Tuned small loop antenna and method for designing thereof
First Claim
1. A tunable small closed loop antenna, having an input admittance, for transmitting or receiving signals within the VHF and UHF frequency band and tunable over a wide range of resonant frequencies while substantially maintaining impedance matching between the antenna and an antenna feeder line comprising:
- a loop conductor having a loop area A, circumferential length S and equivalent conductor radius b;
said loop conductor including feeding taps circumferentially spaced on said conductor wherein said taps are coupled to said antenna feeder line;
a capacitive element connected in series with said loop conductor for providng a resonant circuit having a loaded Q of not less than 20;
characterizing in that said loop area, said circumferential length and said equivalent radius are selected so that the ratio of the resonant frequency fo of said resonant circuit and the resonant frequency fm, at which said input admittance is a minimum, is within the range;
0.5≦
fo /fm ≦
3.0whereby the selected values of A, S and b satisfy the following equation;
##EQU25## where μ
is the permeability of the medium and σ
is the conductivity of the loop conductor, and fm has a value which falls within said range for various resonant frequencies fo existing within a predetermined frequency band.
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Accused Products
Abstract
The invention is directed to a tunable loop antenna design which provides impedance matching between the loop antenna and a feed line despite variations of the resonant frequency fo over a wide range of frequencies. The antenna has a maximum length of one tenth of the wavelength, and comprises a loop conductor and a variable capacitor connected in series with the conductor for providing a resonant circuit. The loop area of the conductor, the circumferential length and equivalent radius thereof are adjusted so that the ratio of the resonant frequency fo of the antenna and the resonant frequency fm, at which the input admittance is a minimum, is within the range:
0.5-fo /fm -3.0.
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Citations
10 Claims
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1. A tunable small closed loop antenna, having an input admittance, for transmitting or receiving signals within the VHF and UHF frequency band and tunable over a wide range of resonant frequencies while substantially maintaining impedance matching between the antenna and an antenna feeder line comprising:
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a loop conductor having a loop area A, circumferential length S and equivalent conductor radius b; said loop conductor including feeding taps circumferentially spaced on said conductor wherein said taps are coupled to said antenna feeder line; a capacitive element connected in series with said loop conductor for providng a resonant circuit having a loaded Q of not less than 20;
characterizing in that said loop area, said circumferential length and said equivalent radius are selected so that the ratio of the resonant frequency fo of said resonant circuit and the resonant frequency fm, at which said input admittance is a minimum, is within the range;
0.5≦
fo /fm ≦
3.0whereby the selected values of A, S and b satisfy the following equation;
##EQU25## where μ
is the permeability of the medium and σ
is the conductivity of the loop conductor, and fm has a value which falls within said range for various resonant frequencies fo existing within a predetermined frequency band. - View Dependent Claims (2, 3, 4)
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5. A tunable small closed loop antenna for receiving signals within the VHF and UHF frequency band comprising:
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a first closed loop antenna having an input admittance, a loop area A, circumferential length S and equivalent conductor radius b comprising a first capacitive element connected in series with the said first loop conductor for providing a resonant circuit having a loaded Q of not less than 20; a second closed loop antenna having an input admittance, a loop area A, circumferential length S and equivalent conductor radius b, said second antenna having a maximum size which is less than said first loop antenna comprising a second capacitive element connected in series with said second loop conductor for providing a resonant circuit having a loaded Q of not less than 20; each of said loop conductor including a pair of feeding taps circumferentially spaced on each conductor wherein each tap pair has an input admittance; means for coupling output signals produced on said feeding taps of said first and second closed loop antenna to an antenna output terminal; characterizing in that the loop area conductor, the circumferential length and the equivalent radius of each of said antennas are selected so that the ratio of the resonant frequency fo of its resonant circuit and the resonant freqency fm, at which said input admittance is a minimum, is within the range;
space="preserve" listing-type="equation">0.5≦
f.sub.o /f.sub.m ≦
3.0,whereby the selected values of A, S and b for each of said loop conductors satisfy the following equation;
##EQU26## where μ
is the permeability of medium and σ
is the conductivity of the loop conduction, and fm has a value which falls within said range for various resonant frequencies fo existing within a predetermined frequency band. - View Dependent Claims (6, 7)
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8. Method for designing a tunable small closed loop antenna having a loop conductor with, a loop area A, a circumferential length S and equivalent radius b, a capacitive means connected in series with said loop conductor for providing a resonant circuit over a wide range of frequencies while substantially maintaining impedance matching between said antenna and an antenna feeder, said loop conductor including feeding taps circumferentially spaced on said conductor wherein said taps are coupled to said antenna feeder line comprising the steps of:
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adjusting the ratio of the resonant frequency fo of the resonant circuit and the resonant frequency fm, at which the input admittance is a minimum, to be within the range;
space="preserve" listing-type="equation">0.5≦
f.sub.o /f.sub.m ≦
3.0,selecting the value of fm which falls within said range for various resonant frequencies fo existing within a predetermined frequency band; selecting the values of S, A and b from the following equation;
##EQU27## where μ
is the permeability of medium and σ
is the conductivity of the loop conductor.
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9. A tunable small loop antenna, having an input admittance, for transmitting or receiving signals within the VHF and UHF frequency band and tunable over a wide range of resonant frequencies while substantially maintaining impedance matching between the antenna and an antenna feeder line comprising:
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a loop conductor having a loop area, circumferential length and equivalent conductor radius; a capacitive element connected in series with said loop conductor for providing a resonant circuit having a loaded Q of not less than 20;
wherein said loop area, said circumferential length and said equivalent radius are selected so that the ratio of the resonant frequency fo of said resonant circuit and the resonant frequency fm, at which said input admittance is a minimum, is within the range;
space="preserve" listing-type="equation">0.5≦
f.sub.o /f.sub.m ≦
3.0feeding taps, circumferentially spaced on said conductor, wherein said feed taps include a first, a second and a third tap, said second tap being positioned between said first and third tap; a first means for supplying the signals appearing between the first tap and the second tap directly to the output terminals of the antenna; a second means, including a high frequency amplifier, supplying the signals appearing between the second tap and the third tap to output terminals of the antenna; and a switching means, coupled to first and second means, for selecting either said first means or said second means.
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10. Method for designing a tunable small loop antenna having a loop conductor with, a loop area, a circumferential length and equivalent radius, a capacitive means connected in series with said loop conductor for providing a resonant circuit over a wide range of frequencies while substantially maintaining impedance matching between said antenna and an antenna feeder, comprising the steps of:
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adjusting the ratio of the resonant frequency fo of the resonant circuit and the resonant frequency fm, at which the input admittance is a minimum, to be within the range;
space="preserve" listing-type="equation">0.5≦
f.sub.o /f.sub.m ≦
3.0;selecting the value of fm which falls within said range for various resonant frequencies fo existing within a predetermined frequency band; substituting the selected value fm in the following equation;
##EQU28## where μ
is the permeability of medium and σ
is the conductivity of the loop conductor;calculating the values of the loop area, the circumferential length and equivalent radius which satisfies said equation where A is the loop area, S is the length and b is the equivalent radius; and constructing a loop antenna having a loop area, length and radius selected from said calculated values.
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Specification