Abstract— E-Band diplexers have been designed to be used as
front-end components in the transceivers of point-to-point
wireless communication systems. They are specified to work at
the frequency bands 71-76 GHz and 81-86 GHz. Three designs
are presented here, two of which are the conventional T-junction
and manifold diplexers, and the third is a novel compact
structure based on coupled resonators.
Keywords—coupled resonator; coupling matrix; diplexer; E-
I. INTRODUCTION AND BACKGROUND
ICROWAVE diplexers are used as front end
components in the transceivers of E-Band systems for
point-to-point broadband wireless Gigabit connectivity.
Conventional diplexers consist of two channel filters
connected to a manifold, or a T-junction, or a circulator. Other
approaches for diplexer/multiplexer design based on coupled
resonator structures have been reported in [1-8]. These
diplexers/multiplexers consist of only resonators without
external energy distribution networks, and hence they are
miniaturized in comparison to the conventional designs.
In this paper, the designs of three waveguide cavity
diplexers for E-Band systems are presented. The diplexers are
specified to work at the frequency bands 71-76 GHz and 81-
86 GHz with desired isolation better than 60 dB and return
loss better than 15 dB. The first diplexer contains a T-junction,
the second contains a manifold and the third is a novel
compact structure formed from only coupled waveguide
cavities. The third design is miniaturized in comparison to the
commercial and conventional T-junction and manifold
diplexers since it consists of only resonators in addition to its
folded structure. The structures of the E-band diplexers are
shown in Fig. 1.
II. CHANNEL FILTERS DESIGN
The approach followed in designing both the T-junction
and manifold diplexers is based on firstly designing the
channel filters independently and then the whole diplexer
structure is optimized using EM full-wave simulator CST.
Each channel filter consists of five waveguide cavities coupled
together via inductive apertures. The coupling coefficients
were calculated from the g-values for a 5th order filter with
Cheybeshev response with reflection loss of 20 dB .
Fig. 1. (a) T-junction diplexer, (b) Manifold diplexer, (c) Coupled-resonator
Talal Skaik, Mahmoud AbuHussain
Electrical Engineering Department, Islamic University of Gaza, P.O. Box 108
Design of Diplexers for E-Band Communication
978-1-4673-5820-0/13/$31.00 ©2013 IEEE
The coupling coefficients and the external quality factors are
calculated for the 71-76 GHz filter for a fractional bandwidth
FBW=6.8% and the computed values are: M12=M45=0.0589,
M23=M34=0.0432, and Qe=14.279. Similarly, the coupling
coefficients and external quality factors for the 81-86 GHz
filter were calculated for fractional bandwidth FBW=5.98%
and their values are: M12=M45=0.0518, M23=M34=0.03808, and
CST has been utilized to find the initial dimensions of the
waveguide cavities and the inductive coupling irises of each
filter. Each pair of coupled resonators has been simulated
separately to find the width of the coupling aperture
corresponding to the required coupling coefficient. The whole
filter structure is then optimized until a return loss of 20 dB is
achieved for both the channel filters.
III. DIPLEX ERS DESIGN
A. T-Junction Diplexer
After the individual channel filters are designed, a T-junction
is added to the structure combining the filters to form the
diplexer as shown in Fig. 1 (a). A ridge has been added within
the T-junction to improve matching. The diplexer is then
optimized including the dimensions of the T-junction arms
and the ridge and the simulation performance is depicted in
Fig. 2. Simulation results of the T-junction E-band diplexer
B. Manifold Diplexer
In manifold waveguide diplexer, the channel filters are
combined using T-junctions and sections of waveguides.
Ridges have also been added within the T-junctions as shown
in Fig. 1 (b) to improve matching. The whole manifold
diplexer is then optimized including the dimensions of the T-
junctions and ridges, the length of the waveguide section
between the T-junctions and the length of the shorted
waveguide section at the end of the structure terminated by a
wall. The simulation performance of the manifold E-band
diplexer is shown in Fig. 3.
Fig. 3. Simulation results of the manifold E-band diplexer
C. Coupled Resonator Diplexer
A structure of twelve resonators, shown in Fig. 1 (c), has been
chosen to meet the required specifications of sharp transitions
and high isolation of E-band diplexer. The diplexer resonator
topology is shown in Fig. 4 (a).
The synthesis of the coupled resonator diplexer is based on
optimization of the coupling matrix for a three-port network
with multiple coupled resonators. The design method is
detailed in . The scattering parameters of the three-port
coupled-resonator circuit are related to a general matrix [A] by
1−− =−= ba
where port 1 is assumed at resonator 1, port i is at resonator b
and port j is at resonator a. The matrix [A] is a general matrix
given by ,
11 1( 1) 1
(1)1 (1)(1) (1)
where qei is the normalized external quality factor of resonator
i, P is the complex lowpass frequency, and mij is the
normalized coupling coefficient.
An optimization technique has been used to obtain the
coupling matrix of the twelve coupled resonators. The
normalized coupling coefficients are as follows: m12=0.7963,
m23=m28=0.3466, m34=m89=0.2101, m45=m9,10=0.1956,
m56=m10,11=0.2035, m67=m11,12=0.2814, m11=m22=0, m33=-
m88=0.5942, m44=-m99=0.6552, m55=-m10,10=0.6635, m66=-
m11,11=0.6652, m77=-m12,12=0.6643. The normalized external
quality factors are qe1=1.4903, qe7= qe12=2.9806. The actual
coupling coefficients Mij are obtained by multiplying the
normalized values mij by the fractional bandwidth
The diplexer is designed using waveguide cavity resonators
and the top view of the structure is shown in Fig. 4 (b). The
diplexer has been designed with a folded configuration for
miniaturization. The whole structure is formed of waveguide
cavities coupled together using inductive irises and the widths
of the irises are initially set according to the optimized
coupling coefficients mij. The fundamental resonant frequency
of each cavity resonator i is set according the optimized
coefficient mii. The simulated performance of the coupled
resonator E-band diplexer is depicted in Fig. 5.
Fig. 4. (a) Coupled resonator diplexer topology, (b) Top view of the
waveguide E-band diplexer.
IV. COMPARISON BETWEEN DIPLEXERS
The simulated results of the three E-band diplexers are
shown in Fig. 6 for performance comparison. It is noticed that
the coupled-resonator diplexer performance has sharper
transitions than the other diplexers since it has more
resonators. A minimum return loss of 14 dB has been obtained
for all the diplexers. Moreover, a minimum isolation of 50 dB
has been achieved for the T-junction and manifold diplexers
whereas a 60 dB minimum isolation is obtained for the
Fig. 5. Simulation results of the E-band coupled-resonator diplexer
Fig. 6. Simulation results of E-band diplexers for comparison
The designs of three diplexers for E-band communication
systems are presented. The first diplexer contains a T-junction,
the second contains a manifold and the third is a novel coupled
resonator diplexer with folded structure. The diplexers are
designed using waveguide cavities coupled together using
inductive irises. The approach followed in designing both the
T-junction and manifold diplexers is based on firstly designing
the channel filters independently and then the whole diplexer
structure is optimized using EM full-wave simulator CST. The
coupled-resonator third diplexer consists of twelve coupled
cavity resonators arranged in a folded structure and its design
technique is based on coupling matrix synthesis using
optimization. The simulation results of the diplexers show that
a return loss better than 14 dB and isolation better than 50 dB
have been achieved.
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