| 摘要 |
RF transmitter for electrically short antenna In known RF transmitters with electrically short antennas, the usable channel bandwidth is limited by the width of the pass-band of the tuned antenna. The present invention targets at efficiently transmitting electromagnetic signals 5 having a bandwidth which exceeds the pass-band of the tuned antenna. The invention is based on a synthetic-frequency RF transmitter (1) for transmitting an electromagnetic signal (TX) via an electrically short antenna (100). The transmitter (1) comprises a reactive energy storage (2) with an effective reactance (C) adapted to form with the antenna (100) a resonance 10 circuit (2, 100) with a resonance frequency (fo) and a driver (3) adapted to provide to the resonance circuit (2, 100) an electric transmission signal having an instantaneous frequency (f) that varies in dependence on an information signal (D). The transmitter (1) is characterised in that the transmitter (1) is adapted to dynamically change the resonance frequency (fo) 15 by changing the effective reactance (C) in dependence on the information signal (D). Thus, the instantaneous pass-band of the resonance circuit (2, 100) may be controlled to substantially always comprise the instantaneous frequency (f) of the electric transmission signal and thus of the electromagnetic signal (TX). 20 The resulting transmitters (1) are relatively simple, efficient and easy to control. -J I Co 'N o o '- N (0 C o @4 N N N Co Co C 10 ~. C Co cv, cv, |
