Dear all, Lately i have been reading that antenna gain increases with frequency, for instance in the 60ghz band antennas are very directive.However i do not quite understand the reason for this phenomena, is this true with any antenna? let's say we have a dipole antenna that at 2.4ghz radiates more or less issotropically, if we take the same dipole and radiate at 60ghz is it going to radiate directionally? Thanks for helping clarify my understanding! Daniel
about antenna gain
Started by ●March 24, 2009
Reply by ●March 24, 20092009-03-24
On 24 Mar, 21:34, "daniao" <danicamp...@yahoo.com> wrote:> Dear all, > > Lately i have been reading that antenna gain increases with frequency, for > instance in the 60ghz band antennas are very directive.However i do not > quite understand the reason for this phenomena, is this true with any > antenna?For any physical antenna: Yes. The reason is that the gain G increases with the antenna size D expressed in terms of wavelength L, maybe G ~ D/L ('maybe' because I don't remember the details - this expression might have to be be squared). Since the physical size D of a given antenna is fixed and the frequency increases, the wavelength L decreaes and the antenna's gain G increases. Rune
Reply by ●March 24, 20092009-03-24
daniao <danicamps81@yahoo.com> wrote:> Lately i have been reading that antenna gain increases with frequency, for > instance in the 60ghz band antennas are very directive.However i do not > quite understand the reason for this phenomena, is this true with any > antenna? let's say we have a dipole antenna that at 2.4ghz radiates more or > less issotropically, if we take the same dipole and radiate at 60ghz is it > going to radiate directionally?This seems a little off topic for DSP, but it is the physics of diffraction. A directional antenna (or any wave source) has to be somewhat larger than the wavelength. -- glen
Reply by ●March 24, 20092009-03-24
Rune Allnor wrote:> On 24 Mar, 21:34, "daniao" <danicamp...@yahoo.com> wrote: >> Dear all, >> >> Lately i have been reading that antenna gain increases with frequency, for >> instance in the 60ghz band antennas are very directive.However i do not >> quite understand the reason for this phenomena, is this true with any >> antenna? > > For any physical antenna: Yes. > > The reason is that the gain G increases with the antenna > size D expressed in terms of wavelength L, maybe > > G ~ D/L > > ('maybe' because I don't remember the details - this > expression might have to be be squared). > > Since the physical size D of a given antenna is fixed > and the frequency increases, the wavelength L decreaes > and the antenna's gain G increases.Just as a bigger lens collects more light, a "bigger" antenna collects more signal. Antennas are measured in wavelengths, so as frequency increases, so dies the "size". Of course, antennas can resonate, and therefor behave like bandpass filters. What's more, their directionality changes with frequency, so radiation nulls can shift around ad grequency changes. A good general understanding of electronics is provided by the ARRL handbook. Right now, last year's edition is available at a bargain price. http://www.arrl.org/catalog/?item=9760#top Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 24, 20092009-03-24
glen herrmannsfeldt wrote:> daniao <danicamps81@yahoo.com> wrote: > >> Lately i have been reading that antenna gain increases with frequency, for >> instance in the 60ghz band antennas are very directive.However i do not >> quite understand the reason for this phenomena, is this true with any >> antenna? let's say we have a dipole antenna that at 2.4ghz radiates more or >> less issotropically, if we take the same dipole and radiate at 60ghz is it >> going to radiate directionally? > > This seems a little off topic for DSP, but ...But we're nice people! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 24, 20092009-03-24
daniao wrote:> Dear all, > > Lately i have been reading that antenna gain increases with frequency, for > instance in the 60ghz band antennas are very directive.However i do not > quite understand the reason for this phenomena, is this true with any > antenna? let's say we have a dipole antenna that at 2.4ghz radiates more or > less issotropically, if we take the same dipole and radiate at 60ghz is it > going to radiate directionally? > > Thanks for helping clarify my understanding! > > DanielThe increase in gain with frequency is for an optimumly configured antenna occupying the given space. At 60 GHz the voltage and current distribution along the 2.4 GHz antenna will not be optimum for radiation in any particular direction and you will see a series of peaks and troughs in the radiation pattern. If however you replace the 2.4 GHz antenna with, say, an end-to-end array of 60 GHz dipoles, covering about the same length as the single 2.4 GHz dipole, and if the feed to each dipole is phased properly then there will be a higher gain. The gain will be in the plane normal to the dipoles. The gain (as a ratio, not dB) will be about equal to the number of dipoles. Physically, to make a high-gain antenna you need to create a large, plane wave-front normal to the direction of transmission. A larger the (approximately) plane part of the wavefront, as measured near the antenna, the less the beam diverges. More power will then be delivered to a distant receiving antenna within the beam. Regards, John
Reply by ●March 24, 20092009-03-24
John Monro wrote:> daniao wrote: >> Dear all, >> >> Lately i have been reading that antenna gain increases with frequency, >> for >> instance in the 60ghz band antennas are very directive.However i do not >> quite understand the reason for this phenomena, is this true with any >> antenna? let's say we have a dipole antenna that at 2.4ghz radiates >> more or >> less issotropically, if we take the same dipole and radiate at 60ghz >> is it >> going to radiate directionally? >> Thanks for helping clarify my understanding! >> >> Daniel > > The increase in gain with frequency is for an optimumly configured > antenna occupying the given space. > > At 60 GHz the voltage and current distribution along the 2.4 GHz antenna > will not be optimum for radiation in any particular direction and you > will see a series of peaks and troughs in the radiation pattern. If > however you replace the 2.4 GHz antenna with, say, an end-to-end array > of 60 GHz dipoles, covering about the same length as the single 2.4 GHz > dipole, and if the feed to each dipole is phased properly then there > will be a higher gain. > > The gain will be in the plane normal to the dipoles. The gain (as a > ratio, not dB) will be about equal to the number of dipoles. > > Physically, to make a high-gain antenna you need to create a large, > plane wave-front normal to the direction of transmission. A larger the > (approximately) plane part of the wavefront, as measured near the > antenna, the less the beam diverges. More power will then be delivered > to a distant receiving antenna within the beam.An antenna's receiving and transmitting patterns are the same. The more effectively an antenna confines transmitted radiation to a particular direction, the more sensitive it will be to signals in from that direction, and the more effectively it rejects signals (and noise!) from other directions. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 24, 20092009-03-24
On Mar 24, 4:34�pm, "daniao" <danicamp...@yahoo.com> wrote:> Dear all, > > Lately i have been reading that antenna gain increases with frequency, for > instance in the 60ghz band antennas are very directive.However i do not > quite understand the reason for this phenomena, is this true with any > antenna? let's say we have a dipole antenna that at 2.4ghz radiates more or > less issotropically, if we take the same dipole and radiate at 60ghz is it > going to radiate directionally? > > Thanks for helping clarify my understanding! > > DanielWell of course if you make your antenna self similar (a fractal design) and feed it at a point of symmetry, then its gain is independent of frequency. This is easliy proved with Maxwell's equations. Now true fractal antennas are impossible to make, but good approximations abound. Your cellphone likely has a fractal antenna, since many modern cellphones use one antenna to handle to handle 4 different wideband signals, eg (cellular apprx 850 MHz), (PCS apprx 1900MHz), (Blue Tooth apprx 2400MHz), and (GPS apprx 1575MHz). IHTH, Clay Turner
Reply by ●March 24, 20092009-03-24
Jerry Avins <jya@ieee.org> wrote: (snip)>> This seems a little off topic for DSP, but ...> But we're nice people!Sorry, I wasn't trying to say otherwise. also, there isn't a comp.asp (analog signal processing) newsgroup. I suppose it isn't so far off here. -- glen
Reply by ●March 24, 20092009-03-24
Jerry Avins <jya@ieee.org> wrote: (snip, someone wrote)>> Physically, to make a high-gain antenna you need to create a large, >> plane wave-front normal to the direction of transmission. A larger the >> (approximately) plane part of the wavefront, as measured near the >> antenna, the less the beam diverges. More power will then be delivered >> to a distant receiving antenna within the beam.> An antenna's receiving and transmitting patterns are the same. The more > effectively an antenna confines transmitted radiation to a particular > direction, the more sensitive it will be to signals in from that > direction, and the more effectively it rejects signals (and noise!) from > other directions.There are some interesting perpetual motion machines that could be built if that wasn't true. I remember seeing a design of a partial elliptical reflector that was supposed to have different absorption and radiation patterns. Of course it didn't work. (It was a drawing, no-one tried to build it.) -- glen
