Traditional Wilkinson power dividers are generally developed using quarter wavelength transmission line sections at the design center frequency.
When a conventional Wilkinson power divider gets an additional transmission line stub in the middle of the input-output connection lines, then the structure is enabled with dual-band technology and is called a dual-band Wilkinson power divider.
In dual-band Wilkinson power dividers using two central transmission line stubs, the two frequencies are selected by changing the lengths and impedances of the transmission lines and the stubs.
The introduction of dual-band and multi-band technologies greatly impacted all microwave components, including power combiners and dividers. At present, most RF and microwave systems are enabled with multi-band operation. Dual-band technology allows microwave components to work at two different frequencies.
Among the various types of power dividers, the most widely used type is the Wilkinson power divider. When a conventional Wilkinson power divider gets an additional transmission line stub in the middle of the input-output connection lines, then the structure is enabled with dual-band technology. These types of Wilkinson power dividers can be called dual-band Wilkinson power dividers.
In this article, we will discuss two types of dual-band Wilkinson power dividers—those that use t-shaped transmission lines and those that use two central transmission line stubs. Let’s first take a look at dual-band Wilkinson power dividers that use t-shaped transmission lines.
Dual-Band Wilkinson Power Dividers Using T-shaped Transmission Lines
Traditional Wilkinson power dividers are generally developed using quarter wavelength transmission line sections at the design center frequency. However, numerous novel structures of Wilkinson power dividers have been introduced to achieve dual-band operation.
When each quarter wavelength section of a conventional power divider is converted into its equivalent T-shaped transmission line section, the obtained structure is a dual-band Wilkinson power divider using a T-shaped transmission line. This particular configuration of dual-band Wilkinson power divider has no short circuit stubs or via holes, but only one open stub, and is often used in lower frequency ratio dual-band frequency operations in wireless systems.
Next, let’s take a closer look at dual-band power dividers that use two central transmission line stubs.
Dual-Band Wilkinson Power Dividers Using Two Central Transmission Line Stubs
The transmission line stub used in a dual-band Wilkinson power divider can be either short-circuited or open-circuited at the end. In this dual-band scheme of Wilkinson power dividers, the two frequencies are selected by changing the lengths and impedances of the transmission lines and the stubs. A lumped resistor is connected between the output ports for output matching and isolation. The value of the lumped resistor is equal to two times the port impedance. As the same value of the lumped resistor is present in the traditional Wilkinson power divider, no extra lumped elements are required in this configuration. Compared to conventional structures, there is minimal structural modification in this dual-band design, which makes it widely used in distributed circuit microwave applications.
Applications of Dual-Band Wilkinson Power Dividers
Dual-band Wilkinson power dividers (WPD) have been utilized for quite some time, especially in wireless communications technologies. However, communications technologies are rapidly developing and approaching near constant change and evolution. As a result, WPD have also had to evolve and change with them. At first, WPD design and simulation methodology shifted to be considered using filter design theory which enabled the compactness of WPDs while also adding complexity of isolation and suppression characteristics.
Filter design theory applications for WPDs are often based around even and odd-mode analysis equations, lumped element circuit simulations, distributed circuit simulations, as well as the traditional necessities of parasitic extraction elements and s-parameter performance. But in increasingly complex band-ranges for communications systems, oftentimes traditional dual-band ideologies are no longer as functional as desired. Some applications for WPDs have been shifting to multi-band or multi-way approaches.
Frequency bands like LTE, WIFI, and the oncoming 5G revolution are all necessary to consider in various communication systems these days. Multi-band PDs have been utilized with quarter-wavelength impedance transformers and paired with composite right and left-handed (CRLH) transmission lines. But out-of-band rejection performance is still a concern even with multi-band PDs. As such, new dual-band WPDs are coming in to play with zero-degree CRLH transmission lines that can reserve full-port matching and maintain low in-band insertion loss.
Electromagnetic simulation analysis is an excellent way to validate the design configurations of dual-band Wilkinson power dividers. Cadence’s software can be utilized to provide comprehensive electromagnetic simulation solutions for all power divider designs.