10-2018

RF & Wireless
UPCT Students Design a Ku-Band Multiplexer
Figure 1: Equivalent circuit for the initial optimization set up in Microwave Office software
Alejandro Pons Abenza
Technical University of
Cartagena
National Instruments
www.ni.com/awr
Company:
The Technical University of Cartagena
(UPCT) is the youngest
technical university in Spain.
This fact is contrasted, however,
by its long history as a university
in the engineering and business
fields, as several of its faculties
date back to the late 19th and
early 20th-century. This unique
status blends youth and tradition,
making it a dynamic and
innovative institution.
Challenge:
Alejandro Pons Abenza, PhD
student at UPCT, recently led
a team that included Alejandro
Alvarez Melcon and Fernando
D. Quesada Pereira of the Information
and Communications
Department at UPCT, Monica
Martinez Mendoza of Thales
Alenia Space, Spain, and Marco
Guglielmi of the Technical University
of Valencia (UVP), in the
design of a manifold multiplexer
using all-inductive rectangular
waveguide dual-mode filters.
Multiplexers, which are used
for multiple RF channel separation/combination
at the input/
output of front ends, are a key
part of communication satellite
payloads. Their performance
significantly impacts the overall
satellite system. The waveguide
technology that is commonly
used has low-loss and
high-power handling capability.
The objective of this multiplexer
design project was to employ a
complex filter topology as channel
filters for the multiplexer.
Although many complex topologies
are used for RF/microwave
industry, the novelty of
this design was the all-inductive
technology that resulted in
a simpler manufacturing process
and faster design times.
Solution
The design team chose the NI
AWR Design Environment platform,
specifically Microwave
Office circuit software, to design
a three-channel, non-contiguous
multiplexer at Ku-band (11 GHz)
using a manifold configuration.
The software was chosen
because simulations and optimizations
are quite fast. Defining
and working with sub-circuits is
also straightforward enough to
develop a large-scale equivalent
circuit model for any N-channel
multiplexer. Figure 1 shows the
equivalent circuit setup for the
initial optimization.
The team defined the channel
filters (coupling matrix, frequency
plan), set up the equivalent
circuit in Microwave Office
software, and then optimized
the channel filters employing a
stepped iterative process using
the lengths of the stubs and the
connections between junctions.
They repeated this process until
the design met desired specifications.
From the process, different
coupling matrices were obtained
for each channel filter.
The equivalent circuit was then
split into a manifold section
(waveguide sections, connecting
junctions, and filters) and channel
filters with each optimized
coupling matrix. Each part was
designed in isolation from the
multiplexer. The manifold section
was designed matching its
S-parameters between the equivalent
circuit and its corresponding
waveguide model using a
full wave simulator.
The channel filters were designed
using the optimized
coupling matrix leveraging a
coupling matrix segmentation
technique. This segmentation
technique consisted of splitting
the design coupling matrix
through each resonator, after
which a scaling was applied.
Using the equivalent circuit of
at-a-glance
Applications:
• Microwave Components
• Multiplexer
Software:
• NI AWR Design Environment
• Microwave Office
Benefits:
• Availability of software
• Ease of use
• Reduction in design time
80 hf-praxis 10/2018