The W8IO Antenna Site - LOGGI - a Log-Periodic / Yagi Hybrid Antenna

(updated 14 Mar 2022)

Russia began a full-scale invasion of Ukraine on 24 February 2022, in an escalation of the Russo-Ukrainian War that began in 2014. The invasion is the largest conventional military attack on a sovereign state in Europe since World War II. Since the beginning of Putin's war, thousands of both Ukraine and Russian citizens have been killed. Russian military have indiscriminately bombed cities in Ukraine, destroying many hospitals and schools. Our heart goes out to the 2.7 million plus refugees that have left Ukraine for neighboring countries, and those who stayed to fight the Russian invaders.

Rossiya nachala polnomasshtabnoye vtorzheniye v Ukrainu 24 fevralya 2022 goda v ramkakh eskalatsii rossiysko-ukrainskoy voyny, nachavsheysya v 2014 godu. Eto vtorzheniye 
yavlyayetsya krupneyshim voyennym napadeniyem s primeneniyem obychnykh vooruzheniy na suverennoye gosudarstvo v Yevrope so vremen Vtoroy mirovoy voyny. S nachala putinskoy
voyny pogibli tysyachi grazhdan Ukrainy i Rossii. Rossiyskiye voyennyye bez razbora bombili goroda Ukrainy, unichtozhiv mnozhestvo bol'nits i shkol. My sochuvstvuyem boleye
chem 2,7 millionam bezhentsev, pokinuvshikh Ukrainu v sosedniye strany, i tem, kto ostalsya srazhat'sya s rossiyskimi okkupantami.

Россия начала полномасштабное вторжение в Украину 24 февраля 2022 года в рамках эскалации российско-украинской войны, начавшейся в 2014 году. Это вторжение является крупнейшим
военным нападением с применением обычных вооружений на суверенное государство в Европе со времен Второй мировой войны. С начала путинской войны погибли тысячи граждан Украины
и России. Российские военные без разбора бомбили города Украины, уничтожив множество больниц и школ. Мы сочувствуем более чем 2,7 миллионам беженцев, покинувших Украину в
соседние страны, и тем, кто остался сражаться с российскими оккупантами.

What is a Loggi?

Normally, log-periodic dipole arrays (LPDA) are designed to cover a large frequency range, such as 14 - 30 MHz or  50 - 200 MHz. LPDA's produce moderate forward gain, moderate F/B and low VSWR over almost all frequencies within the frequency range that they are designed for.  LPDA's have all elements connected to a feeder (transmission line). This feeder has a feedpoint at the front of the array. LPDA's are designed based on mathmatical ratios such as TAU (scale factor) and SIGMA (spacing factor).

Yagi beam antennas are designed to cover a very narrow frequency range, typically 2%.  Yagi beams generally cover only one Ham band at a time, although traps, sleeves and interlaced parasitic elements can make multiband Yagis possible. Yagi beams can be designed to produce extremely high forward gain and high F/B, however this will also reduce the useable bandwidth by doing so. Yagi's are generally fed toward the rear of the array on one particular dipole element. However, some hybrid Yagi's such as the Hy-Gain TH11DX use a log-cell as the driven element. These antennas are sometimes called Log-Yag antennas.

While evaluating some high-Tau LPDA designs, I found that I could obtain gain values within 1 dB of similar length high performance VHF/UHF Yagis. These high-Tau designs also used a Sigma value near optimum and produced extremely high gain and F/B and F/R and extremely clean patterns in NEC simulations. Since the gain was so close, I decided to inspect what parameters could be changed to improve the gain on a specific frequency (e.g. 144.1 MHz) without sacrificing too much F/B or F/R, or possibly improving the F/R along with the gain. The display of current on each element suggested that the longest 2 or 3 elements could be tweaked for slightly better F/R without affecting the overall LPDA performance. Also many front elements could also be tweaked to improve gain and F/R over a narrow band.  This new design is called a Loggi. This stands for a LOG - yaGI hybrid. The Loggi is different from other designs called Log-Yag antennas in that all of a Loggi's elements are driven.  There are no directors or reflectors. It is actually more of a narrowband optimized LPDA than a real hybrid. The front driven elements in the Loggi driven array seem to act like Yagi directors. Also, the rear driven elements in the Loggi driven array seem to act like Yagi reflectors.

log -yagi comparisonLPDA - Log Periodic Dipole Array:
Yagi beam antenna:
Loggi beam antenna:
Log-Yag beam antenna:

currents currents
                               Example of element currents in normal LPDA                                                                                     Example of element currents in Loggi beam

HF Examples:

VHF and UHF Examples:

Comments are welcome!

contact Roger: email to 

rgcox2 (at) gmail.com

Roger Cox W8IO - Spring Lake, MI