^{1}

^{1}

^{*}

^{2}

^{2}

In this paper, two ultra-wide band power dividers are introduced. Compact equal power divider is considered firstly where an extended transmission lines and double open stubs are used in order to increase the bandwidth. Secondly, an unequal UWB power divider is introduced where multi-stage impedance is used. The proposed power dividers are fabricated and measured. The overall sizes of the proposed power dividers are 11.37 × 17.87 mm2 for the equal one and 12.13 × 29.03 mm
^{2} for the unequal power divider. The simulated results are compared with the measured results and good agreement is obtained.

Power dividers play an important role in many microwave systems such as balanced mixers, phase shifters, power amplifiers, and antenna array feed networks. Wilkinson power dividers are the most popular dividers which achieve completely matched output ports with high isolation between them and a fractional bandwidth of 20%. There is a great interest in designing ultra-wideband (UWB) components due to the rapid growth of the short range broadband communications, indoor wireless networks, and UWB radar imaging systems. Different UWB power dividers had been designed [

In [

In this paper, an UWB equal power divider is analyzed and proposed. The analysis is based on the idea of double stub matching. It includes an extended transmission line and double open circuited stubs at each of the output ports in order to increase the bandwidth of operation. Also, an unequal UWB power divider analysis based on the idea of two section transmission line is proposed. On contrary to the unequal power dividers presented in [

_{3}. The double open stubs

open stubs lengths can shift the suppressed harmonics outside the UWB range [

In order to analyze the proposed equal power divider in simple and efficient manner, it can be represented by a cascade connection of five two-port networks using ABCD matrices and even-odd mode analyses. In the even mode, _{3} with

Similarly, for the odd mode case, ^{th}stage will have a value of

The calculated A B C D parameters are converted to S-parameters [

dB equal power divider, the characteristic impedance of the input and output ports are

In the case where two signals of the same magnitude and phase (even mode signals) are applied to ports 2 and 3 of the circuit shown in _{3} and the two open circuited shunt stubs θ_{1} and θ_{2} in addition to their impedances Z_{1} and Z_{2}, the A B C D parameters are obtained using Equation (1) as:

In the case where two signals of the same magnitude but out of phase (180˚ phase shift), such case is known as an odd mode, when such two signals are applied to ports 2 and 3 of the circuit shown in _{3} and the two open circuited shunt stubs θ_{1} and θ_{2} in addition to their impedances Z_{1} and Z_{2}, the A B C D parameters are obtained using Equation (2) as:

Low cost FR4 material with dielectric constant^{2}. The flowchart for illustrating the analysis and simulation trials until the optimized parameters are obtained is shown in

The layout of the proposed UWB power divider is presented in

1.37 | 0.34 | 0.78 | 1.37 |

5 | 7 | 2 | 0.5 |

results are illustrated in

solution of the full wave equation, so some discrepancy must be appearing between analytical and simulation results. The dimensions of the proposed power divider were optimized to obtain good return loss and good isolation between output ports over the UWB frequency range.

characteristic impedance _{2} and Z_{3}). The output quarter wave transformers with characteristic impedances _{2} and Z_{3} into the impedance Z_{c}.

This design can be viewed as a two section quarter wave transformer. By this way, this design will achieve a significant increase in the performance. According to [

where _{c} is the characteristic port impedance which is equal to^{2}. For example, if it is required to design unequal power divider with division ratio, S_{31} = 0.7962 or −1.98 dB and S_{21} = 0.6046 or −4.37 dB, then the power dividing ratio (k) is equal to 1.3168. By substituting into Equations (11)-(14), the values of the characteristic impedances for the power divider are as follows, _{2} = 75 Ω, Z_{3} = 35 Ω, _{0} = 5 mm, L_{1} = 7.88 mm, L_{2} = 6.19 mm, L_{3} = 5.83 mm, L_{4} = 6.09 mm, and L_{5} = 5.91 mm. The calculated S-parameters from the above discussion have been presented in _{31} = 0.7691 or −2.28 dB and S_{21} = 0.5158 or −5.75 dB.

Finally, the proposed UWB equal power divider is fabricated and measured with a vector network analyzer. _{21} and S_{31} are around (−3 dB ± 1) overall the UWB range.

On the same manner, the designed UWB unequal power divider is fabricated and its photo is shown in _{11 }for simulation and measurement

is less than −10 dB over the band 2.5 GHz to 10.8 GHz; that cover the UWB rang. The insertion loss S_{21} is around −3.0 ± 0.8 dB over the bandwidth 3.0 GHz to 9 GHz which cover most of the UWB range. The insertion loss S_{31} is around −5.0 ± 1.5 dB over the bandwidth 3.0 GHz to 8 GHz which cover also most of the UWB range.

The deviations of the measurements from the simulations came from tolerance in fabrications; mismatch due to soldering of launchers and due to the losses of FR4 substrate material especially at higher frequency above 6 GHz.

In this work, an UWB equal power divider based on double stub matching was proposed. The UWB performance was achieved by introducing an extended transmission line and double open circuited stubs to each of the output ports of the Wilkinson power divider. The proposed divider was investigated by using even and odd mode analysis. In addition, the UWB power divider with unequal power ratio was presented. There was a good agreement between simulated and measured results. Simple structure and compact size characteristics of the proposed dividers make them very useful in UWB applications and antenna array feed networks.

Dardeer, O., Abouelnaga, T., Mohra, A. and Elhennawy, H. (2017) Compact UWB Power Divider, Analysis and Design. Journal of Electromagnetic Analysis and Applications, 9, 9- 21. https://doi.org/10.4236/jemaa.2017.92002