorber is small enough, and the reduction of the antenna gain is only 1.1 dB. The rate of the lost power characteristics showed that the absorption improves the mutual couplings. Then the proposed structure for a practical configuration was investigated. The measurement results of the optimized structure tallied well with the simulation results.

To better understand antenna properties in a narrow space such as in a densely-packed device, a circular microstrip antenna in a narrow parallel-plate waveguide is theoretically studied. An analytical expression is derived for the input impedance in a parallel-plate waveguide by using the cavity model with surface admittance on the side wall. The surface admittance is defined by the external magnetic field due to the equivalent magnetic current at the aperture and takes into account the contribution of the parallel plates to the antenna. The magnetic field external to the antenna, that is in the parallel-plate region, is determined by using a dyadic Green's function. The input impedance is then calculated by a basic definition based on the conservation of the complex power. An analytical expression which couples the resonant frequency and the surface susceptance is also formulated. Presented expressions are validated by comparison with experimental results.

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.

In this paper, a novel microstrip hairpin-line bandpass filter which employs a modified Minkowski fractal shape is proposed. Although conventional hairpin-line filters are popular for RF front ends, they suffer from undesired spurious responses located at the second harmonic, which causes asymmetry in the upper skirt band. By proper design, the second harmonic of fractal filters can be significantly suppressed through the use of fractal shape. To validate this novel geometry, the proposed filters are fabricated and measured. Simulated results are in good agreement with measured results.

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.

A broadband microstrip comb-line antenna using a corporate feeding system was developed. The antenna was composed of four colinearly-arranged comb-line antennas with traveling-wave excitation fed by a parallel-feeding circuit of tournament configuration. The total phase deviation due to frequency change became one fourth of the ordinary series feeding from the end of the antenna. Furthermore, the terminations of the inner two comb-lines were connected at the overall center of the developed antenna. Therefore, the narrowband matching elements are not necessary and the amplitude deviation of the aperture distribution for input from one side due to frequency change is compensated by deviation for input from the other side. Broad bandwidth can be expected by using the proposed configuration. The proposed antenna was designed at 76.5 GHz. The effect of the proposed feeding-circuit for broadband operation was confirmed by comparing the measured performances of the antennas fed by other feeding circuits; the end feeding, the center feeding and the ordinary corporate feeding. The bandwidth of the proposed corporate feeding antenna with the center connecting was approximately 14% and 7% wider than the antennas of the center feeding and of the ordinary corporate feeding, respectively.

In this letter, a novel design of a switchable microstrip antenna is proposed for circular polarization diversity. The proposed antenna has a simple construction of inner and outer corner-truncated radiating circular patches for switchable circular polarization. By controlling the state of two PIN diodes, left- and right-hand circular polarizations are easily alternated. The results of experiments show excellent switching radiation performances at the resonant frequency and good agreements with the simulated ones.

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.

Many kinds of microstrip array antennas have been developed in the millimeter-wave band. In order to avoid feeding loss and the decrease of antenna gain by beam shift due to frequency changes, center-fed array antennas are advantageous. In this case, the element spacing around the feeding circuit of the transition from the waveguide to two microstrip lines is larger than one wavelength. Therefore, the sidelobe level grows significantly. In order to suppress the sidelobe level, we propose transitions with slot radiators. Moreover, any polarization angles can be achieved by changing the slot angle. A wide variety from 1.5% to 70% of slot radiator coupling powers can be achieved. To investigate the performance of the proposed transition, 10, 22 and 30-element center-fed microstrip comb-line antennas with the proposed transition were developed at 76.5 GHz, and measured performance was evaluated in the millimeter-wave band.

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.

In this article, a simple structure of the Wilkinson power divider which can suppress the nth harmonics of the Wilkinson power divider is proposed. By replacing the quarter wavelength transmission lines of the conventional Wilkinson power divider with the equivalent P-type transmission lines, a compact power divider which can suppress the nth harmonic is achieved. Design equations of proposed P-type line are achieved by ABCD matrices. To verify the design approach, the proposed power divider is designed, simulated (by ADS, CST Studio, and Sonnet simulators), and fabricated at 1 GHz to suppress the fifth harmonic. The proposed structure is 46% of the conventional Wilkinson power divider, while maintaining the characteristics of the conventional Wilkinson power divider at the fundamental frequency. The insertion losses at the fifth harmonic are larger than 35 dB. Furthermore, the second to seventh harmonic are suppressed by least 10 dB. Here is an excellent agreement between simulated results and measured results.

A novel square patch antenna with reconfigurable circular polarization (CP) is presented in this letter. A circular slot with perturbation is placed beneath the patch. The circular slot that has an inner perturbation yields right-handed CP, but with an outer perturbation slot yields left-handed CP. Experiments show an antenna gain of 2.8 dBic and a 3-dB axial ratio bandwidth of 30 MHz which well match the corresponding simulation results.

A stacked rectangular microstrip antenna with a shorting plate and a helical pin is proposed as a car antenna for triple band operation in ITS. The proposed antenna operates as a conventional stacked microstrip antenna at the highest frequency band. At the middle and the lowest frequency bands, the antenna radiates at low elevation angles from the helical pin and the shorting plate. In this paper, as an example of triple band antennas in the ITS, an antenna is designed that supports PHS, VICS and ETC. The proposed antennas have the proper radiation pattern for each application and are small in size.

In this letter, a new design of a metamaterial-based microstrip antenna is presented using triangular slots embedded on the ground plane to enhance the impedance bandwidth. To improve the impedance bandwidth of the proposed antenna, two resonant mode frequencies are closely allocated using the slotted ground without changing the radiator element. The impedance bandwidth of VSWR < 2.5 is measured at 2.43 GHz (37.6%) centered on 6.46 GHz, from 5.24 GHz to 7.67 GHz in good agreements with the simulated results.

Narrow-wall-connected microstrip-to-waveguide transition using V-shaped patch element in millimeter-wave band is proposed. Since the microstrip line on the narrow-wall is perpendicular to the E-plane of the waveguide, waveguide field does not couple directly to the microstrip line. The current on the V-shaped patch element flows along inclined edges, then current on the V-shaped patch element couples to the microstrip line efficiently. Three types of transitions are investigated. A numerical investigation of these transitions show some relations between bandwidth and insertion loss. It is confirmed that the improved transition exhibits an insertion loss of 0.6 dB from 76 to 77 GHz, and a bandwidth of 4.1% (3.15 GHz) for the reflection coefficient below -15 dB.

In this letter, compact loop resonator type circular polarization (CP) antennas with a square ring and an X-shaped meander loop are presented. Both antennas are fed to a microstrip line with electromagnetic coupling. By adjusting the gap and length of a coupled microstrip line, the magnitude and phase conditions of two orthogonal modes for CP can be determined. The proposed antennas show good axial ratios and also good agreements between experimented and simulated results.

A one-input four-way power divider is developed for feeding circuit of a microstrip comb-line antenna. The four-way power divider is composed of two-stage tournament-configuration of three Y-junctions. To control the sidelobe level and beam width in radiation pattern of the array, the power dividing ratio is assigned for the four-way power divider. Required dividing ratio is designed by changing the line width to control the impedance. To take impedance matching at the connection parts of the Y-junctions, 1/4-wavelength impedance-transformers are applied to the divider and taper structure is supplied at discontinuities. Four-comb-line antennas are designed and fabricated at 76.5 GHz. We evaluated sidelobe level and beam width by experiment to confirm the performance of the power divider.