Test model of the LCR for variable pulse width radiation.

 

 The possibility to radiate the pulse signal of different duration is investigated with the following LCR antenna. The antenna is an array consisting of four radiating elements, which are excited by the pulse power amplifiers assembled with the use of powerful MOSFETs.

Spatial distribution of pulses of the radiated electromagnetic field is similar to the one generated by an electric dipole. There is not any radiation directivity in one plane but there exist gaps and changes of polarity of strength of the radiated pulse field in the other plane.

We have analyzed LCR operation in the switch operation mode and pulse (linear excitation) operation mode.

The switch operation mode allowed us to reach the higher strength of the radiated pulse field, but the radiated pulse duration is not a variable in this mode.

The variation of radiated pulse width in the range from 3ns to 5ns is reached in the linear operation mode. We did not perform any experiments on radiation pulses with longer duration. But there are no visible restrictions on extending radiated pulse.

 The antenna consists of four radiating elements connected to the frame, which is a transistor cooler. Four output power amplifiers were employed in order to enhance the total radiated power of the antenna. A printed circuit board with elements of antenna power supply circuit was connected to the radiator and covered with a lid shielding the radiation from the board conductors. For heat extraction, two ventilators from a Pentium processor are fixed to the cooler on the side that is opposite to the radiating elements. An input signal arrives at the antenna along a coaxial cable and through an RF connector. Supply voltages are also connected to the antenna from this side. The antenna frame is the return loop of this antenna. Matching sections that will continuously transform the wave impedance in the area of radiating element excitation are connected to the frame.

Antenna power consumption from the power supply is approximately 112.5W (supply voltage is 45V, intake current is 2.5A). The measurements of the antenna unit is 550mm X 250mm X 220mm.

Listed below are the parameters of the signals at the power amplifier outputs with a connected antenna system in two possible operation modes of excitation circuit:,one(1) is the switch mode; two(2) is the linear amplification mode:

 

1 Switch mode

· voltage pulse amplitude        45V;

· rise time               2.5ns;

· droop time                4ns;

· overshoot on the peak          50%;

· droop of the peak    10%;

· pulse duration           50ns;

 

 

2 Linear amplification mode

·voltage pulse amplitude         20V;

·minimal rise time   3ns;

·droop time                 3.5ns;

·overshoot on the peak           5%;

·droop of the peak     10%;

·pulse duration  50ns;

 Range dependence of radiated pulse shape in switch mode demonstrates that the LCR is able to radiate "pure" pulses.

The experiments in linear amplification mode shown clearly it is possible to radiate electromagnetic pulses of different duration with the same antenna.

The experiments have shown very clearly that such an antenna design allows one to radiate pulse signals of various duration. But further improvements of the design are needed, particularly the exciting signal shape (maybe by means of placing the switching field transistors by higher-frequent ones). For practical applications, it will be necessary to optimize the radiating element shape, and to develop an electric controllable damping element in the radiator to obtain a more efficient LCR.

 

 

 

 

Detail description of antenna is published in

·         G.P.Pochanin "Pulse Radiation of Four-Element Large Current Radiator" // Section "Multifunction/Multiband Antennas", IEEE Antennas and Propagation Society International Symposium and USNC/URSI National Radio Science Meeting, Orlando, Florida, July 11-16, 1999, Proc. vol. 4, pp. 2722-2726.

 

·        G.P.Pochanin, and I.E.Pochanina "Large Current Radiator With Four Radiating Elements" // International Conference on Antennas and Radio Systems, Voronezh, Russia, May 25-28, 1999.