432 MHz Dish Feed comparison


Content

1. Introduction
2. Disclaimer
3. Dipole in free space
4. Dual dipole feed over a one lambda circular reflector
5. Dual dipole feed over a one lambda square reflector
6. DL4MEA loop feed
7. OK1DFC loop feed
8. XE1XA loop feed
9. One lambda loop over a one lambda circular reflector with BFR
10. SM6FHZ BFR loop feed
11. Single dipole over a one lambda circular reflector
12. Single dipole over a one lambda circular reflector with BFR
13. PY2BS Patch feed
14. Modified PY2BS Patch feed
15. ES5PC Patch feed
16. CT1DMK Annular Ring feed
17. Conclusions
18. Acknowledgments
19. References


1. Introduction

When looking in to the details of choosing a feed for my 0.37 f/D dish on 432 MHz, I realized it was not easy to find the most suitable one. The data available for the different alternatives was scarce and often important data was missing. Even misleading data was found on some of the feed descriptions. I came to the conclusion that it would be both interesting and beneficial for the choice to look further on some of the alternatives.

The good results on 23 cm with the W2IMU dual mode feed lead the thoughts to finding something with similar radiation properties also for 432 MHz. Other criteria was size and ease of polarization rotation, stable / uncritical as well as an easy to build and align design. With respect to radiation properties, equal beam width in E- and H-plane was a major criteria as well as the proper illumination taper at +/- 64 degrees (edge of my dish). The W2IMU Dual Mode feed has about -16.5 dB at +/-64 deg in both E and H-planes.

I had already built the XE1XA Loop feed and wanted to know how it performed. In the description, XE1XA claims that this feed had equal beam width in E- and H-planes and that he had used it in his 5 m, 0.45 f/D dish with success. It all sounded very good to my ears, but I wanted to validate these statements. I had no possibility to get it measured with any kind of decent accuracy so simulation was to most attractive way forward. When simulating the feed it turned out that the beam widths in E- and H-plane were not similar at all. At this point I started to look around for other suitable feeds for the job. I had also been looking at Kildal's paper on the BFR for many years and realized that I now had the tool to evaluate it on 432 MHz. After having done all kinds of simulations and evaluations I put on a BFR on my feed for testing. I am still in the "on the air" evaluation phase.

NOTE! All comparison is made with my 0.37 f/D dish in mind (64 degree edge angle).

Starting from a simple dipole in free space, I made simulations in HFSS on the feeds I could find relevant design data for. On some feeds I had to make some assumptions to get all the needed mechanical dimensions. The simulation models are simplified as much as I thought was OK without jeopardizing the radiation performance accuracy. The results from the simulations are probably on the optimistic side, as any shortcomings in a physical realization will introduce unsymmetries and errors that will make the performance worse than simulated. The feed performance data was put into W1GHZ "Phasepat.exe" (Ref. [1]) for further analysis of the "In Dish" performance.

The Phase Center data are all referred to the surface of the reflector. The Phase Center in the W1GHZ In Dish Performance graphs are referred to the Phase Center I arrived at in my simulation. See comments about Phase Center in the Conclusions part.

I think this comparison will give a good hint on the characteristics of the feeds and aid in the choice of feed for me and for you as well, I hope.

Please enjoy yourself when digging in to the data. I have very much enjoyed making these simulations and arriving at the results and conclusions. Lets go!

2. Disclaimer

Please bear in mind that the results below are from simulations and is not a absolute universal truth! But it is good enough to serve as comparison between the different feeds and to be used as basis for choosing a feed for a particular application.

This report is NOT intended to be a building description to follow step by step to build a particular feed. The purpose is to make a survey among the different feeds that has been described more or less detailed in the HAM literature. For the feeds that are most interesting (best performers) I may try to build and then report the dimensions used. For the dimensions used for the simulations please drop me a mail, and you will get the dimensions I used.

I sincerely apologize for the mediocre picture resolution. As I did not find a way to get the full resolution when transferring the pictures to the web page composer, I have written all important data in the text as well. See the graphs as a way to get a quick overview of the performance of each individual feed examined.

The results presented in this report are not allowed to be used for any commercial purpose without explicit permission from the author. It may be used for Ham, non-commercial, purposes if used together with clear reference to the source of the information. I.E. Normal polite journalistic standards.

3. Dipole in free space

Description:

Half lambda dipole in free space.


Dipole model
Figure 3:1; 432 MHz dipole model

432 MHz dipole 3D radiation pattern
Figure 3:2; 432 MHz dipole 3D pattern

432 MHzdipole E-plane pattern
Figure 3:3; 432 MHz dipole E-plane pattern

432 MHz dipole H-plane pattern
Figure 3:4; 432 MHz dipole H-plane pattern

Comments:

I used the dipole simulation to check the validity of the simulations. As can be seen there is a slight disturbance in the H-plane cut (+/-0.4 dB peak). This can be seen also in the H-plane patterns on the feeds analyzed. This is an minor artifact from the simulation and does not give any major impact on the conclusions from the simulations. I have not spent any time on optimizing the radiation boundary conditions in order to minimize the disturbance. The average directivity of the dipole is very close the the theoretical 2.15 dBi.


4. Dual dipole feed over a one lambda circular reflector

Description:

Two half lambda dipoles quarter of lambda over a one lambda circular reflector. The dipoles are separated one half lambda.

432 MHz dual dipole feed model
Figure 4:1; 432 MHz Dual Dipole feed model


432 MHz dual dipole 3D pattern
Figure 4:2; 432 MHz Dual Dipole feed 3D pattern

432 MHz dual dipole E-plane pattern
Figure 4:3; 432 MHz Dual Dipole feed E-plane Co and Cross polarization patterns

Dual Dipole E-plane Phase pattern
Figure 4:4; 432 MHz Dual Dipole feed E-plane Phase pattern

432 MHz dual dipole H-plane pattern
Figure 4:5; 432 MHz Dual Dipole feed H-plane Co and Cross polar patterns

Dual Dipole feed H-plane pattern
Figure 4:6; 432 MHz Dual Dipole feed H-plane Phase pattern

Dual Dipole feed in dish performance                         Dual dipole inDish performance 10 wl                    
Figure 4:7; 432 MHz Dual Dipole feed in dish performance                                                     Figure 4:8; 432 MHz Dual Dipole feed in dish performance (10 wl diam)
                 
Illumination characteristics:
E-plane: -13.0 / -13.2 dB at +/- 64 degrees
H-plane: -12.8 / -12.9 dB at +/- 64 degrees
Calculated directivity: +10 dBi
FBR: 14.9 dB
Phase center (relative to reflector): +85 mm


Comments:
This is a classic 432 MHz feed for f/D 0.5 to 0.6 dishes. It is a derivative from feed No. 3 below, the EIA standard gain antenna. It shows very well matched beam widths in the E- and H-planes that will give balanced illumination of  the dish. Clean pattern with good front to back ratio as well as very good cross polar discrimination. A good choice even for dishes deeper than 0.5 f/D if you would like a low noise antenna at the expense of slightly reduced gain due to the under illumination that will result. A drawback could be that it is slightly more cumbersome to feed than a loop feed as it has two radiating elements. An more in detail analysis of this feed including suggestions for improvements can be found here.


5. Dual dipole feed over a one lambda square reflector

Description:

Two half lambda dipoles quarter of lambda over a one lambda square reflector. The dipoles are separated one half lambda.

432 MHz square dual dipole feed model
Figure 5:1; 432 MHz Square Dual Dipole feed model

432 MHz square dual dipole 3D pattern
Figure 5:2; 432 MHz Square Dual Dipole feed 3D pattern

432 MHz square dual dipole E-plane pattern
Figure 5:3; 432 MHz Square Dual Dipole feed E-plane pattern

Square Dual Dipole feed E-plane Phase pattern
Figure 5:4; 432 MHz Square Dual Dipole feed E-plane Phase pattern

432 MHz square dual dipole H-plane pattern
Figure 5:5; 432 MHz Square Dual Dipole feed H-plane pattern

Square Dual Dipole H-plane phase pattern
Figure 5:6; 432 MHz Square Dual Dipole feed H-plane Phase pattern

Dual Dipole feed square reflector in dish perfomance                         Square reflector Dual Dipole inDish 10 WL
Figure 5:7; 432 MHz Square Dual Dipole feed in dish performance                                               Figure 5:8; 432 MHz Square Dual Dipole feed in dish performance (10 wl diam)

Illumination characteristics:
E-plane: -13.8 / -13.8 dB at +/- 64 degrees
H-plane: -14.4 / -15.1 dB at +/- 64 degrees
Calculated directivity: +10.3 dBi
FBR: 14.8 dB
Phase center (relative to reflector): +80 mm

Comments:
This is a another classic 432 MHz feed for f/D 0.5 to 0.6 dishes. It is also called the EIA standard gain antenna (Ref. [6]). It shows well matched beam widths in the E- and H-planes but not as good as the dual dipole feed with circular reflector. Clean pattern with good front to back ratio. A good choice even for dishes deeper than 0.5 f/D if you would like a low noise antenna at the expense of slightly reduced gain due to the under illumination that will result. A drawback could be that it is slightly more cumbersome to feed than a loop feed as it has two radiating elements.


6. DL4MEA loop feed

Description:

One lambda loop, one eights of lambda above a 0.65 lambda circular reflector. Described as the DL4MEA loop feed at W1GHZ On Line Antenna Book, Ref.[1]

432 MHz DL4MEA loop feed model
Figure 6:1; 432 MHz DL4MEA loop feed model

432 MHz DL4MEA loop feed 3D pattern
Figure 6:2; 432 MHz DL4MEA loop feed 3D pattern

432 MHz DL4MEA loop feed E-plane pattern
Figure 6:3; 432 MHz DL4MEA loop feed E-plane pattern

DL4MEA Loop feed E-plane Phase pattern
Figure 6:4; 432 MHz DL4MEA loop feed E-plane Phase pattern

432 MHz DL4MEA loop feed H-plane pattern
Figure 6:5; 432 MHz DL4MEA loop feed H-plane pattern

DL4MEA Loop feed H-plane Phase pattern
Figure 6:6; 432 MHz DL4MEA loop feed H-plane Phase pattern

DL4MEA Loop feed in dish performance                         DL4MEA loop feed inDish performance 10 wl
Figure 6:7; 432 MHz DL4MEA loop feed In dish performance                                                          Figure 6:8; 432 MHz DL4MEA loop feed In dish performance (10 wl diam)


Illumination characteristics:
E-plane: -12.4 / -12.6 dB at +/- 64 degrees
H-plane: -7.3 / -6.7 dB at +/- 64 degrees
Calculated directivity: +8.3 dBi
FBR: 11.3 dB
Phase center (relative to reflector): +75 mm

Comments:
A small and neat feed. Unfortunately the E-plane and H-plane beam widths are not equal. The wide H-plane together with the relatively narrow E-plane makes it difficult to find a suitable dish f/D to get a good compromise between gain and low noise. The front to back ratio (FBR) is mediocre, 11.3 dB while most other feeds show close to 15 dB.  Good Cross polar discrimination and low phase error as well as low feed blockage.

7. OK1DFC loop feed

Description:

One lambda loop one eighths lambda above a half lambda diameter circular reflector with choke. OK1DFC recalculated a OM6AA 13 cm design to 70 cm to fit his 0.4 f/D dish.

432 MHz OK1DFC loop feed model
Figure 7:1; 432 MHz OK1DFC loop feed model

432 MHz OK1DFC loop feed 3D pattern
Figure 7:2; 432 MHz OK1DFC loop feed 3D pattern

432 MHz OK1DFC loop feed E-plane pattern
Figure 7:3; 432 MHz OK1DFC loop feed E-plane Co and Cross polar patterns

OK1DFC Loop feed E-plane phase
Figure 7:4; 432 MHz OK1DFC loop feed E-plane phase pattern

432 MHz OK1DFC loop feed H-plane pattern
Figure 7:5; 432 MHz OK1DFC loop feed H-plane Co and Cross polar patterns

OK1DFC Loop feed H-plande phase
Figure 7:6; 432 MHz OK1DFC loop feed H-plane phase pattern

OK1DFC Loop feed in dish performance                                          OK1DFC Loop feed inDish 10wl
Figure 7:7; 432 MHz OK1DFC loop feed in dish performance                                                                             Figure 7:8; 432 MHz OK1DFC loop feed in dish performance (10 wl diam)


Illumination characteristics:
E-plane: -9.0 / -8.7 dB at +/- 64 degrees
H-plane: -7.1 / -6.9 dB at +/- 64 degrees
Calculated directivity: +8.3 dBi
FBR: 14.5 dB
Phase center (relative to reflector): +110 mm

Comments:
A compact feed with good characteristics. This feed is mostly suitable to use with deep dishes. Similar front to back ratio as the other good feeds as well as reasonable equal radiation characteristics in E- and H-planes. Construction seem to be fairly easy and the compact dimensions makes it easy to rotate in the polarization plane. A excellent choice if your dish is on the deep side!


8. XE1XA loop feed

Description:

One lambda circumference loop, one quarter of lambda over a one lambda diameter circular reflector. Described by XE1XA in the "EME newsletter" in 1986.

432 MHz XE1XA loop feed model
Figure 8:1; 432 MHz XE1XA loop feed model

432 MHz XE1XA loop feed 3D pattern
Figure 8:2; 432 MHz XE1XA loop feed 3D pattern

432 MHz XE1XA loop feed E-plane pattern
Figure 8:3; 432 MHz XE1XA loop feed E-plane pattern

XE1XA loop feed E-plane phase
Figure 8:4; 432 MHz XE1XA loop feed E-plane phase pattern

432 MHz XE1XA loop feed H-plane pattern
Figure 8:5; 432 MHz XE1XA loop feed H-plane pattern

XE1XA loop feed H-plane phase
Figure 8:6; 432 MHz XE1XA loop feed H-plane phase pattern

XE1XA Loop feed in dish performance                        XE1XA Loop feed inDich 10wl
Figure 8:7; 432 MHz XE1XA loop feed in dish performance                                                                Figure8:8; 432 MHz XE1XA loop feed in dish performance (10 wl diam)

Illumination characteristics:
E-plane: -12.8 / -12.9 dB at +/- 64 degrees
H-plane: -8.5 / -7.3 dB at +/- 64 degrees
Calculated directivity: +8.8 dBi
FBR: 15.5 dB
Phase center (relative to reflector): +100 mm


Comments:
This feed has the same drawbacks as all other dipole/loop based feeds; unequal illumination in E- and H-planes. The front to back ratio is in the same order as the other large reflector feeds. Clean radiation pattern. Fairly easy to construct and to rotate in polarization.



9. One lambda loop over a one lambda circular reflector with BFR

Description:

One lambda loop, one quarter of lambda over a one lambda circular reflector with Beam Forming Ring (BFR) (diam. 20mm) according to Kildal, Ref [4] and [5]. This trial uses the original dimensions for the BFR suggested by Kildal in his papers.

432 MHz BFR loop feed model
Figure 9:1; 432 MHz BFR loop feed model

432 MHz BFR loop feed 3D pattern
Figure 9:2; 432 MHz BFR loop feed 3D pattern

432 MHz BFR loop feed E-plane pattern
Figure 9:3; 432 MHz BFR loop feed E-plane pattern

BFR Loop feed E-plane Phase pattern
Figure 9:4; 432 MHz BFR loop feed E-plane Phase pattern

432 MHz BFR loop feed H-plane pattern
Figure 9:5; 432 MHz BFR loop feed H-plane pattern

BFR Loop feed H-plane Phase pattern
Figure 9:6; 432 MHz BFR loop feed H-plane Phase pattern

BFR Loop feed in dish performance
Figure 9:7; 432 MHz BFR loop feed in dish performance


Illumination characteristics:
E-plane: -11.6 / -11.5 dB at +/- 64 degrees
H-plane: -12.7 / -11.6 dB at +/- 64 degrees
Calculated directivity: +9.3 dBi
FBR: 13.4 dB
Phase center (relative to reflector): +145 mm

Comments:
This feed shows good equality in beam width between the E- and H-plane thanks to the BFR. The FBR remains the same as without the BFR. This makes it a good feed. The complexity is somewhat higher with the BFR and the required volume increased from the feed without the BFR.


10. SM6FHZ BFR loop feed

Description:

One lambda loop over a one lambda circular reflector with an modified Beam Forming Ring (BFR) (diam. 8mm) compared to the dimensions given by Kildal, Ref [4] and [5] in order to get a more optimized and light weight design.

432 MHz moified BFR loop feed model
Figure 10:1; 432 MHz SM6FHZ BFR loop feed model

432 MHz modified BFR loop feed 3D pattern
Figure 10:2; 432 MHz SM6FHZ BFR loop feed 3D pattern

432 MHz SM6FHZ BFR loop feed E-plane pattern
Figure 10:3; 432 MHz SM6FHZ BFR loop feed E-plane pattern

SM6FHZ BFR loop phase E-plane
Figure 10:4; 432 MHz SM6FHZ BFR loop feed E-plane phase pattern

432 MHz SM6FHZ BFR loop feed H-plane pattern
Figure 10:5; 432 MHz SM6FHZ BFR loop feed H-plane pattern

SM6FHZ BFR loop H-plane phase
Figure 10:6; 432 MHz SM6FHZ BFR loop feed E-plane phase pattern

SM6FHZ BRF Loop feed in dish performance                         SM6FHZ BFR Loop inDish 10wl
Figure 10:7; 432 MHz SM6FHZ BFR loop feed in dish performance                                                      Figure 10:8; 432 MHz SM6FHZ BFR loop feed in dish performance (10 wl diam)

Illumination characteristics:
E-plane: -11.9 / -11.8 dB at +/- 64 degrees
H-plane: -12.3 / -11.5 dB at +/- 64 degrees
Calculated directivity: +9.3 dBi
FBR: 13.3 dB
Phase center (relative to reflector): +130 mm

Comments:
This feed shows good equality in beam width between the E- and H-plane thanks to the BFR. The FBR remains the same as without the BFR. This makes it a good feed. The complexity is somewhat higher with the BFR and the required volume increased from the feed without the BFR. An more in detail analysis of the above loop feeds including suggestions for further improvements can be found here.


11. Single dipole over a one lambda circular reflector

Description:

Half lambda dipole quarter of lambda over a one lambda circular reflector.

432 MHz single dipole feed model
Figure 11:1; 432 MHz Single Dipole Feed model


432 MHz single dipole feed 3D pattern
Figure 11:2; 432 MHz Single Dipole Feed 3D pattern

432 MHz single dipole E-plane pattern
Figure 11:3; 432 MHz Single Dipole feed E-plane pattern

Singel Dipole E-plane Phase pattern
Figure 11:4; 432 MHz Single Dipole feed E-plane Phase pattern

432 MHz single dipole feed H-plane pattern
Figure 11:5; 432 MHz Single Dipole feed H-plane pattern

Singel Dipole H-plane Phase pattern
Figure 11:6; 432 MHz Single Dipole feed H-plane Phase pattern

Dipole reflector feed in dish performance                         Singel dipole reflector inDish performance 10 wl
Figure 11:7; 432 MHz Single Dipole feed in dish performance                                                         Figure 11:8; 432 MHz Single Dipole feed in dish performance (10 wl diam)

Illumination characteristics:
E-plane: -14.3 / -14.7 dB at +/- 64 degrees
H-plane: -7.1 / -7.0 dB at +/- 64 degrees
Calculated directivity: +9.1 dBi
FBR: 15.7 dB
Phase center (relative to reflector): +80 mm

Comments:
Similar characteristics to the loop feed with one lambda reflector. The FBR is slightly higher, but it does not give any real advantage when used as a feed.

12. Single dipole over a one lambda circular reflector with BFR

Description:

Half lambda dipole quarter of lambda over a one lambda circular reflector with a Beam Forming Ring (BFR) (diam. 8mm) according to Kildal, Ref [4] and [5].

432 MHz single dipole BFR feed model
Figure 12:1; 432 MHz Single Dipole BFR Feed model

432 MHz single dipole BFR feed 3D pattern
Figure 12:2; 432 MHz Single Dipole Feed 3D pattern


432 MHz single dipole BFR feed E-plane pattern
Figure 12:3; 432 MHz Single Dipole feed E-plane pattern

Dipole Reflector BFR E-plane Phase pattern
Figure 12:4; 432 MHz Single Dipole feed E-plane Phase pattern


432 MHz single dipole BFR feed H-plane pattern
Figure 12:5; 432 MHz Single Dipole feed H-plane pattern

Dipole Reflector BFR H-plane Phase pattern
Figure 12:6; 432 MHz Single Dipole feed H-plane Phase pattern

Singel dipole BFR in dish performance                         Singel dipole reflector wirh BFR 10 wl
Figure 12:7; 432 MHz Single Dipole feed in dish performance                                                       Figure 12:8; 432 MHz Single Dipole feed in dish performance (10 wl diam)


Illumination characteristics:
E-plane: -13.3 / -13.0 dB at +/- 64 degrees
H-plane: -10.8 / -10.9 dB at +/- 64 degrees
Calculated directivity: +9.5 dBi
FBR: 14.2 dB
Phase center (relative to reflector): +120 mm

Comments:
The BFR shapes up the beam width but not to the same extent as for the loop feed. The loop feed with BFR is still a better choice.

13. PY2BS Patch feed

Description:

Dual polarized patch over a 0.6 lambda circular reflector. The feed includes a tuning disc for each polarization.

Py2BS Patch feed model
Figure 13:1; 432 MHz PY2BS Patch Feed model

PY2BS Patch feed port isolation
Figure 13:2; 432 MHz PY2BS Patch Feed port isolation

PY2BS Patch feed 3D pattern
Figure 13:3; 432 MHz PY2BS Patch Feed 3D total power directivity pattern


PY2BS Patch feed E-plane pattern
Figure 13:4; 432 MHz PY2BS Patch feed E-plane Co and Cross polarization patterns

PY2BS Patch feed E-plane phase
Figure 13:5; 432 MHz PY2BS Patch feed E-plane phase pattern

PY2BS Patch feed H-plane pattern
Figure 13:6; 432 MHz PY2BS Patch feed H-plane Co and Cross polar patterns

PY2BS Patch feed H-plane phase
Figure 13:7; 432 MHz PY2BS Patch feed H-plane phase pattern

PY2BS Loop feed in dish performance                         PY2BS patch feed inDinsh performance 10wl
Figure 13:8; 432 MHz PY2BS Patch feed in dish performance                                                     Figure 13:9; 432 MHz PY2BS Patch feed in dish performance (10 wl diam)


Illumination characteristics:
E-plane: -11.5 / -11.5 dB at +/- 64 degrees
H-plane: -7.2 / -7.3 dB at +/- 64 degrees
Calculated directivity: +7.8 dBi
FBR: 8.1 dB
Phase center (relative to reflector): +25 mm

Comments:
Small and compact feed. F/B ratio not as good as feeds with larger reflector. Unequal dish illumination in E- and H-plane. Quite large phase error in E-plane, probably due to loading of the patch from the probe and tuning disc. Low cross polar ratio, probably due to loading of the patch from the other polarizations probe and tuning disc.

14. Modified PY2BS Patch feed

Description:

Dual polarized patch over a 0.6 lambda circular reflector with choke and low impedance coaxial transformer.

Modified PY2BS Patch feed model
Figure 14:1; 432 MHz modified PY2BS Patch Feed model

Modified PY2BS Patch feed isolation
Figure 14:2; 432 MHz modified PY2BS Patch Feed isolation

Modified PY2BS Patch feed 3D pattern
Figure 14:3; 432 MHz modified PY2BS Patch Feed 3D total power directivity pattern

Modified PY2BS Patch feed E-plane pattern
Figure 14:4; 432 MHz modified PY2BS Patch feed E-plane Co and Cross polarization patterns

Modified PY2BS Patch feed E-plane Phase pattern
Figure 14:5; 432 MHz modified PY2BS Patch feed E-plane Phase pattern


Modified PY2BS Patch feed H-plane pattern
Figure 14:6; 432 MHz modified PY2BS Patch feed H-plane Co and Cross polar patterns

Modified PY2BS Patch feed H-plane Phase pattern
Figure 14:7; 432 MHz modified PY2BS Patch feed H-plane Phase pattern

Modified PY2BS Loop feed in dish performance                        Modified PY2BS patch feed inDish performance 10 wl
Figure 14:8; 432 MHz modified PY2BS Patch feed in dish performance                                      Figure 14:9; 432 MHz modified PY2BS Patch feed in dish performance (10 wl diam)

Illumination characteristics:
E-plane: -7.8 / -7.4 dB at +/- 64 degrees
H-plane: -7.3 / -7.2 dB at +/- 64 degrees
Calculated directivity: +7.9 dBi
FBR: 15.3 dB
Phase center (relative to reflector): +105 mm

Comments:
Small and compact feed. F/B ratio, pattern and phase error improved with choke. 

15. ES5PC Patch feed

Description:

Dual polarized patch over a 0.72 lambda circular reflector (Ref [7]). The design originates from W0LMD, (Ref. [8], according to ES5PC.

ES5PC Patch feed model
Figure 15:1; 432 MHz ES5PC Patch Feed model

ES5PC Patch feed isolation
Figure 15:2; 432 MHz ES5PC Patch Feed isolation

ES5PC Patch feed 3D pattern
Figure 15:3; 432 MHz ES5PC Patch Feed 3D total power directivity pattern

ES5PC Patch feed E-plane pattern
Figure 15:4; 432 MHz ES5PC Patch feed E-plane directivity Co and Cross polarization patterns

ES5PC Patch feed E-plane Phase pattern
Figure 15:5; 432 MHz ES5PC Patch feed E-plane Co-polar phase pattern

ES5PC Patch feed H-plane pattern
Figure 15:6; 432 MHz ES5PC Patch feed H-plane Co and Cross polarization patterns

ES5PC Patch feed H-plane Phase pattern
Figure 15:7; 432 MHz ES5PC Patch feed H-plane Co polar phase pattern

ES5PC Patch feed in dish performance                         ES5PC patch feed inDish performance 10wl
Figure 15:8; 432 MHz ES5PC Patch feed in dish performance                                                  Figure 15:9; 432 MHz ES5PC Patch feed in dish performance (10 wl diam)


Illumination characteristics:
E-plane: -12.7 / -15.1 dB at +/- 64 degrees
H-plane: -8.1 / -8.1 dB at +/- 64 degrees
Calculated directivity: +8.8 dBi
FBR: 9.6 dB
Phase center (relative to reflector): +40 mm

Comments:
Small and compact feed. F/B ratio not as good as feeds with larger reflector. Unequal dish illumination in E- and H-plane. Large phase error in E-plane, probably due to the loading of the patch from the probe. Nice isolation between the ports for the two polarizations.

16. CT1DMK Annular Ring feed

Description:

Dual polarized one lambda capacitively loaded ring 0.09 lambda over a 0.62 lambda circular reflector (Ref [9]).


CT1DMK annular ring feed model
Figure 16:1; 432 MHz CT1DMK Annular Ring Feed model


CT1DMK ring feed 3D pattern
Figure 16:2; 432 MHz CT1DMK Annular Ring Feed 3D total power directivity pattern

CT1DMK ring feed E-plane pattern
Figure 16:3; 432 MHz CT1DMK Annular Ring feed E-plane directivity Co and Cross polarization patterns

CT1DMK ring feed E-plane Phase pattern
Figure 16:4; 432 MHz CT1DMK Annular Ring feed E-plane Co-polar phase pattern

CT1DMK ring feed H-plane pattern
Figure 16:5; 432 MHz CT1DMK Annular Ring feed H-plane Co and Cross polarization patterns

CT1DMK ring feed H-plane Phase pattern
Figure 16:6; 432 MHz CT1DMK Annular Ring feed H-plane Co polar phase pattern

CT1DMK ring feed in dish performance                       
Figure 16:7; 432 MHz CT1DMK Annular Ring feed in dish performance


Illumination characteristics:
E-plane: -12.1 / -14.6 dB at +/- 64 degrees
H-plane: -7.9 / -7.7 dB at +/- 64 degrees
Calculated directivity: +6.7 dBi
FBR: 6.5 dB
Phase center (relative to reflector): +80 mm

Comments:
0.62 lambda reflector size. The Annular Ring, used in this feed, is a derivative of the patch radiator with the inner (center) part removed. It is sometimes used in antennas for cellular systems. This Annular Ring is capacitively loaded in order to match the impedance. It is fed at a high impedance point at the rim of the fictive "patch". Unequal dish illumination in E- and H-plane. Large phase error in E-plane at large angles, probably due to the loading of the patch from the probe and tuning capacitance. No isolation data between the ports for the two polarizations is presented for this feed, as it is simulated as CT1DMK recommends, with the unused port left open. The heavy loading from the tuning also gives high cross polar radiation. The low front to back ratio will steal power form the main beam and consequently not reach the dish surface.

17. Conclusions

Table of summary:
Feed type Level at +/- 64 deg (E-plane) [dB] Level at +/- 64 deg (H-plane) [dB] Directivity [dBi] FBR [dB] Phase center [mm] Comments
W2IMU feed -16.5/-16.5 -16.5/-16.5   28   For comparison
Dual Dipole (square reflector) -13.8/-13.8 -14.4/-15.0 10.3 14.8 +80  
Dual Dipole (square reflector) w. W2IMU           TBD
Dual Dipole (circular reflector) -13.2/-13.2 -12.6/-13.0 10.1 15.2 +85  
DL4MEA loop -12.4/-12.6 -7.3/-6.7 8.7 11.3 +75 Compact feed.
OK1DFC loop -8.7/-9.0 -6.9/-7.1 8.3 14,5 +110 Compact feed for deep dishes
XE1XA loop -12.8/-12.9 -8.5/-7.3 8.8 15.5 +100  
BFR Loop 20 mm -11.8/-11.7 -12.7/-11.6 9.3 13.4 +145  
SM6FHZ BFR Loop  -11.9/-11.8 -12.3/-11.5 9.3 13.3 +130  
PY2BS patch -11.5 / -11.5 -7.2/-7.3 7.8 8.1 +25 Very compact feed.
PY2BS modified patch -7.8 / -7.4 -7.3 / -7.2 7.9 15.3 +105  
ES5PC patch -12.7 / -15.1 -8.1 / -8.1 8.8 9.6 +40  
CT1DMK Annular Ring -12.1 / -14.6 -7.9 / -7.7 6.7 6.5 +80  
Dipole over reflector -14.3/-14.7 -7.1/7.0 9.1 15.7 +80  
Dipole over reflector with BFR -13.3/-13.0 -10.8/-10.9 9.5 14.2 +120  


There is a clear difference between feeds with a one lambda reflector and feeds with a smaller reflector when it comes to beam width and front to back ratio. If you use a loop or a single dipole as the radiating element does not matter, the characteristics are about the same for both. Both have unequal beam with in the E- and H-planes with the H-plane to be the wider one.

One statement I saw in a description for a loop feed was that you could adjust the beam width in E- and H-plane by making the loop oval. This is not correct. It does hardly make any difference at all. You can go the the extreme of a loop; the folded dipole and still have about the same E- and H-plane patterns.

In order to equalize the the beam widths in E- and H-planes one can use one more dipole fed in phase, a Beam Forming Ring (BFR) or a choke (baffle) on the reflector. The two first ones makes the H-plane more narrow to match the E-plane. The choke makes the E-plane wider to match the H-plane.

The feeds with a more narrow beam width and reasonably equal illumination in the E- and H-planes are the Dual Dipole feeds and the Loop feeds comprising a BFR. The BFR-loop feeds have slightly wider beam widths in both planes compared to the dual dipole feeds.

The only feeds examined with wider beam width and reasonably equal illumination in the E- and H-planes is the OK1DFC Loop feed and the modified PY2BS Patch feed. These two feeds fit well into a deep dish.

None of the examined feeds are as narrow as the W2IMU Dual Mode feed used as a reference.

The far field phase error ranges from very good to mediocre to bad on the feeds examined. Some of the Dual Polarized feeds examined suffer from phase distortion in the far field. This seem to be the price you have to pay for Dual Polarization feature in some cases.

The center of rotation for all feeds is in the center of the reflector (X,Y-axises) and in the plane of the phase center (Z-axis). The position of the phase center has been empirically determined by running simulations on different center of rotation (Z-axis). The Phase center has been chosen as a best compromise between E- and H-plane phase error. The Phase center data in this report is always referred to the front surface of the reflector. From experience with sun noise measurements on my XE1XA feed in my 0.37 f/D dish; if you are within 3 to 5 cm from the phase center you can hardly see any deviation in sun noise. This is at the 11 dB level on 432 MHz.

Further work that could be done includes:

18. Acknowledgments

I would like to thank all the "inventors" (CT1DMK, ES5PC, DL4MEA, OK1DFC and PY2BS) of the feeds that I have analyzed for letting me publish the results here. I would also like to send a big thank you to G3LTF, Peter, VK3UM, Doug and W1GHZ, Paul for the support and discussions about the results and the form of this presentation. Your support and comments have been indispensable along the way. Finally, I send my sincere appreciation to my colleagues at QRL (Anders, Lars, Anders, Henrik, Andreas, Ola and Anders) for putting up with my ever lasting questions about simulations, pitfalls and coordinate systems. Without their support I would never had come through this work. And I do not forget to thank my lovely family that had been suffering from heavy loading of our common computer resources from the endless simulations, disrupting all other activities on the computer and the Internet.

19. References

[1] W1GHZ Antenna Book on line:  http://www.w1ghz.org/

[2] OK1DFC web page: http://www.ok1dfc.com/EME/technic/432feed/432feed.htm

[3] 432 MHz and above News, Sept 1986, Vol 14 #10, The XE1XA feed description can also be found at PA3CSG's web page.

[4) Dipole-Disk Antenna with Beam-Forming Ring, Per-Simon Kildal, Svein A. Skyttemyr, IEEE Transactions on Antennas and Propagation, Vol. AP-30, No. 4, July 1982, page 529 - 534.

[5] A Small Dipole-Fed Resonant Reflector Antenna with High Efficiency, Low Cross Polarization, and Low Side lobes, Per-Simon Kildal, IEEE Transactions on Antennas and Propagation, Vol. AP-33, No. 12, December 1985, page 1386 - 1391.

[6] Antenna Performance Measurements, Dick Turrin, W2IMU, QST November 1974, page 35 to 41.

[7] ES5PC Patch feed description: http://www.comnetsys.eu/files/ES5PC/432MHzPatchFeed/432MHz_Patch.pdf  and  http://www.comnetsys.eu/files/ES5PC/432MHzPatchFeed/

[8] W0LMD Patch feed description: http://www.samuelraileyefurd.com/interestingthings/ultimatecharger/dish-feed-u.html

[9] CT1DMK Annular Ring feed description: http://www.qsl.net/ct1dmk/70cm_loop.pdf

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Updated May 31st, 2011.  © Ingolf Larsson, SM6FHZ, December, 2010              http://www.2ingandlin.se/SM6FHZ.htm