Utilization of a Septum Feed Horn for Circular Polarization with Parabolic Dishes by Edward R. Cole KL7UW

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Utilization of a Septum Feed Horn for Circular Polarization with Parabolic Dishes by Edward R. Cole – KL7UW

Credits: This paper gives a concise summary of papers tending to the use of the Septum Polarizer to Amateur Radio recieving wires. Uncommon Thanks to Zdenek Samek and Paul Wade for consent to re-utilize certain figures and tables from their papers. Encourage horn outline for allegorical dishes has for some time been the concentration for some microwave engineers. Add the longing to consolidate roundabout polarization and configuration can get muddled. Novice Radio Astronomers have few encourages to browsed. For Linear Polarization: -dipole with reflector -open waveguide -pyramidal horn -waveguide with cajole test Overview

For Circular Polarization: -hub mode helix (helical bar) -crossed dipoles -orthogonal tests in waveguide utilizing a half and half There are moderate wave strategies: -dielectric pieces -posts at 45-degrees inside waveguide -unbalanced waveguide (crush tube) -septum Many starting radio cosmologists have utilized the helical shaft, yet it is constrained to one feeling of roundabout polarization. The helix does not deliver the most delightful brightening of the dish, with coming about edge overflow and high side projection vitality. This corrupts framework commotion temperature. The utilization of dishes by Amateur Radio for EME (Moonbounce) offers a large portion of these issues. Review

Overview One of the most prevalent EME sustain horns has been the "VE4MA" Feed. It is an area of roundabout waveguide with orthogonal persuade tests. The Quadrature Hybrid that is required with this nourish presents misfortune in front of the LNA which corrupts commotion temperature. Zdenek Samek – OK1DFC presented the Septum encourage at the 2002 Int'l EME Conference in Prague.

What is a Septum Feed Horn Four elements of encourage horns: -Antenna Section: shapes shaft for good light. - Waveguide Section -Polarizer -Excitation Section: waveguide or coaxial test. Chen and Tsandoulas composed of their investigation of the septum polarizer (IEEE, 1973). Their's was an observational review to discover a plan arrangement. Their plan used a square waveguide with metal divider (or septum) isolating this into two rectangular waveguide areas.

Analysis

Analysis The septum isolates the excitation area into two rectangular waveguides where straight polarization exists. The span of the waveguide is been close to the cutoff recurrence so that as a flag enters the horn just a single polarization part is passed into the rectangular segments. In this manner one side gets RHCP and the other LHCP. Wave cancelation in the inverse sides offer impressive confinement of the coaxial ports. Point by point depiction can be found in the referenced papers recorded in the commentaries.

Analysis An inclined septum was observed to be usable over just a 10% band width (however disengagement was close to 40 dB). Experimentation prompted to a ventured outline with 25% band width, 24 dB detachment, and 21 dB of circularity. Zdenek scaled Chen & Tsandoulas' five stage septum to 1296 MHz and later to other microwave frequencies.

Practical Designs I utilized Zdenek's online number cruncher to deliver measurements for 1420 MHz as appeared in Appendix-A Paul Wade, W1GHZ, has made a careful examination of the septum sustain utilizing Ansoft ANSS programming. He found that the square septum configuration has huge back flaps in the recieving wire design. They are just ten dB down from the primary shaft bringing about debasing reception apparatus productivity (60%) with higher clamor temperature.

Practical Designs Since side projections are produced in the opening of the nourish horn the expansion of a flared horn enhances side flaps with dishes of 0.5 to 0.7 F/D proportion. Efficiencies of 65 to 70% are accomplished. A round stifle ring is best diminishing side projections with dishes of 0.3 to 0.45 F/D proportion. Efficiencies of 62% are accomplished.

Super – VE4MA Feed Horn This year Paul researched utilization of the ventured septum in round encouraged horns. In the process he discovered expanded efficiencies utilizing further gag rings with a 0.77 wavelength breadth horn. Expanding ring measurements to 0.4 by 0.6 wavelength, investigation demonstrated hypothetical efficiencies to 80% with low side projections. Estimations of this horn by Tommy Henderson, WD5AGO, measured real 65% productivity!

KL7UW Septum Feed Here is the Square Septum Feed that I worked in fall 2005 and mounted on my 2.4 meter dish. Operation more than 1296 to 1420 MHz with great return-misfortune and segregation. Sun commotion Measurements created 4-dB correlation with chilly sky. Chilly Sky versus Ground commotion with the nourish horn measured 4.5 dB without a stifle ring and 7 dB with a ring. Wide band commotion estimations this spring were not effective because of microwave front-end issues.

KL7UW Septum Feed

Radio Astronomy Application The Septum Feed Horn gives a considerably more straightforward and productive approach to mention multi-extremity radio stargazing objective facts. Both RHCP and LHCP may at the same time be watched utilizing coordinated LNA's on both ports of the septum bolster. Expansion of two-way flag splitters and a quadrature half breed, orthogonal direct extremity can be recuperated. Enhanced System Noise Temperature. Double recurrence perceptions more than 25% partition. Ordinary radio telescope recieving wire productivity is 40-45% in the push to limit side projections beneath 20 dB. The tube shaped ventured septum bolster gives 65% efficiencies. This is identical to a 20% expansion in compelling reception apparatus opening!

Hamming it up on Microwave!

Appendix-A

Appendix-B OK1DFC Septum Feed Horn Performance

Appendix-C OK1DFC Septum with Round Choke Performance

Appendix-D VE4MA Feed Horn