Power Handling of Waveguide Power Combiner, Directional Coupler, Crossguide Coupler and Waveguide to Coax Adapter

SAGE Power Handling

Historically, limited CW power was available in the millimeterwave frequency range, especially in the higher frequency bands, Ka-band and above. Therefore, power handling was not a major concern for most customers, except in the case of certain dedicated high-power applications or programs in which special attention was required. As semiconductor advancement and applications of such increased in scope, technology such as the Gallium Nitride devices (GaN) enables the expansion of 5G, IoT, small satellite and many other commercial, aerospace and military systems. But due to this, the specification for higher power handling capacity is required for even high frequency devices.

Increasingly, many of SAGE Millimeter customers request firmer specifications for power handling on the order of hundreds of Watts on products such as the waveguide power combiner, directional coupler, crossguide coupler and waveguide to coax adapters. These specifications have been either unclear or are missing from many datasheets. While SAGE Millimeter is working to update these datasheets, this blog intends to help customers understand how power handling can be estimated without performing actual testing due to the difficulty of acquiring high-power test equipment.

Furthermore, this blog also intends to explain the conditions under which the devices are to be used so that the maximum power handling potential of these devices can be reached. In addition, there are many other factors that could affect the power handling of a device, such as machining and consistency of assembly and quality of material. Environmental conditions such as temperature, humidity, altitude and dust, could also affect power handling tremendously. It would be difficult or unrealistic to give a general across the board accurate power handling for every model. Instead, SAGE aims to provide a guideline and conservative estimated power handling which may be more practical and useful.

  1. Waveguide Power Combiner, SWP Series

SAGE Millimeter’s waveguide power combiners are Magic Tee based. The input port or power combining port is the H-plane port and the outputs or power division ports are the collinear ports. The E-plane port is terminated with a matching load. In general, the power handling of the waveguide power combiner is limited by the power handling capacity of the termination load. Based on the above, E Band power divider power handling is estimated as follows:

SAGE Fig 1 SWP-71386304-12-E1
Figure 1. E-Band 4-Way Waveguide Power Combiner, Model SWP-71386304-12-E1

The isolation of the E-port to the H-port is 30 dB typical as shown in the E-Band Magic Tee datasheet if the port is well matched. The power handling of the E-Band termination load is around 27 dBm. Therefore, the power handling of the power combiner would be +57 dBm (500 Watts) theoretically. However, it would be too idealistic if a perfect match is assumed. The power handling of the E-Band power divider can then be specified conservatively at +47 dBm (50 Watts) with a 10 dB back-off. Of course, the power combiner may still have a chance to be damaged if the port matching is exceptionally poor and signals at the input ports are close to 100% mismatched in amplitude and phase.

2. Waveguide Directional Coupler, SWD Series

SAGE Millimeter offers several types of waveguide directional couplers: standard 3-port directional coupler, bi-directional coupler and dual directional coupler. Out of these three types, only the bi-directional coupler does not contain an internal termination load. The power handling of the directional coupler is governed by the waveguide coupling configuration. For the E-Band waveguide bi-directional coupler, the estimated power handling should be in the Kilo-Watts range due to the multi-hole mechanical structure. Conservatively, 100 Watts is given with a 10 dB back-off.

For 3-port directional and dual directional couplers, the internal termination loads are the limiting factor. The extreme example is the 3 dB directional coupler. This type of coupler uses an internal load, which can handle +27 dBm (500 mW) power as mentioned in the SWP series. Therefore, the power handling of the coupler would be +30 dBm (1 Watt) by considering the worst case scenario of full power reflection. On the other hand, if the port is well matched, the coupler could handle +43 dBm (20 Watts) aided by the directivity of the coupler specified at 40 dB. The power handling of the coupler is specified at 5 Watts by assuming that the full reflection scenario is rare. From here, the power handling of the 3, 10 and 20 dB 3-port and dual directional V band waveguide couplers are specified as 5 Watts, 10 Watts and 100 Watts, respectively per their coupling levels. The upper limit of 100 Watts power handling tends towards the bi-directional coupler power handling value. Another thing to take into consideration is that the power handling of the low frequency waveguide components is higher than that of high frequency waveguide components due to the power handling capacity of the load material and mechanical structure.

SAGE Fig 2 SWB-1040H-15-SB
Figure 2. V-Band Waveguide Directional Coupler, Model SWB-1040H-15-SB

3. Waveguide Crossguide Coupler, SWX Series

There are two types of waveguide crossguide couplers, 3-port and 4-port. Like the directional coupler, the 3-port version has an internal load and the 4-port does not. Therefore, the power handling consideration is very similar to the directional coupler except the crossguide coupler has about 25 dB less directivity. Because of that, the power handling of the couplers is 25 dB less. In other words, the power handling of the 10 dB E-Band waveguide crossguide coupler would be +37 dBm (5 Watts), 20 dB, +47 dBm (50 Watts) and 30 dB, +57 dBm (500 Watts), respectively. However, the upper limit power handling of the 3-port E band crossguide coupler shall be +50 dBm (100 Watts). As a contrast, the 4-port waveguide directional coupler is +50 dBm (100 Watts) across the board.

SAGE Fig 3 SWX-69390320-12-3B
Figure 3. E-Band 3-Port Waveguide Directional Coupler, Model SWX-69390320-12-3B

4. Waveguide to Coax Adapter, SWC Series

SAGE Millimeter’s waveguide to coax adapter is constructed with custom designed waveguide and commercially available standard coax connectors. The power limitation of the waveguide to coax adapters are limited by the coax connectors. The following is the coax connector power handling table published by Southwest Microwave, a leading coax connector manufacturer. While the actual power handling rate of the standard connectors are higher than published, this chart is calculated and estimated rather conservatively. For instance, the power handling of a 2.92 mm SWC-28KF-R1 connector is specified at +43 dBm (20 Watts). It is discovered that the connector can work well up to 50 Watts CW in the frequency range of DC to 40 GHz at room temperature and sea level. Thus, the published power handling of SAGE Millimeter waveguide to coax adapter, SWC series is intended to be very conservative. A factor of two can be applied to the published power handling of the SWC series adapters.

SAGE Fig 4 Power Handling
Figure 4. Power Handling of the Coax Connector, Courtesy of Southwest Microwave Inc.
SAGE Fig 5 SWC-28KF-R1
Figure 5. Ka Band Waveguide to Coax Adapter, Model SWC-28KF-R1 and SWC-28KM-R1

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