A Novel Switchable Low Phase‐Noise Dual‐Frequency Oscillator Based on Traveling‐Wave Loop‐Directional Filter

A novel switchable low phase‐noise dual‐frequency oscillator based on a four‐port traveling‐wave loop‐directional filter is presented for the first time in this paper. Instead of the conventional diplexer design, three simple traveling‐wave loop resonators are employed to achieve two different output frequency selections. The dual‐band band‐pass filter is formed by cascading microstrip lines appropriately with two different resonant frequency loops, while the other same high‐frequency loop is utilized to select two frequencies independently. The reflectionless characteristic over the entire frequency band mitigates the impact of interference signals on the receiver. Sawtooth coupling is adopted to reduce insertion loss, thereby mitigating the challenge posed by high‐frequency oscillation. Due to the PIN‐based switching technique, the two oscillation channels are effectively controlled, and there is no inter‐modulation interference. Additionally, harmonic suppression is enhanced by the simplified improved low‐pass filter with two notches. For demonstration, a physical prototype was fabricated and measured. The proposed dual‐frequency oscillator can oscillate at 3.578 or 5.849 GHz by only controlling one set of PIN diodes with the output power of 5.27 and 0.82 dBm. The second harmonic suppressions are 60.52 and 45.26 dBc, and the phase noise keeps better than −130.31 and −129.22 dBc/Hz, respectively, at a 1 MHz frequency offset.