Antennas with Non-Foster Matching Networks phần 3 docx

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MOBK060-01 MOBK060-Aberle.cls January 19, 2007 17:23

16 ANTENNAS WITH NON-FOSTER MATCHING NETWORKS

Z0

Z0

Lm

( ) − La + Lm

−Ca

Active matching

network

Two-port model of

antenna

FIGURE 12: Antenna with active matching network using non-Foster reactances

PERFORMANCE OF ESA WITH IDEAL NON-FOSTER

MATCHING NETWORK

A conceptual representation of the simplified ideal active matching network together with

the two-port antenna model is shown conceptually in Fig. 12. The design equations for the

components of the active matching network can be readily extracted from [3, 4] as follows.

To design the active matching network, we first fit the antenna impedance to a simple model.

Since the antenna is an electrically small monopole, the real part of the antenna impedance is

assumed to vary as the square of frequency, and the imaginary part is modeled as a series LC.

This simple model predicts an impedance that is denoted as Z¯ a and given by

Z¯ a = R0

ω

ω0

2

+ j

ωLa − 1

ωCa

. (22)

The parameters of the model may be obtained from the “actual” antenna impedance Za (ob￾tained from simulation or measurement) as

R0 = Re {Za (ω0)}

⎡

⎢

⎢

⎣

ω1

−1

ω1

ω2

−1

ω2

⎤

⎥

⎥

⎦

⎧

⎪⎪⎨

⎪⎪⎩

La

1

Ca

⎫

⎪⎪⎬

⎪⎪⎭

=

⎧

⎪⎨

⎪⎩

Im {Za (ω1)}

Im {Za (ω2)}

⎫

⎪⎬

⎪⎭ .

(23)

whereω0 is the design frequency (in radians per second),ω1 andω2 define the band of frequencies

over which the model is being applied, and Re (Za ) and Im (Za ) are the real and imaginary