The Bridge - Issue 3, 2023 - 22

Feature
Empowering Communities Through Emerging Technologies:
Advances in Antennas for Software Defined Radios
communication across different networks and protocols.
Recent works on multifunctional antennas are documented
in [7]-[13]. In [8], a multi-functional and reconfigurable
antenna is realized using a pair of split ring resonators
(SRRs) and PIN diode loaded in the coplanar waveguide
(CPW) feed lines, which constitute a dual- state filter
section, exhibiting frequency-notched or narrow band-pass
response depending on the status (ON/OFF) of the PIN
diode as shown in Fig. 2. Due to this integrated dual-state
filter section, the antenna exhibits a unique frequency
reconfiguration capability that transforms a frequencynotched
wideband antenna into a narrowband antenna.
Thus, a single printed monopole antenna loaded with SRRs
and PIN diodes on the feed section provides the dual
functionality. The design is realized using a printed circular
monopole antenna with a wide bandwidth, as shown in Fig.
2(a). It was further demonstrated that the notch frequency
and the narrowband frequency can be tuned by changing
the physical dimension of the SRR geometry as well as
the shape of the SRRs without perturbing the radiator
dimension. Potent applications of such reconfigurable
antennas are: i) multiple-input multiple-output (MIMO)
systems used for high-data-rate applications; ii) cognitive
radio (CR) systems of SDR, which demand wideband and
narrowband antennas [14], and iii) multiservice, multiband,
and multi-standard radio (MSR).
Active Phased Array Antenna for SDRs: The RF
environment is often polluted by noise, with interference
signals falling in the band of interest with a multipath fading
effect on the desired frequency. An active phased array
antenna is an array of antenna elements designed to adapt
and change the antenna radiation pattern in order to adjust
to the radio frequency (RF) environment. The adaptations
are realized by performing electrical beam tilting, and
beam width adjustments. The antennas can direct beams
toward particular users and track user movement; they
are also able to steer nulls, reduce sidelobes and self-heal
in case one of the array elements stops functioning. An
active phased array antenna system helps reduce signal
fading, phase cancellation due to multipath and co-channel
interference. A combination of antenna array and digital
signal processing (DSP) running algorithms makes it
possible for the antenna to transmit and receive signals,
adapt, and hence perform smart beamforming measures.
Every active array comes equipped with a passive radiating
element connected to each transmit receive module in the
RF subsystem, as shown in Figure 3.
The flexibility inherent in SDRs pairs well with active
phased array antennas. These arrays can dynamically
adjust their radiation patterns, polarization, and
beamforming characteristics to optimize communication
in varying environments. This adaptability will be crucial
for maintaining reliable connections in scenarios with
changing interference, propagation conditions, and network
requirements.
Miniaturization and Integration: The trend towards smaller,
more compact devices extends to antennas as well.
Antennas integrated into SDR modules or devices will
need to be designed with miniaturization in mind. This
is particularly important for applications like wearables,
IoT devices, and portable communication tools used in
humanitarian efforts or remote areas.
Figure 2(a): SRR loaded multifunctional wideband monopole antenna [8]
Figure 2(b): Measured realized peak gain of the SRR coupled PIN diode
loaded CPW fed printed circular monopole active antenna with diodes OFF
and ON conditions [8]
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Figure 3: Block diagram of an active antenna
The Bridge - Issue 3, 2023

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