Combiner system can be used for combining output powers of two transmitters or for switching from one to the other. This can be done when pair of transmitters operate on same frequency and carriers are phase coherent as by excitation from single exciter

Leu, R. K.

Wiggins, C. P.

English

NASA Technical Reports Server

June 1975	 B75-10122 
NASA TECH BRIEF 
NASA Pasadena Office	
A £ 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Transmitter Switch for High-Power Microwave Output 
S
The problem: 
Mechanically-operated waveguide switches are 
often used to combine the outputs of two transmitters 
to yield a high-power microwave output. The switches 
are relatively slow and are subject to wear. In 
addition, they cause energy losses which generate 
heat. The result is that klystrons can fail prematurely 
due to high heat stresses. 
The solution: 
A new high-power microwave switch has been 
developed which has no moving parts. The switch can 
combine the outputs of two 250-kW klystrons. 
How it's done: 
The switch is based on a four-port 90° hybrid 
junction, or combiner, as shown in Figure 1. The 
combiner is essentially two parallel waveguides 
Port 	 Port  
/Coupling / /  
 )J , ,
	
j' SlotJ/  
J' Port 2.	 / Port  
Input	 input 
Figure 1. Simplified Diagram of Combiner
connected by a coupling slot. When a signal is applied 
to port 1, a signal of one-half the power will appear at 
port 3 in phase and one-half the power will appear at 
port 4 advanced 900 in phase relative to the signal at 
port 1. When a second signal of the same power is 
applied at port 2, -90° out of phase with the signal at 
port 1, the two combine at port 3 with a total power 
almost equal to the sum of the signals at ports 1 and 2. 
A small component of output power at port 4 
(typically 30 dB less than the power level at port 3) is a 
function of the unbalance in the hybrid. 
By changing the phase of the port 2 signal by ±90° 
with respect to the signal at port 1, the two combine so 
that most of the power output is at port 4 and the 
small residue is at port 3. Thus a ±90° biphase change 
in one input signal with respect to the other transfers 
the signal from one output port to the other. 
A functional block diagram of the switch! 
combiner, 400-kW microwave system is shown in 
Figure 2. Two klystron power amplifiers feed the 
inputs into the 4-port combiner through two 
microwave switches, respectively. By switching the 
phase switch or modulator to ±90°, the output of the 
klystron amplifiers can be switched to port A or B. 
From port A the microwave power is applied to the 
transmit/receive microwave switch for radiation from 
the antenna and the dissipation of the loss power (due 
to hybrid unbalance) from port B through the 
coupler. Power due to loss is dissipated through the 
microwave switches and power dividers into the RF 
loads. The power dividers connected to the RF loads 
split the power for dissipation into two loads each, 
since a total of 400 kW must be dissipated during 
initial phasing of the klystrons. A phase sensor and 
power monitor, together with .phase control, provide 
closed-loop phase compensation for the carrier 
frequency and monitoring of the power level. 
(continued overleaf) 
This document was prepared under the sponsorship of the Nalionaf	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
S
https://ntrs.nasa.gov/search.jsp?R=19750000122 2020-03-19T20:24:23+00:00Z
AF	 rower 1	 1	 RF 
•	 Load	 Divider	
f ]
Load
To 
•I Coupler TransmitlReceive Microwave Switch 
I	
Transmitter Power Amplifier
/e\Switch 
F+	 1	 1 Al I 1 1 (250kW) I. I  ______________ 
I	 Single 
I	 Exciter
_______  
I	 Phase Switch 
I	 or •uii( 
_
- Four Port 
Combiner I and L	 Sensor Power I -	 Phase Error	 - Modutator	 ______________ Monitor _______________ 
F	
Transmitter F""j Power Amplifier ___________ BI ________________________________________ _ I 2 (250 kW) 1 
' Phase
Microwave 
Switch 1 11111.1 Coupter }...._iiii.j Power DividerS Control I _____________ _____________ 
__
I J	 power I	 !	 AF Load' Divider Load 
L----------------------------_J 
Figure 2. RF .Power Switch and Combiner System 
As mentioned previously, the power switch and Note: 
combiner system can be used for combining the Requests for further information may be directed 
output powers of two transmitters or for switching to: 
from one to the other. This can be done when a pair of Technology Utilization Officer S transmitters operate on the same frequency and the NASA Pasadena Office 
carriers are phase coherent as by excitation from a 4800 Oak Grove Drive 
single	 exciter.	 The • carrier	 source	 may	 be	 any Pasadena, California 91103 
combination	 of transmitters	 used	 in	 radar	 or Reference: TSP75-10122
communications. If calorimetric RF loads are used, 
the total transmitted power can be measured when the
	
Patent status: 
phase is selected so the output power is combined at 	 -NASA has decided not to apply for a patent. 
port B of the combiner.
Source: Cecil P. Wiggins and Richard L. Leu of 
Caltech/JPL 
•	 under contract to 
•
	
	 NASA Pasadena Office 
(NPO-13439) 
B75-10122	 Category: 02 (Electronics Systems) 


Transmitter switch for high-power microwave output

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