Patent GB-591353-A (GB)
Title: Arrangements for alternately blocking and unblocking transmission lines to high frequency energy and the application thereof to antenna and the like switching systems
IPC: H01Q5/00
Filed: 1943-09-28
Abstract: 591,353. High-frequency transmission. STANDARD TELEPHONES & CABLES, Ltd. Sept. 28, 1943, No. 15950. Convention date, Nov. 12, 1941. [Class 40 (iv)] [Also in Group XL] Arrangements for alternately blocking and unblocking a transmission line to high-frequency energy comprises a quarter-wave section of transmission line short-circuited at one end and inductively coupled to said transmission line, means including vacuum tube control means connected across said section and forming a variable shunt reactance across said section, means for applying varying potentials to said vacuum tube control means for varying said reactance alternately to tune said section to resonance at the operating frequency and to detune said section. Fig. 1 shows a circuit arrangement in which a single antenna 10 is employed for transmitting pulses from a transmitter 11 and receiving reflected pulses which are fed to a receiver 13 during the intervals between transmitted pulses. Antenna 10 is directly coupled by a transmission line 12 to the transmitter 11, and by a transmission line 14 to the receiver 13. A pulse generator 19 supplies pulses to the transmitter 11 through a delay network 21 and to a blocking circuit 20 for disabling the receiver during the transmission of pulses. The pulses from circuit 20 are arranged to commence a little before and finish a little after the pulses sent out from transmitter 11. According as a pulse is being received or transmitted, transmission line 12 or 14 is blocked to prevent the dissipation of energy. This is done by short-circuited quarterwave lines 15, 16 coupled to lines 12, 14 and having circuits 17, 18 which are influenced by pulses from the blocking circuit 20 to bring the lines 15, 16 into resonance so as to block line 12 or 14. When a pulse is transmitted, a pulse from blocking circuit 20 acts on circuit 18 to bring line 16 to resonance so as to block line 14. At the same time the pulse, after inversion at 22, brings line 15 to a condition of non- resonance, thus opening line 12. In the interval between pulses, line 12 is blocked and line 14 is open. Alternatively, circuit 17 may be arranged to produce non-resonance on the occurrence of a pulse of the same sign as one which produces resonance when applied to circuit 18. In this case, the inverter 22 is unnecessary. Fig. 2 shows a valve circuit suitable for use at 17 or 18. Valve 24 has its anode connected through blocking condenser 32 to a point 30 on a short-circuited quarter-wave line 23. The grid is connected through resistance 33 and condenser 31 to a point 29, the voltage of which is 180 degrees out of phase with the voltage at point 30. The values of 31, 33 are chosen so that, together with the internal capacity of the valve, they produce a 90 degrees phase shift and, since the grid voltage and anode current are in phase, the current at point 30 leads the voltage by 90 degrees and the valve simulates a shunt capacity, the value of which depends on the variable grid bias from potentiometer 28 and the value of pulse supplied through condenser 26. The length of the section 23 is chosen so as to be brought to resonance by the connection of the shunt capacity. This may occur either on applying a pulse, or in the absence of a pulse, and the pulses may be positive or negative, according to the setting of the grid bias. In a modification, Fig. 3 (not shown), the quarterwave line is tuned by means of a one-eighth wavelength line shunted by a pair of tandemconnected valves. The mutual conductance is altered by the applied pulses so as to produce a sufficient change of phase at the connection of the two lines to effect resonance.