12704_SCTE_Broadband_Nov2016_COMPLETE_lowres

technical

A Design Procedure The design of a physically small, equal phase and equal power 1-to-4 ultra- wideband Wilkinson power divider is presented. Initially, a 1-to-2 divider was designed and optimised for the 3.1GHz-to-10.6GHz range. The 1-to-4 divider was then built using three 1-to-2 dividers and further optimised for full-band insertion loss, return loss and isolation. The circuits were constructed using a 0.75mm thick Rogers RO3035 substrate, and experimentally validated. By Ammar H. Ali, Professor Raed A. Abd-Alhameed, Yim Fun Hu, Mark B. Child and Costas Kyriacou for a 1-to-4 Ultra-Wideband Wilkinson Power Divider

Introduction Power dividers are important for impedance matching in many microwave and RF systems. In 1960, E.J. Wilkinson added an isolation resistor to a T-junction power divider, making a quarter- wave impedance transformer to enhance the return loss and isolation between outputs [1]. This design has the disadvantage of narrow operational frequency bandwidth. Several methods have been adopted to increase the bandwidth such as the introduction of additional sections [2] or stabs to a section [3], combining these two previous methods [4] or using a slotted ground technique [5]. Since the commercial use of Ultra-Wideband (UWB) technology started in 2002 [6], a large number of papers have been published by researchers and industry especially for the 3.1-10.6GHz spectrum band. The UWB power divider must satisfy bandwidth requirement, constant insertion loss and a high degree of isolation between ports [7].

UWB power divider design This article concerns the design and validation of a 1-to- 4 power divider. The first step is to design a 1-to-2 power divider, afterwards combining three of them to make a two- stage 1-to-4 divider. Generally, a single section Wilkinson power divider consists of two branches of 70.7Ω quarter-wave transformers terminated with a 100Ω resistive load. However, such power dividers have narrow bandwidths [8]. To increase this, additional sections of quarter wave transformers could be added and also terminated with resistive loads to increase output port isolation [9]. Examples of quarter-wave transformers and their resistive loads can be found in several tables and charts [9-11]. Initial section impedances and load values for the single-stage UWB power divider used in this work are shown in Table 1 - the equations on page 58 allow the width and length of each section to be calculated [12]:

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Vol. 38 No. 4 - November 2016 Issue