Hee-Ran Ahn

General design equations, small-sized impedance transformers, and their application to small-sized three-port 3-dB power dividers

In this paper, design equations for three-port power dividers have been derived. These design equations are available for both arbitrary power divisions and arbitrary termination impedances, and many sets of design equations are possible. Therefore, the design equations may be called general design equations and an arbitrary design impedance A is introduced to describe them. On the basis of the derived general design equations, a coplanar three-port power divider with a power split ratio (3 dB) terminated by 50, 60, and 70 /spl Omega/ is designed with A=33.33 /spl Omega/, so that a commercially available resistor 100 /spl Omega/ can be used for the isolation resistance. Additionally, to reduce the size of transmission-line impedance transformers, two types of small-sized impedance transformers are designed, named a constant VSWR-type transmission-line impedance transformer (CVT) and a constant conductance-type transmission-line impedance transformer (CCT) and compared with conventional reduced-sized impedance transformers. These impedance transformers are designed in the low-Q region on the Smith chart. Therefore, they show wide-band properties. To make sure that the derived design equations of CVTs and CCTs are reasonable, four 1;6:1 impedance transformers, CVT 20/spl deg/, CVT 30/spl deg/, CCT 15/spl deg/, and CCT 20/spl deg/ have been fabricated in microstrip technology and measured. The measured results show the expected tendency. Based on the CVTs and CCTs, small-sized three-port 3-dB power dividers are constructed and named a constant VSWR-type three-port 3-dB power divider (CVT3PD) and a constant conductance-type three-port 3-dB power divider (CCT3PD). For the CVT3PD and CCT3PD, perfect isolation conditions are derived, and it is shown that the perfect isolation circuit (I.C) must be composed of resistance combined with capacitance or inductance in the case that the length of transmission lines is not /spl lambda//4. These I.Cs are quite different from conventional ones composed of only resistance. Finally, on the basis of the derived perfect isolation impedance, CVT3PD and CCT3PD are designed and simulated, giving the possibility that a CCT3PD can be realized with the electrical length 15.30/spl deg/ of the transmission lines.

Miniaturized 3-dB ring hybrid terminated by arbitrary impedances

In the UHF or VHF band, the new design method of a small-sized 3-dB 0/spl deg//180/spl deg/ ring hybrid terminated by arbitrary impedances using both lumped and distributed elements is presented. At the center frequency of 900 MHz, the small sized 3-dB 0/spl deg//180/spl deg/ hybrid terminated by arbitrary impedances is designed, analyzed and tested. Good agreement is obtained between measured and predicted results. Since both lumped and distributed elements are used, the proposed hybrid occupies about 30% of an all distributed-type hybrid. >

Arbitrary termination impedances, arbitrary power division, and small-sized ring hybrids

If a ring hybrid is terminated by arbitrary impedances, design equations can not be derived with conventional methods because symmetry planes for even and/or odd symmetries are not available. Therefore, under these conditions new design equations for ring hybrids have been derived. They can be applied to both ring hybrids with arbitrary termination impedances and arbitrary power division ratios. Also, new design equations for small sized ring hybrids have been developed. They allow that arbitrary power divisions, arbitrary termination impedances and specially small sized ring hybrids can be designed. On the basis of these derived design equations, a simulation of ring hybrids with 4 arc lengths of 75/spl deg/, arbitrary termination impedances and a power split ratio of 4 dB was performed using ideal CPS crossover.

Asymmetric four-port and branch-line hybrids

Two different asymmetric branch-line hybrids, a conventional-direction asymmetric branch-line hybrid (CABH) and an anti-conventional-direction asymmetric branch-line hybrid (AABH) are discussed and their design equations are derived. On the basis of the derived design equations, a uniplanar CABH was fabricated with coplanar waveguide (CPW) technology and measured.

Asymmetric ring-hybrid phase shifters and attenuators

A new structure of asymmetric ring-hybrid phase shifters and attenuators is presented. Each consists of an asymmetric ring hybrid and reflecting terminations, and it does not have any additional 90/spl deg/ phase delay line for utilizing symmetric reflecting terminations that conventional phase shifters use. To analyze these asymmetric ring-hybrid phase shifters, normalized impedance ratios NI/sub b/ and NI/sub d/ are introduced, and the possibilities to reduce the size of the reflecting terminations are presented. Using the new structure of the asymmetric ring-hybrid phase shifters, asymmetric ring-hybrid attenuators are synthesized. To analyze the attenuators, normalized resistance ratios NR/sub Lb/ and NR/sub Ld/ are introduced, so that the resistances in the reflection terminations can arbitrarily be determined. On the basis of the derived new structures, a uniplanar asymmetric ring-hybrid -135/spl deg/ phase shifter and a microstrip asymmetric 4-dB attenuator with 45/spl deg/ phase shift have been fabricated and measured. They show good agreement between measured and simulated results and they may be used for impedance transformers besides their original functions.

Arbitrary termination impedances, arbitrary power divisions and small-sized ring hybrids

If a ring hybrid is terminated by arbitrary impedances, design equations can not be derived with conventional methods because symmetry planes for even and/or odd symmetries are not available. Therefore, under these conditions new design equations for ring hybrids have been derived. They can be applied to both ring hybrids with arbitrary termination impedances and arbitrary power division ratios. Also, new design equations for small sized ring hybrids have been developed. They allow that arbitrary power divisions, arbitrary termination impedances and specially small sized ring hybrids can be designed. On the basis of these derived design equations, a simulation of ring hybrids with 4 arc lengths of 75/spl deg/, arbitrary termination impedances and a power split ratio of 4 dB was performed using ideal CPS crossover.

Small-sized wideband CVT- and CCT-ring filters

Two types of small-sized wideband CVT- (constant VSWR impedance transformer) and CCT- (constant conductance impedance transformer) ring filters are introduced, designed, simulated and one of two, a CCT-ring filter, is tested. They consist of CVTs and CCTs, and two short stubs are connected at the 90/spl deg/ and 270/spl deg/ positions of each ring. The circumference of the ring can be reduced theoretically up to 60/spl deg/ and two of many cases having about 300/spl deg/ circumference are simulated. The simulated results show more than 100% fractional bandwidth, which can be obtained with more than 5 stages in conventional design techniques. A CCT ring filter suggested in this paper has been fabricated in microstrip technology and the measured results show good agreement with the simulated ones.

Novel Ring Filters As Wide-Band 180° Transmission Lines

A novel ring fiter as a wide-band 180° transmission line is introduced, designed and analyzed. Most of conventional ring filters have used gaps between a ring and the feeding lines as a coupling element Due to the gap discontinuities, the circuits realized with a ring together with feeding lines suffer from high-insertion lost To reinforce this weak point, two feeding lines are directly connected at the 0° and 180° points and two ¿g/4 stubs are short-circuited at the 90° and 270° point of the ring. These two stubs are necessary to reject the power at even multiples of the design center frequency and as resonators for a filter characteristics. As the ring filter is designed with the concept of power division at the input port and power combining at the output port, two different parts of the combined power have the same phases in the whole frequency range if the transmission lines are ideal. Therefore, simulation performances are quite good with an insertion loss of ¿0.034 dB and a return loss less than ¿20 dB in a relative bandwidth of about 2.2: 1. Also, it is shown that this ring filter can be used as a wide-band impedance transformer.

Asymmetric Three-Port 45° Power Dividers Composed of Small-Sized Impedance Transformers

It has been demonstrated that two types of small-sized impedance transformers, constant VSWR-type transmission-line impedance transformers (CVTs) and constant conductance-type transmission-line impedance transformers (CCTs) may be utilized not only as impedance transformers but also as phase shifters. The CVTs and CCTs have arbitrary phase shifts less than 90°, which is quite different from that a conventional impedance transformer has odd multiple of 90° phase shift. Using the CCTs with 45° phase shift, asymmetric three-port 45° power dividers terminated by arbitrary impedances have been constructed and their design equations have been derived. Finally, a uniplanar asymmetric three-port 45° power divider terminated by 30¿, 60 ¿ and 50 ¿ has been fabricated on Al2O3 substrate (¿l = 9.9 and h = 635 um) in CPWs (coplanar wave guides) and tested.