[Keywords] monopole whip antenna the electrical properties VSWR direction Figure 1 INTRODUCTION whip antenna due to the small size, compact structure and in the types of communications equipment widely used in its study design and therefore attracted widespread attention. Various terrestrial radio and car radio is equipped with various forms whip antenna the ships also often see the antenna bristling whip. whip antenna physical size is still small antenna, especially the HF band low-end, resistance small electric Kang Da, matching difficult, so most of the whip antenna applications in narrowband work status, a bandwidth of approximately 5% to 10% [1]. monopole whip antenna belonging to whip class structure is quite simple a suitable for car and portable work, small size, high radiation efficiency, and erected.

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Wherein Im represents antinode current Im = I0/sinβl, θ = 90 °-δ l = h (I0 of the input current, Δ elevation angle, h is the height of the monopole antenna. Substituting into the above equation to give:

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(2

(3 If the height of the monopole antenna is taken of λ / 2, it is equivalent to a full-wave transducer in the free space, theoretically compared to h = λ / 4, the gain to improve 1.67dB. However, such a high input impedance of the antenna , is not easy and the coaxial connection, this must be an impedance switch. reposted in the free papers Download Center http://eng.hi138.com

2.2 electrical characteristics of effective height: the effective length of the monopole antenna Introduction is the effective height, it can be said that the strength of the radiation of the antenna, is an important indicator of the upright antenna. assumptions on the antenna current is sinusoidal distribution, and β is the propagation constant is defined in accordance with the effective height of:

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When the transducer is very short, the current is approximately triangular distribution, therefore the effective height of half of the actual height h = λ / 4, he = 0.5λ / π.

The direction coefficients: first discuss the radiation resistance, and then by the direction of the calculation of the radiation resistance coefficient. Monopole antenna radiation resistance and free-space symmetry in infinite perfectly conducting ground exactly the same method of calculation of the radiation resistance of the oscillator, only because of a monopole antenna The mirror portion is not radiated power, its radiation resistance for a free space of the same arm length (l = h half of the radiation resistance of the symmetric oscillator When h = λ / 4, for the radiation resistance of the thin wire antennas 36.50Ω when h the = λ / 8

(5

Analysis Conclusion This article on the electrical characteristics of a simple structure and a monopole whip antenna, and adding a metal sleeve in the design improvements to effectively improve the bandwidth and gain of the antenna, this antenna sizes small, easy to carry, in the can play an important role in modern communication.

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