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SKEW PLANAR WHEEL ANTENNA

Skew Planar Wheel Antenna for 435MHz. November 2012.


Skew-Planar antenna has had little attention in the amateur radio community despite being present in QST by Robert H. Mellen, W1IJD, and Carl T. Milner, W1FVY in late 1963. The only other information of this antenna relating to amateur radio is an article published in the November/December 2006 issue of TCA, The Canadian Amateur magazine by Graham Ide, VE3BYT, with David Conn, VE3KL.

The popular usage of the Skew-Planar antenna appears to be RC (Radio Control) enthusiasts as an ideal aircraft antenna due to its omnidirectional and circularly polarization.  The low omnidirectional pattern and the circularly polarization characteristics of this antenna should also be suitability for LEO (Low Earth Orbiting) satellite operations.

 

Photo 1 Skew Planar Wheel Antenna for 435MHz completed assembly.
Photo 1 Skew Planar Wheel Antenna for 435MHz completed assembly.

Construction  

Skew-Planar antenna constructed around a standard male N connector is favoured format for many of my VHF and UHF antennas as it facilitates easy antenna change over. See: Generic Antenna Mount.  

Figure 1 Antenna general layout. 

Referring to Photo 1 and Figure 1, showing how everything fits together.  The elements are assembled on the hub with the long section of each element (the half element length part) at 45 degrees to the horizontal, for right-hand circular polarization slanted up to the right when you are looking at the closest element.  The upper end of each element goes into the lug on the top stack at 100 - 110 degrees counter clockwise from its lug on the bottom stack.  

Figure 2 Element layout. See Table 1 element lengths for various bands.

Figure 2 Element layout. See Table 1 element lengths for various bands.

Skew-Planar antenna constructed around a standard male N connector and a 33mm diameter aluminium radial mounting disk with a 15mm centre hole for attachment to the N connector with the standard coax gland screw cap. The four radiating loop elements have been attached to the radial mounting disk with tinned crimp lugs and 2mm diameter pop-rivets. The other end of the loop is attached to the centre N connector pin which has a stainless steel screw thread sleeved to the pin and each of the elements have crimp lugs with attached atop of each other to the screw tread.

The screw tread 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 ensure the assembly is water proof. See Photo 1 and Fig 3.

David Conn (VE3KL)'s analysis of the Skew-Planar antenna confirmed that the element lengths should be longer than a free-space wavelength at the chosen design frequency by a factor of about 4.5 percent.  element lengths for various bands are shown in the below Table 1 for Fig 2.

Each element is shaped as shown in Figure 1 & 2 and in Photos 1.  On each end of an element at the 1/4 length point, make a bend around a fairly tight radius - for the 435 MHz antenna this was around a radius of about 10mm.  The half element portion is curved out so that the straight 1/4 length sections meet and form an angle with each other of about 100 to 110 degrees.  If necessary, adjust slightly the curvature where the one-quarter and the half element lengths meet.

Table 1  Dimensions for some bands  

Frequency (MHz)

Wavelength (mm) (B) 1/2 Element Length (mm) (A) 1/4 Element Length (mm) (Including attachment hardware)
145.5 2062 1077 539
222.0 1351 706 353
435.0 690 360 180
915.0 328 171 86
1296.0 233 122 61
2401.0 125 65 33

Table of Skew-Planar antenna element dimensions for various local Australian and some international amateur radio bands.

Photo 2 'N' Connector element hub

Figure 3 'N' Connector element hub
Photo 2 'N' Connector element hub Figure 3 'N' Connector element hub

 

Figure 4 Radial element mounting disk

Figure 4 Radial element mounting disk

The antenna mounting is a standard antenna mirror mount bracket with a female to female N connector bulkhead socket fitted. See: Generic Antenna Mount.

Figure 5 A three dimensional view of the radiation pattern of the Skew Planar Wheel Antenna at 435MHz. Radiation plot was produced by MMANA-GAL Antenna Analyser software.
Figure 5 A three dimensional view of the radiation pattern of the Skew Planar Wheel Antenna at 435MHz. Radiation plot was produced by MMANA-GAL Antenna Analyser software.

 

Figure 6 Azimuth and Elevation Radiation pattern of the Skew Planar Wheel Antenna at 435MHz.
Figure 6 Azimuth and Elevation Radiation pattern of the Skew Planar Wheel Antenna at 435MHz.

MMANA-GAL Antenna Analyser predicted the following results from the model.

       Gain: 5.75dBi = 0dB (Vertical polarization)

       Freq: 435.00MHz

       Z: 45.411 - j24.294Ohms

       SWR: 1.7 (50.0 Ohms)

 

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

 

References

 

A brief description of the Skew-Planar Wheel Antenna see: http://www.ve3byt.com/SkewPlanarAntenna/

 

The above radiation plots were produced using MMANA-GAL Antenna Analyser software by JE3HHT, Makoto (Mako) Mori at http://hamsoft.ca/  

 

3D Cad movie of Skew-Planar Wheel

The Skew-Planar Wheel (SPW) circular polarized omni antenna by IBCrazy

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Page last revised 23 November 2012 
 

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