# C Band 360\({}^{\circ}\) Triangular Phase Shift Detector for Precise Vertical Landing RF System
## 3 Circuit Design  
### Theoretical Design  
The main block diagram of the novel 360\({}^{\circ}\) triangular phase detector is detailed in Figure 7, where the initial values of the design are shown in parentheses. The design starts from the dynamic range specifications of the input signals, defined on the minimum and maximum expected signal. The dynamic range is set at 50 dB without taking into account the receiver sensitivity (\(S_{min}\)), since the system will operate over relatively short distances. Therefore, two voltage-controlled attenuators (HMC973) are included to ensure a range of 28 dB and insertion loss of 5 dB (from \(-5\) dB to \(-33\) dB at 5 GHz). The dynamic range of the variable attenuator is achieved with a voltage variation from 0 to 3.5 volts. Figure 6: **(a)** Simplified schematic of the IQ and IQ-\(\beta\) phase detector. **(b)** Output voltages for the product \(I\) (switch = 1) and \(Q\) (switch = 2) for the IQ-\(\beta\) modulator. Figure 7: Simplified schematic of the novel 360\({}^{\circ}\) triangular phase detector. In parentheses are the final values after adjustments. The next device that determines the design of the phase detector is the multiplier (mixer). The mixer selected is the MA4 EX600L because it works well in the working band and is available in our laboratories. The manufacturer recommends a minimum local oscillator (OL) power level of 3 dBm [44] for it to function properly as a mixer. However, the device has been experimentally verified to provide a voltage of about 200 mVpp when the RF and OL inputs are \(-\)4 dBm and 5 GHz. This power level is selected to obtain the rest of the power balance since it guarantees a correct operation as a phase detector. The output signal of the multiplier has polarity, so it is necessary to add an offset and amplification circuit to be able to use the analog-to-digital converter (ADC) of the Arduino Uno that supports signals between 0 and 5 V (Figure 8b). The signal is distributed between the multipliers through the power dividers (PD4859), which introduce an insertion loss of 3.5 dB. A half-dB margin is established, so the signal at the reference point (Test Port 1 in Figure 7) is 0 dBm. This power is taken as the reference signal throughout the receiver and is the measurement point for the automatic gain control (AGC). Since the slope of the variable attenuator is positive (HMC973), i.e., the greater the attenuation, the higher the control voltage, the power detector must have a positive slope. The PFC06073A directional coupler is connected just before the reference point to obtain the input signal to the AGC power detector (\(-\)10 dBm). The power detector (ADL5906) should be set with the VSET voltage around 2.3 V, corresponding to the \(-\)10 dBm input power desired to be maintained about 5 GHz (Figure 3 in [45]). The circuit values are shown in Figure 8c, obtained from [45], as discussed below. A voltage level adjustment circuit is connected between the output of the power detector and the control input of the variable attenuators (HMC973). The input matching circuit consists of a 60.4 \(\Omega\) parallel connected resistor. The CRMS capacitor value selected is 100 nF as a compromise between noise (40 mVpp on the output voltage signal) and response speed, which is determined by the rise (30 \(\mu\)s) and fall (1 ms)  
Figure 8: Auxiliary circuits. (**a**) Voltage converter circuit of the Arduino Uno control signal from 0–5 V to 0–3 V (control voltage of the PE42553 switch). (**b**) DC offset and gain of the multiplier output voltage, from \(\pm\)100 mVpp to 0–5 V. (**c**) Schematic of the ADL5906 power detector that operates as part of the AGC. (Figure 50 in [45]). A response time smaller than 1 ms is more than enough, taking into account that the approach maneuver of the drone to the LP is relatively slow and, therefore, the amplitude variations in the input signal. The time could even be longer, but the noise improvement would be very small.