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Gain of a Quarter Wave Ground Plane Antenna? Oct 9th 2017, 10:39 3 9,228 on 9/8/22

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Gain of a Quarter Wave Ground Plane Antenna? WA6EJO on 9/8/22
I finally answered my own question. Claims of -0.85 dBi to +5.31 dBi are just nuts! I decided to measure it myself using the two-identical antenna technique and the Friis equation. I made two ¼-wave ground plane antennas for 449.9 MHz. Tuned to 1.01:1 SWR. Excited with approx 5W. Received with a HP 478A/432C microwave power meter. The measurement was extremely difficult due to the reflection effects for omnidirectional antennas. If ever there was a time to use a RF anechoic chamber or two mountaintops, this was it! It took 39 gain readings to get the confidence to say that the gain of a ¼-wave ground plane is 1.32 dBi +/-0.4 dBi. To verify my technique and math I then measured the gain of the only other two identical antennas I had at hand, Two Seavey Engineering SGA-20 standard gain horns. Performed at 2.4 GHz I came within about 3% of the specified gain.

73, Steve J. Noll WA6EJO

Gain of a Quarter Wave Ground Plane Antenna? WA6EJO on 9/10/17
What is the gain of a quarter wave ground plane antenna?
Simple question? Everyone has an opinion. Which one is correct?
Assumption: a dipole is 2.15 dBi.

-0.85 dBi
“...the "1/4 wave" antenna has 0.85 dB loss as compared to an isotropic source.”
A Discussion of Antenna Theory by Paul Graham (K9ERG)

1.15 dBi
“Gain is slightly lower than a dipole (about 1 dB less)...” [2.15 - 1]
US Naval Academy EE302 Lesson 13: Antenna Fundamentals, page 19.

2.15 dBi
“The performance of a quarter wave antenna (either well grounded or using a counterpoise) is essentially the same as a half-wave dipole antenna.”
US Naval Academy EE302 Lesson 13: Antenna Fundamentals, page 21.

2.15 dBi
“λ/2 dipole has 2.15 dBi gain – Ground-plane gain equivalent to λ/2 dipole”
Antennas 101

2.15 dBi
“A monopole over an infinite ground plane is theoretically the same (identical gain, pattern, etc., in the half-space above the ground plane) as the dipole in free space.”
Antenna System Guide, NIJ Guide 202-00 - NCJRS

2.2 dBi
“The following discussion of antenna types assumes an “adequate´ ground plane is present...A single radiating element approximately 1/4 wavelength long. Directivity 2.2 dBi, 0 dBd.
Antenna Basic Concepts

5.15 dBi
“If the directivity of a dipole of length 2L has a directivity of D1 [decibels], then the directivity of a monopole antenna of length L will have a directivity of D1+3 [decibels].” [2.15 + 3]
The Monopole Antenna

5.16 dBi
“Thus, the gain of a quarter-wave monopole should have twice the gain of a corresponding
half-wave dipole, or 5.16 dB.”
Dipole and Monopole Antenna Gain Effective Area for Communication Formulas

5.19 dBi
“...a quarter-wave monopole, the most common type, will have a gain of 2.19 + 3 = 5.19 dBi...”
Wikipedia entry for Monopole antenna.

5.31 dBi
“Therefore, we deduce the antenna gain of a quarter-wave monopole antenna above virtual ground as 5.31 dB which is little bit more than twice the gain of a center-fed half-wave dipole antenna that is 2.16 dB.”
Radiation Characteristics of a Quarter-Wave Monopole Antenna above Virtual Ground

73, Steve J. Noll, WA6EJO

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