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VHF/UHF Biconical Antenna for Testing Applications

This example shows how to design and analyze a wire biconical antenna that can be used in various testing applications. Wire biconical antennas are used as a standard victim in any compliance test lab in a variety of testing applications such as immunity testing, emission testing, spectrum monitoring, and shielding effectiveness etc.

  • Immunity Testing: Radiated immunity testing requires the device under test (DUT) to operate when illuminated with high fields of electromagnetic energy. Wire biconical antennas are capable of generating those high fields at a lower range from 20MHz to 80MHz and in a higher range from 80MHz to 300MHz. A larger wire biconical antenna can produce higher fields.

  • Emission Testing: Radiation emission testing is the most common type of compliance testing. It can measure the field strength of the DUT generally in 30MHz to 1GHz. Wire biconical antennas are an excellent choice for portable applications.

  • Shielding Effectiveness: Wire biconical antenna have a coaxial wound balun that can handle high radio frequency fields.

  • Spectrum Monitoring: Radio surveillance covers a broad operating range. Wire biconical antennas are the ideal solution for these applications because of their broad bandwidth and omnidirectional radiation pattern.

Half-wave dipole antennas were used in such applications earlier. However, these antennas require more time in testing as the length of the antenna has to be adjusted for each frequency of interest. Whereas, wire biconical antennas are advantageous in that respect because of their broad bandwidth and omnidirectional pattern.

This example designs a wire biconical antenna with stable impedance over a wide frequency band of 300MHz to 1GHz. This frequency band has flat gain characteristics, which is omnidirectional in the H-plane and bidirectional in the E-plane like the half-wave dipole antenna.

Define Parameters

The dimensions shown in this figure are used to create a wire biconical antenna to cover the frequency range 300MHz to 1GHz, which is the UHF range for EMI and EMC testing application.

N  = 12;
Sw = 12e-3;
Hh = 150e-3;
Ch = 405.2e-3;
Nr = 35e-3;
Br = 353.2e-3;
Fh = 25e-3;
Fw = 18e-3;

Create Wire Biconical Antenna

Create a wire biconical antenna with the defined parameters.

ant = biconeStrip;
ant.NumStrips    = N;
ant.StripWidth   = Sw;
ant.HatHeight    = Hh;
ant.ConeHeight   = Ch;
ant.NarrowRadius = Nr;
ant.BroadRadius  = Br;
ant.FeedHeight   = Fh;
ant.FeedWidth    = Fw;
figure;
show(ant);
title('Wire Biconical antenna')

Figure contains an axes. The axes with title Wire Biconical antenna contains 9 objects of type patch, surface. These objects represent PEC, feed.

Impedance

The wire biconical antenna operates like the dipole antenna except that its skeleton has a conical-shaped element. This antenna exhibits a stable impedance for the wide frequency band ranging from 300MHz to 1000MHz. A balanced feed system should be used between the antenna and transmitter and receiver system.

freq = linspace(300e6,1e9,101);
figure;
impedance(ant,freq);

Figure contains an axes. The axes with title Impedance contains 2 objects of type line. These objects represent Resistance, Reactance.

Reflection Coefficient

The designed wire biconical antenna provides a reflection coefficient of less than -10dB for the desired operational frequency, without the matching network or balun. Thus, the designed antenna is preferred in EMC applications. Broadband coverage and compact size are prime advantages of this antenna. We choose the frequency range of 0.3 GHz to 1 GHz and calculate the S-parameters of the antenna.

s11 = sparameters(ant,freq);
figure;
rfplot(s11);

Figure contains an axes. The axes contains an object of type line. This object represents dB(S_{11}).

Radiation Pattern

The radiation pattern of a wire biconical antenna is similar that of a half-wave dipole antenna. The wire biconical antenna displays an omnidirectional pattern (circular shape) in the H-plane and and a bidirectional (eight-shaped) pattern in the E-plane, as shown in this figure. The antenna is used in field surveillance and spectrum monitoring applications because of its H-plane beam width.

Plot the 3-D radiation pattern of the antenna at 300MHz.

f = 300e6;
figure;
pattern(ant,f);

Figure contains an axes and other objects of type uicontrol. The axes contains 9 objects of type patch, surface.

The wire biconical antenna shows the omnidirectional pattern for the frequencies ranging from 300MHz to 1000MHz with the gain varying between 2.04dB to 3.283dB.

Plot the elevation pattern of the antenna at different frequencies.

p1 = patternElevation(ant,300e6);
p2 = patternElevation(ant,600e6);
p3 = patternElevation(ant,1000e6);
figure; polarpattern(p1);
hold on; polarpattern(p2);
hold on; polarpattern(p3);
legend 300MHz 600MHz 1000MHz;

Conclusion

The wire biconical antenna plays a major role in testing applications due to its advantages over other antennas. Its chief advantages are compact size and broadband characteristics along with omnidirectional radiation pattern. Regardless of the type of test (standard compliance test or simple field monitoring test), the antenna displays efficient performance characteristics.

Reference

"SCHWARZBECK MESS- ELEKTRONIK”, [Online]. https://www.yumpu.com/en/document/read/35274071/schwarzbeck-mess-elektronik.

See Also

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