RF Chain

RF chain models for transmit power, losses, noise temperature, and cascaded stage analysis.

The simple RFChainModel is documented in Core Models. This page covers the cascaded multi-stage chain.

RF Stage

RFStage dataclass

RFStage(name, gain_db, nf_db, iip3_dbm=None)

A single RF stage (LNA, filter, mixer, PA, etc.).

Parameters:

Name	Type	Description	Default
name	str	Human-readable stage identifier (e.g., "LNA", "BPF", "PA").	required
gain_db	float	Stage gain in dB. Use negative values for lossy elements (filters, cables).	required
nf_db	float	Noise figure in dB. For a passive loss of L dB, NF = L dB.	required
iip3_dbm	float | None	Input-referred third-order intercept point in dBm. None means the stage is assumed linear (e.g., passive filter).	None

Cascaded RF Chain

CascadedRFChain

CascadedRFChain(stages, tx_power_w=1.0)

Multi-stage RF chain with Friis noise cascade and IIP3 cascade.

Supports both TX and RX chain analysis. For a receive chain the key output is cascaded noise temperature; for a transmit chain the key output is total gain/loss from PA to antenna feed.

Parameters:

Name	Type	Description	Default
stages	list of RFStage	Ordered list of stages from input to output.	required
tx_power_w	float	Transmit power at PA output in watts (default 1.0).	1.0

Examples:

>>> chain = CascadedRFChain([
...     RFStage("LNA", gain_db=20.0, nf_db=1.5),
...     RFStage("BPF", gain_db=-2.0, nf_db=2.0),
... ])
>>> chain.cascaded_nf_db()
1.52

Source code in src/opensatcom/rf/cascade.py

def __init__(self, stages: list[RFStage], tx_power_w: float = 1.0) -> None:
    if not stages:
        raise ValueError("CascadedRFChain requires at least one stage")
    self._stages = list(stages)
    self._tx_power_w = tx_power_w

total_gain_db

total_gain_db()

Total cascaded gain in dB (sum of all stage gains).

Returns:

Type	Description
float	Total gain in dB.

Source code in src/opensatcom/rf/cascade.py

def total_gain_db(self) -> float:
    """Total cascaded gain in dB (sum of all stage gains).

    Returns
    -------
    float
        Total gain in dB.
    """
    return sum(s.gain_db for s in self._stages)

total_gain_lin

total_gain_lin()

Total cascaded gain as a linear ratio.

Returns:

Type	Description
float	Total gain as a linear power ratio.

Source code in src/opensatcom/rf/cascade.py

def total_gain_lin(self) -> float:
    """Total cascaded gain as a linear ratio.

    Returns
    -------
    float
        Total gain as a linear power ratio.
    """
    return db10_to_lin(self.total_gain_db())

cascaded_nf_db

cascaded_nf_db()

Cascaded noise figure in dB using Friis formula.

F_total = F_1 + (F_2 - 1)/G_1 + (F_3 - 1)/(G_1 * G_2) + ...

Returns:

Type	Description
float	Cascaded noise figure in dB.

Source code in src/opensatcom/rf/cascade.py

def cascaded_nf_db(self) -> float:
    """Cascaded noise figure in dB using Friis formula.

    F_total = F_1 + (F_2 - 1)/G_1 + (F_3 - 1)/(G_1 * G_2) + ...

    Returns
    -------
    float
        Cascaded noise figure in dB.
    """
    return lin_to_db10(self._cascaded_nf_lin())

cascaded_noise_temp_k

cascaded_noise_temp_k()

Equivalent input noise temperature from cascaded NF.

T_e = T_ref * (F - 1) where T_ref = 290 K.

Returns:

Type	Description
float	Equivalent noise temperature in Kelvin.

Source code in src/opensatcom/rf/cascade.py

def cascaded_noise_temp_k(self) -> float:
    """Equivalent input noise temperature from cascaded NF.

    T_e = T_ref * (F - 1)  where T_ref = 290 K.

    Returns
    -------
    float
        Equivalent noise temperature in Kelvin.
    """
    return T_REF_K * (self._cascaded_nf_lin() - 1.0)

cascaded_iip3_dbm

cascaded_iip3_dbm()

Cascaded input-referred IIP3 in dBm.

1/IIP3_total = 1/IIP3_1 + G_1/IIP3_2 + G_1*G_2/IIP3_3 + ...

Returns:

Type	Description
float or None	Cascaded IIP3 in dBm, or None if no stage has IIP3 defined.

Source code in src/opensatcom/rf/cascade.py

def cascaded_iip3_dbm(self) -> float | None:
    """Cascaded input-referred IIP3 in dBm.

    1/IIP3_total = 1/IIP3_1 + G_1/IIP3_2 + G_1*G_2/IIP3_3 + ...

    Returns
    -------
    float or None
        Cascaded IIP3 in dBm, or None if no stage has IIP3 defined.
    """
    # Collect stages with IIP3
    has_iip3 = any(s.iip3_dbm is not None for s in self._stages)
    if not has_iip3:
        return None

    inv_iip3_total = 0.0
    cumulative_gain = 1.0
    for i, stage in enumerate(self._stages):
        if stage.iip3_dbm is not None:
            iip3_lin = db10_to_lin(stage.iip3_dbm / 10.0 * 10.0)  # dBm to mW
            inv_iip3_total += cumulative_gain / iip3_lin
        cumulative_gain *= db10_to_lin(stage.gain_db)

    if inv_iip3_total == 0.0:
        return None
    return lin_to_db10(1.0 / inv_iip3_total)

tx_losses_db

tx_losses_db()

Total TX loss (negative of total gain when gain < 0).

For a TX chain where stages represent post-PA losses (feed, cable, filter), this returns the magnitude of loss in dB (positive number).

Returns:

Type	Description
float	Total TX-path loss in dB (positive number, 0.0 if net gain).

Source code in src/opensatcom/rf/cascade.py

def tx_losses_db(self) -> float:
    """Total TX loss (negative of total gain when gain < 0).

    For a TX chain where stages represent post-PA losses (feed, cable,
    filter), this returns the magnitude of loss in dB (positive number).

    Returns
    -------
    float
        Total TX-path loss in dB (positive number, 0.0 if net gain).
    """
    total = self.total_gain_db()
    return -total if total < 0 else 0.0

to_simple_rf_chain

to_simple_rf_chain()

Convert to the simple RFChainModel for backward compatibility.

Maps cascaded noise temp to rx_noise_temp_k and cascaded losses to tx_losses_db.

Returns:

Type	Description
RFChainModel	Simplified RF chain model.

Source code in src/opensatcom/rf/cascade.py

def to_simple_rf_chain(self) -> RFChainModel:
    """Convert to the simple RFChainModel for backward compatibility.

    Maps cascaded noise temp to ``rx_noise_temp_k`` and cascaded
    losses to ``tx_losses_db``.

    Returns
    -------
    RFChainModel
        Simplified RF chain model.
    """
    return RFChainModel(
        tx_power_w=self._tx_power_w,
        tx_losses_db=self.tx_losses_db(),
        rx_noise_temp_k=self.cascaded_noise_temp_k(),
    )