How to implement SWaP-C satcom antenna arrays using SMD power dividers and directional couplers
Figure 5: The coupled port (P3) of a power divider passes on some fraction of the power delivered to the input port (P1), with the rest passing through the transmitted port (P2). The isolated port (P4) is terminated with an internal or external matched load. Image source: Spinningspark at Wikipedia
performance of the antenna array.
These characteristics include the following: ■ The main line loss should be minimized to enhance antenna array gain. This loss is due to resistive heating of the main line and is separate to the coupling loss. The total main line loss is the combination of resistive heating loss plus coupling loss ■ The coupling loss is the reduction in power due to the energy transferred to the coupled and isolated ports. Assuming a reasonable directivity, the power transferred unintentionally to the isolated port should be negligible compared to that transferred intentionally to the coupled port ■ The return loss should be minimized. This is a measure of the amount of the signal that
EIRP and potentially change the radiation pattern of a beam- forming antenna array
typically delivers a fraction of the energy of the main line and often features a smaller connector to distinguish it from the main line Ports 1 and 2. The coupled port can be used to obtain signal power level and frequency information without interrupting the main power flow in the system. Power entering the transmitted port flows to the isolated port and does not affect the output of the coupled port (Figure 5). The key characteristic of a coupler is the coupling factor.
Key antenna array components: directional coupler The directional coupler is another component that performs an important role in antenna arrays by consistently measuring the transmit and receive power of the array elements. The directional coupler is a passive device which couples a known amount of transmission or receive power through to another port from where it can be measured. The coupling is typically achieved by positioning two conductors close to each other such that the energy passing through one line is coupled to the other. The device has four ports: input, transmitted, coupled and isolated. The main transmission line is situated between Ports 1 and 2. The isolated port is terminated with an internal or external matched load (typically 50 Ω), while the coupled port (3) is used to tap the coupled energy. The coupled port
This is defined as:
C 3,1 = 10 log (P 3 /P 1 ) dB The simplest form of coupler
features a right-angled topology whereby the coupled lines run adjacent for one quarter of the wavelength of the input signal (e.g., 5 mm for a 15 GHz signal). This type of coupler typically produces half the input power at Port 3 (i.e., it has a coupling factor of 3 dB), with the power at the transmitted port also reduced by 3 dB. (Figure 6). As is the case with the power divider, there are some key characteristics of the directional coupler that impact the
Figure 6: The simplest form of directional coupler features coupling lines running adjacent for a quarter wavelength of the input signal frequency. Image source: Spinningspark at Wikipedia
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