HYBRID LFA YAGI OBLONG ANTENNAS

 

Is there anyone who did not hear IK3MAC via EME? Well, his 24x23 ele monster antenna system for 144 MHz does the job! There are a few photos of his antenna system available on Internet. You can see that the antennas are a combination of yagi and loop elements but no details are available. I started investigating the secret.

My first step was to take EZNEC files of some good yagi designs and to convert them into the hybrid antennas and look at the simulations. I chose some of my 200 Ohms LFA yagis and also some of YU7EF yagis converted to LFA. First, with only the last director changed, a better gain and G/T was achieved. The feed impedance remained at 200 Ohms. Every subsequent director converted gave better and better results. Well, not quite! When the conversion process got to the elements close to the radiator, the antenna loss temperature started to increase, and despite the fact that the gain was a bit higher, the overall G/T ratio decreased. At the same time, the impedance became unacceptable, so some changes in element position have to be made, which made the G/T even worse.

The best solution I found was to keep the reflector, radiator and first two to five directors as yagi elements. and change the rest to loop elements.

And...this is just what the IK3MAC design approximately looks like! The antenna outperforms all existing ordinary yagi or loop antennas!

I do not know if Graziano will publish his design. I have found the rectangle with a width/height ratio = 1 gave the best results. This ratio gives an additional benefit, as you will see later. Probably, the IK3MAC round loop is still better, but for me it is practicaly impossible to make round model for EZNEC.

                I have to say that I have modelled several antennas for 50 Ohms feed impedance. The performance achieved was not as good as for 200 Ohm. Therefore, all my models unless otherwise stated, are designed for 200 Ohm impedance, and the feed point is at DE2. That means that a WL coaxial balun is required for matching and balancing.

                Here are two of my most successful hybrid models:

 

ANTENNA QY21105XL4

This antenna consists of 7 yagi and 4 oblong elements, made of Al rods 5mm diameter:

Fig 1: QY21105XL4

 

Performance

ANTENNA

TYPE

No of ele

Length

(mm)

Gain

(dBi)

F/B

(dB)

F/Sh

(dB)

F/Sv

(dB)

H lobe

(◦)

V lobe

(◦)

TA

(◦K)*

G/T

(dB)*

Central

f (MHz)

Δf for SWR=1,5

Lower

Upper

QY21105

XL4

11

6000

15,43

28,34

18,92

18,26

33,2

35,6

220,4

-8,00

144,500

143,200

146,100

15,33

28,22

18,90

18,25

33,2

35,6

222,5

-8,14

Table 1 - The first row gives free space data with no losses, the lower row gives data with losses for aluminum included.

 

Comparison table

Type

Length (mm)

Gain (dBi)

TA

G/T

Freq (MHz) for SWR=1,5

QY21105XL4

6000

15,43

220,4

-8,00

143,200 146,100

15,33

222,5

-8,14

EF0211B-5

5980

15,13

229,1

-8,47

140,600 145,210

15,03

230,8

-8,60

G0KSC 12ELKKA

6048

15,22

228,7

-8,37

142,500 145,470

15,14

229,8

-8,47

Table 2 - The first row gives free space data with no losses, the lower row gives data with losses for aluminum included.

 

 

Dimensions

 

RE

DE1

DE2

D1

D2

D3

D4

D5

DQ1

DQ2

DQ3

DQ4

Position

0

265

345

415

705

1250

1934

2695

3535

4355

5245

6000

Length

1018

1018

850

946

958

932

916

900

522

500

492

476

Table 3 - All elements made of Alu rods 5 mm. The height of oblong elements 500 mm. No boom correction included

 

As you can see, the reflector and the first four directors are yagi elements. The directors DQ1 to DQ4 are oblong elements, 500 mm high, and their horizontal sides are given in the table. Material for all elements is 5 mm diameter aluminium rod.

 

Simulation results

a) no loss condition

 

 

 

b) losses included for aluminum)

 

Fig. 3: Azimuth plot QY21105XL4

Fig. 4: Elevation plot QY21105XL4

Fig. 5: SWR plots QY21105XL4 (simulation)

 

 

 

 

ANTENNA QY21308XL4

This antenna consists of  7 yagi and 6 oblong elements, all made from 8 mm diameter Al tube:

Fig. 6: QY21308XL4 layout

 

Performance

ANTENNA

TYPE

No of ele

Length

(mm)

Gain

(dBi)

F/B

(dB)

F/Sh

(dB)

F/Sv

(dB)

H lobe

(◦)

V lobe

(◦)

TA

(◦K)*

G/T

(dB)*

Central

f (MHz)

Δf for SWR=1,5

Lower

Upper

QY21308XL4

13

7845

16,37

31,11

28,32

18,39

30,2

31,4

217,7

-7,01

144,500

143,200

146,200

16,28

31,43

28,29

18,38

30,2

31,2

219,5

-7,14

Table 4 -The first row gives free space data with no losses, the lower row gives data with aluminium losses included.

 

 

Comparison table

Type

Length (mm)

Gain (dBi)

TA (K)

G/T (dB)

Freq (MHz) for SWR=1,5

QY21308XL4

7845

16,37

217,7

-7,01

143,200 146,200

16,28

219,5

-7,14

G0KSC 13ELKKB

7855

16,13

229,1

-7,28

142,650 145,370

16,03

221,1

-7,42

EF0213-5

8155

16,40

224,8

-7,12

143,660 144,620

16,25

227,6

-7,32

Table 5 - The first row gives free space data with no losses, the lower row gives data with aluminium losses included.

 

 

Dimensions

 

RE

DE1

DE2

D1

D2

D3

D4

D5

DQ1

DQ2

DQ3

DQ4

DQ5

DQ6

Position

0

180

330

401

705

1251

1938

2705

3525

4355

5233

6128

6995

7845

Length

1012

990

868

942

951

925

907

887

526

504

496

486

476

456

Table 6 - All elements made of 8 mm Al rod. The height of oblong elements 500 mm. No boom correction included

 

Simulation results

a) no loss condition)

 

 

b) Aluminium losses taken into account

 

 

Fig. 7: Azimuth plot QY21308XL4

Fig. 8: Elevation plot QY21308XL4

Fig. 9 SWR plots QY21308XL4 (simulation)

 

Fig. 10: QY21105XL4 built by S52FO

Fig. 11 & 12: Details of the driven elements