electronics

Article
Design a Compact Printed Log-Periodic Biconical Dipole Array
Antenna for EMC Measurements
Abdulghafor A. Abdulhameed 1,2, * and Zdeněk Kubík 1

1 Department of Electronics and Information Technology, Faculty of Electrical Engineering,

University of West Bohemia, 301 00 Pilsen, Czech Republic
2 Department of Electrical Techniques, Qurna Technique Institute, Southern Technical University,
Basra 61001, Iraq
* Correspondence: abdalhme@fel.zcu.cz

Abstract: This article presents the design, modeling, and fabrication of a printed log-periodic bicon-
ical dipole array antenna (PLPBDA) for electromagnetic compatibility (EMC) measurements. The
proposed structure used bow tie-shaped dipoles instead of typical dipoles to achieve a size reduction
of 50% and bandwidth enhancement of 170% with the help of PCB technology. Furthermore, the
balanced feeding method and the modifications in bow tie-shaped dipole dimensions were utilized
to obtain broad bandwidth of 5.5 GHz (from 0.5 GHz to 6 GHz). This structure comprises 12 dipole
elements with a compact size of 170 × 160 × 1.6 mm, reflecting low fluctuations gain of about (4.6–7)
dBi with the help of an extra dipole. Moreover, the achieved frequency and radiation characteristics
(simulated and measured) agree with each other and are compatible with the results of classical EMC
antennas. The achievements of this structure showed promising results compared to both literature
reviews and reference antenna Hyper LOG® 7060 offered for sale.

Keywords: antenna factor; biconical antenna; EMI; bowtie; PLPBDA; EMC measurement

Citation: Abdulhameed, A.A.; Kubík,

Z. Design a Compact Printed 1. Introduction
Log-Periodic Biconical Dipole Array
With the rapid growth of wireless communications, the need to use Ultra-wideband
Antenna for EMC Measurements.
antennas in such systems has appeared in various applications. Furthermore, the antenna
Electronics 2022, 11, 2877. https://
design is the key to every wireless system since it can control its radiation characteristic
doi.org/10.3390/electronics11182877
according to the application’s specifications [1]. Ultra-wideband antennas are used in
Academic Editor: Massimo Donelli different applications, e.g., in radio systems for communications and in electromagnetic
Received: 19 August 2022
compatibility (EMC) for measurement applications. The evolutions in wireless systems
Accepted: 8 September 2022
have motivated researchers to develop new communication forms to exploit the spectrum
Published: 11 September 2022
in the best way and enhance the reception quality [2–5]. Therefore, the cognitive radio
technology was the best solution for this matter as it consists of two different antennas, one
Publisher’s Note: MDPI stays neutral
for sensing with Ultra-wideband of (3.1–10 GHz) to identify the state of the band-idle or
with regard to jurisdictional claims in
active, while the other antenna is a communication antenna (reconfigurable antenna) [6–11].
published maps and institutional affil-
This research focuses on the EMC applications, whereas an Ultra-wideband antenna can be
iations.
used as a reference antenna for emission and immunity tests of the device under the test
(DUT) inside the EMC chamber [12]. Several antenna configurations have been utilized to
measure electromagnetic interference (EMI) based on the operation frequency and radiation
Copyright: © 2022 by the authors.
characteristics. For instance, in [13], the authors showed the AF characteristics of the sleeve
Licensee MDPI, Basel, Switzerland. dipole antenna for EMC measurement by changing the sleeve dipole parameters, which
This article is an open access article offered an 86% size reduction compared to the conventional biconical antenna with similar
distributed under the terms and characteristics. The performance of the log-periodic dipole array antenna was improved
conditions of the Creative Commons in [14] using a saw-tooth shape feedline. The successive dipoles will be arranged in the
Attribution (CC BY) license (https:// same horizontal plane, eliminating the unwanted vertical electric field component. A
creativecommons.org/licenses/by/ complimentary log-periodic dipole array with cross-polarization was proposed in [15].
4.0/). This structure has a set of dipole antennas orthogonal to conventional log-periodic dipole

Electronics 2022, 11, 2877. https://doi.org/10.3390/electronics11182877 https://www.mdpi.com/journal/electronics

Electronics 2022, 11, 2877 2 of 20

antennas, offering a circular polarization without any hybrid junction. A pair of printed
broadband Vivaldi antennas with a coaxial feeding method operating from 0.5 GHz to
4 GHz was designed, fabricated, and tested [16]. Moreover, the proposed design served as
a reference antenna for EMC measurement since it exhibited stable radiation characteristics
and a maximum gain of 6.2 dBi. The width of the ridge of the double ridge guide horn
(DRGH) antenna was tapered linearly in [17]. This process maximized the effective radi-
ation aperture and reduced the beamwidth compared to conventional 1–18 GHz DRGH.
Another horn antenna with miniature size and wide bandwidth was presented in [18],
where the idea of extending the lower frequencies was inspired by the fishtail structure and
classical ridge structure. UWB skeletal antenna was proposed in [19]. This antenna showed
good results in VSWR compared with the biconical antenna in the band up to 200 MHz,
which is considered another wire UWB antenna family. Ref. [20] presented a novel UWB
monopole antenna for EMC measurement applications, and this antenna covered two
bands (0.79–1 GHz) and (1.37–10 GHz). In Ref. [21], the authors proposed a novel method
for optimizing small elliptical planner dipole antenna for ultra-wideband EMC applications.
The characteristics of this antenna-like wide band (1–5 GHz) and flatness gain enabled it to
be a powerful tool for EMC measurements. The LPDA antenna is extensively used because
it provides a high directivity and flat gain over the wideband spectrum [22].
Moreover, an LPDA antenna is called frequency-independent when the ratio of higher
frequency to the lower frequency is more than ten times, where the impedance and radiation
characteristics remain constant as a function of frequency. The lower operating frequency
of the LPDA determines its size and, consequently, the length of the most extended dipole.
Since the aimed wide operation frequency band starts from 500 MHz, the LPDA length
will be considerably large. To overcome this LPDA size limitation, the printed log-periodic
dipole array (PLPDA) antenna has been presented recently utilizing printed circuit board
(PCB) technology that offers good specifications such as low cost, low profile, small size,
and easy fabrication [23]. In PLPDA, all the parameters of the conventional LPDA antenna
√
are divided by the square root of the effective dielectric substrate ( ε e f f ).
The majority of EMC reference antennas are dedicated to serving in the band starting
from 700 MHz to 2.4 GHz since this band is occupied by different applications such as
GSM 850–900 MHz, mobile 1800 MHz, 3G 2100 MHz, and Wi-fi 2400 MHz and has a high
probability to interference [24]. On the other hand, the band from 2.5 GHz to 6 GHz must
be taken into account due to the fact it is occupied with another set of critical applications
such as WiMAX 3.5 GHz and 5.3 GHz, mid bandwidth for 5G 2.5–3.8 GHz, PAN 4.8 GHz,
and WLAN 5.8 GHz [25].
In the last decade, several structures of PLPDA serving different applications were
presented; some offer size reduction, while others provide wide bandwidth. For instance,
Casula et al. [26] showed an ultra-wideband (4–18 GHz) printed log-periodic dipole array
antenna design with 15 dipoles. An infinite balun was realized using two symmetrical
coaxial cables attached at the top and bottom sides. Moreover, this antenna was designed to
stabilize its radiation pattern without changing the phase center during the operating band.
Step-by-step design procedures for PLPDA antenna were illustrated in [27]. The design
started with nine dipole elements according to the spacing and scaling factor values of
0.78 and 0.14. Then, three extra dipoles were added to satisfy the condition (S11 < −10 dB)
through the whole operation band. Therefore, this antenna offered wide bandwidth starting
from 800 MHz to 2.5 GHz with size reduction using only 12 dipoles. In [28], a PLPDA
antenna with a balanced feed structure was presented. The authors modified the width of
the feeding lines to compensate soldering effect and offer broadband impedance bandwidth
starting from 500 MHz to 3 GHz. Furthermore, a stable high gain with low tolerance of
0.5 dB was achieved. In [29], 48 dipole elements were utilized to obtain wide bandwidth of
8.5 GHz using the hat-loaded technique for the first three dipoles and the technique of T-
shaped loaded for the following three dipoles. Moreover, wide impedance bandwidth was
achieved using meandered line and trapezoid stub methods. Another wideband PLPDA
structure (0.5–10) GHz with 25 dipole elements was presented in [30]. Wide bandwidth and
Electronics 2022, 11, 2877 3 of 20

size reduction were achieved using dual-band dipole technology. Ref. [31] offered PLPDA
of (0.8–2.5) GHz bandwidth using 12 dipole elements with a small size. These 12 dipoles
were arranged in a way so that the length of each one decreases gradually relative to
the next one, and each dipole resonates at its center frequency to cover the overall EMC
spectrum L-band. A wideband printed LPDA antenna (0.4 GHz to 8 GHz) was proposed
in [32]. The low-frequency response of this structure was improved by replacing the most
extended traditional dipole with a triangular shape and optimizing the width, length, and
spacing of the following four dipoles. The upper-frequency range of the proposed PLPDA
antenna in [33] was increased to operate from 780 MHz up to 18 GHz by introducing a ratio
factor parameter that used the truncate method to improve the properties of this antenna.
One of the motivations for using a compact PLPDA antenna rather than the classical
one in EMC measurement is the shorter measurement distance. The shorter measurement
distance can achieve a high strength field in the uniform field area (UFA) without increasing
the input power in the radiated immunity test. Furthermore, radiation emission and
radiation immunity are essential criteria for EMI measurements and should be performed
in the far-field region. Figure 1 depicts the EMC measurements setup according to CISPR
standards. The radiation pattern of the reference antenna must cover the device under
the test to obtain a proper response. Usually, the devices under the test have different
dimensions. Therefore, other reference antennas are required to obtain the maximum field
strength. Unfortunately, having many antennas in one EMC laboratory is not the right
choice. The alternative solution is to have a small number of reference antennas. The
maximum field strength is achieved by changing the measurement distance according to
the device under the test. Therefore, the compact antennas are fit with changing the test
distance since the DUT is still in the far-field region of these antennas [34].

Figure 1. The EMC measurements chamber according to the CISPR standards.

The minimum measurement distance is controlled by the largest dimension of the

antenna (D), DUT dimension, and the maximum resonance frequency (above 1 GHz)
according to CISPR 16-1-2 [35]
D2
d= (1)
2λ
Let us compare the classical log periodic dipole array antenna, which has the highest
dimension, D = 340 mm, with the compact antenna having D = 170 mm. Both antennas
are operating up to 6.5 GHz. According to (1), the shorter measurement distance for the
classical antenna should be ds ≥ 3 m. On the other hand, the minimum measurement
distance for the proposed antenna should be ds ≥ 0.6 m, while it must be ≥1 m according
to CISPR standard [35]. Due to the compact size of the proposed antenna, the measurement
distance (ds) could be alternated to 1.25 m in the case of small DUTs, and in this case, the
illumination area will be 1.5 m, making it suitable for most DUTs.
The other motivation is the test configuration issue. Based on EMC standards,
i.e., CISPR 16-2-3, the minimum distance between the reference antenna and the ground
Electronics 2022, 11, 2877 4 of 20

plane must not exceed 25 cm. The main problem will occur through the test with the vertical
orientation of the antenna, where the antenna will be very close to the ground, especially at
low frequency. This problem will lead to wrong measurements due to interference between
the reference antenna and the ground plane [36]. This problem will not be an issue in the
printed reference antenna due to the small size they have by using a substrate with high
relative permittivity ε r = 4.3 to minimize the size, and hence, it satisfies the condition
even with low frequencies. This paper presents an analytical study for a small-size printed
log-periodic dipole array antenna based on bow tie-shaped dipoles instead of the typically
printed dipoles. This structure aims to tackle both goals—bandwidth enhancement and
size reduction—to serve as a reference antenna in EMC measurements for the band starting
from 0.5 GHz to 6.5 GHz. Section 2 describes the comparative analysis of conventional
and bow tie-shaped dipoles. The basic design of the log-periodic antenna is illustrated in
Section 3. Section 4 briefly discusses the various feed techniques and their effect on the
antenna characteristics, while Section 5 demonstrates the simulation and measurement
results by comparing the literature reviewed and the proposed design. Finally, Section 6
presents a comprehensive conclusion with recommendations.

2. Comparative Analysis of Conventional and Biconical Dipoles

This section focuses on the benefits of using a biconical dipole instead of a classical
one. The size reduction and bandwidth enhancement benefits have been demonstrated by
designing and simulating two dipoles—conventional dipole and biconical dipole—using
CST Microwave studio with a discrete feeding port, as shown in Figure 2. Furthermore,
both dipoles have a length of (L = 170 mm) and widths (w1 = 6 mm and w2 = 16 mm,
respectively). The proposed structures are based on an FR-4 substrate with a size of
Ls = 180 mm and Ws = 160 mm.

Figure 2. Two dipoles are modeled in CST Microwave Studio: (a) conventional dipole;
(b) biconical dipole.

Figure 3 shows the reflection coefficient in dB versus frequency. It is clear that the pro-
posed dipole requires a length less than a conventional one to achieve the same resonance
frequency, and this process will develop by using an array of these dipoles. Moreover,
the proposed dipole offers wider bandwidth than the traditional one, as is evident in the
biconical dipole impedance curve in Figure 4, which is flatter with frequency than the
conventional dipole curve. Figure 5 shows the role of dimension d in mm for tuning the
bandwidth of the biconical antenna. This feature is valuable in the following design steps
to obtain the optimum dimensions of the PLPDA antenna. It can be concluded that keep-
ing the starting points of the electromagnetic waves close to each other directly impacts
broadening the bandwidth [1], which is why the biconical dipole has wider bandwidth
than the conventional one.
Electronics 2022, 11, 2877 5 of 20

Figure 3. Reflection coefficient versus frequency for conventional and biconical dipole.

Figure 4. Input impedance versus frequency for conventional dipole and biconical dipole.
Electronics 2022, 11, 2877 6 of 20

Figure 5. S11-parameter versus frequency for different values of d in mm.

3. Printed Log-Periodic Dipole Array Antenna Design

The log-periodic dipole antenna was first derived from the conventional dipole (radiate
at half wavelength) by Isbell [37]. It consists of several dipoles, and each one resonates at
its wavelength corresponding to the length. It is worth mentioning that all dipoles whose
lengths are higher than wavelength act as reflectors, whereas they would act as directive
dipoles if their lengths are smaller than the wavelength [38]. Moreover, the classical analysis
method was described by Carrel [39], which presents straightforward procedures for the
design using the following six steps:
1. According to the desired directivity, scaling factor (τ) and spacing factor (σ) can be
evaluated from the point intersection of the straight line σ = 0.243 τ − 0.051.
2. Using Equations (2)–(4) to find out the maximum number of dipoles

log BS
N = 1+ (2)
log τ1
f upper
BS = B· Bar = × Bar (3)
f lower
4σ
Bar = 1.1 + 7.7(1 − τ )2 (4)
1−τ
where BS and Bar present the structure bandwidth and the active region bandwidth, respectively.
3. The length of the most extended dipole (first one), which matches the lowest frequency,
can be found from Equation (5).

1 3 × 108
L1 = × (5)
2 f lower
4. The distance between each successive dipole can be calculated using Equation (6).

L1 − L2 4σ
R1 − R2 = × (6)
2 1−τ
5. The dipoles’ width can be evaluated using Equations (7) and (8).
   
377 Ln
Z0 = ln − 2.25 (7)
π an
Electronics 2022, 11, 2877 7 of 20

Wn = π × an (8)
6. Equations (9)–(11) are used to calculate the length, distance, and width of
successive dipoles.

L n +1 = τ × L n (9)
R n +1 = τ × R n (10)
Wn+1 = τ × wn (11)
Finally, the length of the dipoles, the width of the dipoles, and the spacing between
dipoles should be divided by the square root of the effective dielectric constant, √Lε n , √Wε n ,
ef f ef f

and √Rn , respectively [32]. The effective dielectric constant is described by Equation (12).
εe f f

 1
h −2

εr + 1 εr + 1
εe f f = + 1 + 12 (12)
2 2 w

According to the EMC measurement application, low bandwidth and large size were
the main issues in designing printed log-periodic antennas. Using an antenna as a reference
in EMC measurements requires wide bandwidth to cover the electromagnetic interference
(EMI) with the communications bands that spread in the whole spectrum. On the other
hand, the size was a considerable impact factor in the shorter measurements distance
and test configuration. Therefore, the classical dipole elements were replaced with a
trapezoidal shape to form a biconical array antenna instead of the typical dipole array
since the biconical antenna offered a wider bandwidth than a classical dipole antenna [40].
By doing so, the proposed design has achieved both bandwidth improvement and size
reduction simultaneously. The geometrical shapes for both conventional and biconical
dipole array antennae are presented in Figure 6.

Figure 6. The geometrical structure of 11 elements of (a) conventional design and (b) proposed design.

The spacing between adjacency dipoles becomes smaller as it approaches the high-
frequency dipoles. In contrast, low frequencies at the longest dipoles have higher band-
width than the lowest length dipoles, which have sharp bands. Therefore, the spacing
should be obtaining small to make these sharp bands close to each other, and consequently,
it leads to achieving a wide band. Figure 7 shows the reflection coefficient of the con-
ventional and proposed designs. The biconical dipoles have significantly impacted the
impedance bandwidth (from 0.5 GHz to 5.5 GHz) compared with linear dipoles (from
Electronics 2022, 11, 2877 8 of 20

0.7 GHz to 3.3 GHz). Hence, the biconical dipoles have better performances than the
conventional dipoles.

Figure 7. S11-parameter versus frequency with/without biconical structure.

Even with this promising result of the reflection coefficient of biconical dipoles array
antenna, the voltage standing wave ratio still does not satisfy the condition VSWR < 2,
especially at 2.4 GHz, in which the reflection coefficient is approximate −9 dB. Hence, an
extra dipole (conventional one) is designed and optimized to eliminate this reflection, and
the result is shown in Figure 8. This additional dipole was inserted between the input port
and the biconical element number 11 [27]. It is clear that through the whole frequency band
from 0.5 GHz to 6 GHz, the VSWR < 2, and the reflection coefficient value is now below
−10 dB. Furthermore, it was found that the changing of the extra additive dipole length has
also significantly affected the gain values. Figure 9 presents the gain variation with different
lengths of this extra dipole. The length L12 = 10 mm reflects the lowest gain fluctuations,
which is necessary to achieve a good antenna factor result with low uncertainty. However,
the gain could be flatter with increasing the length of the additive dipole, but it will corrupt
the impedance matching since there is a trade-off process. Therefore, L12 = 10 mm is the
optimum value for both the s-parameter and the gain.

Figure 8. S11-parameter versus frequency with/without extra dipole.

Electronics 2022, 11, 2877 9 of 20

Figure 9. Simulated gain with different lengths of extra dipole.

Figure 10a shows the optimized geometrical shape of the design, while Table 1 illus-
trates the optimum values of each dipole element’s parameter. The width of the dipole is
set at the value of 10 mm except for the first dipole‘s width (W1 = 13 mm) and the extra
dipole’s width (W12 = 5 mm). On the other hand, parameter (d) plays a vital role in having
broadband impedance matching since it is the central part of modifying every dipole’s bi-
conical shape, as shown previously in Figure 5. Finally, an optimization process took place
on the overall dimensions to obtain better performances using Microwave CST Studio’s
facilities [41]. The utilized structure is epoxy FR-4 relative permittivity ε r = 4.3, and loss
tangent of tanδ = 0.025. Figure 10b depicts the cross-section area of the proposed structure.

Figure 10. (a) The optimized structure of the biconical dipole array antenna; (b) cross-section area for
the biconical dipole array antenna.
Electronics 2022, 11, 2877 10 of 20

Table 1. Illustration of optimum values of the parameters.

No. 1 2 3 4 5 6 7 8 9 10 11 12
L (mm) 77.5 65 60 55 50 45 40 31.8 27.5 21.2 15 10
W (mm) 13 10 10 10 10 10 10 10 10 10 10 5
R (mm) 20 19 19 17 13.7 12 12 12 12 12 12 –
d (mm) 20 30 27.5 13.75 11.25 11.25 11.25 5 5 5 5 –

4. Feeding Techniques
The feeding techniques play a vital role in designing the log-periodic dipole antenna
array. The typical feeding method consists of two non-radiated microstrip lines attached to
each substrate’s side to connect the successive dipoles. There will be a 180◦ phase difference
between every two consecutive dipoles, ensuring the energy will radiate only from the
exciting dipole. At the same time, there is no contribution by the coupling from the next
dipole, which has a reverse direction. The width of each microstrip feeding line w f can be
calculated using Equation (13) [40].

87 5.98 × h
z0 = √ ln( ) (13)
ε r + 1.41 0.8 × wf

where h is the height of the substrate, z0 represents the characteristic impedance 50 Ω. In

this work, the balance feeding method is employed. The top microstrip line has a width
w f 1 = 3.5 mm while the width of the bottom microstrip line is w f 2 = 5 mm, The 50 Ω
impedance point is usually located near the narrow tip of the PLPDA antenna. To achieve
impedance bandwidth less than −10 dB for all elements in the array, a parametric sweep
has been performed to change the width of the transmission line by creating a balun to
balance the surface currents distribution between the two sides of the transmission line as
described in [28]. These optimum values are obtained with the help of CST Microwave
studio to obtain wider impedance bandwidth starting from 0.5 GHz to 6 GHz.

5. Simulation and Measurement Results

The proposed design has been fabricated and tested in the EMC laboratory at the
University of West Bohemia, Faculty of Electrical Engineering. Furthermore, the fabrication
process takes place with the help of an LPKF ProtoMat S100 CNC machine. The utilized
structure is epoxy FR-4 with relative permittivity ε r = 4.3, and loss tangent of tanδ = 0.025.
The phototype of the fabricated design is shown in Figure 11.

Figure 11. The prototype of the proposed design: (a) front view; (b) back view.
Electronics 2022, 11, 2877 11 of 20

5.1. S11-Parameter
The reflection coefficient of the proposed design has been measured using the RIGOL
DSA875 Spectrum Analyzer (9 kHz–7.5 GHz) with directional couplers (RIGOL VB 1032
and RIGOL VB 2032), as shown in Figure 12a. These two directional couplers are utilized
simultaneously to cover the band up to 8 GHz (RIGOL VB 1032 (0.1–3.2 GHz) and RIGOL
VB 2032 (2 to 8 GHz)). Figure 12b shows the simulated and measured return losses. It
can be seen that the design offers a wide impedance bandwidth of 0.55–6 GHz in both
simulation and measurement results.

Figure 12. (a) The reflection coefficient measurement setup of the proposed structure; (b) simulated
and measured return losses versus frequency.

5.2. Surface Current Distribution

The surface current distribution is the best way to take a deep sight of the structure’s
behavior, and fortunately, this property exists in the simulation of CST Microwave studio
software. Figure 13 demonstrates the surface current distribution at various frequency
bands. The active region’s transition from the large dipoles to the smaller ones coincides
with the resonance frequency transition. The active region’s smooth and continuous
transition will reflect high gain and radiation pattern stability.

Figure 13. Surface current distribution at: (a) 0.7 GHz; (b) 1.2 GHz; (c) 2.2 GHz; (d) 4.5 GHz.
Electronics 2022, 11, 2877 12 of 20

5.3. Radiation Pattern

EMC chamber at the University of West Bohemia was utilized for radiation pattern and
gain measurements, as shown in Figure 14. The proposed antenna is rotated around its axle
360◦ in both vertical and horizontal directions to achieve the results of the E-plane and H-
plane, respectively. The simulated and measured radiation patterns in both the E- plane and
H-plane are shown in Figures 15 and 16, respectively. Furthermore, the measured radiation
patterns in both planes are agreeable with the simulated results from CST Microwave studio.
The direction of the main lobe is at 90◦ for both elevation and azimuth plane. The back
lobe of the azimuth plane is prominent at low frequencies and decreases gradually with
high frequencies. The radiation pattern deterioration is clearly observed at high-frequency
bands in both E-field and H-field presented in Figures 15 and 16, respectively [42].

Figure 14. Radiation pattern setup for the proposed antenna inside EMC chamber.

Figure 15. E-plane radiation pattern: (a) 0.7 GHz; (b) 1.2 GHz; (c) 2.2 GHz; (d) 4.5 GHz.
Electronics 2022, 11, 2877 13 of 20

Figure 16. H-plane radiation pattern at: (a) 0.7 GHz; (b) 1.2 GHz; (c) 2.2 GHz; (d) 4.5 GHz.

5.4. Axial Ratio, Co and Cross-Polarization

One of the important parameters in designing a reference antenna is the Co-polarization
(desired radiation) and Cross-polarization (orthogonal to the desired radiation) of the radi-
ation pattern in both azimuth and elevation planes. The EMC reference antenna is required
to be linearly polarized in the design. However, a slight difference in behaviors will appear
from the designers’ intentions. For instance, even the log-periodic dipole array antenna
that uses opposite dipoles arrangement to provide smooth phase transportation between
the elements shows an elliptical polarization. Furthermore, unwanted radiation will show
up when the phase is not in the main element (cross-polarization), and this part cannot be
eliminated. Instead, it could be minimized with the proper design. According to the EMC
applications, the acceptable limit of cross-polarized rejection ratio is (14 dB to 20 dB) [43].
According to EMC standards, the cross-polarized in both E-plane and H-plane for the
proposed antenna have been satisfied.
The term axial ratio (AR) demonstrates the type of polarization, whether circular,
elliptical, or linear. The axial ratio of the circular polarization pounces between 0 and 3 dB,
the AR of elliptical polarization is higher than 3 dB, and finally, the linear polarization will
stand for AR going to infinity (theoretically). In fact, there is no practical/industrial norm
for differentiating elliptically polarized antenna from linearly polarized antenna in terms
of the axial ratio. Authors in [44] claimed the proposed design exhibits linear polarization
with AR > 10 dB in planes (ϕ = 0, θ = 0) and (ϕ = 90, θ = 0) since linear polarization may be
viewed as a special case of elliptical polarization. The phase difference between the two
gain components was close to zero in the direction (θ = 0), indicating linear polarization
raised from the radiation pattern properties [45]. The proposed structure offered linear
polarization with more than 20 dB AR except for some frequencies, as shown in Figure 17.
Electronics 2022, 11, 2877 14 of 20

Figure 17. The simulated axial ratio in dB versus frequency.

5.5. Realized Gain and Antenna Factor

As we mentioned earlier, the bandwidth and the antenna factor are critical factors in
designing the reference antenna. Wide bandwidth allows the detection of the EMI over a
wide range of applications. At the same time, the antenna factor measures how much the
structure is good to work as a reference antenna. The antenna factor is dedicated to finding
out the incident field in space by knowing the received voltage. According to Equation
(14), it is clear that the antenna factor is inversely proportional to the wavelength times the
root square of the realized gain [16]. Equation (15) is used to calculate the antenna factor in
(dB/m) from the realized gain of the antenna in (dBi).

Er 9.73
AF = = √ (14)
Vr λ· G
" r #
2π 2.4
AF = 20 log (15)
λ 10(G(dBi)/10)
The simulated and measured realized gain (dBi) are depicted in Figure 18. Relatively
small fluctuations in gain values (4.6–7) dBi reflect good behavior in antenna factor values
(24–41) dBm−1 . Figure 19 shows the antenna factor versus frequency, while the antenna
factor values are listed numerically for each frequency band in Table 2. It can be seen
that the gain and, consequently, the antenna factor are in line with the typical values of a
standard EMC antenna [46].

5.6. Comparison with the Literature Reviewed

In the last decade, several structures of PLPDA antenna were proposed to work as
a reference antenna inside the chamber for EMC measurement, and these articles have
used different techniques for size reduction and bandwidth enhancement. Table 3 lists the
design specifications and achievements for these literature articles.
Electronics 2022, 11, 2877 15 of 20

Figure 18. Presentation of the simulated and measured realized gain in dBi versus frequency.

Figure 19. Presentation of the simulated and measured antenna factor in dBm−1 versus frequency.

Table 2. Illustration of optimum values of the antenna factor and corresponding gain versus frequency.

Freq./GHz 0.7 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

AF/dBm−1 18 24.5 28.1 31.5 32.9 34.3 35.1 36.2 37.7 39.5 39.5 41.1
AG/dBi 7 5.7 5.6 4.7 5.2 5.4 6 6 5.5 4.7 5.4 4.6
Electronics 2022, 11, 2877 16 of 20

Table 3. A comprehensive comparison between the proposed design and the literature papers.

Our
Rf. [27] [28] [29] [30] [31] [32]
Work
Freq./GHz (0.8–2.5) (0.5–3) (0.55–9) (0.5–10) (0.8–2.3) (0.4–8) (0.5–6)
FBW 103% 143% 177% 181% 96.7% 180% 170%
εr 4.3 4.3 3.5 3.5 4.3 4.3 4.3
τ 0.78 0.86 0.93 0.91 0.86 0.9 0.86
Gain/dBi 6.5 7–7.5 2.4–7.8 3–6 4.5–6.3 2.5–6.9 4.6–7
No.of
12 12 48 25 12 25 12
dipoles
Size/λo 0.426 × 0.4 0.44 × 0.25 0.49 × 0.35 0.36 × 0.43 0.426 × 0.37 0.36 × 0.37 0.28 × 0.26
Feeding Typical Balanced Typical Typical Optimized Typical Balanced
Application EMC EMC EMC EMC EMC EMC EMC

It is worth mentioning that the relative bandwidth (FBW) presents the percentage of
increased bandwidth and can be evaluated using Equations (16) and (17). Additionally, the
size here is in terms of the wavelength that matches the lower frequency band (fl ).

fh − fl
FWB = × 100 (16)
f av

fh + fl
f av = (17)
2
Table 3 illustrates the design specifications for several proposed designs that have
been presented to serve as a reference antenna for EMC measurements inside the cham-
ber [27–32]. The bandwidth enhancements and the size reduction are the main goals for all
these works as they are controlled by the number of dipole elements and the spacing factor.
For instance, [29] offers wide impedance bandwidth of about 8.5 GHz (FBW = 177%) with a
fluctuating gain of 2.4–7.8 dBi, while it is required 48 elements with a size of 0.49 × 0.355 λ L .
Authors in [30] use the dual-band dipole element technique to achieve a wide bandwidth
of 9.5 GHz (FBW = 181%), with a gain of 3–6 dBi, while it requires 25 elements with a size
of 0.36 × 0.43 λ L . On the other hand, our work aims to tackle bandwidth enhancement and
size reduction goals. The proposed design uses a biconical dipole to obtain wide impedance
bandwidth of 5.5 GHz (FBW = 170%), with a relatively low fluctuated gain of 4.6–7 dBi,
and it requires only 12 elements based on a small size of 0.28 × 0.26 λ L . Table 4 presents the
miniaturization techniques that have been used in [29,30] and the size reduction percentage
compared to our works. Moreover, the constant gain behavior in the whole frequency band
reflects a good antenna factor compared to the commercial design.

Table 4. Comparison between the miniaturization techniques used in [29,30] and the proposed work.

Ref. Size Reduction Miniaturization Technique

[29] 27% and 20% Using Hat loading and Top loading
[30] 40% Using Dual-band dipoles
This work 50% and 50% Using biconical dipoles

5.7. Comparison with the Commercial LPDA Antenna (HyperLOG® 7060)

A comprehensive comparison between the proposed structure and the commercial de-
sign HyperLOG® 7060 from the AARONIA AG website is listed in Table 5 [47]. HyperLOG®
7060 antenna has relative bandwidth of 158% with a size of 340 × 200 × 25 mm. On the
other hand, the proposed antenna has better relative bandwidth of 170% with a compact
size of 170 × 160 × 1.6 mm. Moreover, both commercial and proposed designs have an
acceptable low variation gain related to the EMC applications and reflect good antenna
factor values (AF).
Electronics 2022, 11, 2877 17 of 20

Table 5. Comparison between the proposed antenna and commercial antenna.

Specifications HyperLOG® 7060 Proposed Design

Dimensions/mm 340 × 200 × 25 170 × 160 × 1.6
Design Logarithmic-periodic Logarithmic-periodic
Substrate - FR-4
Weight/g 250 70
Gain/dBi 3.1–5.5 4.6–7
Frequency range/MHz 700–6000 500–6000
Antenna Factor *(1) /dBm−1 26–41 24.5–41.18
SMA Female SMA Female
RF Connector
Picture

*(1) frequency range from 0.7 GHz to 6 GHz.

The Antenna factor (AF) measures how much the proposed design is suitable to serve
as a reference antenna by comparing the AF of the proposed structure with the standard
AF. Unfortunately, none of the reviewed literature presents the antenna factor. In this work,
the antenna factor of the reviewed literature, whose cover band is up to 6 GHz, and the
proposed design were calculated from its given gain in dBi using Equation (15). The results
are compared with the commercial Hyperlog 7060, as shown in Table 6. The AF of the
proposed design has lower tolerance than the commercial Hyperlog 7060 due to the tiny
fluctuations in the realized gain.

Table 6. Antenna factor comparison of the proposed design, the literature reviewed papers, and
commercial design HyperLOG 7060.

Freq./GHz AF [29] AF [30] AF [32] Proposed Design AF [HyperLOG 7060] [47]

0.5 20 20 22 18.1 –
1 23 25.5 29.5 24.5 26
1.5 27 28.5 30 28.1 29
2 30 31.5 30.5 31.5 31.5
2.5 32 33.5 32 32.9 33
3 34 36 34 34.3 35
3.5 35 37.5 35 35.1 36.5
4 36 39 36.5 36.2 37.25
4.5 37 40 37 37.78 37.75
5 37.9 41 38 39.5 38.5
5.5 39 41.5 38.5 39.54 40.5
6 40 42 40 41.18 41

It is worth mentioning the minimum 3 dB beamwidth of the proposed antenna is

agreeable with the standard limits of the classical PLPDA in CISPR 16.1.2, as shown in
Table 7. The minimum dimension of w can be calculated using Equation (18), where w
is the minimum dimension of the line tangent to the DUT formed by the minimum 3 dB
beamwidth (∅3dB), as shown in Figure 1.

w = 2 × d × tan(0.5 × ∅3dB) (18)

where, d is the minimum measurement distance between the reference antenna and the
DUT and can be either 1 m, 3 m, or 10 m.
Electronics 2022, 11, 2877 18 of 20

Table 7. Comparison between the minimum distance w in both CISPR 16.1.2 standard and proposed
antenna at minimum measurement distance d = 1 m.

∅3 dB CISPR w of CISPR ∅3dB Proposed w of Proposed

Frequency/GHz
16.1.2/◦ 16.1.2/m Design/◦ Design
1 60 1.15 112 2.95
2 55 1.04 141 4.28
4 55 1.04 55 1.04
6 55 1.04 46.4 0.85

6. Conclusions
A Compact size log-periodic dipole array antenna is designed, modeled, and fabri-
cated. This design is dedicated to serving as a reference antenna for EMC measurement.
The use of dipoles with biconical shapes rather than normal ones has reflected a size re-
duction of (50%) and bandwidth enhancement (relative bandwidth of 170%). Furthermore,
the balance feeding method is deployed to obtain wideband impedance matching (from
0.5 GHz to 6 GHz). The compact size has given the freedom to change the measurement
distance to 1.25 m in the case of a small DUT, and in this case, the illumination area will
be 1.5 mm, which is suitable for most DUTs. A good value of the realized gain has been
achieved with tiny fluctuation (4.6–7) dBi through the whole bandwidth with the help of
an extra dipole. Calculating the antenna factor and comparing it with the standard result
of the conventional LPDA antenna is a trusted investigation method to show the validity
of the proposed design. For instance, an antenna factor (23–41) dB/m for the proposed
design is compared to the antenna factor (26–41) dB/m for a commercial (0.7–6) GHz LPDA
antenna (HyperLOG® 7060). Moreover, more investigations could be performed on this
antenna for future work, such as the calibration and modeling of an equivalent circuit.

Author Contributions: Conceptualization, A.A.A. and Z.K.; methodology, A.A.A.; investigation,

A.A.A. and Z.K.; resources, A.A.A. and Z.K.; writing—review and editing, A.A.A. and Z.K. All
authors have read and agreed to the published version of the manuscript.
Funding: This research was supported by the Ministry of Education, Youth, and Sports of the
Czech Republic under the project OP VVV Electrical Engineering Technologies with High-Level
of Embedded Intelligence CZ.02.1.01/0.0/0.0/18_069/0009855 and by the project SGS-2021-005:
Research, development, and implementation of modern electronic and information systems.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.

References
1. Abdulhameed, A.A.; Alhamdawee, E.M.; Hayder, I.M. Review of reconfigurable/UWB antenna for interweave cognitive radio
applications. Aust. J. Electr. Electron. Eng. 2019, 16, 96–101. [CrossRef]
2. Bakr, M.S.; Alterkawi, A.B.A.; Gentili, F.; Bosch, W. Reconfigurable ultra-wide-band patch antenna: Cognitive radio. In
Proceedings of the 2017 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and
THz Applications (IMWS-AMP), Pavia, Italy, 20–22 September 2017; pp. 1–3.
3. Al-Yasir, Y.I.A.; Abdulkhaleq, A.M.; Parchin, N.O.; Elfergani, I.T.; Rodriguez, J.; Noras, J.M.; Abd-Alhameed, R.A.; Rayit, A.;
Qahwaji, R. Green and Highly Efficient MIMO Transceiver System for 5G Heterogenous Networks. IEEE Trans. Green Commun.
Netw. 2022, 6, 500–511. [CrossRef]
4. Jasim, A.M.; Al-Anbagi, H.N. A comprehensive study of spectrum sensing techniques in cognitive radio networks. In Pro-
ceedings of the 2017 International Conference on Current Research in Computer Science and Information Technology (ICCIT),
Sulaymaniyah, Iraq, 26–27 April 2017; pp. 107–114.
5. Al-Anbagi, H.N.; Vertat, I. Cooperative Reception of Multiple Satellite Downlinks. Sensors 2022, 22, 2856. [CrossRef] [PubMed]
Electronics 2022, 11, 2877 19 of 20

6. Das, A.; Chatterjee, D.; Bhattacharya, A.; Majumder, S.; Chakravarty, D.; Byabarta, N. Comparative study of different techniques
to design ultra wideband antenna in cognitive radio. In Proceedings of the 2017 4th International Conference on Opto-Electronics
and Applied Optics (Optronix), Kolkata, India, 2–3 November 2017; pp. 1–7.
7. Mohammed, A.A.; Alnahwi, F.M.; Abdullah, A.S.; Hameed, A.G.A.A. A compact monopole antenna with reconfigurable band
notch for underlay cognitive radio applications. In Proceedings of the 2018 International Conference on Advance of Sustainable
Engineering and its Application (ICASEA), Wasit-Kut, Iraq, 14–15 March 2018; pp. 25–30.
8. Abdulhameed, A.A.; Alnahwi, F.M.; Swadi, H.L.; Abdullah, A.S. A compact cognitive radio UWB/reconfigurable antenna system
with controllable communicating antenna bandwidth. Aust. J. Electr. Electron. Eng. 2019, 16, 1–11. [CrossRef]
9. Tu, Y.; Al-Yasir, Y.I.A.; Ojaroudi Parchin, N.; Abdulkhaleq, A.M.; Abd-Alhameed, R.A. A Survey on Reconfigurable Microstrip
Filter–Antenna Integration: Recent Developments and Challenges. Electronics 2020, 9, 1249. [CrossRef]
10. Abdulhameed, A.A.; Alnahwi, F.M.; Al-Anbagi, H.N.; Kubík, Z.; Abdullah, A.S. Frequency reconfigurable key-shape antenna for
LTE applications. Aust. J. Electr. Electron. Eng. 2022, 1–9. [CrossRef]
11. Al-Yasir, Y.I.A.; Ojaroudi Parchin, N.; Tu, Y.; Abdulkhaleq, A.M.; Elfergani, I.T.E.; Rodriguez, J.; Abd-Alhameed, R.A. A Varactor-
Based Very Compact Tunable Filter with Wide Tuning Range for 4G and Sub-6 GHz 5G Communications. Sensors 2020, 20, 4538.
[CrossRef] [PubMed]
12. Kubík, Z.; Skála, J. Shielding effectiveness measurement and simulation of small perforated shielding enclosure using FEM. In
Proceedings of the 2015 IEEE 15th International Conference on Environment and Electrical Engineering (EEEIC), Rome, Italy,
10–13 June 2015; pp. 1983–1988.
13. Kim, K.-C.; Choi, B.J.; Jung, S.W.J. Characteristics of the Sleeve Dipole Antenna Used for EMC Applications. IEEE Access 2020, 8,
86957–86961. [CrossRef]
14. Bang, J.; Han, C.; Jung, K.; Choi, J. High-frequency performance improvement of LPDA for EMC/EMI measurements. In
Proceedings of the 2020 International Symposium on Antennas and Propagation (ISAP), Osaka, Japan, 25–28 January 2021;
pp. 621–622.
15. Kawakami, H.; Tanioka, M.; Wakabayashi, R. Circularly polarized log periodic dipole antennas. In Proceedings of the 2020
International Applied Computational Electromagnetics Society Symposium (ACES), Monterey, CA, USA, 27–31 July 2020; pp. 1–2.
16. Ivšić, B.; Friščić, F.; Dadić, M.; Muha, D. Design and analysis of Vivaldi antenna for measuring electromagnetic compatibility.
In Proceedings of the 2019 42nd International Convention on Information and Communication Technology, Electronics and
Microelectronics (MIPRO), Opatija, Croatia, 20–24 May 2019; pp. 491–495.
17. Gerber, M.; Odendaal, J.W.; Joubert, J. DRGH antenna with improved gain and beamwidth performance. IEEE Trans. Antennas
Propag. 2019, 68, 4060–4065. [CrossRef]
18. Jiang, J.; Pan, S.; Wang, S.; Li, G. Miniaturization design of VHF broadband directional radiation TEM horn antenna. In
Proceedings of the 2020 International Conference on Microwave and Millimeter Wave Technology (ICMMT), Shanghai, China,
20–23 September 2020; pp. 1–3.
19. Mallahzadeh, A.; Pazoki, R.; Karimkashi, S. A new UWB skeletal antenna for EMC applications. In Proceedings of the 2007
International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, Hangzhou,
China, 16–17 August 2007; pp. 543–546.
20. Hacene, Y.; Shuguo, X. Study of a novel ultra-wideband monopole antenna for EMC measurement applications. In Proceedings
of the 2012 6th Asia-Pacific Conference on Environmental Electromagnetics (CEEM), Shanghai, China, 6–9 November 2012;
pp. 393–395.
21. Tziris, E.N.; Lazaridis, P.I.; Zaharis, Z.D.; Cosmas, J.P.; Mistry, K.K.; Glover, I.A. Optimized Planar Elliptical Dipole Antenna for
UWB EMC Applications. IEEE Trans. Electromagn. Compat. 2019, 61, 1377–1384. [CrossRef]
22. Kuhn, W.; Peterson, G.; Welch, J. Broadband Antenna Probe for Microwave EMC Measurements. In Proceedings of the 2018 IEEE
27th Conference on Electrical Performance of Electronic Packaging and Systems (EPEPS), San Jose, CA, USA, 14–17 October 2018;
pp. 199–201.
23. Abdulhameed, A.A. Circular slotted monopole printed antenna with grounded stub WLAN band-notch for UWB applications.
Aust. J. Electr. Electron. Eng. 2017, 14, 59–63. [CrossRef]
24. Abdulhameed, A.A.; Kubík, Z. Investigation of Broadband Printed Biconical Antenna with Tapered Balun for EMC Measurements.
Energies 2021, 14, 4013. [CrossRef]
25. Alnahwi, F.M.; Abdulhameed, A.A.; Swadi, H.L.; Abdullah, A.S. A planar integrated UWB/reconfigurable antenna with
continuous and wide frequency tuning range for interweave cognitive radio applications. Iran. J. Sci. Technol. Trans. Electr. Eng.
2019, 44, 729–739. [CrossRef]
26. Casula, G.A.; Maxia, P.; Mazzarella, G.; Montisci, G. Design of a printed log-periodic dipole array for ultra-wideband applications.
Prog. Electromagn. Res. C 2013, 38, 15–26. [CrossRef]
27. Limpiti, T.; Chantaveerod, A.Y. Design of a printed log-periodic dipole antenna (LPDA) for 0.8–2.5 GHz band applications. In
Proceedings of the 2016 13th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and
Information Technology (ECTI-CON), Chiang Mai, Thailand, 28 June–1 July 2016; pp. 1–4.
28. Yu, L.; Chai, S.; Huang, H.; Ding, L.; Xiao, K.; Zhao, F. A printed log-periodic dipole antenna with balanced feed structure.
In Proceedings of the 2016 Progress in Electromagnetic Research Symposium (PIERS), Shanghai, China, 8–11 August 2016;
pp. 2035–2038.
Electronics 2022, 11, 2877 20 of 20

29. Kyei, A.; Sim, D.-U.; Jung, Y.-B. Compact log-periodic dipole array antenna with bandwidth-enhancement techniques for the low
frequency band. IET Microw. Antennas Propag. 2017, 11, 711–717. [CrossRef]
30. Anim, K.; Jung, Y.-B. Shortened log-periodic dipole antenna using printed dual-band dipole elements. IEEE Trans. Antennas
Propag. 2018, 66, 6762–6771. [CrossRef]
31. Mistry, K.K.; Lazaridis, P.I.; Zaharis, Z.D.; Xenos, T.D.; Tziris, E.N.; Glover, I.A. An optimal design of printed log-periodic antenna
for L-band EMC applications. In Proceedings of the 2018 IEEE International Symposium on Electromagnetic Compatibility and
2018 IEEE Asia-Pacific Symposium on Electromagnetic Compatibility (EMC/APEMC), Suntec City, Singapore, 14–18 May 2018;
pp. 1150–1155.
32. Mistry, K.K.; Lazaridis, P.I.; Ahmed, Q.; Zaharis, Z.D.; Loh, T.H.; Chochliouros, I.P. A printed LPDA antenna with improved low
frequency response. In Proceedings of the 2020 XXXIII General Assembly and Scientific Symposium of the International Union of
Radio Science, Rome, Italy, 29 August–5 September 2020; pp. 1–4.
33. Kubacki, R.; Czyżewski, M.; Laskowski, D. Enlarged Frequency Bandwidth of Truncated Log-Periodic Dipole Array Antenna.
Electronics 2020, 9, 1300. [CrossRef]
34. Wu, Q.; Ding, X.; Su, D. A compact dipole antenna with curved reflector for 1.0–4.2 GHz EMC measurement. IEEE Trans.
Electromagn. Compat. 2015, 57, 1289–1297. [CrossRef]
35. CISPR16-1-2; Specification for Radio Disturbance and Immunity Measuring Apparatus and Methods—Part 1–2: Radio Disturbance
and Immunity Measuring Apparatus-Ancillary Equipment-Conducted Disturbances. International Electrotechnical Commission:
Geneva, Switzerland, 2006.
36. Microwave Vision Group. Considerations in EMI Antenna Design. Available online: http://www.interferencetechnology.com/
wp-content/uploads/2021/02/Whitepaper-EMC-Considerations-in-EMI-Antenna-Design.pdf (accessed on 8 August 2022).
37. Isbell, D. Log periodic dipole arrays. IRE Trans. Antennas Propag. 1960, 8, 260–267. [CrossRef]
38. DuHamel, R.; Isbell, D. Broadband logarithmically periodic antenna structures. In Proceedings of the 1958 IRE International
Convention Record, New York, NY, USA, 21–25 March 1966; pp. 119–128.
39. Carrel, R. The design of log-periodic dipole antennas. In Proceedings of the 1958 IRE International Convention Record, New
York, NY, USA, 21–25 March 1966; pp. 61–75.
40. Balanis, C.A. Antenna Theory: Analysis and Design; John Wiley & Sons: Hoboken, NJ, USA, 2015.
41. Dassault Systemes. CST Computer Simulation Technology AG (2016); Dassault Systemes: Darmstadt, Germany, 2014.
42. Vieira, G.C. Log-Periodic Dipole Antennas in Printed Circuit Technology; Instituto Superior Tecnico: Lisboa, Portugal, 2018.
43. Alexander, M.; Salter, M.; Gentle, D.; Knight, D.; Loader, B.; Holland, K. Calibration and Use of Antennas, Focusing on EMC
Applications; National Physical Laboratory: Teddington, UK, 2004.
44. Patre, S.R.; Singh, S.; Singh, S.P. Effect of dielectric substrate on performance of planar trapezoidal toothed log-periodic antenna.
In Proceedings of the 2013 Students Conference on Engineering and Systems (SCES), Allahabad, India, 12–14 April 2013; pp. 1–4.
45. Kim, J.I.; Safaai-Jazi, A.J. Log-periodic loop antennas with high gain and linear polarization. Microw. Opt. Technol. Lett. 2000,
27, 66–68. [CrossRef]
46. McLean, J.; Sutton, R.; Hoffman, R.J. Interpreting Antenna Performance Parameters for EMC Applications: Part 3: Antenna Factor; TDK
RF Solutions Inc.: Cedar Park, TX, USA, 2004.
47. Shop, A. HyperLOG® 7060. Available online: https://aaronia-shop.com/products/broadband-antenna-hyperlog7060 (accessed
on 8 August 2022).