Simult. RH & LH Circ. Pol.
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From: Tomas Ferrel on 31 May 2010 04:15 "Antennas with orthogonal elements that are combined in phase quadrature such as the crossed dipole with external 90 degree hybrid coupler. This type of antenna can produce right-hand and left-hand circular polarization simultaneously." "Simultaneously"? Can anyone explain how this works? What is the confguration of the coil and how is the signal applied to produce this effect? I don't understand how the "simultaneous" LH and RH fields would not cancel each other out. Perhaps they mean the applied signal can cycle intermittently between LH and RH. Tomas Ferrel
From: Wimpie on 31 May 2010 05:40 On 31 mayo, 10:15, tomasfer...(a)lopsler.com (Tomas Ferrel) wrote: > "Antennas with orthogonal elements that are combined in phase > quadrature such as the crossed dipole with external 90 degree hybrid > coupler. This type of antenna can produce right-hand and left-hand > circular polarization simultaneously." > > "Simultaneously"? Can anyone explain how this works? What is the > confguration of the coil and how is the signal applied to produce this > effect? > > I don't understand how the "simultaneous" LH and RH fields would not > cancel each other out. Perhaps they mean the applied signal can cycle > intermittently between LH and RH. > > Tomas Ferrel Hello, If you combine a LH and RH circular polarized field with same amplitudes and arriving from same direction, the result will be a linear polarized field. A linear polarized field can be received by both a LH and RH circular polarized antenna, but with 3 dB loss with respect to the optimum case. In my opinion, the word "simultaneous" has no meaning here, you can only switch between LH, RH or linear. It can only have some meaning in the receive case where you have amplifiers connected to both dipoles and do the phasing after the amplifiers. In this receive case you can have an antenna (with amplifiers) that has a LH and RH circular polarized output. Best regards, Wim PA3DJS www.tetech.nl without abc, PM will reach me.
From: amdx on 31 May 2010 08:12 "Tomas Ferrel" <tomasferrel(a)lopsler.com> wrote in message news:4c036e30.9773984(a)news.tpg.com.au... > "Antennas with orthogonal elements that are combined in phase > quadrature such as the crossed dipole with external 90 degree hybrid > coupler. This type of antenna can produce right-hand and left-hand > circular polarization simultaneously." > > "Simultaneously"? Can anyone explain how this works? What is the > confguration of the coil and how is the signal applied to produce this > effect? > > I don't understand how the "simultaneous" LH and RH fields would not > cancel each other out. Perhaps they mean the applied signal can cycle > intermittently between LH and RH. > > Tomas Ferrel Might be worth a post on rec.radio.amateur.antenna Mike
From: Tim Williams on 31 May 2010 08:37 "Simultaneous" sounds like a misnomer.. you can produce a given pattern at any given time, varying it by adjusting phase and drive, but you can't produce all "simultaneously". Vertical and horizontal are orthogonal and form a basis set equivalent to RH and LH. A linear combination (phased, so it's an imaginary coefficient) allows you to produce one from the other. Also, from either given perspective, the other one seems to be recieving an equal mixture (e.g., a RH antenna is -3dB when recieving V or H). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "Tomas Ferrel" <tomasferrel(a)lopsler.com> wrote in message news:4c036e30.9773984(a)news.tpg.com.au... > "Antennas with orthogonal elements that are combined in phase > quadrature such as the crossed dipole with external 90 degree hybrid > coupler. This type of antenna can produce right-hand and left-hand > circular polarization simultaneously." > > "Simultaneously"? Can anyone explain how this works? What is the > confguration of the coil and how is the signal applied to produce this > effect? > > I don't understand how the "simultaneous" LH and RH fields would not > cancel each other out. Perhaps they mean the applied signal can cycle > intermittently between LH and RH. > > Tomas Ferrel
From: Phil Hobbs on 31 May 2010 10:37 Wimpie wrote: > On 31 mayo, 10:15, tomasfer...(a)lopsler.com (Tomas Ferrel) wrote: >> "Antennas with orthogonal elements that are combined in phase >> quadrature such as the crossed dipole with external 90 degree hybrid >> coupler. This type of antenna can produce right-hand and left-hand >> circular polarization simultaneously." >> >> "Simultaneously"? Can anyone explain how this works? What is the >> confguration of the coil and how is the signal applied to produce this >> effect? >> >> I don't understand how the "simultaneous" LH and RH fields would not >> cancel each other out. Perhaps they mean the applied signal can cycle >> intermittently between LH and RH. >> >> Tomas Ferrel > > Hello, > > If you combine a LH and RH circular polarized field with same > amplitudes and arriving from same direction, the result will be a > linear polarized field. A linear polarized field can be received by > both a LH and RH circular polarized antenna, but with 3 dB loss with > respect to the optimum case. > > In my opinion, the word "simultaneous" has no meaning here, you can > only switch between LH, RH or linear. It can only have some meaning > in the receive case where you have amplifiers connected to both > dipoles and do the phasing after the amplifiers. In this receive case > you can have an antenna (with amplifiers) that has a LH and RH > circular polarized output. > > Best regards, > > Wim > PA3DJS > www.tetech.nl > without abc, PM will reach me. You could do simultaneous RH & LH if they were on different frequencies, but not otherwise. There are two degrees of freedom in the polarization of a plane wave, so there are always two orthogonal polarizations--however you choose the basis set. Horizontal is orthogonal to vertical, RH is orthogonal to LH, and so on. Linear and circular are special cases of elliptical polarization. Given a general elliptical polarization, you can construct the orthogonal one by keeping the same eccentricity, swapping the helicity (e.g. RH to LH), and making the major axes perpendicular. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
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