435MHz 5 Petal Cloverleaf tower mounted antenna. November 2016

Requiring a horizontally polarised 70cm band antenna for SSB (Single Side Band) work and also needing to develop a horizontally polarised omnidirectional (HPOD) antenna for both the 2 metre band and 70 centre-metre band for a proposed beacon site, I decided that a 5 Petal Cloverleaf or sometimes referred to as a Big Wheeled antenna could be constructed as a robust unit that would be easily replicated and require little maintenance.


The antenna is constructed around a standard male N connector with a 100mm diameter aluminium radial mounting disk with a 15mm centre hole to attach to the N connector with the standard coax gland screw cap as shown in Figure 4 and Photos 3 ~ 10. The elements have been attached with 3mm diameter pop-rivets to the mounting disks

The smaller upper disk is fitted to a standard male N connector's coax centre pin and positioned in the N connector and secured with two part epoxy. A small rubber grommet has been fashioned to fit tightly in the end of the N connector body with a smearing of marine grade silicon to make to assembly water proof. 

The antenna mounting is a standard antenna mirror mount bracket with a female to female N connector bulkhead socket fitted for a range of similar antennas that are constructed around male N connectors. See: Generic Antenna Mount.


Photo 1 435MHz 3 Petal Cloverleaf assembled shown from above.

Photo 2 435MHz 3 Petal Cloverleaf assembled shown from below.

Figure 1 3 Petal Cloverleaf general layout.


Figure 2 Cloverleaf element dimensions.


144.5 145.5 146.5 222 430 435 440
mm mm mm mm mm mm mm
RAD A 701 696 691 459 241 239 236
RAD B 59 58 58 39 20 20 20
LGTH C 651 646 642 426 224 222 220
LGTH D 625 620 616 409 215 213 210
LGTH E 20 20 20 20 20 20 20
LGTH F 6 6 6 6 6 6 6
TOTAL LENGTH 2102 2088 2074 1377 724 716 708
TOTAL SECTION LENGTH 2076 2062 2048 1351 698 690 682

Figure 3 Cloverleaf element dimensions table.


Figure 4 Cloverleaf antenna hub plates dimensions.


Figure 5 Cloverleaf hub assembly with element attachment.

 Adjusting the distance D1 with the top plate and stud screw was use to adjust for the lowest SWR.


Photo 3  5 Petal Cloverleaf hub plates.


Photo 4  5 Petal Cloverleaf lower hub plate assembled.


Photo 5  5 Petal Cloverleaf lower hub plate assembled.


Photo 6  Threaded stud mated with N Connector pin.


Photo 7  Threaded stud mated with N Connector pin including heat-shrink tube.


Photo 8 435MHz 5 Petal Cloverleaf hub and stud assembled.



Photo 9 435MHz 5 Petal Cloverleaf antenna hub complete assembled.


Photo 10 435MHz 5 Petal Cloverleaf antenna hub complete assembled with elements attached.

Antenna testing

With the antenna assembled on an easily accessible test mast well clear of the ground and surrounding metallic objects, the antenna was connected to an AIM UHF antenna analyser to ascertain how the antenna loaded up. 
The goal here is to find the lowest SWR for the operating frequency of 435MHz and ideally have the resonant frequency as close as is possible to the same frequency 
The AIM UHF produces a display of all relevant data and most importantly it can project it's analysis to the antenna end of the coax giving a truer picture of the antenna. 
With modest adjustment an SWR of 1.24 was realised at 435MHz with a resonant frequency at 453MHz. The SWR was low across the full 70cm band with only maximum of 1.5 at the edges of the band (420 - 450MHz). The phase angle shown in purple displays a shallow zero angle crossing at 453MHz indicating the resonant frequency of the antenna.

Figure 7 435MHz 5 Petal Cloverleaf AIM UHF antenna analyser plot.


AIM UHF antenna analyser explanation;

SWR Standing Wave Ratio.
Zmag Total Impedance.
Phase Phase angle between voltage and current.


Details of the generic antenna mount. See: Generic Antenna Mount.


Page last revised 18 September, 2017  


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