Yoshihiro Kokubo

Dual-Band Wilkinson Power Dividers Using a Series RLC Circuit

This paper describes a novel Wilkinson power divider operating at two arbitrary different frequencies. The proposed divider consists of two-section transmission lines and a series RLC circuit connected between two output ports. The circuit parameters for a dual-band operation are derived by the even/odd mode analysis. Equal power split, complete matching, and good isolation between two output ports are numerically demonstrated. Dual-band and broadband Wilkinson power dividers can be successfully designed. Finally, verification of this design method is also shown by electromagnetic simulations and experiments.

Directivity improvement of microstrip coupled line couplers based on equivalent admittance approach

The present paper suggests a simple and effective technique for remarkably improving the directivity of inhomogeneous coupled line couplers such as a microstrip coupler. The technique is based upon the equivalent admittance approach and requires only properly designed matching networks. In this paper, we treat a 1/4-wave parallel-coupled microstrip coupler of 15.8 dB, and obtain the directivity improvement of 20 or more dB over a bandwidth of about 1.2 GHz at a center frequency of 3.5 GHz. Finally the design results are confirmed by an em-simulator.

A design method of dual-frequency wilkinson power divider

This paper treats a novel Wilkinson power divider operating at two arbitrary different frequencies. The proposed divider consists of two-section transmission lines and a series RLC circuit connected between two output ports. The circuit parameters for a dual-frequency operation are derived by the even/odd mode analysis. Equal power split, complete matching, and good isolation between two output ports are demonstrated. Finally, verification of this design concept is shown by using an electromagnetic simulator.

Broadband lumped-element 180-degree hybrids utilizing lattice circuits

This paper suggests a novel lumped-element 180/spl deg/ hybrid utilizing lattice circuits. The present hybrid possesses a wide-band property differently from ordinary lumped-element hybrids composed of /spl Pi/ or/and T networks. The bandwidth ratio is 2.4 for a regular type and can be increased to 7.13 by adding a lattice type impedance transformer at each port. The validity and usefulness of this idea also are demonstrated by electromagnetic simulation for a uniplanar circuit pattern.

Miniature Broad-Band CPW 3-dB Branch-Line Couplers in Slow-Wave Structure

This paper presents some structures of artificial coplanar waveguide with very slow phase velocity and their applications to a design of compact 3-dB branch-line couplers. The slow-wave structure is constructed by periodically loading both of series inductance and shunt capacitance. First, a basic miniature branch-line coupler is designed and consequently considerable size-reduction of about 1/4 is obtained. Next, a broadband design technique is described using open-circuited quarter-wavelength series-stubs added at each port as a matching network. By size-reducing the series-stubs and branchline sections, a very compact broad-band coupler with a good hybrid performance over a wide bandwidth of 31 percent or more is realized. The design concepts and procedures are verified both numerically and experimentally.

Wide Band Metallic Waveguide With In-Line Dielectric Rods

Conventional rectangular metallic waveguides are seldom used at frequencies higher than twice the cutoff frequency because of higher mode propagation. Single-mode propagation is available for a metallic waveguide with arrayed dielectric rods at the center of the waveguide in the frequency under twice the cutoff frequency region using the TE20 mode, and in the frequency over twice the cutoff frequency region using the TE2o mode. If the metallic waveguide and dielectric loss tangent are assumed to be WR-90 (fc ap6.55 GHz) and 3times10-4, respectively, then the attenuation constants are smaller than 0.25 dB/m in the frequency range from 7 to 10 GHz, 15 to 16.5 GHz, and from 17.2 to 21 GHz.

Design of broadband semi-lumped and lumped element quadrature hybrids

Band-broadening techniques for semi-lumped and lumped element quadrature 3 dB hybrids are described. A semi-lumped hybrid is spiral-inductor-free, and the occupied area is about 1/150 compared with a distributed-element one at 1 GHz band. In lumped-element version, two kinds of matching networks are dealt with; one consists of an admittance inverter and a parallel tuned circuit, and the other makes good use of a series one. The former is marked by lower inductance values and the latter by less devise count and wider bandwidth. The frac- tional bandwidths of the designed hybrids are 20-27% for return loss better than 20 dB and amplitude balance tolerance 0.18 dB. Index Terms — directional couplers, lumped element micro- wave circuits, microwave integrated circuits, passive circuits.

Cavity-type directional couplers with simple structure

This paper treats directional couplers consisting of a rectangular cavity with four waveguide ports. Since the present couplers possess a very simple structure, they are useful for applications at higher microwave and millimeter-wave frequencies, and in a high-power microwave system. Directional couplers with various power-split ratios at X-band are investigated theoretically and experimentally. Furthermore, improvement of their bandwidth is presented.

Wide Band Metallic Waveguide with Asymmetric In-Line Dielectric Rods

A system that has an array of dielectric rods at the center of a waveguide was previously suggested for single mode propagation with a wide frequency range. However, it is difficult to introduce the wave source from a coaxial cable, due to use of the TE 10 -like and TE 20 -like modes. In this investigation, an asymmetric setup of the dielectric rods is proposed for better coupling efficiency of the TE 10 mode.

Dual-band metallic waveguide with low dielectric constant material

A metallic waveguide with dual in-line dielectric rods can propagate electromagnetic waves more than two times higher than the cutoff frequency region without higher modes. This type of waveguide, however, requires many rods with a high dielectric constant such as 29.5. Sintered alumina, with a dielectric constant around 9, may be more suitable for dielectric rods, as it is a popular material for use in microwave systems. Attenuation constants for alumina and for a high dielectric constant material were calculated using the finite-difference time-domain method and compared. Although the attenuation constant for alumina is higher than that of the high dielectric constant material due to its high loss tangent, it is not so high to make it practicable.