1063-7397/05/3406- © 2005 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 34, No. 6, 2005, pp. 344–355. Translated from Mikroelektronika, Vol. 34, No. 6, 2005, pp. 408–419.
Original Russian Text Copyright © 2005 by Mokerov, Gnatyuk, Lisitskii.
Phased-array radar systems increasingly employ
monolithic microwave integrated circuits (MMICs)
owing to the progress of high-electron-mobility tran-
sistors (HEMTs) and heterojunction bipolar transis-
tors (HBTs) [1–3]. These devices are made in III–V
compound semiconductors, which allow one to
reduce carrier transit time and dissipation to the
highest extent while providing bandgap-variation
The main component of a phased array is the
transmit–receive (TR) module. Each of its two paths
typically includes a low-noise ampliﬁer, preampli-
ﬁer, power ampliﬁer, and beam former made up of a
phase shifter and an attenuator. Yet another impor-
tant part is a TR switch; this allows one to use the
same beam former for transmission and reception.
With fewer devices employed, it is possible to
increase the reliability of a TR module and to signif-
icantly reduce its mass, overall dimensions, power
dissipation, and cost.
switches designed for phased arrays
could also provide a basis for creating
for other applications, such as communications systems
and spectrum analyzers.
This paper reports on the development of a new
X-band TR switch that essentially uses a stub direc-
2. BASIC SWITCH
A multithrow microwave switch is made up of iden-
tical component switches that have a pass and a reﬂect
mode of operation, selected by a control signal. Most
component switches are classiﬁed as series, shunt, or
series–shunt switches, according to the manner in
which the active elements are connected to the trans-
mission line. The literature indicates that the series con-
ﬁguration offers the maximum bandwidth and is the
simplest to implement; on the other hand, it cannot pro-
vide good isolation at the higher end of its frequency
range, due to the reactance of its active element. The
other conﬁgurations, though inferior in bandwidth,
offer better isolation .
Most MMIC TR switches for phased arrays use
i–n diodes or ﬁeld-effect transistors (FETs), namely,
HEMTs or metal–semiconductor ﬁeld-effect transistors
(MESFETs). With p–i–n diodes, power dissipation is
large and complicated bias circuits are required, lead-
ing to lower switching speeds in most cases. FET-
based switches often suffer from higher passband
loss . On the other hand, unlike p–i–n diodes,
HEMTs allow one to apply the same fabrication
process to the switch and the other MMICs of a TR
module. Moreover, the HEMT strategy makes it
possible to implement a number of functions of a
TR module in one MMIC, increasing the reliability
of the module and reducing its cost.
It follows from published reports that most TR
switches have the series–shunt conﬁguration,
employing different matching circuits [6–10]. At the
same time, insufﬁcient consideration has been given
to using stub directional couplers in multithrow
This paper is concerned with the design and optimi-
zation of a reciprocal single-pole double-throw (SPDT)
switch that is based on a stub directional coupler using
quarter-wavelength microstrip transmission lines, as
shown in Fig. 1. Depending on the control signal, the
directional coupler offers a very low or a very high
resistance to input microwave signals, implementing
the pass or the reﬂect mode of operation, respectively.
The active elements are sub-0.25-
HEMTs (PHEMTs) based on the n-
AlGaAs/InGaAs/GaAs heterostructure; they are
inserted into the arms of the directional coupler.
X-Band Monolithic Transmit–Receive Switch Based
on a Stub Directional Coupler
V. G. Mokerov, D. L. Gnatyuk, and A. P. Lisitskii
Institute of UHF Semiconductor Electronics, Russian Academy of Sciences, Moscow, Russia
Received April 21, 2005
—A new circuit realization of X-band transmit–receive switch is proposed that is based on a PHEMT-
controlled stub directional coupler. The operation of the switch is analyzed. The impedances of the stubs are
optimized to yield a considerably larger bandwidth of the switch. It is shown that the circuit can serve as a build-
ing block for multithrow switches.